U.S. patent application number 13/056367 was filed with the patent office on 2011-10-27 for solar light collecting method in multi-tower beam-down light collecting system.
This patent application is currently assigned to ABU DHABI FUTURE ENERGY COMPANY PJSC. Invention is credited to Hiroshi Hasuike, Yutaka Tamaura, Minoru Yuasa.
Application Number | 20110259320 13/056367 |
Document ID | / |
Family ID | 41610331 |
Filed Date | 2011-10-27 |
United States Patent
Application |
20110259320 |
Kind Code |
A1 |
Yuasa; Minoru ; et
al. |
October 27, 2011 |
SOLAR LIGHT COLLECTING METHOD IN MULTI-TOWER BEAM-DOWN LIGHT
COLLECTING SYSTEM
Abstract
It enhances heat collecting efficiency of sunlight received by
heliostats. It is a solar light collecting method in a multi-tower
beam-down light collecting system, including a tower selection. The
multi-tower beam-down light collecting system is a system in which,
in a field where a plurality of beam-down light collecting towers
are present, light primarily reflected by heliostats 1 around each
tower 4 is secondarily reflected by a reflector 3 at a top part of
the tower 4 and is collected on a receiver 3 on the ground, and the
tower selection is a process in which, assuming that the heliostat
1 in a given position receives sunlight and reflects the sunlight
toward each of optionally selected two of the towers 4, 4, a light
receiving quantity on the receiver 3 of each of the towers 4 is
compared, and one of the towers 4 in which the light receiving
quantity is relatively large is selected to reflect the sunlight
toward the one of the towers 4.
Inventors: |
Yuasa; Minoru; (Tokyo,
JP) ; Hasuike; Hiroshi; (Tokyo, JP) ; Tamaura;
Yutaka; (Tokyo, JP) |
Assignee: |
ABU DHABI FUTURE ENERGY COMPANY
PJSC
Abu Dhabi
AE
COSMO OIL CO., LTD.
Tokyo
JP
|
Family ID: |
41610331 |
Appl. No.: |
13/056367 |
Filed: |
July 23, 2009 |
PCT Filed: |
July 23, 2009 |
PCT NO: |
PCT/JP2009/063154 |
371 Date: |
March 14, 2011 |
Current U.S.
Class: |
126/601 ;
126/685 |
Current CPC
Class: |
G02B 7/1824 20130101;
F24S 50/00 20180501; H01L 31/052 20130101; F24S 20/20 20180501;
F24S 2050/25 20180501; F24S 30/45 20180501; F24S 2023/87 20180501;
Y02E 10/41 20130101; F24S 23/79 20180501; Y02E 10/40 20130101 |
Class at
Publication: |
126/601 ;
126/685 |
International
Class: |
F24J 2/18 20060101
F24J002/18; F24J 2/38 20060101 F24J002/38 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 31, 2008 |
JP |
2008-197955 |
Claims
1. A solar light collecting method in a multi-tower beam-down light
collecting system, comprising a tower selection, wherein the
multi-tower beam-down light collecting system is a system in which,
in a field where a plurality of beam-down light collecting towers
are present, light primarily reflected by a heliostat is
secondarily reflected by a reflector at a top part of one of the
towers and is collected on a receiver on the ground, and wherein
the tower selection comprises comparing, assuming that the
heliostat in a given position receives sunlight and reflects the
sunlight toward each of optionally selected two of the towers, a
light receiving quantity on the receiver of each of the towers, and
selecting one of the towers in which the light receiving quantity
is relatively large to reflect the sunlight toward said one of the
towers.
2. The solar light collecting method in the multi-tower beam-down
light collecting system as set forth in claim 1, wherein, in the
tower selection comprises comparing, assuming that the heliostat in
the given position receives the sunlight and reflects the sunlight
toward each of the optionally selected two of the towers, an angle
formed by an directional vector of incident light and a directional
vector of reflection light seen from the heliostat, evaluating the
magnitude of the angle formed by the directional vector of the
incident light and the directional vector of the reflection light
seen from the heliostat, determining that a tower with respect to
which the angle formed by the directional vector of the incident
light and the directional vector of the reflection light seen from
the heliostat is smaller is the tower in which the light receiving
quantity is relatively large, and selecting said tower.
3. The solar light collecting method in the multi-tower beam-down
light collecting system as set forth in claim 1, wherein the tower
selection is performed based on results of a receiver
light-receiving-quantity calculation, a whole-sky division, and a
receiver light-receiving-quantity comparison, wherein the receiver
light-receiving-quantity calculation comprises calculating a light
receiving quantity in each receiver assuming that a given heliostat
reflects the sunlight toward each tower when the sun is in a given
position, wherein the whole-sky division comprises finding, based
on the result of the receiver light-receiving-quantity calculation,
a boundary line on the whole sky along which the light receiving
quantity in each receiver becomes the same assuming that the given
heliostat reflects the sunlight toward each tower, and dividing the
whole sky by the boundary line, wherein the receiver
light-receiving-quantity comparison comprises, with respect to each
area of the whole sky divided by the whole-sky division, comparing
the light receiving quantity to be received by the receiver of each
tower assuming that the heliostat reflects the light toward each
tower, and evaluating the magnitude of the light receiving quantity
to be received by the tower, and wherein the tower selection
comprises determining, based on the result of the receiver
light-receiving-quantity comparison, which tower is to be selected
when the sun is in the given position, controlling an orientation
of the heliostat so that the heliostat reflects the sunlight toward
the tower that is determined to be large in light receiving
quantity, and reflecting the sunlight received by the heliostat
toward the selected tower.
4. The solar light collecting method in the multi-tower beam-down
light collecting system as set forth in claim 3, wherein the
receiver light-receiving-quantity calculation comprises calculating
the light receiving quantity to be received by the receiver of each
towers assuming that the heliostat reflects the sunlight toward
each tower when the sun is in a position of a given solar
orientation and a given solar elevation.
5. The solar light collecting method in the multi-tower beam-down
light collecting system as set forth in claim 3, wherein the
receiver light-receiving-quantity calculation comprises calculating
the light receiving quantity to be received by the receiver of each
towers assuming that the heliostat reflects the sunlight toward
each tower when the sun is in a position of a given solar
orientation and a given solar elevation; and wherein the whole-sky
division comprises finding a solar elevation at which the light
receiving quantity to be received by the receiver of each towers
adjacent to each other becomes the same in the given solar
orientation to find the boundary line along which the light
receiving quantity to be received by the receiver of each towers
adjacent to each other becomes the same, and dividing the whole sky
by the boundary line.
6. The solar light collecting method in the multi-tower beam-down
light collecting system as set forth in claim 1, wherein the tower
selection is performed based on results of a receiver
light-receiving-quantity calculation and a receiver
light-receiving-quantity comparison; wherein the receiver
light-receiving-quantity calculation comprises calculating the
light receiving quantity to be received by the receiver of each
tower assuming that a given heliostat reflects the sunlight toward
each tower when the sun is in a given position; the receiver
light-receiving-quantity comparison comprises comparing, based on
the result of the receiver light-receiving-quantity calculation,
the light receiving quantity to be received by the receiver of each
tower assuming that reflection is made toward each tower; and the
tower selection comprises determining, based on the result of the
receiver light-receiving-quantity comparison, which tower is to be
selected, controlling an orientation of the heliostat so that the
heliostat reflects the sunlight toward the tower that is determined
to be large in the light receiving quantity to be received by the
receiver, and reflecting the sunlight received by the heliostat
toward the selected tower.
7. The solar light collecting method in the multi-tower beam-down
light collecting system as set forth in claim 1, wherein two or
more towers are arranged at intervals among a group of heliostats
dispersedly arranged on the ground, and each of the heliostats
selects, in accordance with the tower selection, a specified tower
such that the light receiving quantity to be received by the
receiver becomes the largest.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method of enhancing light
collecting efficiency of solar energy in a multi-tower beam-down
light collecting system.
BACKGROUND ART
[0002] Of renewable natural energy, solar thermal energy is very
promising as energy to replace fossil fuel, owing to its abundant
potential quantity (potential quantity of energy resource). The
intensity of solar thermal energy, though it varies depending on
locations, is about 1 kW/m.sup.2. Thermal energy of sunlight can be
sufficiently utilized as an energy source for operating a
thermochemical reaction plant, a power generation plant or the
like. In order to utilize the solar thermal energy as an energy
source, it is required to be efficiently converted into chemical
energy or electric energy, and in order to enhance the conversion
efficiency, it is required to efficiently collect the sunlight.
[0003] The position of the sun relative to a point on the ground
changes over time due to the rotation of the earth. Therefore, in
order to collect the sunlight and to collect solar energy
efficiently, it is required to track the sun. A device for tracking
the sun is called a heliostat.
[0004] In conventional heliostat sun-tracking-systems, a
centralized control of each heliostat through wire and wireless
communication, or a control by means of optical sensors have been
performed.
[0005] In order to collect sunlight and to efficiently obtain the
thermal energy, it is required to make the heliostats accurately
track the position of the sun. The energy obtained by collecting
the sunlight is theoretically proportional to the total area of
mirror surfaces of the heliostats. Therefore, an issue in
installing the heliostats is that, in order to obtain large
quantity of energy, it is necessary to increase the mirror surface
area of the heliostats or to increase the number of heliostats.
[0006] When obtaining thermal energy of collected sunlight using a
large number of heliostats, it is necessary to make each heliostat
track the sun, and to concentrate the reflection light of the
sunlight received in each heliostat at one point while controlling
the orientation of each heliostat.
[0007] Meanwhile, systems for collecting the sunlight received in
heliostats are classified broadly into a tower-top light collecting
system and a beam-down light collecting system. The tower-top light
collecting system includes a heliostat group and a receiver
disposed on a tower top, and is a system which collects the light
reflected by the heliostat group at the receiver on the tower top.
The beam-down light collecting system includes a heliostat group, a
reflector disposed on a tower top, and a receiver disposed on the
ground, and is a system which secondarily reflects the sunlight,
which has been primarily reflected by the heliostat group, and
collects the light on the receiver.
[0008] Further, the tower-top light collecting systems are
classified, on the basis of the shape of the receiver (heat
collector), into three types, namely, a flat receiver type, a
cavity receiver type, and a cylindrical receiver type. In the flat
receiver type, a flat receiver (heat collector) is arranged on a
top part of a tower vertically and northwardly (in a case of the
northern hemisphere), and heliostats are arranged only on the north
side of the tower to collect the reflection light on the receiver
on the tower. In the cavity receiver type, a cavity receiver (heat
collector) is arranged on a top part of a tower so that an opening
thereof faces northward and obliquely downward (in a case of the
northern hemisphere), and heliostats are arranged only on the north
side of the tower to collect the reflection light on the receiver
on the tower. In the cylindrical receiver type, a cylindrical heat
collector is arranged on a top part of a tower, and heliostats are
arranged around the tower to collect the light reflected from the
respective heliostats on the receiver on the tower.
[0009] On the other hand, according to the beam-down light
collecting system, which includes a heliostat group, a reflector
and a receiver, and is a system in which the light primarily
reflected by the heliostat group is secondarily reflected by the
reflector on a top part of the tower and the secondarily-reflected
light is collected on the receiver arranged on a bottom part of the
tower (on the ground), arranging the heliostats around the tower
enables light collection from periphery of the tower (see Patent
Documents 1 to 3).
[0010] In the beam-down light collecting system, two or more towers
may be arranged at intervals among the heliostats that are
dispersedly arranged on the ground, and this is called as a
multi-tower beam-down light collecting system.
[0011] Also, in the cylindrical receiver type tower-top light
collecting system, two or more towers may be arranged at intervals
among the heliostats that are dispersedly arranged on the ground,
and this is called as a multi-tower tower-top light collecting
system.
[0012] When comparing the functions of the multi-tower tower-top
light collecting system and the multi-tower beam-down light
collecting system, as for the multi-tower tower-top light
collecting system, in a case in which the heliostats are
continuously arranged in the east-west direction as shown in FIG.
12 and the sun is on the east side for example, there is a large
difference in light collecting quantity between the east-side
surface and the west-side surface of the receiver (heat collector)
on the top part of the tower.
[0013] In such a case, on the east-side surface of the heat
collector, the light collecting quantity becomes deficient, with
the result that the heat collecting efficiency decreases
significantly. To the contrary, in the multi-tower beam-down light
collecting system, as shown in FIG. 13, the light from the
heliostats disposed in any direction is, in theory, collected
uniformly on the upper surface of the receiver that is disposed on
a bottom part of the tower. Therefore, it is possible to suppress
the decrease of the heat collecting efficiency due to the shortage
of the light collecting quantity which is caused in the multi-tower
tower-top light collecting system, whereby high heat-collecting
efficiency is obtained.
[0014] For such reason, the multi-tower beam-down light collecting
system is advantageous as compared with the multi-tower tower-top
light collecting system.
[0015] Nevertheless, the advantage of the multi-tower beam-down
light collecting system is only in comparison with the heat
collecting efficiency of the multi-tower tower-top light collecting
system.
Patent Document 1: JP 2951297 B2
Patent Document 2: JP 2000-146310 A
Patent Document 3: JP 2004-37037 A
DISCLOSURE OF THE INVENTION
Problem that the Invention is to Solve
[0016] While the multi-tower beam-down light collecting system is
advantageous as compared with the multi-tower tower-top light
collecting system, this is only in comparison with the multi-tower
tower-top light collecting system, and a problem that the invention
is to solve is that there is room for further improvement also in
the multi-tower beam-down light collecting system.
Means for Solving the Problem
[0017] The most distinctive feature of the present invention is to
select, in a multi-tower beam-down light collecting system, a tower
toward which a heliostat reflects light, in accordance with
according a position of the sun so as to increase light collecting
quantity.
[0018] More specifically, the present invention is a solar light
collecting method in a multi-tower beam-down light collecting
system, having a tower selection,
[0019] the multi-tower beam-down light collecting system being a
system in which, in a field where a plurality of beam-down light
collecting towers are present, light primarily reflected by a
heliostat is secondarily reflected by a reflector at a top part of
one of the towers and is collected on a receiver on the ground,
and
[0020] in which the tower selection includes comparing, assuming
that the heliostat in a given position receives sunlight and
reflects the sunlight toward each of optionally selected two of the
towers, a light receiving quantity on the receiver of each of the
towers, and selecting one of the towers in which the light
receiving quantity is relatively large to reflect the sunlight
toward the one of the towers.
[0021] As a practically simple method, for example, the tower may
be selected such that, assuming that the heliostat in a given
position receives the sunlight and reflects the sunlight toward
each of the optionally selected two of the towers, an angle formed
by an directional vector of incident light and a directional vector
of reflection light seen from the heliostat is compared, the
magnitude of the angle formed by the directional vector of the
incident light and the directional vector of the reflection light
seen from the heliostat is evaluated, and a tower with respect to
which the angle formed by the directional vector of the incident
light and the directional vector of the reflection light seen from
the heliostat is smaller is determined as the tower in which the
light receiving quantity is relatively large.
ADVANTAGE OF THE INVENTION
[0022] According to the present invention, in the multi-tower
beam-down light collecting system, each of the heliostats that are
dispersedly arranged on the ground are made to select the tower
toward which the reflected sunlight is to be collected, whereby
conversion efficiency of the solar energy can be enhanced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a diagram showing a basic structure of a beam-down
light collecting system as a solar light collecting system using
heliostats;
[0024] FIG. 2 is a diagram showing an example of a configuration of
a heliostat;
[0025] FIG. 3 is a diagram showing an example of a configuration of
a reflector;
[0026] FIG. 4(a) is a plan view showing an example of a
configuration of a multi-tower beam-down light collecting system,
and FIG. 4(b) is a sectional view taken along the line A-A in FIG.
4(a);
[0027] FIG. 5 is a diagram showing a relation between a tower to be
selected and a position of the sun;
[0028] FIG. 6 is a diagram showing an example in which a tower,
toward which sunlight is to be reflected, is selected based on the
magnitude of an angle formed by the sun S and a neighboring tower
seen from an heliostat;
[0029] FIG. 7 is a diagram showing an example in which a tower
having larger light receiving quantity on the receiver is selected
from the respective towers;
[0030] FIG. 8 is a diagram showing a case in which two towers are
lined on the east and west as a calculation example of tower
selection using a light collecting simulator;
[0031] FIG. 9 is a diagram showing a comparison of reflected energy
quantity between when a tower toward which the sunlight is to be
reflected is selected and when not selected;
[0032] FIG. 10 is a diagram showing a rate of the reflected energy
quantity increased by selecting the tower toward which the sunlight
is to be reflected;
[0033] FIG. 11 shows the reflected energy quantity from a heliostat
in a day, in which (a) is a diagram showing the reflected energy
quantity in a case of a single-tower light collecting system, and
(b) is a diagram showing the reflected energy quantity in a case in
which a tower selection is carried out successively such that an
angle formed by a reflector (upper focus) and the sun seen from a
heliostat becomes smaller;
[0034] FIG. 12 is a diagram showing a light collection in a
multi-tower tower-top light collecting system; and
[0035] FIG. 13 is a diagram showing a light collection in a
multi-tower beam-down light collecting system.
EMBODIMENTS OF THE INVENTION
[0036] An object to select a tower such that light receiving
quantity becomes the largest when a heliostat receives sunlight of
the sun in a given position is achieved by evaluating the magnitude
of the light receiving quantity on a receiver of the tower, finding
a relation between a position of the sun and a tower to be
selected, and controlling the heliostat.
Embodiment 1
[0037] A multi-tower beam-down light collecting system is a system
in which, in a field where a plurality of beam-down light
collecting towers are present, light primarily reflected by
heliostats around each tower is secondarily reflected by a
reflector on a top part of the tower to collect the light on a
receiver on the ground. FIG. 1 shows a basic structure of a
beam-down light collecting system as a solar light collecting
system using heliostats. In FIG. 1, the beam-down light collecting
system is configured by a combination of a group of heliostats 1,
1, . . . dispersedly arranged on the ground and a tower 4 including
a reflector 2 and a receiver 3. The reflector 2 is a reflection
mirror disposed in a position of an upper focus at a top part of
the tower 4, and the receiver 3 is disposed in a position of a
lower focus at a bottom part of the tower 4 (on the ground) so as
to face the reflector 2. The beam-down light collecting system is a
system in which the sunlight primarily reflected by the heliostats
1 is secondarily reflected by the reflector 2, thereby collecting
the light on the receiver 3.
[0038] The heliostat (a primary reflection mirror) 1 is, as shown
in FIG. 2, a device which can orient a mirror 5 in any direction to
reflect the sunlight in the direction toward which the mirror 5 is
oriented. The reflector (a central reflection mirror, a secondary
reflection mirror) 2 is, as shown in FIG. 3, a device which
reflects again the sunlight b1 reflected from the heliostat 1
toward the receiver 3 by a mirror surface 6. The reflector 2 may be
a hyperboloid-of-revolution type, a segment type or the like.
Further, the receiver 3 is a light collector for receiving the
collected light, and is classified into a flat type, a cylindrical
type, a cavity type, and the like based on its shape.
[0039] FIG. 4 shows an example of a configuration of the
multi-tower beam-down light collecting system. The multi-tower
beam-down light collecting system is configured by a combination of
the tower 4 and a group of heliostats 1, 1 . . . around the tower
4. According to the present invention, the combination of the tower
targeted by each heliostat and the respective heliostats is not
necessarily identified. Therefore, as an embodiment, the towers are
arranged at certain intervals among groups of heliostats 1, 1 . . .
arranged dispersedly on the ground.
[0040] According to the present invention, each of the heliostats 1
selects, from some of the towers 4 set up nearby, a specified tower
4 such that the light receiving quantity on the receiver becomes
the largest, and sends forth the reflected sunlight toward the
reflector 2 of the specified tower 4 that has been selected. This
will be referred to as a tower selection.
[0041] More specifically, the tower selection is a process in
which, the light receiving quantity on the receiver 3 of the tower
4 is compared, assuming that the heliostat 1 in a given position
receives the sunlight and reflects the sunlight toward each of
optionally selected two towers 4, 4, and the tower 4 in which the
light receiving quantity is relatively large is selected to reflect
the sunlight toward that tower 4.
[0042] FIG. 4(a) shows a relation between the heliostats 1 arranged
dispersedly on the ground and a tower to be selected by each group
of heliostats 1 at a given time. In FIG. 4(a), large circles show
the towers 4 each including the reflector 2 and the receiver 3, and
small circles, triangles and rectangles therearound show the
heliostats 1. Circular, triangular and rectangular marks indicated
inside the respective large circles show that the tower is selected
by the heliostats 1 of the same mark.
[0043] While the heliostats 1 are aligned in the longitudinal and
lateral directions in this drawing, a group of heliostats that
targets the same tower forms a hexagonal formation, and the tower 4
which collects the light is located in the lower right position
therein. When focusing attention on the individual heliostats, each
of the heliostats 1 reflects the sunlight toward the selected tower
in accordance with the tower selection, regardless of the distance
to the tower as shown in FIG. 4(b), and the selected tower 4
collects the sunlight received on the reflector 2 at the receiver 3
on the ground.
[0044] The collected sunlight is thermally stored, for example, in
molten salt through the receiver (heat collector) and is used for
various purposes. Alternatively, the collected sunlight is further
collected by a secondary light collector called CPC and,
thereafter, produces chemical energy fuel through an endothermic
chemical reaction in a chemical energy conversion receiver (heat
collector for chemical energy conversion).
[0045] In order to make the heliostat 1 reflect the sunlight toward
the selected tower 4, the orientation of the heliostat 1 is
controlled. The orientation control is performed by a calendar
method and/or a sensor method described below.
[0046] (a) Calendar Method
[0047] Among the methods in which a directional vector of the
heliostat is calculated from coordinates of the heliostat,
coordinates of a target, and a directional vector of the sun to
control the orientation so as to face in that direction, the
calendar method is a method in which the directional vector of the
sun is calculated from the latitude, longitude and the time. This
calculation may be performed either independently for each
heliostat or on a computer which centrally controls the plurality
of heliostats.
[0048] (b) Sensor Method
[0049] The sensor method is a method of controlling the orientation
of the heliostat using a reflection light sensor provided in each
heliostat. Since this method is not influenced by the installation
error of the heliostat or an error in a control mechanism, it can
perform the control with good accuracy. However, when using the
sensor method, the same number of sensors as the number of
selectable towers is required for each heliostat. Further, there is
limit in a sensitivity range of the sensor. Therefore, the control
based only on this method is difficult. Accordingly, this method is
usually used in combination with the calendar method.
[0050] An example of a heliostat orientation controlling method
using the calendar method will be described below. However, the
heliostat orientation controlling method is not limited to this
method. In accordance with the following steps, calculation is
performed, in which, when seen from the heliostat, S is a
directional vector of the sun and F is a directional vector to a
target point on the tower.
[0051] Step S1: In accordance with the following expression, a
heliostat directional vector (normal vector) N is calculated.
N=(S+F)/|S+F|
[0052] Step S2: Since the orientation of the heliostat is
controlled by an azimuth A and an elevation angle E, the respective
values are calculated.
E=a sin(Nz)
A=a tan(Ny/Nx) (Range of A is 0 degree to 360 degrees)
Step S3: Based on the values obtained in Step S2, the heliostat is
controlled so as to be in the calculated orientation. Step S4: The
above steps are repeated with change of the solar directional
vector, and the orientation of the heliostat is sequentially
changed accordance with the change of the solar directional
vector.
[0053] In the invention, assuming that the heliostat in a given
position collects the light toward a given tower when the sun is in
a given position, the quantity of light collected on a receiver of
the given tower may be obtained, not necessarily through an actual
measurement, but by finding a relation between the solar position
and a tower to be selected in advance through calculation using a
light collecting simulator.
[0054] In the beam-down light collecting system, the sunlight
reflected by the heliostat 1 is reflected again by the reflector 2
of the tower 4 and is collected on the receiver 3. Nevertheless,
the quantity of light received on the heliostat 1 is not the same
as the quantity of light received on the receiver 3, and decreases
due to various factors. By performing light collecting calculation,
these factors are taken into consideration, and the quantity of
light to be received on the receiver 3 is obtained.
[0055] The light collecting calculation is performed, for example,
by a ray tracing method in which each light ray of the sun is
traced one by one in accordance with the procedure of the following
steps.
[0056] Here, the light ray is what puts three elements together,
namely a pass point (a point on the ray including a starting point
and an end point) p, a directional vector v, and intensity e.
[0057] Procedure of light-collection calculating method
(light-collection calculation with a given solar position)
Step T1: Tracing a light ray which is emitted from a given position
on the solar surface (because the sun is not a point light source
but a surface light source) and reaches a given position
(determination of initial light ray vector). Step T2: Determining
whether the light ray hits a given heliostat (Cosine factor). Step
T3: Determining whether the light ray is shielded, before reaching
the given heliostat, by another heliostat or other obstacles
(Shadowing). Step T4: Reflecting the light ray by the heliostat
(primary reflected ray) (Attenuation based on reflectance and
cleanliness; Variation of reflection angle due to mirror
installation error, and the like) Step T5: Determining whether the
primary reflected ray is shielded by another heliostat or other
obstacles (Blocking). Step T6: Determining whether the primary
reflected ray hits a reflector (Spillage in reflector). Step T7:
Reflecting the primary reflected ray by a central reflection mirror
(secondary reflected ray) (Attenuation based on reflectance,
cleanliness and air; Variation in reflection angle due to mirror
installation error, and the like) Step T8: Determining whether the
secondary reflected ray enters a receiver opening (Spillage in
receiver). Step T9: The secondary reflected ray reaching a receiver
(Attenuation by air). Step T10: Repeating the above steps
[0058] In the invention, the processing of comparing the magnitude
of light collecting quantity, assuming that a given heliostat
receives the light from the sun in a given position, between
receivers of two optional neighboring towers, and selecting the
tower in which the light collecting quantity is larger, may be
performed by means of a simulator. When selecting the tower using a
simulator, a light collecting simulator is used, receiver
light-receiving-quantity calculation, whole-sky division for tower
selection, and receiver light-receiving-quantity comparison are
performed and, thereafter, the tower selection is performed based
on results of these processing. In the tower selection, the tower
selection when the sun is in a given position is performed, and the
sunlight is collected to the selected tower.
[0059] More specifically,
[0060] the receiver light-receiving-quantity calculation is a
processing of calculating the light receiving quantity assuming
that the heliostat reflects the sunlight toward each tower when the
sun is in a given position;
[0061] the whole-sky division is a processing of, based on the
result of the receiver light-receiving-quantity calculation,
dividing the whole sky by a boundary, on a position of which the
respective light receiving quantities of the adjacent towers are
the same; and
[0062] the receiver light-receiving-quantity comparison is a
processing of comparing the light quantity to be received the
receiver in each area of the whole sky divided by the whole-sky
division, and indicating the tower in which the light receiving
quantity is larger. In the tower selection, based on the result of
the receiver light-receiving-quantity comparison, the tower
determined to be large, when the sun is in a given position, in
light receiving quantity is selected, the orientation of the
heliostat is controlled so that the heliostat reflects the sunlight
toward the selected tower, and the sunlight received by the
heliostat is reflected toward the selected tower.
[0063] As a calculation example of the tower selection by means of
the light collecting simulator, a case where two towers are
arranged east and west will be described below (see FIG. 5).
[0064] Calculation Conditions
Tower position: Tower 4L (-150, 0, 100), Tower 4R (150, 0, 100)
Heliostat position: (50, 50, 0) Setting of heliostat focal
distance: 150 m (Distance at which the reflection light from the
heliostat focuses an image: the heliostat forms a pseudo concave
mirror by a plurality of facet mirrors.)
[0065] (1) Receiver Light-Receiving-Quantity Calculation:
[0066] The light receiving quantity of the receiver in each tower
when the sun is in a position of a given solar elevation and a
given solar orientation has been found by calculation and a result
of table 1 has been obtained. In the table 1, Azimuth represents a
solar orientation angle (deg), Elevation is a solar elevation angle
(deg), H1 ref represents the light reflection quantity in case that
the light is collected to the tower 4L, H1rec represents the
receiver light receiving quantity in case that the light is
reflected by the tower 4L, H2ref represents the heliostat light
reflection quantity in case that the light is reflected to the
tower 4R, and H2rec is the receiver light receiving quantity in
case that the light is reflected to the tower 4R. Further, in the
table 1, the east is taken as an origin (0 degree), the north is
taken as 90 degrees, the west is taken as 180 degrees, and the
south is taken as 270 degrees. Further, the heliostat
light-refection quantity is described as reference.
TABLE-US-00001 TABLE 1 Relation between solar position and light
collecting quantity in each tower Azimuth Elevation H1ref H1rec
H2ref H2rec 0 10 387.107 111.348 818.153 721.408 0 30 722.318
264.046 1552.12 1373.04 0 50 996.741 476.059 1605.81 1420.28 0 70
1211.01 605.066 1575.43 1392.81 0 90 1381.06 732.076 1497.86
1313.85 30 10 400.628 113.258 1232.86 1078.77 30 30 732.622 270.056
1473.2 1298.44 30 50 1000.5 482.421 1517.26 1339.68 30 70 1205.42
605.175 1532.73 1350.64 30 90 1382.77 733.951 1489.51 1308.01 60 10
637.249 240.888 1066.38 891.28 60 30 870.539 372.101 1345.8 1159.97
60 50 1099.73 555.989 1432.51 1252.26 60 70 1256.74 671.049 1481.53
1298.95 60 90 1379.92 731.819 1494.19 1310.74 90 10 537.104 259.238
622.865 479.06 90 30 1152.33 582.08 1160.49 926.496 90 50 1254.83
675.23 1313.84 1117.27 90 70 1329.92 729.002 1413.87 1229.91 90 90
1386.68 736.765 1489.63 1307.18 120 10 1122.59 614.479 686.932
359.932 120 30 1368.38 740.107 1006.47 690.428 120 50 1410.18 775.2
1208.37 976.036 120 70 1411.49 774.331 1368.6 1175.46 120 90
1380.99 733.381 1494.17 1311.5 150 10 1298.5 726.513 616.878
271.147 150 30 1515.53 818.465 928.588 580.749 150 50 1518.28
825.833 1165.5 908.623 150 70 1472.55 802.038 1352.93 1157.21 150
90 1382.05 731.96 1490.44 1306.51 180 10 818.153 486.185 596.38
319.166 180 30 1532.76 820.542 980.201 646.047 180 50 1578.88
846.465 1191.85 957.465 180 70 1512.52 816.713 1363.41 1168.66 180
90 1384.49 735.477 1490.01 1307.22 210 10 1392.83 763.178 819.831
571.754 210 30 1607.49 856.642 1118.98 885.979 210 50 1589.52
848.509 1282.89 1087.7 210 70 1509.99 813.816 1406.05 1218.9 210 90
1381.45 733.063 1495.52 1312.11 240 10 1299.37 719.02 1031.55
843.348 240 30 1519.1 821.573 1296.54 1106.12 240 50 1520.06
823.841 1404.77 1226.27 240 70 1472.05 803.354 1467.1 1286.72 240
90 1382.28 734.209 1489.57 1306 270 10 655.82 366.929 765.71
672.311 270 30 1352.06 730.564 1453.26 1276 270 50 1394.38 765.643
1523.65 1342.85 270 70 1409.34 772.71 1530.19 1346.49 270 90
1384.16 734.556 1492.39 1308.74 300 10 905.019 443.264 1335.93
1176.92 300 30 1138.19 573.582 1573.53 1390.71 300 50 1242.71
661.241 1601.43 1415.84 300 70 1328.35 724.13 1568.51 1384.77 300
90 1383.42 731.767 1495.13 1311.45 330 10 585.233 221.102 1367.5
1206.57 330 30 897.412 382.687 1618.07 1430.86 330 50 1092.07
552.002 1634.83 1444.97 330 70 1256.41 662.566 1586.16 1400.28 330
90 1383.15 733.239 1499.22 1315.26
(2) Whole-Sky Division:
[0067] In this processing, from the result of the table 1,
regarding the relation between the tower to be selected and the
solar position, the solar elevation at which the receiver light
receiving quantity (H1rec) of the tower 4L and the receiver light
receiving quantity (H2rec) of the tower 4R become the same is found
for each solar orientation, and the whole sky is divided by a
boundary line connecting the obtained elevation positions. Here,
from the solar elevation and the light receiving quantity (Table
1), the solar elevation at which the light collecting quantity of
each tower becomes the same is found for each solar orientation.
The results are shown in Table 2.
TABLE-US-00002 TABLE 2 Relation between solar orientation and solar
elevation at which light collecting quantities of towers 1 and 2
become the same Azimuth Even ref Even rec 0 0 0 30 0 0 60 0 0 90 0
0 120 75.49625 33.96615 150 80.49252 44.83379 180 81.7119 42.22403
210 79.53534 27.34219 240 70.88204 0 270 0 0 300 0 0 330 0 0
[0068] The results in the Table 2 are expressed in polar coordinate
in which the zenith is taken as zero, as shown in Table 3 (In the
elevation angle, a ground level is taken as 0 degree and the zenith
is taken as 90 degrees. In the polar coordinate, the zenith is
taken as 0 degree and the ground level is taken as 90 degrees.)
Further, the table 3 is plotted with the polar coordinate as shown
in FIG. 6.
[0069] Here, a circle shows the whole sky. A center is the zenith
and the circumference becomes the ground level. When the sun lies
in the position of a dotted line, the receiver light receiving
quantity in each tower in case that the heliostat reflects the
sunlight toward each tower becomes equal. When the sun lies in the
position of a solid line, the reflection quantity from the
heliostat in case that the heliostat reflects the sunlight toward
each tower becomes equal. In the actual case, by shortening each
interval of the azimuth and the elevation angle in this
calculation, more exact figure can be created.
TABLE-US-00003 TABLE 3 Relation between solar orientation and solar
elevation at which light collecting quantities of towers 4L and 4R
become the same (polar coordinate) Azimuth Even ref Even rec 0 90
90 30 90 90 60 90 90 90 90 90 120 14.50375 56.03385 150 9.507478
45.16621 180 8.288104 47.77597 210 10.46466 62.65781 240 19.11796
90 270 90 90 300 90 90 330 90 90
[0070] (3) Receiver Light-Receiving-Quantity Comparison:
[0071] The light receiving quantity (H1rec, H2rec) in relation to
the solar azimuth is compared between the respective towers, and
the magnitude of the light receiving quantity is evaluated.
Firstly, from the Table 1, it is found that: when the azimuth is 0,
30, 60, 90, 240, 270, 300, or 330 degrees, the light receiving
quantity H1rec is always smaller than the light receiving quantity
H2rec. Namely, when the solar orientation is in this range, it is
better that the tower 4R is always selected. Here, for convenience
sake, the elevation at which the light receiving quantity becomes
the same is taken as 0 degree.
[0072] Next, from the Table 1, it is found that: when the azimuth
is 120, 150, 180, or 210 degrees and when the solar elevation is
low, the light receiving quantity Hlrec is larger than the light
receiving quantity H2rec; and when the solar elevation is high, the
light receiving quantity H1rec is smaller than the light receiving
quantity H2rec. Considering this result, the tower having the
larger light receiving quantity in each of the divided areas of the
whole sky is as shown in FIG. 7.
[0073] (4) Tower Selection
[0074] When the sun is in a given position, a tower to be selected
can be selected by means of FIG. 7.
[0075] Further, though the light collecting quantity decreases due
to various factors in the light calculation, it is also possible to
perform simply the tower selection in consideration of the decrease
due to only a cosine factor of their factors. In this case, it can
be said that the tower selection is processing of performing
control so that an angle formed by the sun and each upper focus
becomes small.
[0076] Namely, as shown in FIG. 8, comparison is performed between
an angle .theta.1 formed by the sun S and a neighboring tower 4a
when seen from a given heliostat 1, and an angle .theta.2 formed by
the sun S and another neighboring tower 4b. In case that
.theta.1<.theta.2, the tower 4a is selected, whereby the
reflection amount from the heliostat is made substantially largest
and the effective use of solar energy can be made. However, the
light receiving quantity of the receiver is determined by other
many factors. Therefore, in this case, compared with the case where
the tower selection is rigorously performed by means of the light
collecting simulator, the light collecting quantity decreases.
[0077] Next, regarding how effective such the tower selection in
consideration of the decrease due to only such the cosine factor
is, in the multi-tower beam-down light collecting system, in the
example where such a tower that the angle formed by the sun and
each tower seen from the heliostat becomes small is selected and
the sunlight is collected to the selected tower, the calculation
has been performed using the model in FIG. 5 described before. In
FIG. 5, an X-axis represents an east-west direction, and a Y-axis
represents a zenith direction. It is assumed that: on an X-Y plane,
the sun rises from the east at 6:00 a.m., passes through the zenith
at 12:00, and sinks at 6:00 p.m.
[0078] Here, the direct normal irradiance (DNI) is taken as 1.0
kW/m.sup.2, the two towers are set respectively in the position of
X=150 m and in the position of X=-150 m, and the positions (heights
of upper focus) of the reflectors in the both towers are taken as
Y=100 m. The area of a mirror per heliostat is taken as 1.0
m.sup.2, and the thirty heliostats have been arranged between the
both towers. Blocking and shadowing among the heliostats are not
taken into consideration.
[0079] FIG. 9 shows the reflected energy quantity of the heliostat
in a day. O-mark shows the reflected energy quantity in case that
the heliostat collects the light to the left tower, and
.quadrature.-mark shows the reflected energy quantity in case that
the heliostat collects the light to the right tower. .DELTA.-mark
shows the reflected energy quantity in case that the tower in which
the angle formed by the reflector (upper focus) and the sun which
are seen from the heliostat becomes small is selected as needed.
Further, FIG. 10 shows the rate of the reflected energy quantity
increased by performing the tower selection. As clear from these
results, it has been found that the reflected energy quantity of
each heliostat in a day increases by 5% to 22% due to the tower
selection, compared with the case of the single-tower light
collecting system. At the same time, it has been found that the
heliostat located in an intermediate point between the two towers
is highest in rate of its increase.
[0080] Further, FIG. 11 shows the reflected energy quantity of the
heliostat in a day. In this figure, the towers are located on both
sides of a rectangular filed. FIG. 11(a) shows the reflected energy
quantity in case of a single-tower light collecting system, and (b)
shows the reflected energy quantity in case that the tower in which
the angle formed by the reflector (upper focus) and the sun which
are seen from the heliostat becomes small is selected as needed. It
has been found from this figure that the area of a region where the
reflection quantity from one heliostat becomes 10.5 kWh and more is
about 13 times, compared with that in the single-tower light
collecting system.
[0081] Than the above simple tower selection, the tower selection
by means of the result of the elevation calculation and the result
of the light receiving quantity comparison in FIGS. 6 and 7 becomes
more suitable. Namely, as clear from FIG. 6, in comparison between
a case (solid line) where the tower light receiving quantity
becomes simply equal in consideration of only the angle and a case
(dashed line) where the tower light receiving quantity becomes
equal by performing the elevation calculation, the area of region
surrounded by the dashed line where the light is reflected toward
the tower 4R is larger than that surrounded by the solid line, the
tower selection is appropriately performed there and the tower
light receiving quantity becomes larger.
[0082] As described above, in the invention, in case that the sun
is in a given position, the light collecting calculation is
performed and the tower selection is performed. In case that the
invention is actually applied to the control of heliostat, such the
calculation is performed in advance and its calculation result can
be used also in control of the heliostat operation. Further, by
simultaneously carrying out the high-speed calculation processing
of the light collecting simulator during the heliostat operation,
when the light of the sun lying in the solar position at that time
is received, during the operation, the magnitude of the light
collecting quantities of the receivers in the two optional towers
near the heliostat is evaluated, whereby the processing of
selecting the tower in which the light collecting quantity is large
may be performed. When the tower selection is performed by
simultaneously performing the high-speed calculation processing of
the light collecting simulator, the receiver
light-receiving-quantity calculation is performed by the light
collecting simulator, and the tower selection is performed on the
basis of the result of the receiver light-receiving-quantity
comparison. Therefore, the whole-sky division may be applied as
needed.
INDUSTRIAL APPLICABILITY
[0083] The sunlight, as a renewable energy source, has an enormous
quantity of energy, and is a clean energy source which has no
environment pollution. The sunlight enables fuel production which
utilizes the concentrated solar thermal energy in endothermic
reaction of chemical reaction, and the stable supply of the
generated electric power by concentrating the thin solar energy as
the solar thermal power generation system. Further, by applying the
sunlight to technology of synthesizing methanol from hydrogen and
carbon monoxide which have been manufactured by coal gasification
and natural gas steam reforming, it is possible to manufacture
methanol of which heat quantity is 6-10% or more larger than total
heat quantity of coal and methane of raw materials, and the
sunlight is greatly expected as what can significantly reduce
emission of carbon dioxide in the methanol manufacturing
process.
DESCRIPTION OF REFERENCE SIGNS
[0084] 1 Heliostat [0085] 2 Reflector [0086] 3 Receiver [0087] 4
Tower [0088] 5 Mirror [0089] 6 Mirror Surface
* * * * *