U.S. patent application number 15/121594 was filed with the patent office on 2017-01-19 for ultra high efficiency, high temperature solar collection and storage.
The applicant listed for this patent is Ronald S. ACE. Invention is credited to Ronald S. ACE.
Application Number | 20170016649 15/121594 |
Document ID | / |
Family ID | 51428682 |
Filed Date | 2017-01-19 |
United States Patent
Application |
20170016649 |
Kind Code |
A1 |
ACE; Ronald S. |
January 19, 2017 |
ULTRA HIGH EFFICIENCY, HIGH TEMPERATURE SOLAR COLLECTION AND
STORAGE
Abstract
High-temperature solar trap collectors provide near ambient
temperature solar entry surfaces and negligible thermal radiation
losses by counterflowing low velocity transparent gases or liquids
(fluids) to nullify internal thermal diffusion and radiative heat
losses at the solar entry surface. Small steradian (sr) baffling
plus wavelength-selective materials trap the entire 0.35 u to 2.7 u
incoming solar spectrum and heat highly absorbing internal surfaces
to high temperatures; only a small solid angle of the 2.pi.
steradians--on the order of 0.01 sr--of internal thermal radiation
escapes. A nearly 100% efficient flat panel solar trapping
embodiment exhibits alpha (.alpha.) absorption nearing 1.0 and
radiant emission losses nearing 0.0 even at solar collection
temperatures in excess of 1,000.degree. K. Ultra high collection
efficiency counterflow configurations are ideal for solar hot
water, space heating, cooling, energy storage, and electric power
generation applications.
Inventors: |
ACE; Ronald S.; (Laurel,
MD) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ACE; Ronald S. |
Laurel |
MD |
US |
|
|
Family ID: |
51428682 |
Appl. No.: |
15/121594 |
Filed: |
February 25, 2014 |
PCT Filed: |
February 25, 2014 |
PCT NO: |
PCT/US14/00023 |
371 Date: |
August 25, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61851083 |
Mar 1, 2013 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F24S 10/25 20180501;
F24S 80/20 20180501; Y02B 10/20 20130101; Y02E 10/40 20130101; F24S
10/70 20180501; F24S 10/00 20180501; F24S 10/50 20180501; F24S
10/80 20180501; Y02E 10/44 20130101; F24S 20/20 20180501 |
International
Class: |
F24J 2/07 20060101
F24J002/07; F24J 2/24 20060101 F24J002/24; F24J 2/46 20060101
F24J002/46; F24J 2/04 20060101 F24J002/04 |
Claims
1. An exceptionally high efficiency, high temperature; solar energy
collector, comprising: an enclosure having a front portion and a
rear portion; a solar entrance at said front portion to allow
incoming solar radiation to enter said enclosure; a fluid inlet at
said front portion of said enclosure to receive a counterflowing
working fluid at substantially ambient temperatures; at least one
baffle positioned laterally across said enclosure between said
front and rear portions to guide the flow of said fluid through
said enclosure toward said rear portion, said at least one baffle
allowing said incoming radiation to be nearly fully absorbed and
converted to heat within said enclosure; a fluid exit at said rear
portion, wherein said at least one baffle further preventing
radiation which is generated within the enclosure from escaping,
whereby the fluid is heated and exits the enclosure at said fluid
exit as a highly heated working fluid.
2. The energy collector of claim 1, further comprising a solar
spectrum absorption surface within the said enclosure, wherein said
baffle permits an effective passage of said counterflowing fluid
between said solar entrance surface and said absorption
surface.
3. The energy collector of claim 2, further comprising a plurality
of baffles within said enclosure, each said baffle being gradually
heated by reradiated and conductive energy within said enclosure
and by incoming solar energy, as said working fluid flows from said
front portion of the enclosure where it is at ambient temperature,
toward said rear portion, whereby said fluid exits the enclosure as
a very high temperature working fluid.
4. The energy collector of claim 3, wherein said solar incoming
radiation heats said fluid, said baffles, and said rear portion,
wherein said heated fluid and heated baffles reradiate energy, and
wherein each baffle is fabricated of, or is coated by, a material
which exhibits selective wavelength absorption, whereby solar
radiation passes through said baffle toward said rear portion and
reradiated energy is substantially prevented from reaching said
front surface.
5. The energy collector of claim 3, wherein said baffles are
honeycombs which exhibit angular selectivity to impinging
radiation, wherein said incoming solar radiation heats said fluid,
said baffles, and said rear portion and any reradiated energy from
said heated fluid, said heated baffles, or said rear portion is
substantially prevented from reaching said front portion.
6. The energy collector of claim 1, wherein said at least one
baffle produces substantially laminar fluid flow in said enclosure
in a direction that is substantially perpendicular to the direction
of said incoming solar radiation and also follows a serpentine
counterflow path from said front portion to said rear portion.
7. The energy collector of claim 6, wherein said at least one
baffle is nonporous and transparent to incoming radiation and
exhibits an index of refraction substantially the same as the
working fluid flowing through the enclosure.
8. The energy collector of claim 7, further comprising a plurality
of baffles in said enclosure to produce said serpentine path,
wherein said incoming radiation is solar energy to heat said fluid
and said rear portion, wherein said heated fluid and said heated
rear portion reradiate energy, and wherein each baffle exhibits
selective wavelength absorption, whereby solar radiation passes
through said baffles toward said rear portion and reradiated energy
is substantially prevented from reaching said front surface.
9. The energy collector of claim 1, wherein the rear portion of
said enclosure incorporates a solar spectrum absorber.
10. The energy collector of claim 8, wherein said solar entrance
includes a transparent aperture for admitting said solar
radiation.
11. The energy collector of claim 1, wherein said solar entrance
includes a transparent aperture for admitting said solar
radiation.
12. A method for collecting solar radiant energy, comprising the
steps of: directing solar radiant energy through a front portion of
an enclosure toward a solar spectral absorbing rear portion of the
enclosure to trap heat in the enclosure; supplying a counterflowing
working fluid to said enclosure at a relatively low temperature;
causing said fluid to flow generally away from said front portion
of the enclosure toward said rear portion of the enclosure to be
heated by absorbed incoming solar radiant energy in said absorbing
rear portion; preventing heat from within said enclosure from
exiting said enclosure while the fluid is still within said
enclosure; and directing heated fluid out of said enclosure.
13. The method of claim 12, further including causing the working
fluid to have a substantially laminar flow within said enclosure in
a direction generally perpendicularly away from said front
portion.
14. The method of claim 12, wherein the step of preventing heat
from within the enclosure from exiting includes
wavelength-selectivity.
15. The method of claim 12, wherein the step of preventing heat
from within the enclosure from exiting includes
angular-selectivity.
16. The method of claim 12, further including thermally insulating
the enclosure.
17. The method of claim 12, wherein causing said fluid to flow
generally away from said front portion of the enclosure toward said
rear portion of the enclosure includes providing a plurality of
wavelength selective or angle selective baffles.
18. The method of claim 12, wherein causing said fluid to flow
generally away from said front portion of the enclosure toward said
rear portion of the enclosure includes a plurality of
flow-direction baffles extending across said enclosure.
19. The method for making a solar energy collector, comprising the
steps of: providing an enclosure having a front portion and a rear
portion; providing a solar entrance at said front portion to allow
incoming solar radiation to enter said enclosure; providing a fluid
inlet at said front portion of said enclosure to receive a
counterflowing working fluid at substantially ambient temperatures;
providing at least one baffle positioned laterally across said
enclosure between said front and rear portions to guide the flow of
said fluid through said enclosure toward said rear portion, said at
least one baffle allowing said incoming radiation to be nearly
fully absorbed and converted to heat within said enclosure; and
providing a fluid exit at said rear portion, wherein said at least
one baffle further preventing radiation which is generated within
the enclosure from escaping, whereby the fluid is heated and exits
the enclosure at said fluid exit as a heated working fluid.
20. The method of claim 19, wherein said baffles are honeycombs
which exhibit angular selectivity to impinging radiation.
Description
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 61/851,083, entitled "Ultra High Efficiency,
High Temperature Solar Collection and Storage", Filed Mar. 1, 2013,
the disclosure of which is hereby incorporated herein in its
entirety by reference.
BACKGROUND OF INVENTION
[0002] Field of the Invention
[0003] The present application relates, in general, to a method and
apparatus for achieving low-cost, renewable global energy utilizing
an ultra efficient solar trap that is capable of meeting even
centuries more of civilization's relentless 2% per year
exponentially rising energy demands.
[0004] Discussion of Prior Art
[0005] Conventional easy-access, cheap energy is already depleted
and unsustainable energy economic ceilings are being breached, but
international prosperity can be restored by adopting a new
abundant, dramatically lower cost energy source, such as clean
solar energy. Solar energy, the world's largest energy resource,
once harnessed in a useful form, such as high temperature thermal
energy, can be readily stored and transformed into almost all other
forms of energy, such as chemical energy, mechanical energy,
electrical energy, and others. See chart 10 in FIG. 1 for mankind's
300-year energy consumption history and the apparent
straightforward 300-year energy consumption trajectory.
[0006] Energy costs have risen from less than 1% of the global
economy and are now approaching 14% of the $70 trillion world
economy. The cost of energy, not energy abundance, now limits
global prosperity--including fresh water, agricultural food
production, manufactured products, and almost all jobs. All
products and transportation are inexorably linked to energy costs
and almost all jobs are inexorably linked to manufacturing and
transporting all products. An entirely new, far larger, cheaper,
and cleaner prime energy source is absolutely essential, unless
gross human depopulation begins to occur within about one
generation. Patch-work energy alternatives cannot meet the need.
There is little debate that the industrial revolution was triggered
by the combustion powered steam engine invention in 1712, and our
energy appetite has exponentially grown since--enabling 300 years
of unparalleled global prosperity. However, underpinning this long
period of prosperity was abundant very low-cost energy--typically
costing less than about five percent of the global economy. Rapidly
rising and unsustainable energy recovery obstacles now govern the
world economy, not to mention the almost totally ignored larger
costs associated with air, land, and sea pollution. Energy, per se,
is essentially unlimited if energy prices could be ignored. But,
prices cannot be ignored. Thus, affordable energy governs life as
we know it. The world urgently needs an immediate transition to a
far larger, cleaner, and considerably less expensive alternative
prime source of energy. Until the present invention, the world's
largest energy resource--solar energy, which is 10,000 times larger
than man's present energy needs--has not been either affordable or
reliable. For just one example, the well-known prior art
concentrating solar mirrors and photovoltaic solar panels shown at
12 and 14 in FIGS. 2 and 3, and again at 16 and 18 in FIGS. 4 and 5
are very inefficient in that the solar tracking panels cast long
shadows and typically collect or harvest only about 1/3.sup.rd to
1/4.sup.th of the available solar energy per acre.
SUMMARY OF THE INVENTION
[0007] In essence, the subject invention is a one way solar energy
valve which enables entry of the entire solar spectrum into a solar
trap, wherein solar energy is cumulatively absorbed and converted
to exceptionally high usable temperatures, but does not allow the
usual thermal radiation to escape from within. In other words, a
solar trap device is provided which simulates a high temperature
blackbody absorber with little to no emissive losses, similar in
some ways to an astronomical black hole which grows in temperature
with little escaping energy. Solar traps efficiently concentrate
very high temperature thermal energy which can be densely stored
and thereafter used on demand for an unlimited number of energy
applications. This new very high temperature solar trapping
technology can theoretically approach 100% efficiency per acre of
solar collection, which exceeds by many times the surface area
collection efficiency of all prior art solar technologies.
[0008] Briefly, the present invention is directed to an
exceptionally high efficiency solar energy collector which
incorporates an enclosure having an outermost entrance aperture to
allow incoming radiation to enter the aperture. A working fluid is
supplied to the enclosure at substantially ambient temperature and
flows laminarly through the enclosure in a direction of flow that
is substantially perpendicular to the outermost entrance aperture,
whereby the incoming radiation is absorbed within the enclosure to
heat the working fluid within before it exits as a very hot working
fluid. At least one optical radiation mechanical and/or fluidic
baffle is positioned to allow the incoming radiation to ultimately
heat the exiting fluid within the enclosure but to prevent spectral
radiation which is generated within the enclosure from escaping the
enclosure. This ensures that the fluid will exit the enclosure as a
highly heated working fluid, containing essentially all of the
incident solar energy for directly powering thermal processes or
for storage and later use as thermal energy on demand.
[0009] The invention further comprises a method for collecting
solar energy, the method including the steps of directing the
incoming solar spectrum through an entrance surface, which may be a
wide or narrow aperture, into a container, and supplying a
substantially ambient temperature working fluid to the container so
as to have a laminar flow within the container in a direction that
is parallel to the incident solar light direction. The method
includes absorbing solar energy within the container to directly or
indirectly heat the flowing working fluid and also preventing
thermal energy within the container from exiting the container.
Finally, the method includes directing the heated fluid out of the
container to provide useful high temperature thermal energy.
[0010] The subject invention meets all of the high temperature,
high collection efficiency, and long term reliable solar energy
storage objectives of practical solar thermal energy--all at many
times lower costs than prior arts. As will be illustrated herein,
high temperature solar collection nearing 100% efficiency can be
achieved by the subject invention--thereby leaving negligible room
for all other solar technology improvements. The subject invention
advocates the use of the most abundant raw materials on earth to
construct low-cost solar traps and inexpensively store unlimited
solar thermal energy--thereby paving a path to the lowest possible
cost solar power technology. Such a combined breakthrough leaves
little impetus for others to do better than the subject invention.
For the first time in history, the subject invention employs
essentially all of the fundamental physics energy functions to
economically satisfy almost all of man's energy needs--not just
electricity, space conditioning, and hot water--for centuries of
exponentially rising energy demands.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The foregoing, and additional objects, features and
advantages of the present invention will be understood by those of
skill in the art from the following detailed descriptions of
preferred embodiments when taken with the accompanying drawings, in
which:
[0012] FIG. 1 is a 700 year time versus global energy consumption
chart, depicting mankind's past 360 years and projected 340 years
of rising energy consumption, plus a depiction of the best
available estimates of conventional ("affordable") combustion
energy resources, all supporting the need for an urgent transition
to a new prime energy resource that must be more than 100 times
larger, less costly, safer, and far cleaner than all currently
known energy resources;
[0013] FIGS. 2 and 3 diagrammatically illustrate prior art
Concentrated Solar Power (CSP) parabolic Troughs and Central Tower
CSP technologies, respectively, which attempted for many decades to
generate and store high temperature solar energy in a cost
effective way, and, thus far, have failed to become a cost
competitive or a reliable energy source, and have largely depended
on the exponentially rising cost of conventional energy to justify
the existence of very high-cost prior solar arts;
[0014] FIGS. 4 and 5 diagrammatically illustrate prior art
photovoltaic (PV) solar technologies which have also failed to
become cost competitive or, especially not a reliable energy
source;
[0015] FIG. 6 is a chart illustrating a short list of thermal
diffusivity values of transparent and semi-transparent fluids,
including selected gases and liquids at ambient temperatures as
well as high operating temperatures;
[0016] FIG. 7 is an efficiency vs. operating temperature chart
comparing a one-sun, flat panel, solar trap in accordance with the
present invention to prior art one-sun flat panel collectors
operating in less than 10.degree. C. (winter) bright sunlight
noontime conditions;
[0017] FIG. 8 is a chart illustrating the
temperature-to-the-forth-power radiation obstacle of prior art
solar thermal receivers, including the efficiency of one-sun and
100-sun solar concentration on absorbing hot surfaces--given that
hotter surfaces naturally become more undesirable emitters;
[0018] FIG. 9 is a chart illustrating the peak oil availability per
year, suggesting that known natural oil reserves are rapidly being
depleted and that new conventional oil discoveries are inadequate
to keep up with projected exponentially increasing demands within a
few decades--the global consequences of which are ominous;
[0019] FIG. 10 is an expansion of a portion of the chart of FIG. 9,
illustrating the "peak oil" problem and how diminishing oil
reserves place large demands on remaining conventional energy
sources, thereby displaying the extreme urgency of finding and
implementing an entirely new and many times larger prime energy
source, such as low-cost solar energy, which is capable of meeting
the rapidly rising present 520.times.10.sup.15 BTU/yr (.about.$9
trillion) annual global energy demand;
[0020] FIGS. 11(a) through 11(d) illustrate computer generated
temperature vs. distance thermal diffusivity plots of four specific
common gaseous, liquid, and solid materials at only 100.degree. C.,
it being understood that diffusivity is not constant for each
material and that diffusivity markedly changes with temperature and
the plots dramatically change with material thickness ("X") in
accordance with equation 3;
[0021] FIG. 12 is a chart of absorption vs. wavelength properties
of liquid water, illustrating the desirable spectral absorbance
properties of liquids like water and liquid silicon oils, which can
be used, like many other fluids, as a counterflowing selective
wavelength fluid "baffle" in the present solar trap invention:
[0022] FIG. 13 is a diagrammatic depiction of a counterflowing
solar trap device in accordance with the present invention,
illustrating an example wherein 100 suns of narrow divergence solar
energy is applied to an entry surface, with the input solar energy
passing through one or more light baffles, and wherein
counterflowing fluid progressively heats before exiting the
enclosure and continues to flow, as a working fluid, to heat a
thermal storage mass, and exits the thermal storage mass at near
ambient temperatures before the fluid is returned to the solar
entry surface to be reheated;
[0023] FIG. 14 illustrates computer generated thermal diffusion
plots of four solar trap devices such as that illustrated in FIG.
13, each filled with various thicknesses of one of the Nitrogen,
Argon, Sulferhexafluoride (SF6), and Xenon gases which laminarly
counterflow perpendicularly away from the solar entry surface of
the device at the approximate correct velocities indicated in order
to nullify their normal thermal diffusion velocities toward the
solar entry surface, thereby radiating almost no thermal energy at
the entry surface, and so that the fluids can exit the respective
solar trap devices at about 900.degree. C. (1,200.degree. K,
1,652.degree. F.) as a hot working fluid with only one sun applied
at the flat panel solar entry surface;
[0024] FIG. 15 is a diagrammatic depiction of a basic
counterflowing solar trap device in accordance with an embodiment
of the invention without thermal storage, to illustrate how to
maintain the solar entry surface at ambient temperature and thus to
produce little to no thermal radiation losses from the entry
surface, and yet produce a very hot exiting working fluid;
[0025] FIG. 16 is a diagrammatic depiction of a high temperature
solar trap device in accordance with a third embodiment of the
invention, having a very long-term thermal storage device
retrofitted to an existing high temperature steam thermoelectric
power plant or, in the alternative, a city-wide space conditioning
(heating/cooling) system employing potable water such as that
illustrated in U.S. Pat. No. 6,688,129;
[0026] FIG. 17 is a diagrammatic depiction of a layered serpentine
counterflow solar trap in accordance with the present invention,
which also exhibits the essential optical and thermal properties of
previously depicted counterflow configurations, but instead of
fluids flowing substantially perpendicularly away from the solar
input surface, the serpentine flow is substantially parallel to a
solar input surface, followed by a series of parallel flows, each
flow working its way father away from the incident solar surface
and eventually exiting the serpentine solar trap as a very hot
working fluid;
[0027] FIG. 18 is a diagrammatic depiction of a pipe-layered
serpentine counterflow solar trap presenting an alternative
geometry to the paneled counterflow serpentine in FIG. 17.
ADDITIONAL DETAILED PRIOR ART INFORMATION
[0028] FIGS. 2 and 3 illustrate examples of mirror type
solar-thermal CSP (Concentrated Solar Power) devices as known in
the prior art. Heliostated solar troughs are depicted in FIG. 2 at
12, and FIG. 3 depicts at 14 a central tower receiver in a
heliostated mirror field. Note the exposed receiver thermal
radiation potential as well as convection exposure in both of these
prior art systems. Their net efficiency is low due to very high
T.sup.4 thermal radiation losses, as illustrated by efficiency
comparison chart 20 in FIG. 7. Curve 22 illustrates the efficiency
of a one-sun, flat panel, solar trap in accordance with the
invention (to be described), while curve 24 illustrates the
efficiency of a typical prior art one-sun, commercially available,
high quality prior art flat panel vacuum tube type solar collector
(not illustrated) operating in less than 10.degree. C. (winter)
bright sunlight noontime conditions. Not shown in FIGS. 2 and 3 is
the very expensive thermal energy storage technology used in the
prior an, which typically costs 25% of an entire CSP power plant
installation for only a few hours of storage drawdown. Thus,
scaling up prior art storage to many days/weeks (e.g.
.about.10-fold to only days of storage time) to achieve dependable
power could easily more than double or triple the already
prohibitively expensive cost of prior art solar power. It is these
costly prior art heliostated mirror systems, receiver systems,
storage systems, and many other problems with prior art solar,
which have prevented the widespread adoption of CSP even in optimal
desert locations. Similar shortcomings apply to solar dish CSP
prior art technologies, not depicted.
[0029] The preferred embodiments of the subject solar trap
invention that will be described below can readily exceed
1200.degree. K collection temperatures with only one-sun applied
instead of the typical 100-sun mirror concentration of the prior
art, while simultaneously exhibiting exceptionally high collection
efficiencies in excess of 90%. Prior solar art one-sun flat panels
typically fall to near 0% collection efficiency at under
500.degree. K (200.degree. C.), and typical prior art
mirror-concentrating solar tower receivers fall to 0% efficiencies
at about 1200.degree. K (900.degree. C.). If the subject one-sun
invention is augmented by the use of optical mirror concentration,
such an embodiment would have no known upper temperature limits,
even in excess of 1200.degree. K, while still retaining high
collection efficiencies, thereby illustrating more than a 10-fold
to 100-fold improvement over the prior art. This latter embodiment
can be better appreciated by emphasizing that radiation losses in
prior art devices skyrocket by a factor of T.sup.4, which means
that radiative losses normally rise by 16-fold each time the
absolute collection temperature is doubled. The subject invention
does not suffer from the usual prior art hot surface radiative
losses. As will also be illustrated, collecting and storing just
twice higher temperatures does not merely double the useful stored
energy, but can surprisingly provide 10-fold or higher useful
draw-down energy, which translates to an opportunity to slash
storage costs by more than 10-fold.
[0030] FIG. 8 also illustrates the radiative loss shortcomings of
prior art flat panel collectors and the very expensive prior art
mirror type CSP collectors depicted in FIGS. 2 and 3. The radiative
losses can be compared to the poor area-collection efficiencies of
prior art Photovoltaic (PV) technologies illustrated in FIGS. 4 and
5. Prior art high-cost heliostated PV array installations are not
only costly, but are also very energy-inefficient. Although
laboratory rated at nearly 20% efficiency, the actual
field-performance of PV systems is nearer to 12% efficiency. The
underground power lines and computer-controlled circuits required
for such heliostated systems are not visible in FIGS. 2 through 5.
Note the large shadows 13, which force large spacing between the
heliostated PV panels, similar to the spacing requirements of CSP
mirror systems. Non-heliostated PV farms still cast shadows and
suffer from reduced collection efficiency by not tracking the sun.
All prior art PV panels run hot in the sun, and such absorbed waste
heat further reduces PV efficiency. Low durability and constantly
decreasing efficiencies with time require frequent PV panel
replacements, which represent another long term PV cost obstacle.
Macro electrical energy storage and conversion from DC to AC are
still other factors which make PV uneconomical and especially
unsuitable for 24/7 performance. Battery type PV energy storage is
prohibitively expensive. Conversion of electrical PV energy to
chemical storage fuels is inefficient, very expensive, and the
recovery of such chemical energy is even more inefficient,--all of
which reduces net PV efficiency and reliability. The final
re-conversion of stored chemical energy back to useful power is a
particularly costly and inefficient process. All of these, and
other factors, cause even futuristic theoretical PV technology to
be uneconomical when compared to conventional combustion fuel
technologies, not to mention PV demands on scarce materials, which
many believe cannot be scaled up to a global energy demand scale.
An entirely new, much more efficient, and far lower cost
macroscopic solar energy breakthrough is needed, such as the
unbeatable ultra high efficiency solar traps described herein.
[0031] Until the advent of the present invention, all prior art
solar thermal collection technologies have suffered from huge
thermal radiation losses, even at very low collection temperatures.
FIG. 7, described above, illustrates the severe "one sun" prior art
flat panel deficiencies, depicting prior art rooftop style flat
panel thermal performance in comparison to the subject invention
and illustrating the dramatic thermal radiation losses of the prior
art starting below 100.degree. F. As a result of such low prior an
collection temperatures and low efficiencies, much larger rooftop
surface area collectors and very much larger and unaffordable
storage technologies are required. As illustrated by curve 22, the
solar trap device of the subject invention can collect far greater
than 200.degree. F.; in addition, it can be physically many times
smaller and less costly, and can store 10-100 times more useful
draw-down energy when stored at much higher temperatures. The
subject invention can slash costs and improve performance by
approximately 10-fold, while simultaneously achieving massive, long
term, low cost energy storage. Storage, in useful forms, has always
been the key to stand-alone solar reliability.
[0032] It is the very high temperature plus the very high
efficiency distinction of the subject invention that differentiates
it from all prior solar arts. This distinction is only possible by
overcoming the formidable T.sup.4 infrared radiation losses from
heated surfaces that are depicted by chart 30 in FIG. 8, which
losses have barred prior art systems from efficiently collecting
high temperature solar thermal energy. And yet, exceptionally high
temperatures are a fundamental Carnot efficiency (equation 1)
prerequisite of all thermal engines such as turbine thermoelectric
powerplants:
.eta. = W Q H = 1 - T O T H . eq 1 ##EQU00001##
Where W is the work done by the system (energy exiting the system
as work),
[0033] Q.sub.H is the heat put into the system (heat energy
entering the system),
[0034] T.sub.C is the absolute temperature of the cold sink
reservoir, and
[0035] T.sub.H is the absolute temperature of the hot source
reservoir.
Clearly, the highest thermal efficiencies are achieved by employing
the highest T.sub.H source temperatures (and/or the coldest T.sub.C
sink temperatures such as in deep space). Exceptionally high
temperatures are also a fundamental requirement of the lowest cost,
highest energy-density storage technologies. Thus, prior art solar
thermal collection technologies have been restricted to low Carnot
efficiency devices, high cost solar collectors, and costly, short
term thermal storage, and these formidable restrictions create
unaffordable and unreliable solar power. As emphasized above, all
of these items govern energy costs, products, jobs, and economic
prosperity, not to mention the very long list of environmental
consequences. FIG. 8 also provides a glimpse of the dramatic
improvements possible with the subject solar trap invention.
[0036] FIG. 8 depicts the domination of T.sup.4 radiation effects
in prior art solar systems which severely limits their collection
efficiency at the desired high temperatures. For example, the best
flat panel thermal collectors (0.9 emissivity), with one sun (1000
watts/m) noontime illumination, infrared-radiates 100% (1000
W/m.sup.2) of its received energy at a panel temperature of only
.about.404.degree. K (104.degree. C., 219.degree. F.), which
represents zero percent output efficiency. Therefore, typical high
performance flat panels are limited to roughly 350.degree. K (160
F) at only .about.50% efficiency. Similarly, intensely concentrated
solar power from a field of solar mirrors (e.g. "100 suns" or
100,000 watts/m.sup.2) can only achieve about 60% efficiency at
900.degree. K (600.degree. C.), and 0% efficiency at receiver
temperatures nearing only 1200.degree. K (900.degree. C.). Thus,
thousands of costly mirrors are needed just to overcome radiation
losses and are useless for producing energy. The subject solar trap
invention can collect temperatures far in excess of 1200.degree. K
(900.degree. C.) while maintaining nearly 100% collection
efficiency. Also note in FIG. 8 how efficiency is severely impacted
by radiation losses if a receiver front surface is allowed to rise
by just 5.degree. K (31 w/m.sup.2), 10.degree. K (64 w/m.sup.2),
50.degree. K (392 w/m.sup.2) and 100.degree. K (992 w/m.sup.2,
almost 0% efficiency with 1-sun applied).
[0037] The total radiation intensities curve 32 in chart 30 of FIG.
8 can be calculated from equation 2 below:
P.sub.net=A.sigma..epsilon.(T.sup.4-T.sub.0.sup.4). eq 2
Where, P is the total radiation is 2.pi. steradians and across all
wavelengths, in waits;
[0038] A is area of the radiating surface in m.sup.2
[0039] .sigma.=a constant 5.67.times.10.sup.-8 W m.sup.-2
K.sup.-4
[0040] .epsilon.=emissivity of the specific material (0 to 1)
[0041] T=temperature of surface
[0042] T.sub.o=temperature of the environment into which the
radiation is liberated.
[0043] Once energy is captured in a truly usable form, such as high
temperature thermal energy, it can be directly employed as thermal
energy or it can be efficiently transformed into almost any other
form of energy, such as electricity or chemical energy. That fact
envelopes almost 100% of civilization's energy needs such as direct
conversion of high temperature thermal energy into cold
refrigeration energy; direct space heating of buildings; direct
high temperature industrial thermal process manufacturing;
conversion of thermal energy into liquid or gaseous fuels; and
direct thermoelectric power generation. Such ultra-efficient and
low-cost solar energy invites the use of a wide array of
thermo-chemical technologies to produce lower cost synthetic liquid
or solid fuels. For example, thermal depolymerization chemical
industries can mass produce lower cost synthetic liquid and solid
fuels. Likewise, much lower cost hydrogen fuels, having no
greenhouse footprint, can also be produced at high temperatures and
saved at ambient temperatures. Of course, stored synthetic fuels
often suffer gross inefficiencies when the stored energy is
retrieved (usually by way of combustion processes).
[0044] The actual need for liquid fuels can be almost eliminated if
the many promising superior battery technologies mature to enable
85% efficient electric vehicles instead of 20% efficient combustion
based vehicles. If mass produced electric vehicles replace
combustion vehicles, then the subject solar invention can also be
the clean electric source for electric transportation.
[0045] Overarching man's long term energy dependence is the grim
prospects of no energy wiggle room. Combustion, nuclear fission,
fusion, deep geothermal, wind, tidal, and all other energy sources
are simply inadequate, unsafe, polluting, environmentally
destructive, and above all, too expensive. All prior solar arts
have been unaffordable, despite the 10,000-fold abundance of solar
energy. The present vastly improved solar technology removes all of
the previous solar barriers. Sheer "abundance" of clean energy is
no longer the prime objective. Cost is now the primary barrier.
[0046] Chart 40 in FIG. 1 plots energy consumption over time, and
vividly illustrates that if man's relentless 2% per year energy
progression is projected just 35 more years, humanity will require
2 times more energy per year; a humbling 4 times more energy per
year in 70 years; an astronomical 8 times more in only 140 years,
and; a staggering 400 times more energy per year in about three
centuries--all relatively tiny time increments compared to man's
>200,000 year evolution. According to speculating nuclear
physicists, it could take three more centuries to master the
ultimate energy--true nuclear matter annihilation energy--almost
1000 times more powerful than our current meager nuclear fission
and fusion sciences. We can't gamble or wait 300 years, or probably
even 30 years, for conventional combustion fuels to become scarce
and decimate global economies. A Manhattan Project scale transition
to ultra clean solar energy would be a wise and immediately
deployable, safe option.
[0047] The immediate need for an urgent transition to a new much
larger prime energy resource is an understatement. It is widely
acknowledged that conventional affordable energy resources will be
largely exhausted within as little as 52 to 56 years at our current
2% per year exponential consumption rate. Some cavalierly refute
the 50 year premise with disregard to exponentially rising demands;
to the soaring energy recovery costs; to the dire global
environmental harm; or the severely adverse economic impacts.
Clearly, starting a transition away from combustion fuels 50 years
from now is too late, when it's all gone. A complete transition
will likely take 50 years, if started today. The small percentage
of combustible fuels that will be left for posterity, after a full
transition to an alternative energy, will likely not be much. Many
other products that require these precious hydrocarbon commodities
might be scarce. Hydrocarbons simply should never be burned.
Instead, they should be used and recycled.
[0048] Many are convinced that the above worrisome energy
consequences will adversely impact international peace several
decades before the world's conventional energy coffers are empty.
But it would likely take several decades to transition from
combustion and nuclear fuels and to preserve a meaningful fraction
of our versatile finite material resources for posterity. If peace
is important, it is essential that other far larger and especially
less expensive, alternative energy resources be introduced
immediately, not later.
[0049] It is widely acknowledged that global conventional energy
costs will continue to sharply rise as the world's finite and
easy-access resources dwindle. Thus, man's practical options are
reduced to two: 1. either do without unaffordable/unavailable
energy or, 2. find a way to capture and store vastly superior solar
energy far less expensively. The first sacrificial option can
reverse man's ascent. The second option can accelerate the ascent
with abundant food, water, jobs, shelter, productivity, and human
population, like few can imagine, and like mankind has never
experienced. It can be vividly shown that about 98-99% of products,
services, jobs, and survival itself, are inexorably linked to
energy--and now--no longer the abundance of energy, but to the
sheer cost of energy.
[0050] History (FIG. 1) shows that energy has subtly become the
very foundation of almost all of our approximate $70 trillion
global economy and life itself. During the past millennium, energy
consumption per capita has insidiously crept up 100-fold from near
zero external energy consumption (just 2,000 btu/day--24 watts
averaged over 24 hours, or "one manpower" plus negligible animal
power), all the way to about 200,000 btus per capita per day which
equals 2,440 continuous watts.
[0051] Thus, humanity itself is now 98% dependent on about 198.000
btus per capita per day of external machine energy (.about.2,440
continuous watts per person per 24 hours). Human survival or
extinction has subtly become inexorably linked to non-human energy.
Modern life, and more importantly, man's future, depends on it.
[0052] The above per capita approximations are readily supportable.
The total theoretical net output power of 7 billion healthy adult
males laboring at a maximum of 50 watts for 10 hours every day
equals "only" 5.times.10.sup.15 btus per year (5 quads). But, the
fact is that 7 billion of us actually consume 520.times.10.sup.15
btus per year (520 quads)--104 times more energy than humans alone
can provide. Thus, a mere 5 quads of manpower alone, can only
supply .about.1% of humanity's real energy dependence. 99% must be
supplemented by external energy from the likes of combustion fuels,
nuclear, hydro, bio, wind, and, preferably, the largest of them
all--solar energy. This firmly illustrates how insidiously our
external energy dependence has grown from near zero, now surpassing
99%--illustrated in FIG. 1.
[0053] To drive the above 99% energy dependence image
home--envision the impacts of energy shortages. Energy-intense
farming and food production, electric and water shortages, reduced
transportation of people and goods, jobs, and peace, can all be
decimated without energy. Human extinction is not an option,
especially when there is now one hopeful solution--affordable and
reliable solar energy. Emergency-scale solar energy preparations
can only do good by providing massive new jobs, improving economic
prosperity, saving the environment, and preserving our finite
natural resources.
[0054] Cheap, easily accessible oil and gas will be the first to
go. FIG. 9 is a stark summary of so called "peak oil." Conventional
cheap oil reserves are drying up, new oil discoveries are abruptly
slowing, and the more costly new discoveries are rapidly increasing
oil prices and crippling international economies. In 1956, M. King
Hubbert, PhD, was first to accurately predict the 1978 U.S. peak
oil crisis, which has since progressed to a global "peak oil"
controversy. But Hubbert went on to illustrate the direct linkage
of human population and "available" energy. The assumption is that
he meant "affordable" energy because mere "available" energy is
unlimited if there were no imposed upper price limits. Since then,
unfortunately, the cost of energy has topped the energy priority
list because energy costs have risen hundreds of percent higher
than global inflation. Global energy is now teetering on
"unaffordable" which has become completely synonymous with
"unavailable" to most of the world's population.
Unaffordable/unavailable have become interchangeable because both
words now have identical consequences. Many assert that the
continuing 2008 global economic troubles are directly linked to
global energy costs which have reached about 14% ($9+ trillion) of
the $70 trillion economy. Others assert that many more global
economic meltdowns are likely if energy approaches 18% of the
global economy (a mere 29% higher energy prices than in 2013).
Regardless of the controversies, there is now a non-debatable dire
need of a crisis-paced transition to an entirely new less costly,
safer, cleaner, much larger, reliable energy source. Almost all of
the scarcity controversies seem to neglect environmental
destruction as having a dollar impact. If the countless
environmental restoration cost impacts were factored in, the real
prices of energy would be many times higher than quoted today.
[0055] FIG. 10 depicts a mere 25 year optimistic global energy
consumption, which might not be realistically met because the vital
and unknown energy price ingredient is omitted from this flawed
official EIA report. In 25 years, no new mammoth low-cost energy
discoveries are predicted and most predictions assert that
international demands could be fierce long before 2035. An economic
breaking point has either been already breached, or is very near.
For example, the EIA predicts a doubling of "renewables" which is
particularly flawed if "renewable" costs remain several times
higher than the already high conventional energy prices. Likewise,
the exceptionally high cost of current nuclear energy, coupled with
frequent nuclear disasters and much higher future "safer" nuclear
costs, leads to projecting much less than the doubling of nuclear
energy that the EIA chart suggests. EIA optimism is
unsupportable.
[0056] Improved energy efficiencies are always highly recommended
but those bandaids can only modestly prolong the inevitable
environmental destruction and energy depletion. The need of a
historic paradigm energy transition remains inescapable--unless a
dramatic human depopulation somehow becomes an acceptable option.
Even then, an inescapable energy transition is still required to
preserve global environments. The sooner the inescapable energy
transition the better for the environment, the economy, and for
peace. In all cases, energy costs still need to fall, not merely be
maintained.
[0057] Civilization's future energy consumption (up to 400 times
our current needs; see chart 40 in FIG. 1) can not be economically
met by more inaccessible conventional energy reserves. And if
history continues to be our teacher, then imagine evolving to 400
times more energy consumption during the next mere three
centuries--wherein civilization is expected to consume in one day
that which we presently consume in a year. The subject historic and
benign solar trap invention is uniquely poised to meet many times
the current geopolitical demands for many centuries, and can do so
much less expensively, safely, and reliably.
[0058] Inaccurate reports of "hundreds of years" and even some
extremist reports of "a thousand years" of nuclear energy reserves
are simply unsupportable by the raw facts. Study after study
supports a relatively abrupt end to affordable conventional energy
reserves and resources. Even optimistic nuclear physicists
proclaiming a "thousand years" of energy seem to completely ignore
the shocking impact of a mere 2% per year exponential increase of
energy demand, which destroys such optimism [e.g. a possible 400
times our current annual consumption PER YEAR in just .about.300
years]. For vivid clarity, the above most optimistic "1000 years"
of conventional nuclear fuels could be consumed in just one or two
years if, in the future, mankind actually does consume "hundreds of
times" more energy PER YEAR (see FIG. 1). The objective facts stand
in the face of unrealistic and overly optimistic nuclear physics
projections, thereby leaving but one sufficiently large energy
choice--reliable solar energy--which absolutely must be made many
times less expensive. The subject invention can achieve those
goals. In just 150 years, the probability is high that humanity
will be consuming 100 times todays annual demands. Put in another
way, within just 150 years, FIG. 1 predicts that man will consume,
in one year, an entire century of today's demand.
[0059] Prior art solar technologies all fail on cost, efficiency,
and long term storage. Typical 100-sun prior art Concentrating
Solar Power (CSP) thermal solar collection technologies fail vital
collection efficiency tests--roughly 60% efficient at meager
500-600.degree. C. collection temperatures. Far worse, prior art
CSP technologies typically achieve near 0% collection efficiencies
(radiation losses equal to incoming solar flux) at only 900.degree.
C. (1200.degree. K) as depicted in FIG. 4. To be vividly clear
about "near 0% efficiency," it means that thousands of very costly
concentrating mirrors producing 100-sun intensities would be
essentially useless and they would produce near zero net output
power.
[0060] In other words, if 100-suns (100,000 watts per square meter)
of solar power were concentrated on a highly absorbing 900.degree.
C. (1200.degree. K) solar receiver surface, each square meter of
hot receiver surface would radiate and lose an equal
amount--100,000 watts--of longer wavelength light. Unfortunately,
even 900.degree. C. is not hot enough to achieve the lowest cost
energy storage. If a hypothetical state of the art high efficiency
800.degree. C. (1472.degree. F.) turbine were powered by a
hypothetical 900.degree. C. solar storage source, the storage
source would rapidly drop only 100.degree. C. to below the
800.degree. C. design turbine temperature and efficiency would
suffer as the storage temperature decreases. By comparison, a much
higher storage temperature, of the same physical size, could supply
the same turbine design temperature and it could remain efficient
many times longer. Thus, higher temperatures permit higher energy
densities, physically smaller units, and can be much less
expensive. FIG. 8 emphasizes the formidable radiation loss physics
barriers which have plagued prior arts, and which can be soundly
overcome by the subject invention.
[0061] The scientific community is much more familiar with thermal
"conductivity" (k) than thermal "diffusion", alpha (symbol
".alpha."). Thermal conductivity is a measure of the steady state
rate of heat flow in w/mK, whereas a is related to the time
required for heat to propagate a specified distance. Thermal
diffusion is a vital component of the subject invention and thus, a
brief explanation is in order. FIG. 6 provides a few alpha (symbol
".alpha.") values of select materials.
Thermal diffusion is mathematically defined:
.differential.T/.differential.t=(k/cp*.rho.)(.differential..sup.2T/.diff-
erential.x.sup.2) Eq. 3
[0062] Where: T: temperature, K [0063] t: time, s [0064] x:
propagation distance, m [0065] .alpha.=k/(cp.rho.): thermal
diffusivity, m.sup.2/s [0066] k: thermal conductivity at T,
W/(m.quadrature.K) [0067] cp: specific heat capacity at T,
J/(kg.quadrature.K) [0068] .rho.: density at T, kg/m.sup.3
[0069] The thermal diffusion graphs in FIGS. 11(a) through 11(d)
for CO.sub.2 gas, liquid water, liquid silicone oil, and solid
copper, respectively, at modest temperatures were computer plotted
using equation 3. The computer program employing equation 3 was
interfaced with scientific chart plotting software called Scilab
5.1 (GUI). It is not obvious to those only familiar with common
thermal conductivity (k) values that thermal propagation through
materials can take so much time. For example, the thermal
conductivity of water (FIG. 11(b)) is about 0.6 w/mK and that of
silicone oil (FIG. 11(c)) (0.04 w/mK) is about 15 times less than
water. It takes about 2500 seconds for heat to propagate through 1
meter of non-convective water, but about 300 times longer (800,000
seconds) to propagate through the same thickness of silicone oil.
For an extreme example of thermal diffusion, heat generated deep in
the sun takes 100,000 years to propagate (diffuse) to the surface
and escape as radiation. Note in the chart of FIG. 6 the large
changes in the alpha (a) term in equation 3 versus temperature.
Also, particularly note how thermal propagation is related to the
square of the distance ("X") in equation 3. This distance feature,
and the propagation function exponentially controlled by it, is
critically employed in designing counterflowing solar traps
[0070] The low thermal diffusion time property of materials enables
the subject invention to overcome one of the most problematic
barriers of prior art solar collection. If the working fluid in a
solar collector is purposely flowed through the solar collector at
the correct velocity to prevent heat from ever conductively or
convectively reaching the solar entry surface, then the surface
cannot heat or radiate (lose) energy. This diffusion phenomenon
will be referenced in the invention section below, but it is not
the only feature which enables the subject invention to reach
extremely high temperatures and remain so energy efficient.
Wavelength selectivity and angular geometric radiation
directivity/selectivity are also features which greatly help to
make the subject solar traps ultra efficient at extremely high
operating temperatures. Each of the features and physics phenomena
is expanded in the preferred embodiments below.
PREFERRED EMBODIMENTS OF THE INVENTION
[0071] As illustrated diagrammatically in FIG. 13, one embodiment
the present invention--includes an exceptionally high efficiency
solar trap or solar collector system generally shown at 50, which
includes an enclosure, or container 52, having a back-most wall 54
and a front-most optically clear solar entrance aperture surface
56, to allow incoming solar radiation 58 to enter the container.
The container may be generally in the form of a rectangular box,
for example. A working fluid 60 such as a suitable liquid or gas,
is supplied to the container by way of an inlet supply line 62, the
fluid entering the container at substantially ambient temperatures
and flowing through the container in a direction that is
substantially perpendicular to the surface receiving the solar
energy, and thus perpendicular to the solar entrance aperture
surface 56. This is a laminar flow through the enclosure 50, with
at least one mechanical baffle 64 allowing the fluid to flow in a
direction indicated by arrows 66. Incoming radiation 58 is
minimally absorbed by the working fluid 60 or by the mechanical
baffles 64 within the enclosure, but maximally absorbed at the
highly absorbing internal bottom surface 90--all of which heat
ultimately is conductively transferred to the working fluid to
achieve a high temperature before the fluid exits the solar trap at
pipe 70. The highly absorbing hot bottom surface 90 radiates or
emits intense and highly dispersed radiant energy in a 2.pi.
steradian (6.28 steradian) dispersion pattern backward toward the
entry surface aperture 56 and counter to the fluid flow direction.
At least one optical baffle 64 is positioned to allow the nearly
parallel .about.0.01 steradian incoming solar radiation to travel
relatively unobstructed through the fluid and baffle(s) 64 within
the enclosure all the way to the highly absorbing bottom surface 90
of the enclosure. However, the highly dispersed 2.pi. steradian
nature of the emitted radiation from the hot bottom surface is
almost completely obstructed by the very narrow steradian openings
of the baffle(s) 64 to prevent it from reaching the entry surface
of the enclosure. Thus, narrow aperture baffles absorb 2.pi.
radiant energy by multi reflection and absorption effects. The
counterflowing fluid 60 conductively cools the radiantly heated
baffle(s) 64. Heat at the hot back surface 90 is not just radiantly
emitted toward the front aperture 56, heat energy also diffusively
conducts toward the front surface 56, which if allowed to reach and
heat the front surface 56, would then radiate into the environment
as a very large energy loss. However, the natural slow thermal
diffusion of heat through the working fluid toward the front
surface 56 is completely nullified by the slow velocity of the
counterflowing transparent fluid 60, which maintains the front
surface 56 at ambient temperatures at all times. It should also be
noted that a very slight positive counterflowing fluid pressure
also completely nullifies any possibility of internal fluids
convectively making it to the front entry surface 56. Thus,
counterflowing fluid 60 may be referred to as a thermal diffusion
and convection nullifier, while the mechanical baffle(s) 64 nullify
almost all of the radiation from the hot back surface 90--the
combined thermal nullification processes resulting in maintaining
the frontmost surface 56 near ambient temperature, and therefore,
preventing the entire solar trap from losing internal thermal
energy. Clearly, the exterior non-optical walls of the solar trap
enclosure 50 can be thermally insulated to almost any amount
desired. As will be illustrated later, an alternate embodiment of
the subject invention employs no mechanical baffles, but instead,
employs at least one counterflowing fluid which exhibits its own
highly selective transmission and absorption spectral properties,
without the need for mechanical structures, in order to provide
selective wavelength optical properties instead of angular
selectivity properties.
[0072] The flowing fluid 60 retains or traps an exceptionally large
proportion of the received solar energy as heat, and the resulting
highly heated working fluid is directed out of solar trap 50 by way
of an outlet passageway, or pipe 70 to a heat storage mass vessel
72 which may contain a porous mass 74, through which hot fluids
flow from the solar trap 50 and exit at 75 near ambient
temperature. A second heat extraction fluid may enter storage
vessel 72 at 76 and exit as a very hot fluid at 78 so that the hot
fluidic heat energy may power, on demand from storage, almost any
heat engine such as powerplants or other thermal machines 80
[0073] In another aspect, the invention is directed to a method for
collecting solar energy which may be briefly stated as including
the steps of directing radiant energy into a container, or trap,
supplying a working fluid to the container, causing the working
fluid to have a laminar flow within the container in a direction
perpendicular to the entrance aperture surface to nullify
conductive and convective thermal losses, employing one or more
baffles to nullify internal emission losses, and to convert such
solar energy almost totally into thermal energy in order to
ultimately heat a working fluid, while preventing almost all
internal energy from conductively or radiantly escaping from within
the container, and followed by directing the heated fluid out of
the container for energy storage or for direct usage.
[0074] In another preferred embodiment, many of the subject solar
traps may be mounted on a single central tower to be used as
dramatically improved central tower receivers in a well known
mirror field CSP (Concentrated Solar Power) configuration, such as
that illustrated in FIG. 3, wherein sunlight is directed by just a
few mirrors (not an entire field of mirrors) to a central tower
where one or more flat-panel solar trap receivers may be located.
This preferred embodiment will produce several surprising results,
including over 900.degree. C. operating temperatures and up to
100-fold reduction in thermal emission losses. Such exceptionally
high temperatures and unparalleled high efficiencies, exceeding
90%, create several other surprising results. These include the
elimination of thousands of the expensive heliostated mirrors which
would have been required by the prior art to make up for massive
prior art emission losses, while simultaneously achieving higher
CSP powerplant output power and storing much more energy at such
higher temperatures for much longer full generating power levels.
In other words, grouping small numbers of heliostated mirrors and
aiming them at each of a large group of solar traps mounted on one
central tower can dramatically increase the power output efficiency
of turbines, store dramatically more useful energy, and
dramatically reduce the number of costly mirrors in what is
normally a field of thousands of mirrors.
[0075] Prior art tower receivers attempt to increase efficiencies
by employing thousands of mirrors to greatly intensify the solar
flux received at a central receiver surface, and by brute force,
overcome the well known thermal reradiation losses when producing
temperatures of only 600.degree. C. This was illustrated and
mathematically shown in the discussion of FIG. 8 to be very
inefficient even at temperatures lower than 600.degree. C.
(900.degree. K), falling to essentially 0% efficiency at about
900.degree. C. (1200.degree. K).
[0076] Note that prior art central towers are designed so that a
typical 90 degree wide azimuth angle of mirrors are accepted by a
single central receiver hot surface having a typical absorbance of
0.92 and an emissivity of roughly the same 0.9. As will be shown
below, a preferred form of the present invention takes advantage of
a very narrow solar beam, typically a solid angle of 0.01 to 0.001
steradians (less than 0.3 degrees), as indicated in FIG. 13. Thus,
if only about 100 mirrors, in a field of thousands, are aimed at
one solar trap 50, then roughly 100 suns can illuminate each of
several side-by-side solar traps. Computer controlled mirror
heliostats can readily produce many small solid angle (.about.0.01
to 0.1 steradian) solar irradiance patterns of about 100 suns per
square meter from within a field of thousands of mirrors. Shown in
FIG. 13 is just one central tower solar trap example. Many solar
traps can be mounted on one central tower, as previously
suggested.
[0077] The back surface 90 of each solar trap enclosure 54 depicted
in FIG. 13 is heated by parallel solar energy that makes it through
the one or more illustrated baffles 64. The mechanical baffles may
be in the form of honeycombs, screens, or meshes which extend
laterally across the enclosure and are substantially parallel to
the front surface 56, and which are gradiantly heated from the hot
radiant surface 90 and constantly cooled by the counterflowing
fluid 60, as indicated by arrows 66, from the region of the front
optical window surface 56. The fluid ultimately passes through the
highest temperature porous heat exchanging surface 90 and finally
exits the solar trap container 52 as a very high temperature
working fluid into outlet pipe 70, where it enters a porous thermal
energy storage container 72. The hot back surface 90 thermally
radiates in a 2.pi. steradian pattern but only a very small
percentage of the 2.pi. (6.28) steradians can escape through, for
example, a honeycomb baffle which has an approximate 0.01 steradian
optical passage. Thus, in this example, approximately 0.01/6.28 or,
1.6% of the total back surface 90 radiation can escape the
honeycomb/screen/baffle network 64 and proceed towards the front
window surface 56. Using 900.degree. C. (1200.degree. K) as the
example working temperature of surface 90, equation 2 predicts a
total back surface 90 radiation of .about.117,114 w/m.sup.2.
However, this solar trap example suggests that only about 1.6% of
117,114 watts (or, 1,874 watts) can escape. The startling
conclusion is that with 100) suns incident (100,000 watts), only
1,874 watts, or just 1.9% of the incoming solar power from a small
group heliostated field mirrors, can escape just one of the several
proposed solar traps 50 which can be located on one central tower.
Thus, this example of a central tower solar trap array, would be
roughly 98.1% efficient at the extraordinary 900.degree. C.
collection temperature, compared to approximately 0% prior art
central tower efficiencies at 900.degree. C. illustrated in FIG.
8.
[0078] As will be further explained below, the term "baffle"
applies to more than just mechanical structures such as solid angle
constrictor honeycombs (polygons), screens, fibrous wool, and the
like. Such mechanical baffles can also be constructed from
materials which selectively reflect and absorb solar and infrared
radiation. Mechanical baffles can also be coated with selective
wavelength materials such as SiO.sub.2.
[0079] To be more clear about honeycomb (triangular, square,
hexagonal, polygon) mechanical "baffles" and especially "selective
wavelength" baffles, equation 4 can help design exceptionally sharp
multiple reflection selective wavelength baffles:
Net reflective transmission=(R.sub..lamda.).sup.n Eq. 4.
where: (R.sub..lamda.) defines the decimal reflection of one
surface at a given wavelength and n is the number of reflections of
light on a path through a selective wavelength baffle
[0080] A selective wavelength baffle, such as the baffle 64 used in
the embodiment of FIG. 13, transmits almost 100% of parallel
incoming sunlight where it undergoes few to no reflections in the
baffles on its path to the porous high absorption (hottest) bottom
surface 90 of the subject solar trap 50. Grazing angles of solar
light incident on the internal surfaces of baffles yield almost
total (100%) reflectivity on the incoming path to hot surface 90
However, the 2.pi. emitted radiation from the hot bottom surface 90
to baffle 64 is quite different. Steep angles of incidence from the
hot bottom radiation onto the baffle surfaces cause numerous
internal baffle surface reflections on the way toward the ambient
temperature aperture surface 56. In such multiple reflection
conditions, the total transmission of solar wavelength light,
according to equation 4, even after ten hypothetical 98% internal
reflections, would still yield (0.98).sup.10 or, 81.7% transmission
of solar light to the hottest bottom surface 90. The 18.3% absorbed
solar light along the way during the ten reflections, would
contribute to slight heating of the thin baffles 64. However, the
counterflowing fluid indicated by arrows 66 would absorb that small
absorbed solar energy inside the baffles as the fluid migrates from
the front to the rear of the container 54, slightly increasing the
fluid temperature from its original ambient temperature on its way
to the hottest porous bottom 90, where it is greatly heated and
exits as a very hot working fluid. In this example it will be
assumed that a selective wavelength coating is provided on the
baffle walls, which exhibits a slightly absorbing 64% reflection at
each longer wavelength than the incoming solar wavelengths. In
other words, in this example, the coating is designed to absorb 36%
of the radiant long wavelengths that radiate in a 2.pi. steradian
pattern away from the hot bottom surface. The bulk of the 2.pi.
steradian radiation that hits the baffle surfaces will not only be
more absorbed upon incidence of the baffle surfaces, most of the
escaping 2.pi. steradian light will also be reflected many more
times than the incoming grazing angle solar light. For a brief
appreciation of the greatly magnified escaping selective wavelength
absorption, merely assume the same number escaping reflections as
incoming reflections, namely 10 reflections. In accordance with
equation 4, the 10 outgoing reflections (at longer wavelengths)
will undergo (R.sub..lamda.).sup.n net transmission but this time
with R=0.64 and the net transmission would be (0.64).sup.10, or,
only 1.2% net transmission would escape. The vast bulk (98.8%) of
the longer wavelength radiation from hot surface 90 would be
absorbed in the selective reflective baffle, thereby radiatively
heating the baffles, and prevented from escaping. But the absorbed
baffle-heat is designed to be removed (cooled) by the much cooler
counterflowing fluid 60 headed in the direction toward the hottest
bottom of the solar trap 90. Thus, almost all of the far
less-absorbed incoming solar wavelength power (1.2%), plus almost
all (98.8%) of the intense escaping long wavelength radiation that
combine to heat this example's selective wavelength baffle, will be
recycled by the counterflowing fluid before the fluid is greatly
heated at 90 before it finally escapes the solar trap as a hot
working fluid in outlet 70. Equation 4 illustrates the considerable
flexibility in designing highly wavelength selective plus angular
selective solar traps having very narrow steradian escape paths as
well as (R.sub..lamda.).sup.n exponentially magnified wavelength
selective absorption characteristics.
[0081] Even more broadly, the term "baffle," as employed herein,
also applies to selective transmitting and absorbing gaseous or
liquid fluids--water and many oils being examples of highly
selective transmitters of solar spectrums and highly absorbing
infrared absorbing "baffles." See FIG. 12 for an example of
tabulated transmission calculations 49 and absorption spectrum
curve for a simple liquid water, highly wavelength-selective
"baffle."
[0082] The solar trap system 50 depicted in FIG. 13 illustrates
only one profound improvement over prior art CSP central tower
receivers. The example demonstrates that there are pronounced
improvements possible in powerplant efficiencies at higher
temperatures, with far lower cost thermal storage, and dramatic
reductions in the number and cost of heliostat mirrors--discussed
in more detail below. The FIG. 13 example illustrates more than a
60-fold reduction in radiation losses (only 1,874 watts/m.sup.2
lost vs. 100,000 incoming watts/m.sup.2) compared to near total
loss prior art 900.degree. C. central tower receivers. More
optimized performance than the exemplary 0.01 steradian system of
FIG. 13 is possible. Temperatures far in excess of 1000.degree. C.
and over 90% efficiency are believed to be achievable, for there is
no known upper temperature limit for counterflowing CSP solar
traps. The narrow steradian baffle aperture is a powerful
performance tool, but selective wavelength coatings on the proposed
honeycomb or baffle surfaces) can further reduce radiation losses.
Likewise, various prior art selective wavelength materials and
coatings on entry surface 56 can still further reduce radiation
losses. Moreover, numerous low emissivity absorber materials, known
in the prior art, may be applied to hot surface 90. Finally,
wavelength-selective reflective coatings--also well known in the
prior art, can be applied to the incoming solar aperture surface 56
to further reduce remnant radiative losses from solar traps. In
other words, once the bulk of the prior art inefficiency factors
are solved and eliminated by solar traps, there are numerous small
improvements still possible, leading up to the statement that solar
traps have no known upper performance limits. Clearly, the example
in FIG. 13 demonstrates, in broad terms, how to greatly reduce the
number of heliostat mirrors--the single largest cost of prior art
CSP solar thermal farms, while simultaneously slashing the size and
cost of extremely long term thermal storage to create reliable
solar power. Counterflowing solar traps make it all possible.
[0083] The first priority of counterflowing solar traps is that of
maintaining the solar entry surface 56 at non-radiative near
ambient temperatures as previously computed in the emission
discussion relating to FIG. 8. Counterflow working fluids; that is,
fluids flowing counter to the direction of reradiated heat from the
trap out of the front entry surface 56, such as nitrogen, argon,
neon, krypton, xenon, CO.sub.2, and SF.sub.6, at the correct
counterflow velocities, are one key to maintaining the front entry
surface at ambient temperatures. Heat cannot convectively or
conductively flow against a slow laminar counterflow fluid if the
counterflow velocity is equal to or greater than the thermal
diffusion velocity.
[0084] The curves 100, 102, 104 and 106 in FIGS. 14(a) through
14(d), respectively, illustrate approximate computer plots of
thermal diffusion time and velocity parameters (Temperature vs.
Distance from bottom surface 90 to entry surface 56) of
high-temperature N.sub.2, Ar, SF.sub.6 and Xe gases (not their
ambient temperature properties). Plotting these gaseous properties
is helpful as part of the calculation to achieve roughly
900.degree. C. solar trap exit gas (working fluid) temperatures
with one sun applied. It should be noted that there are no known
transparent liquid working fluids capable of withstanding much
higher than about 575.degree. C. Thus gaseous fluids are used to
achieve very high solar trap temperatures. Reliable high
temperature thermal conduction, heat capacity, and other gaseous
constants at such high temperatures are required to make thermal
diffusion calculations. Common ambient temperature properties
cannot produce accurate diffusion answers. However, high
temperature gaseous properties are not as precisely documented or
readily available in the literature at 1000.degree. K or higher.
Thus, the computer modelings here shown are only good first
approximations. As a footnote, numerous trace gases such as bromine
gas, iodine gas, and SF.sub.6 gas can be non-reactively introduced
to counterflowing inert gases to produce desirable selective
optical absorbing features to gaseous solar traps to further
improve solar energy efficiencies. Thermal properties of gaseous
mixtures are even less readily available in published
literature.
[0085] FIGS. 13 and 14 deserve more detailed explanations. FIG. 14
provides approximate laminar counterflow gas velocities required to
nullify thermal conduction (and convection) from the hottest bottom
surface 90 to the outermost exposed solar entry surface 56 of the
solar trap collector 50. By preventing the solar entry surface
temperature from rising above ambient, thermal radiation losses at
that surface can be almost eliminated. A second internal radiation
would be the direct emitted radiation from the hottest bottom
surface 90 directly through the baffle(s) and intercepted by the
front surface 56 prior to being thermally radiated into the
environment by surface 56. There are several ways to block those
internal radiation losses from escaping a solar trap, while
simultaneously allowing gases (fluids) to laminarly counterflow. As
previously detailed, one good method suggests the use of one or
more thin membrane honeycombs having small steradian optical
honeycomb apertures. Honeycombs can be constructed of thin foil
metals or even thin glass films and shaped to allow free passage of
fluids and yet provide only a very narrow solid angle of internal
radiation from escaping. Honeycomb surfaces can be highly
reflective to parallel incoming solar wavelengths, especially at
steep angles of solar incidence from a small group of mirrors, as
previously discussed. The same honeycombs can simultaneously highly
absorb longer wavelengths of internal thermal radiation light. This
represents a selective wavelength option. The combination of narrow
steradian beamwidths and the selective wavelength absorption both
bar the vast majority of the 2.pi. steradian internal radiation
escape. Such mechanical honeycomb radiation blockage prevents
thermal conduction, thermal convection, and radiation losses which
dominate the potential energy losses. Honeycombs are not the only
mechanical means to block internal radiation. Transparent and
porous thin films (films with holes), or several thin screens or
meshes, can function somewhat like honeycombs to totally block
convection and conduction losses in the presence of a
counterflowing working fluid. Similarly, extremely thin wire
screens or fibers can also pass almost all of the incoming
sunlight, absorb infrared, and permit counterflowing fluids. All of
these options are herein broadly called mechanical "baffles."
[0086] Another advantage of counterflowing fluids is the continuous
cooling effects on the fluid-cooled baffle surfaces. Radiation,
which is so T.sup.4 dependant, can be largely kept in check by the
cooler counterflowing fluid. In other words, the highest
temperatures nearest the bottom surface 90 and the associated
extraordinarily intense radiation therefrom, is absorbed deep in
the honeycomb where that heat is re-absorbed and convectively
carried by the counterflowing fluid deeper into the trap 50 towards
surface 90. When the correct fluid velocity is employed, the end
result is a fixed thermal standing wave between the ambient entry
surface 56 and the bottom hottest surface 90.
[0087] Still another advantage of counterflowing fluids in a solar
trap is that they can be employed as the working fluid throughout
the entire solar collector and its thermal storage container, shown
at 72 in FIG. 13.
[0088] Referring to FIG. 13, the counterflowing fluid 60 forms a
loop through the solar trap system 50. Ambient temperature fluid 60
is introduced at inlet pipe 62 immediately behind, at the side of,
and substantially parallel to the solar entry surface window 56.
The window can be a thin transparent glass or even a thin UV
absorbing plastic membrane because it is always maintained near
ambient temperatures. The ambient fluid slowly counterflows toward
bottom 90 of the solar trap container 54, and this "working fluid"
then exits the solar trap container 54 at high temperatures through
pipe 70, which conveys it to the top of the high mass 74, porous
solar storage container 72. The porous thermal storage mass 74 can
be glass beads or simply low cost SiO.sub.2 sand or
rocks--materials which are capable of withstanding
.about.1650.degree. C. (3000.degree. F.). The working fluid heats
the porous thermal storage bed to its highest temperature near the
top of the bed and then exits the bottom of the thermal bed, at
almost ambient temperature, into pipe 62 for recirculation through
the system 50, again at nearly ambient temperatures. The bottom of
the thermal mass bed would eventually rise in temperature were it
not for a second counterflowing heat extraction loop 77
incorporating embedded heat exchanger tubes 75 inside the storage
bed, as shown in FIG. 13. This counterflow heat extraction" loop
produces the highest temperature exit fluids or hot gases, that may
be used, for example, to supply heat to the boilers of an efficient
powerplant 80 or some other thermal machine, whereafter the heat
exchange fluid can be returned, at near ambient temperature to the
thermal storage bed at 76
[0089] As is well known by those skilled in powerplant technology,
river water or some other means is needed to keep powerplant
turbine condensers as cool as possible in order to meet equation 1
Carnot efficiency requirements. Thus, the exiting working fluid
from a powerplant (or other thermal machine) can be returned to the
bottom of the thermal storage bed 72 by way of loop 77 return pipe
76 at or near ambient temperatures. The bottom of a counterflowing
storage bed can be maintained at ambient temperatures while the top
portion of the bed can be maintained at the highest possible
temperatures from the solar trap. Should the collected solar energy
be excessive and saturate the entire solar storage medium, several
fail-safe features can automatically limit and protect the solar
trap. For example, if the working fluid were returned to the solar
entry surface at roughly 90 to 100.degree. C., the front surface 56
of the solar trap will radiate and lose about 1000 watts/m.sup.2,
an amount equal to the most intense incoming solar energy. Thus,
solar trap collection can be self limiting. The counterflowing
fluid 60 can also be halted or slowed, thereby also limiting the
collection of solar energy. Finally, if snow starts to build on top
of solar traps, the counterflowing fluid temperature can be briefly
increased to melt the snow with a surprisingly small amount of
stored energy, thereby preventing snow accumulation. The thermal
energy to melt snow (80 calories/gram) is not a large drain on a
well designed solar storage system.
[0090] The counterflowing working fluids 60 can be selected from a
wide variety of gases/fluids. The preferred gases, but by no means
limited to these gases, are the inert gases such as N.sub.2, Ar,
Ne, CO.sub.2, SF.sub.6, Kr, Xe, or mixtures thereof, with or
without selective absorbing spectral gas additives. Some would
argue that SF.sub.6 gas is a potent global warming greenhouse gas
and should not be industrially used. However, the very purpose of
solar energy is to eliminate gigatons of CO.sub.2 greenhouse
emission gases. Thus, employing a small charge of a very potent
greenhouse gas has the profound effect of eliminating millions of
times of combustion greenhouse gas emissions. SF.sub.6 is fully
justified in all solar trap configurations proposed herein. Xenon
is another controversial gas. Xenon, which has no greenhouse
impacts, is a very rare and expensive gas. Nonetheless, Xe is one
of the best gases to use in solar traps and the cost savings of
physically smaller solar trap systems can offset the one-time cost
of expensive Xe gas. Over 10 million liters of Xe gas is currently
a byproduct of air separation technologies in producing mostly
liquid nitrogen and oxygen. Low purity Xenon could, in principal,
be practically given away while negligibly impacting LN2 and oxygen
revenues. Xenon atmospheric concentrations are about 87 parts per
billion (about 4.3.times.10.sup.11 kg in earth's atmosphere or,
about 76 billion cubic meters--far more than needed to solar power
civilization). Similar arguments can be made in favor of employing
10 times more abundant and 10-fold less expensive krypton or
mixtures of Kr and Xe.
[0091] Solar traps used as receivers in central tower (CSP) systems
offer additional indirect performance advantages. As previously
stated, the first large advantage includes the possibility of more
power output from a powerplant as a result of higher Carnot
operating turbine temperatures. The highest turbine powerplant
efficiencies (over 60%) are presently possible in state-of-the-art
760.degree. C. (1400 F) ultra critical steam temperature
powerplants. Compare that efficiency with just over 35%
efficiencies of most of the world's current coal burning
powerplants. Such high solar operating temperatures can almost
halve the number and cost of CSP mirror fields--while providing
much higher thermal storage temperatures. Recall that storage
temperatures drop when called into service and thus, ideally, much
higher storage temperatures can maintain full powerplant
efficiencies. Very high CSP solar trap efficiencies make capturing
and storing extremely high temperatures possible, which slashes the
number of field mirrors by more than 50%. And the cost of thermal
storage can also be reduced dramatically in surprising ways. Thus,
the employment of the subject gaseous solar trap embodiment can
reduce the cost of CSP electricity more than 3 to 5 fold. That
helps to make solar electricity even more competitive than the
least expensive electricity on earth--even before financially
accounting for the far cleaner land, air, and sea environments.
[0092] Thus far, only one CSP preferred embodiment of the subject
invention has been illustrated. Another, non-CSP embodiment of the
invention has an even greater impact by totally eliminating
heliostated concentrating mirrors. The embodiment of the invention
depicted in FIG. 13, illustrating up to .about.100-suns,
counterflowing gases, selective absorption, and angular geometric
mechanical radiation baffling, can also be applied to one-sun flat
panels on land or on commercial building rooftops such as office,
industrial, and shopping mall rooftops, and even on commercial
parking lots. Such flat panel solar traps only collect one-sun
(1000 watts/m.sup.2) not 100,000 watts/m.sup.2 as in the above CSP
solar mirror farms. But, flat panel one-sun collectors do not
suffer from mirror shadows 13 between heliostated mirrors.
Therefore, flat panel collectors have the advantage of collecting
roughly 3 to 4 times more solar energy per acre compared to costly
mirror fields.
[0093] No sacrificial solar land is required if flat panel solar
traps are located on existing rooftops and atop existing parking
lot land. In just the U.S., there exist about 7,000 square miles
(18 billion sq meters) of potential solar rooftops and solar
parking lots. At high noon, 18 billion m.sup.2 of sunshine equates
to about 18,000 gigawatts of solar power (.about.30 trillion kwhrs
per year of cloudless skies . . . about $3 trillion at $0.10/kwh).
30 trillion kwhrs equates to about 100 quads (100 quadrillion BTUs)
per year or, the total U.S. energy demand of all electricity,
liquid fuels, natural gas, and nuclear energy combined. Of course,
this first approximation assumed cloudless days. But even with
normal cloud coverage plus large energy storage, the total actual
clean energy available on rooftops and parking lots would provide a
very large fraction of the total U.S. energy demands.
[0094] With emphasis, this flat panel, one-sun embodiment
illustrates the broad applications of the subject invention,
inviting the use of a wide range of materials, working fluid
choices, and geometric configurations, to increase temperatures and
optimize solar trap performance. Estimates have shown that the
retail value of solar energy which can be collected and sold from
shopping center rooftops (as space heating, cooling and
electricity) can exceed the typical rental revenues that can be
generated by mall owners under shopping mall roofs.
[0095] The key to one-sun, flat panel solar trap performance
remains similar to 100-sun CSP solar receiver operations. In other
words, a one-sun solar trap can achieve the same 98% efficiency if
only 20 watts/m.sup.2 of the available 1000 watts/m.sup.2 were lost
(instead of 1,845 watts/m.sup.2 of 117,000 radiative watts at
900.degree. C.). See the FIG. 13, small-mirror groups (narrow
collection angles) and 100-sun calculations. Thus, the similar
solar trap assumptions previously made for 100-suns, but with just
one sun applied, can produce a similar 98% efficiency if the
maximum temperature achieved were reduced from 900.degree. C.
(1200.degree. K) to about 400.degree. C. to about 500.degree. C.
(>700.degree. K, 752.degree. F.). The dominant T.sup.4 feature
of radiation governs the maximum temperature achievable, given the
same 0.01 steradian baffle assumptions. However, if only 90% (not
98%) one-sun efficiency is acceptable, the maximum radiation loss
allowed would be 10% of 1000 w/m.sup.2 or, a 100 watt loss in the
FIG. 13 embodiment would occur at about 700.degree. C.
(1000.degree. K, 1290.degree. F.). Thus, a 90% efficient one-sun.
700.degree. C. flat panel solar trap is readily achievable, given
the many additional prior art enhancementa previous listed (low
emissivity materials, selective wavelength reflector, etc) without
the need of any costly heliostated concentrating mirrors. And,
one-sun flat panel solar traps only require roughly 1/3 to 1/4 as
much solar collection acreage because flat panels can be located
side by side with little to no shadows cast between them.
[0096] One-sun flat panel solar traps can be gas filled or liquid
filled for counterflow purposes. Few optically clear room
temperature liquids can withstand prolonged exposure to much more
than 500.degree. C. (800.degree. K, 932.degree. F.), whereas many
gases can withstand prolonged exposure to more than 10,000.degree.
C. One optically clear liquid which boils at about 575.degree. C.
is a common vacuum diffusion pump silicon oil known as
1,1,3,5,5-pentaphenyl-1,3,5-trimethyl-siloxane oil. Very thin
(centimeters thick) flat panel solar traps of the subject invention
can work with silicone oils, but even higher temperatures can be
trapped using inert gases, particularly high atomic weight Xenon
gas. A thin, "flat panel" solar trap is illustrated in its simplest
form at 120 in FIG. 15. Such Xenon gas filled solar traps can be
thin, extremely lightweight, and achieve very high temperatures and
very high efficiencies. See FIGS. 3 and 14 for thermal diffusivity
calculations of Xenon and Silicone oils which were computer
generated using equation 3. Notice the divisor term "X.sup.2" in
equation 3, where X is the thermal propagation distance (in
meters). That means that the propagation time exponentially
increases by the square of the propagation length or, in this case,
by the thickness of the working fluid. Note also that the thermal
propagation time (in seconds) and the propagation distance (in
meters) yields a velocity of heat propagation in meters/second.
That propagation velocity is the first of two values to be
calculated in order to build a solar trap having an equal but
opposite counterflowing velocity to completely nullify the thermal
diffusivity of a fluid.
[0097] Once a thermal diffusion velocity is computed for a given
fluid, and under high temperature conditions (where all of the
fluid properties, such as density and thermal conductivity, change
with temperature), a second calculation can be performed knowing
the input solar energy per second. In the Xenon flat panel solar
trap example of FIG. 15, the solar input power of one-sun,
illustrated as arrows 122, is directed onto a solar entry surface
124 of a container, or receiver 126, which may be in the form of a
rectangular box having a bottom wall 128 and side walls 130. The
solar trap receiver 126 may incorporate one or more fine wire
screens, illustrated at 132 and 134, plus one or more small
steradian honeycomb baffles 136 and 138, extending across the solar
trap parallel to and spaced below the entry surface 124. A working
fluid 140 is supplied to the receiver 126 at the top of wall 130 in
a direction parallel to the front entry surface 124, and flows
downwardly through the receiver, and through the screens and
baffles, toward the bottom wall 128, as illustrated by arrows 142.
Within the solar trap receiver 126 and spaced above the bottom wall
128 is a solar spectrum absorption black porous layer 144 which
provides an exit plenum 146 which allows the heated working fluid
to flow out of the solar trap receiver, as indicated by arrow 148
to flow to a suitable storage unit, such as unit 172 illustrated in
FIG. 13, or to a suitable thermal machine.
[0098] The solar input power 122 to a flat solar trap receiver 120
may be assumed as 1000 watts/m.sup.2 or 1 kj/sec. To achieve the
highest solar trap operating temperature a sufficiently high fluid
thickness, X (Eq. 3), and a sufficiently slow counterflow velocity
must be selected so as to obtain the longest possible solar
exposure time in order to heat the fluid to the desired temperature
before it exits the solar trap. The latter calculation simply
requires knowledge of the exposure time (which is determined by the
solar trap thickness; i.e., the distance between the entry surface
124 and the black porous layer 144, and the fluid velocity) and
having access to the density and the specific heat values of the
chosen fluid at the desired high operating temperature. These are
reasonably straightforward calculations done by those skilled in
these arts, using equation 3, plus the fluid thermal constant
values, such as specific heat values, at elevated temperatures. The
latter calculations have been performed for Xenon gas exiting at
900.degree. C. and it was found that a Xenon solar trap must be
about 15 cm thick and must counterflow inside the trap at a
velocity of about 0.75 cm/second under a one-sun exposure
intensity. See FIG. 14(d).
[0099] Higher temperatures can be achieved if the exemplar Xenon
solar trap is made thicker than 15 cm and thus, the counterflow
velocity slowed considerably (by "1/X.sup.2"). As illustrated in
FIG. 15, once thermal diffusion is nullified, as indicated by arrow
160, by the ambient temperature counterflowing fluid 140, and the
solar energy entry surface 124 radiation losses are minimized, the
only large remaining thermal radiation loss, which must also be
minimized, is the intense 2.pi. thermal radiation losses from deep
within the solar trap, indicated by arrows 170 emanating from the
high temperature region of bottom black porous surface 144. The
latter radiation losses can be minimized by employing the host of
angle selective mechanical and wavelength-selective baffles 132,
134, 136, and 138 previously discussed, which in combination are
able to achieve almost any degree of radiative re-absorption and
counterflow-recycling of thermal energy desired, leaving only a
very small quantity of radiation to escape, as indicated at 180.
This is why it was previously stated that the subject solar traps
have no known upper temperature limits with just one-sun (or less)
applied, and even more so if a small group of highly collimated CSP
mirror optics are also employed with solar trap receivers.
Moreover, it is unnecessary to remind those skilled in these arts
that even higher solar trap temperatures can be achieved by
employing well known low emissivity materials for absorbing surface
144; high infrared absorbing thin films on the inner surfaces of
honeycombs (as previously stated); and even employing well known
wavelength-selective entrance optical windows at 124, which can be
coated with infrared reflective materials--all well known in the
prior art. Thus, in addition to the yet unknown upper temperature
limits of the subject very high temperature counterflowing solar
trap invention, the temperature and efficiency limits can be pushed
even higher by employing a variety of well known prior art
absorption and reflection techniques.
[0100] As illustrated in FIG. 16, it is anticipated that thousands
of existing coal powerplant or other sources of steam 190 can be
retrofitted with very high temperature, thick, gas filled, flat
panel, solar traps 192, to provide a clean solar-steam-generating
source of power via outlet line, or conduit 194. In the example of
this figure, steam from source 190 is conventionally supplied to
drive a powerplant turbine 196 to drive a generator 198, with the
condensed steam being returned by way of line 200 and heat
exchanger 202 to the be reheated at 190. The solar trap 192 may be
connected into the conventional system by directing the output
fluid from the heat exchange 202 via line 204 to be circulated
through the solar trap, as described above with respect to FIG. 15,
where it is heated and supplied to the steam generator 190. As
illustrated, the return line 200 is broken at 206 to direct the
fluid to the solar trap. This arrangement, which requires no costly
heliostated mirror fields, provides a simplified solar energy
retrofit of a conventional combustion powerplant. The main retrofit
requirement is enough flat panel solar trap acreage--about
1,000,000 square meters (.about.0.4 square mile, 250 acres) per
gigawatt of cloudless solar collection, plus a heat exchanger 202
and a sufficiently large thermal storage field to accommodate the
longest sustained cloud coverage in the selected geographic
location. But since coal fuel represents, by far, the greatest long
term powerplant operating cost, the cost of a one time solar
retrofit is dwarfed by the cost of coal over the lifespan of a coal
powerplant, not counting the numerous other financial and
environmental benefits of solar energy retrofitting.
[0101] Also shown in FIG. 16 at 210 is an optional non-powerplant
solar energy application; namely, that of district or city-wide
space heating and space cooling which employs the system described
in U.S. Pat. No. 6,688,129; namely, a nearly free thermal energy
delivery technology which employs the existing underground potable
water infrastructure to deliver nearly unlimited solar powered
ice-cold potable water in summer months or, solar pre-warmed
potable water in winter months.
[0102] High temperature commercial and industrial rooftop solar
raps discussed above can be scaled down for use on residential
rooftops, which represent many thousands of square miles of solar
surface area in the U.S. Furthermore, residential solar traps
applications offer several unexpected benefits far beyond those
provided by prior art supplemental hot water rooftop technology.
FIG. 7, discussed above, also depicts the shortcomings of such
prior art solar rooftop heaters. The ability of solar traps to
collect at hundreds of degrees higher temperatures, allows tens of
times more useful energy storage, not just for supplemental hot
water but, for total hot water, total space heating, total space
cooling, and total residential electric demands as well.
[0103] A typical 150 m.sup.2 residential rooftop can collect up to
1000 watts/m for 5 or more hours per day or, about 750 kwhrs (2.55
million BTUs) per day (930 million BTUs/year). Even if such a
typical residence needed 30,000 BTUs/hr (8.8 kw/hr) of winter space
heating (720,000 BTUs per day), there would be 1.85 million extra
BTUs per day left for hot water (typically 100,000 BTUs/day) and
electricity (2 kwhrs.times.24 hrs=48 kwhrs, or 163,000 BTUs per
day)--leaving about 1.567 million BTUs/day for sale during winter
months if there were a way to sell the excess solar energy at each
residence. In this example, the total 2.55 million BTUs/day or, 930
million BTUs/year, annual rooftop energy, based on a current retail
energy price of about $4 per 140,000 BTUs, would be worth about
$26,592 per year. Just the excess 1.567 million BTUs per hour (572
million BTUs/year) rooftop energy would be currently retail valued
at about $16,118 per year, if a way to sell the excess thermal
rooftop energy was available. There are at least two ways that
excess residential energy can be sold. One obvious high temperature
option would be to generate electricity on site and sell the
electricity using the existing power lines feeding the building.
If, for example, a mere 25% efficient turbine generator produced
25%.times.572 million BTUs per year of electricity--or 167,637
kwhrs/year--the electricity might be valued at 10 cents/kwhr, and
the excess electricity alone would be worth $16,764 and the waste
heat (429 million BTUs) from the 25% efficient generator, would
have an additional value of $12,257--a total excess energy sale
potential of $16,764 plus $12, 257 (or, $29,021/year)--again,
provided a means to sell the waste heat existed.
[0104] U.S. Pat. No. 6,688,129 discloses a means to sell such waste
heat. The patent describes an exceptionally low-cost method to
distribute either pre-warmed or pre-cooled potable water using the
existing potable water lines feeding residential buildings. And if
high temperature residential rooftop units are partially used to
generate on site electricity, not only can the excess electricity
be sold using the existing power grid, but the inefficient waste
heat from miniature residential thermoelectric power generators can
be employed on site for residential heating, and the excess
thermoelectric waste heat can also be sold using the nation's
existing potable water infrastructure. There is possible a nearly
100% efficient use of residential solar energy. Almost all of the
solar collected heat can go towards generating electricity (which
can all be sold at the highest prices), and the remaining waste
heat can be used for winter space heat and to provide for hot water
on site in the solar residence. Solar heat beyond the needs of the
on site solar residence can be sold as warm potable water to heat
nearby buildings as detailed in U.S. Pat. No. 6,688,129. In summer
months, super efficient, high temperature, solar traps are ideal
for highly efficient heat-powered, prior art, Absorption Cooling
technology. Excess ice-cold space cooling water can be sold via the
existing national potable water infrastructure.
[0105] FIG. 17 illustrates at 220 a serpentine counterflow
embodiment of the subject invention, generally indicted at 220,
which employs an indirect, serpentine counterflow geometry. In the
embodiments of FIGS. 13 and 15, the counterflowing fluid travels
from the solar entrance surfaces 56 and 124, respectively, in a
substantially perpendicular direction toward the respective hottest
bottom surfaces 90 and 144, and exits as a hot working fluid. In
this embodiment, a working fluid 222 enters a receiver, or chamber
224 having a serpentine fluid flow that is substantially parallel
to a solar entry surface 226. This path is defined by a series of
thin transparent walls or baffles 230 extending substantially
across the width of the chamber but open at alternate ends to
define a series of pathways 232 to provide a serpentine flow path
for the fluid though the length of the chamber from the entry
surface 226 to a solar spectrum absorbing final black wall 240, as
indicated by arrows 234. The thin transparent baffles 230 not only
define the serpentine flow path of the fluid through the receiver,
but also preferably is a glass or a film that exhibits an index of
refraction almost exactly the same as the working fluid flowing
through the solar trap 220. The working fluid velocity is highest
in the first serpentine cavity 242 in contact with the solar entry
surface 226 and slowest in the last serpentine chamber 244 of the
solar trap. Thus, the solar entry surface is maintained at the
coolest temperature, near ambient, as in pervious solar trap
embodiments. The working fluid 222 undergoes a "U" turn at the end
of each serpentine layer of flow, as shown by the arrows 234, and
it continues its serpentine flow through the receiver chamber
toward the hottest end 244 before the working fluid exits at 250.
With index matching, there would be almost zero reflection losses
inside of the entire solar trap, and all of the entering solar
spectrum can be absorbed partially in the transparent
counterflowing fluid or, better-still, fully absorbed in serpentine
chamber at 240 prior to exiting at 250, as a very hot fluid, to a
thermal storage mass (not shown). If the chosen counterflow
serpentine fluid is water based, the upper temperature limit of the
nearly 100% efficient solar trap, obviously would be less than
about 50.degree. C. But, as previously suggested, many other higher
boiling point liquids, including silicon or hydrocarbon oils, which
exhibit spectral properties similar to water, can achieve nearly
100% solar collection efficiencies at unparalleled temperatures up
to about 550.degree. C. (.about.850.degree. K, 1022.degree. F.).
Such extreme one-sun solar collection efficiencies, with almost no
thermal energy losses, allow physical thermal storage vessels to be
10-100 times smaller, while also providing extreme longevity
thermal drawdown times. The combination of low-cost super efficient
high temperature collection plus dramatically lower cost storage,
is unparalleled in solar history.
[0106] Since transparent liquid fluids greatly limit the operating
temperature of the subject solar trap invention to less than about
550.degree. C., unlimited temperature gas fluids can be employed in
the serpentine counterflow solar trap to achieve the highest
operating temperatures. However, gas fluids do not offer optical
index matching opportunities as do transparent liquids.
Fortunately, slightly absorbing, extremely broad band thin films
can be coated on each transparent serpentine layer 230 to nearly
eliminate all reflections within a serpentine solar trap. Such
slightly infrared absorbing layers 230 and absorbing thin films
offer additional benefits to trapping thermal radiation as well.
Beer's law and equation 4 come into play here, as discussed
previously concerning selective wavelength baffling, and as
depicted in FIG. 12 concerning the selective transmission
properties of water. Thus, instead of liquid serpentine solar
traps, gaseous serpentine traps can achieve much higher operating
temperatures, limited only by the endurance of materials. The
ambient temperature entrance side of serpentine solar traps is
always much cooler than the hottest end near surface 240. Thus, it
is obvious from previous discussions that extremely high
temperature transparent windows, such as fused silica glass or even
optically transparent screens can be employed at the hottest end of
serpentine solar traps. In fact, it has been made clear in other
embodiments of the subject invention, that screens, windows,
honeycombs, can be combined without departing from the general
counterflow embodiments--all aiming to maintain the entrance
surface at near ambient temperatures.
[0107] The diagrammatic serpentine flow illustrated in the
embodiment of FIG. 17 does not have to provide smoothly "layered"
or "paneled" flowing fluids. Instead, in another embodiment of the
invention diagrammatically illustrated in FIG. 18, a solar trap
chamber 260 may incorporate a series of layers of serpentine pipes,
or channels 262 carrying fluids depicted by arrows 264, without
departing from the general serpentine counterflow concept. FIG. 18
illustrates a windowless front solar entry portal generally
indicated at 266, with only four layers of varying diameter and
varying spaced solar-absorbing pipes 268, 270, 272, and 274. The
counterflowing liquid or gas enters the smallest diameter pipes, at
entrance 280, traveling at the highest velocity, which maintains
the solar entry pipe layer 268 at or near ambient temperature, and
thereafter flows at slower velocities through the larger pipes
until it reaches the hottest pipes 274 before exiting as a working
fluid at portal 282 before entering a thermal storage mass (not
shown).
[0108] A serpentine counterflow solar trap offers all of the high
solar spectrum entry opportunities of other solar traps detailed
herein, including the elimination of thermal diffusion and entry
surface thermal radiation losses; including the ability to
re-absorb and recycle intense internal thermal radiation; and the
opportunity to achieve exceptionally high solar trapping
efficiencies at exceptionally high efficiencies. Therefore, such
high temperatures at high efficiencies, offers the same
opportunities to long-term densely store solar thermal energy at
the lowest cost for reliable on-demand solar energy for unlimited
applications.
[0109] Low velocity counterflowing liquid and gaseous working
fluids in the subject solar trap invention have been illustrated to
totally nullify thermal conductivity, thereby eliminating almost
all front solar entry surface radiation losses in solar thermal
collection technology. Wavelength selective and mechanical angular
selectivity blockage of internal hot surface radiation has also
been shown to prevent thermal radiation from escaping the subject
thermal solar traps. The combined results of the breakthrough solar
trap technology plus much lower cost energy storage enables many
times less expensive solar power, thereby enabling worldwide
implementation of the most abundant energy resource on earth as the
least expensive and cleanest energy on earth. Quad generation, the
world's most efficient use of energy for electrical power, space
heating, cooling, and hot water is also disclosed.
[0110] Several very high temperature preferred embodiments of the
subject invention illustrate how it can dramatically improve
existing central tower CSP technology; how it can retrofit existing
combustion and nuclear powerplants with clean, reliable, high
temperature solar energy; and how solar energy technology can
rapidly progress beyond the concept of large central power
utilities by implementing small, highly profitable distributed
rooftop solar energy. And it has been shown that distributed
rooftop solar technology can meet the energy needs of entire
nations without demanding any dedicated solar land. High
temperature solar collection has been shown to economically store
vastly higher useful solar energy for as long as desired, thereby
making solar energy reliable without the need for extremely costly
standby conventional backup power.
[0111] It has also been shown how potable water U.S. Pat. No.
6,688,129 can be an integral component in delivering vast
quantities of perfectly clean and cheap solar energy to buildings,
and at incredibly low delivery costs, for space heating, cooling,
and hot water--over of the world's energy demand. Likewise, it has
been shown how low-cost distributed solar electricity generation
can employ the existing grids to power nations, especially if ultra
efficient electric cars are popularized.
[0112] Solar energy not only can, but must, become the world's
least expensive energy resource. There is no larger, cleaner or,
better option. The subject invention can more than meet that need.
It offers an unparalleled boost to prosperity. And, to the more
conscientious people, the most important consequence of a rapid
transition to a solar age, are the free environmental bonuses and
the preservation of the world's versatile and finite hydrocarbon
resources for posterity. Mankind can finally stop excavating for
energy and stop burning our valuable resources.
[0113] Thus, it will be understood by those skilled in the several
arts described herein that the subject invention and its many
described embodiments and numerous variations may employ a wide
variety of mechanical structures and numerous transparent and
semi-transparent liquids and gaseous fluids to produce a
counterflowing effect, wherein a working fluid opposes thermal
conduction, thermal convection, and/or internal reradiation
effects, to reduce energy loss to near zero, and thereby increase
solar energy collection efficiency, without departing from the
spirit and scope of the invention, as set forth in the following
claims. It will be understood that the upper temperature limits
discussed herein are by no means the maximum temperatures or the
maximum solar efficiencies achievable by the subject invention and
that an unlimited combination of spectrally selective solids,
liquids, gases, and coatings can be employed in and with
counterflowing working fluids and, in general, to "baffles" for
higher performance solar traps, without departing from the spirit
of the subject invention.
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