U.S. patent application number 13/018247 was filed with the patent office on 2012-08-02 for heliostat assignment in a multi-tower field.
This patent application is currently assigned to GOOGLE INC.. Invention is credited to Alec Brooks, Andrew B. Carlson, John S. Fitch, Ross Koningstein.
Application Number | 20120192857 13/018247 |
Document ID | / |
Family ID | 46576304 |
Filed Date | 2012-08-02 |
United States Patent
Application |
20120192857 |
Kind Code |
A1 |
Carlson; Andrew B. ; et
al. |
August 2, 2012 |
Heliostat Assignment in a Multi-Tower Field
Abstract
Methods, systems, and apparatus, including computer programs
encoded on one or more computer storage devices, for collecting
solar energy using heliostats arranged about a collection of solar
energy receivers. For each heliostat, estimated efficiencies of the
heliostat in directing solar rays to two or more receivers at
various times of day are determined. Each heliostat is assigned to
direct solar rays to two or more different receivers at two or more
different times of day, wherein each heliostat directs solar rays
to one receiver at a time and the assigning is based on the
determined estimated efficiencies for the heliostat at the various
of times of day. In some implementations, the receivers are
repositionable.
Inventors: |
Carlson; Andrew B.;
(Atherton, CA) ; Brooks; Alec; (Pasadena, CA)
; Fitch; John S.; (Los Altos, CA) ; Koningstein;
Ross; (Menlo Park, CA) |
Assignee: |
GOOGLE INC.
Mountain View
CA
|
Family ID: |
46576304 |
Appl. No.: |
13/018247 |
Filed: |
January 31, 2011 |
Current U.S.
Class: |
126/573 ;
126/572; 126/714 |
Current CPC
Class: |
F24S 50/20 20180501;
Y02E 10/47 20130101; F24S 50/00 20180501; F24S 23/70 20180501; Y02E
10/40 20130101; F24S 20/20 20180501 |
Class at
Publication: |
126/573 ;
126/714; 126/572 |
International
Class: |
F24J 2/38 20060101
F24J002/38; F24J 2/40 20060101 F24J002/40; F24J 2/00 20060101
F24J002/00 |
Claims
1. A method for operating a multi-tower heliostat field,
comprising: for each heliostat of a plurality of heliostats that
are arranged about a plurality of receiver towers, determining a
plurality of estimated efficiencies of the heliostat in directing
solar rays to two or more receiver towers at a plurality of times
of day, wherein each receiver tower has a receiver mounted to the
tower that is configured to receive solar rays reflected from
heliostats included in the plurality of heliostats; assigning each
heliostat to direct solar rays to two or more different receiver
towers at two or more different times of day, wherein each
heliostat directs solar rays to one receiver tower at a time and
the assigning is based on the determined estimated efficiencies for
the heliostat at the plurality of times of day.
2. The method of claim 1, wherein: determining a plurality of
estimated efficiencies of each heliostat further comprises
determining a plurality of estimated efficiencies of the heliostat
in directing solar rays to the two or more receiver towers at a
plurality of times of day on a plurality of days of a year; and
assigning each heliostat to direct solar rays to two or more
different receiver towers is further based on the determined
estimated efficiencies at the plurality of times of day on the
plurality of days of the year.
3. The method of claim 1, wherein assigning each heliostat to
direct solar rays to two or more different receiver towers
comprising assigning each heliostat to direct solar rays to two or
more different receiver towers that are each positioned south of
the heliostat for a heliostat field in the northern hemisphere and
that are each positioned north of the heliostat for a heliostat
field in the southern hemisphere.
4. The method of claim 1, further comprising: for each heliostat,
controlling positioning of one or more reflective surfaces included
on the heliostat based on a position of the Sun and which receiver
tower the heliostat is assigned to direct solar rays toward.
5. The method of claim 1, wherein each receiver is configured to
receive solar rays at a receiver face, the method further
comprising: selectively moving one or more receivers mounted to one
or more receiver towers to adjust positions of the one or more
receiver faces.
6. The method of claim 5, wherein the positions of the one or more
receiver faces are adjusted in accordance with positions of
heliostats assigned to direct solar rays to the one or more
receivers corresponding to the receiver faces.
7. The method of claim 5, wherein the positions of the one or more
receiver faces are adjusted based on an azimuth direction of the
Sun.
8. The method of claim 5, wherein moving one or more receivers
comprises rotating the one or more receivers about a vertical axis
to adjust the positions of the one or more receiver faces.
9. The method of claim 5, wherein moving one or more receivers
comprises rotating the one or more receivers about a horizontal
axis to adjust the positions of the one or more receiver faces.
10. The method of claim 5, wherein moving one or more receivers
comprises moving the receiver towers that correspond to the one or
more receivers to adjust the positions of the one or more receiver
faces.
11. The method of claim 1, wherein assigning each heliostat to
direct solar rays to two or more different receiver towers at two
or more different times of day further comprises: for a particular
heliostat, determining whether a benefit of reassigning the
particular heliostat from a first receiver tower to a second
receiver tower outweighs a cost of the reassigning, wherein the
assigning is based at least in part on the determination.
12. The method of claim 1, wherein assigning each heliostat to
direct solar rays to two or more different receiver towers at two
or more different times of day further comprises: for a particular
heliostat, determining flux distributions over surfaces of a first
receiver and a second receiver when the heliostat is assigned to
direct solar rays to first and second receiver towers that
correspond to the first and second receivers, wherein the assigning
is based at least in part on the determination of flux
distribution.
13. A method for operating a multi-tower heliostat field,
comprising: for each receiver tower of a plurality of receiver
towers about which are arranged a plurality of heliostats,
assigning a set of heliostats to direct solar rays to the receiver
tower, wherein each receiver tower has a receiver mounted to the
tower that is configured to receive solar rays reflected from
heliostats included in the plurality of heliostats; and for each
receiver tower, based on a level of solar energy absorbed by the
receiver mounted to the tower, reassigning which heliostats from
the plurality of heliostats are included in the set of heliostats
that are assigned to direct solar rays to the receiver tower.
14. The method of claim 13, further comprising: for each receiver
tower, monitoring the level of solar energy absorbed by the
receiver mounted to the tower during daylight hours.
15. The method of claim 14, wherein when the monitored level of
solar energy drops below a first predetermined threshold value for
one or more of the receiver towers, closing in a subset of the
receiver towers and reassigning the heliostats included in the sets
of heliostats assigned to direct solar rays to the closed-in subset
of receiver towers to different receiver towers included in the
plurality of receiver towers.
16. The method of claim 15, wherein when the monitored level of
solar energy rises above a second predetermined threshold value for
one or more of the receiver towers, re-activating one or more of
the closed-in receiver towers and reassigning at least some of the
heliostats to direct solar rays to the reactivated one or more
receiver towers.
17. The method of claim 13, further comprising: for each heliostat,
controlling positioning of one or more reflective surfaces included
on the heliostat based on a position of the Sun and which receiver
tower the heliostat is assigned to direct solar rays toward.
18. The method of claim 13, wherein each receiver is configured to
receive solar rays at a receiver face, the method further
comprising: selectively moving one or more receivers mounted to one
or more receiver towers to adjust positions of the one or more
receiver faces.
19. The method of claim 18, wherein the positions of the one or
more receiver faces are adjusted in accordance with positions of
heliostats assigned to direct solar rays to the one or more
receivers corresponding to the receiver faces.
20. The method of claim 18, wherein the positions of the one or
more receiver faces are adjusted based on an azimuth direction of
the Sun.
21. The method of claim 18, wherein moving one or more receivers
comprises rotating the one or more receivers about a vertical axis
to adjust the positions of the one or more receiver faces.
22. The method of claim 18, wherein moving one or more receivers
comprises rotating the one or more receivers about a horizontal
axis to adjust the positions of the one or more receiver faces.
23. The method of claim 18, wherein moving one or more receivers
comprises moving the receiver towers that correspond to the one or
more receivers to adjust the positions of the one or more receiver
faces.
24. The method of claim 13, wherein reassigning which heliostats
from the plurality of heliostats are included in the set of
heliostats that are assigned to direct solar rays to the receiver
tower, further comprises: determining whether a benefit of
reassigning the heliostats from a first receiver tower to a second
receiver tower outweighs a cost of the reassigning, wherein the
reassigning is based at least in part on the determination.
25. The method of claim 13, wherein reassigning which heliostats
from the plurality of heliostats are included in the set of
heliostats that are assigned to direct solar rays to the receiver
tower, further comprises: determining flux distributions over
surfaces of a first receiver and a second receiver the heliostats
are assigned to direct solar rays to first and second receiver
towers that correspond to the first and second receivers, wherein
the reassigning is based at least in part on the determination of
flux distribution.
26. A method for operating a multi-tower heliostat field,
comprising: for each receiver tower of a plurality of receiver
towers about which are arranged a plurality of heliostats,
assigning a set of heliostats to direct solar rays to the receiver
tower, wherein each receiver tower has a receiver mounted to the
tower that is configured to receive solar rays reflected from
heliostats included in the plurality of heliostats; and based on
estimated levels of solar ray intensity at different times of the
day, closing in a subset of the receiver towers during one or more
time periods a day and reassigning the heliostats included in the
sets of heliostats assigned to the closed-in subset of receiver
towers to different receiver towers included in the plurality of
receiver towers during those time periods.
27. The method of claim 26, wherein closing in a subset of the
receiver towers and reassigning the heliostats is further based on
estimated levels of solar ray intensity at different times of the
day and at different times of the year.
28. The method of claim 26, further comprising: for each heliostat,
controlling positioning of one or more reflective surfaces included
on the heliostat based on a position of the Sun and which receiver
tower the heliostat is assigned to direct solar rays toward.
29. The method of claim 26, wherein each receiver is configured to
receive solar rays at a receiver face, the method further
comprising selectively moving one or more receivers mounted to one
or more receiver towers to adjust positions of the one or more
receiver faces.
30. The method of claim 29, wherein the positions of the one or
more receiver faces are adjusted in accordance with positions of
heliostats assigned to direct solar rays to the one or more
receivers corresponding to the receiver faces.
31. The method of claim 29, wherein the positions of the one or
more receiver faces are adjusted based on an azimuth direction of
the Sun.
32. The method of claim 29, wherein moving one or more receivers
comprises rotating the one or more receivers about a vertical axis
to adjust the positions of the one or more receiver faces.
33. The method of claim 29, wherein moving one or more receivers
comprises rotating the one or more receivers about a horizontal
axis to adjust the positions of the one or more receiver faces.
34. The method of claim 29, wherein moving one or more receivers
comprises moving the receiver towers that correspond to the one or
more receivers to adjust the positions of the one or more receiver
faces.
35. A heliostat field system comprising: a plurality of heliostats;
a plurality of receiver towers, wherein each receiver tower has a
receiver mounted to the tower that is configured to receive solar
rays reflected from a set of heliostats included in the plurality
of heliostat, wherein the set of heliostats are assigned to direct
solar rays to the receiver tower; and an assignment control system
configured to assign each heliostat to direct solar rays to two or
more different receiver towers at two or more different times of
day, wherein each heliostat directs solar rays to one receiver
tower at a time and the assigning is based on estimated
efficiencies of the heliostat in directing solar rays to the two or
more receiver towers determined for a plurality of times of
day.
36. The heliostat field system of claim 35, further comprising: a
heliostat tracking control system configured to control, for each
of the plurality of heliostats, positioning of one or more
reflective surfaces included on each heliostat based on a position
of the Sun and which receiver tower the heliostat is assigned to
direct solar rays toward.
37. The system of claim 35, wherein the assignment control system
is further configured to assign the plurality of heliostats to
direct solar rays to a subset of the receiver towers, such that the
remaining receiver towers are closed-in, based on estimated levels
of solar ray intensity at different times of the day.
38. The system of claim 35, wherein the assignment control system
is further configured to assign the plurality of heliostats to
direct solar rays to the plurality of receiver towers, such that
the closed-in receiver towers are reactivated, based on the
estimated levels of solar ray intensity at different times of the
day.
39. The system of claim 35, further comprising: a solar energy
level monitoring system configured to monitor, for each of at least
some of the receiver towers, a level of solar energy absorbed by
the receiver mounted on the receiver tower; wherein the assignment
control system is further configured to assign each heliostat to
direct solar rays to two or more different receiver towers based on
the monitored levels of solar energy.
40. The system of claim 39, wherein the assignment control system
is further configured to assign the plurality of heliostats to
direct solar rays to a subset of the receiver towers, such that the
remaining receiver towers are closed-in, when at least some of the
monitored levels of solar energy are below a predetermined first
threshold value.
41. The system of claim 40, wherein the assignment control system
is further configured to assign the plurality of heliostats to
direct solar rays to the plurality of receiver towers, such that
the closed-in receiver towers are reactivated, when at least some
of the monitored levels of solar energy are above a predetermined
second threshold value.
42. The heliostat field system of claim 35, wherein at least one or
more of the receiver towers includes a receiver that is
repositionable such that a face of the receiver that receives solar
rays can be repositioned.
43. The heliostat field system of claim 42, wherein the face of the
receiver is repositionable in accordance with positions of the
heliostats assigned to direct solar rays to the receiver.
44. The heliostat field system of claim 42, wherein the face of the
receiver is repositionable based on an azimuth direction of the
Sun.
45. The heliostat field system of claim 42, wherein the assignment
control system is further configured to control repositioning of
the face of the at least one receiver.
46. The heliostat field system of claim 42, wherein the at least
one receiver is configured to rotate about a vertical axis to
adjust the position of the receiver face.
47. The heliostat field system of claim 42, wherein the at least
one receiver is configured to rotate about a horizontal axis to
adjust the position of the receiver face.
48. The heliostat field system of claim 42, wherein the receiver
tower on which is mounted the at least one receiver is a receiver
tower that is configured to move.
49. The heliostat field system of claim 35, wherein the assignment
control system is further configured to: for a particular
heliostat, determine whether a benefit of reassigning the
particular heliostat from a first receiver tower to a second
receiver tower outweighs a cost of the reassigning, wherein the
assigning is based at least in part on the determination.
50. The heliostat field system of claim 35, wherein the assignment
control system is further configured to: for a particular
heliostat, determine flux distributions over surfaces of a first
receiver and a second receiver when the heliostat is assigned to
direct solar rays to first and second receiver towers that
correspond to the first and second receivers, wherein the assigning
is based at least in part on the determination of flux
distribution.
51. A method for operating a multi-tower heliostat field,
comprising: for each receiver mounted to a receiver tower of a
plurality of receiver towers about which a plurality of heliostats
are arranged, assigning a set of multiple heliostats to direct
solar rays to a receiver face of the receiver; and adjusting a
position of the receiver face at a plurality of times throughout
the coarse of a day.
52. The method of claim 51, wherein adjusting the position of the
receiver face is based on an azimuth direction of the Sun at the
plurality of times throughout the coarse of the day.
53. The method of claim 51, wherein adjusting the position of the
receiver face comprises rotating the receiver about a vertical
axis.
54. The method of claim 51, wherein adjusting the position of the
receiver face comprises rotating the receiver about a horizontal
axis.
55. The method of claim 51, wherein adjusting the position of the
receiver face comprises moving the receiver tower.
56. The method of claim 51, further comprising: for each receiver,
determining a plurality of estimated efficiencies of the receiver
in receiving solar rays at the receiver face from the set of
multiple heliostats at a plurality of times of day; wherein
adjusting the position of the receiver face is based on the
estimated efficiencies for the receiver at the plurality of times
of day.
57. The method of claim 51, wherein adjusting the position of the
receiver face is based on a level of solar energy absorbed by the
receiver.
58. The method of claim 51, wherein adjusting the position of the
receiver face is based on estimated levels of solar ray intensity
at different times of the day.
59. The method of claim 51, further comprising: for each heliostat
of the plurality of heliostats, determining a plurality of
estimated efficiencies of the heliostat in directing solar rays to
two or more receiver towers of the plurality of receiver towers at
a plurality of times of day; and wherein assigning a set of
multiple heliostats to direct solar rays to a receiver face of the
receiver comprises assigning a plurality of sets of multiple
heliostats to direct solar rays to the receiver face at a plurality
of times of the day based on the determined estimated efficiencies
of the plurality of heliostats.
Description
TECHNICAL FIELD
[0001] This specification relates to heliostat assignment in a
multi-tower field of heliostats.
BACKGROUND
[0002] Heliostats can be used to collect radiation from the Sun.
Specifically, a heliostat can include one or more mirrors to direct
solar rays toward a receiver mounted on a receiver tower. Some
types of heliostats are capable of moving their one or more
reflective surfaces, i.e., mirrors, as the Sun moves across the
sky, both throughout the day and over the course of the year, in
order to more efficiently direct solar rays to the receiver. Solar
rays that are directed to the receiver can then be used to generate
solar power. A field of heliostats can be placed surrounding one or
more receivers to increase the quantity of radiation collected and
optimize the amount of solar power that is generated. The solar
power is converted to electricity by either the receiver or a
generator that is coupled to the receiver.
SUMMARY
[0003] In general, one innovative aspect of the subject matter
described in this specification can be embodied in methods that
include the following. For each heliostat, of multiple heliostats
arranged about multiple receiver towers, where each receiver tower
has a receiver mounted to the tower that is configured to receive
solar rays reflected from, multiple estimated efficiencies of the
heliostat in directing solar rays to two or more receiver towers at
multiple times of day are determined. Each heliostat is assigned to
direct solar rays to two or more different receiver towers at two
or more different times of day, wherein each heliostat directs
solar rays to one receiver tower at a time and the assigning is
based on the determined estimated efficiencies for the heliostat at
the multiple times of day.
[0004] These and other embodiments can each optionally include one
or more of the following features. Determining multiple estimated
efficiencies of each heliostat may further include determining
estimated efficiencies of the heliostat in directing solar rays to
the two or more receiver towers at a multiple times of day on
multiple days of a year, and assigning each heliostat to direct
solar rays to two or more different receiver towers is further
based on the determined estimated efficiencies. The assignment of
each heliostat to direct solar rays to two or more different
receiver towers may include assigning each heliostat to direct
solar rays to two or more different receiver towers that are each
positioned south of the heliostat for a heliostat field in the
northern hemisphere and that are each positioned north of the
heliostat for a heliostat field in the southern hemisphere. For
each heliostat, the position of one or more reflective surfaces
included on the heliostat may be controlled based on a position of
the Sun and which receiver tower the heliostat is assigned to
direct solar rays toward.
[0005] The cost and the benefit of reassigning a heliostat from one
receiver to another can be determined, and the if the benefit
outweighs the cost, then the heliostat can be reassigned, otherwise
the heliostat assignment can remain unchanged. Flux distribution
over a surface of two or more receivers when a particular heliostat
is assigned to direct solar rays to them can be determined, and the
heliostat assignment can be based on this determination, such that
flux distribution over a receiver surface can be managed.
[0006] In another aspect, a method for operating a multi-tower
heliostat field includes, for each receiver tower of multiple
receiver towers about which are arranged multiple heliostats,
assigning a set of heliostats to reflect solar rays to the receiver
tower. Each receiver tower has a receiver mounted to the tower that
is configured to receive solar rays reflected from the assigned set
of heliostats. For each receiver tower, based on a level of solar
energy absorbed by the receiver mounted to the tower, reassigning
which heliostats are included in the set of heliostats that are
assigned to direct solar rays to the receiver tower.
[0007] These and other embodiments can each optionally include one
or more of the following features. The level of solar energy
absorbed by the receiver mounted to the tower during daylight hours
may be monitored for each receiver. When the monitored level of
solar energy drops below a first predetermined threshold value for
one or more of the receiver towers, a subset of the receiver towers
may be closed and included in the sets of heliostats assigned to
direct solar rays to the closed-in subset of receiver towers may be
reassigned to different receiver towers included in the plurality
of receiver towers. When the monitored level of solar energy rises
above a second predetermined threshold value for one or more of the
receiver towers, one or more of the closed-in receiver towers may
be reactivated and at least some of the heliostats may be
reassigned to direct solar rays to the reactivated one or more
receiver towers. For each heliostat, the positioning of one or more
reflective surfaces included on the heliostat may be controlled
based on a position of the Sun and which receiver tower the
heliostat is assigned to direct solar rays toward.
[0008] In another aspect, a method for operating a multi-tower
heliostat field includes, for each receiver tower of multiple
receiver towers about which are arranged multiple heliostats, a set
of heliostats are assigned to direct solar rays to the receiver
tower. Each receiver tower has a receiver mounted to the tower that
is configured to receive solar rays reflected from the assigned set
of heliostats. Based on estimated levels of solar ray intensity at
different times of the day, a subset of the receiver towers are
closed in during one or more time periods a day and the heliostats
included in the sets of heliostats assigned to the closed-in subset
of receiver towers are reassigned to different receiver towers
during those time periods.
[0009] These and other embodiments can each optionally include one
or more of the following features. Closing in a subset of the
receiver towers and reassigning the heliostats may be based on
estimated levels of solar ray intensity at different times of the
day and at different times of the year. For each heliostat,
positioning of one or more reflective surfaces included on the
heliostat may be controlled based on a position of the Sun and
which receiver tower the heliostat is assigned to direct solar rays
toward.
[0010] In another aspect, a heliostat field system includes
multiple heliostats, and multiple receiver towers, where each
receiver tower has a receiver mounted to the tower that is
configured to receive solar rays reflected from a set of
heliostats. The set of heliostats are assigned to direct solar rays
to the receiver tower. The system further includes a assignment
control system configured to assign each heliostat to direct solar
rays to two or more different receiver towers at two or more
different times of day. Each heliostat directs solar rays to one
receiver tower at a time and the assigning is based on estimated
efficiencies of the heliostat in directing solar rays to the two or
more receiver towers determined for a multiple times of day.
[0011] These and other embodiments can each optionally include one
or more of the following features. The heliostat field may also
include a heliostat tracking control system configured to control,
for each of the heliostats, positioning of one or more reflective
surfaces included on each heliostat based on a position of the Sun
and which receiver tower the heliostat is assigned to direct solar
rays toward. The assignment control system may be further
configured to assign the heliostats to direct solar rays to a
subset of the receiver towers, such that the remaining receiver
towers are closed-in, based on estimated levels of solar ray
intensity at different times of the day. The assignment control
system may be further configured to assign the heliostats to direct
solar rays to the receiver towers, such that the closed-in receiver
towers are reactivated, based on the estimated levels of solar ray
intensity at different times of the day.
[0012] A solar energy level monitoring system may be configured to
monitor, for each of at least some of the receiver towers, a level
of solar energy absorbed by the receiver mounted on the receiver
tower. The assignment control system can be further configured to
assign each heliostat to direct solar rays to two or more different
receiver towers based on the monitored levels of solar energy. The
assignment control system may be further configured to assign the
heliostats to direct solar rays to a subset of the receiver towers,
such that the remaining receiver towers are closed-in, when at
least some of the monitored levels of solar energy are below a
predetermined first threshold value. The assignment control system
may be further configured to assign the heliostats to direct solar
rays to the receiver towers, such that the closed-in receiver
towers are reactivated, when at least some of the monitored levels
of solar energy are above a predetermined second threshold
value.
[0013] Other embodiments of the above described aspects include
corresponding systems, apparatus, and computer programs, configured
to perform the actions of the methods, encoded on computer storage
devices.
[0014] Particular embodiments of the subject matter described in
this specification can be implemented so as to realize one or more
of the following advantages. The solar energy collection of a solar
energy collection facility that includes multiple heliostats
assigned to direct solar rays to multiple receivers can be
improved. Cosine losses can be reduced, thereby improving the
efficiencies of the heliostats in directing solar rays to
receivers. The efficiencies of receivers can be improved, for
example, by closing-in some receivers for certain portions of a
day, therefore improving the efficiency of the activated receivers
and the overall efficiency of the solar energy collection facility.
If a particular receiver is over heated or inactive for maintenance
or otherwise, heliostats that may have typically been assigned to
the receiver can be assigned to neighboring receivers thereby
making better use of the neighboring receivers and extending their
number of productive hours in a day. Flux distribution over a
surface of a receiver can be managed, so as to optimize a
temperature of a working fluid receiving solar heat from the
receiver. The efficiency of a solar energy collection facility can
be optimized by determining whether the benefit of re-assigning a
heliostat from one receiver to another outweighs the cost of the
reassignment.
[0015] The details of one or more embodiments of the subject matter
described in this specification are set forth in the accompanying
drawings and the description below. Other features, aspects, and
advantages of the subject matter will become apparent from the
description, the drawings, and the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIGS. 1A-1C illustrate examples of the cosine effect for two
heliostats located on opposite sides of a solar energy receiver in
a solar energy collection facility.
[0017] FIG. 2 is an example of a fixed assignment of heliostats and
solar energy receiver towers in a solar energy collection
facility.
[0018] FIGS. 3A-3C illustrate example configurations of a solar
energy collection facility 300 that improve solar energy collection
efficiency.
[0019] FIG. 4 is a schematic representation of the Sun's position
in the sky throughout an example day.
[0020] FIGS. 5A-5C show example configurations of heliostats to
concentrate available solar energy under varying daylight
conditions.
[0021] FIG. 6 is a flow diagram of an example process for assigning
and reassigning a collection of heliostats among a collection of
solar energy receiver towers in a solar energy collection
facility.
[0022] FIGS. 7A-7B illustrate example configurations of heliostats
and solar energy receiver towers in all north field
configuration.
[0023] FIG. 8 is a block diagram of an example heliostat field
system.
[0024] FIG. 9 is a schematic representation of an example receiver
mounted on a receiver tower in a heliostat field.
[0025] FIG. 10 is a schematic diagram of an example of a generic
computer system.
[0026] Like reference numbers and designations in the various
drawings indicate like elements.
DETAILED DESCRIPTION
[0027] A heliostat is assigned to direct solar rays toward a
receiver that is typically mounted on a receiver tower. Various
factors can affect the efficiency of the heliostat in directing the
solar rays to the receiver, including the position of the Sun
relative to the heliostat's reflective surface or surfaces,
weather, and environmental conditions affecting Sun intensity. In
terms of the position of the Sun relative to the heliostat's
reflective surface(s), the cosine effect represents the difference
between the amount of energy falling on a surface pointing at the
Sun, and a surface parallel to the surface of the earth. As this
concept applies to heliostats and other types of solar reflectors,
a heliostat generally reflects the greatest amount of solar energy
when the plane of the heliostat's reflective surface is oriented
substantially perpendicular to the incoming rays of sunlight.
However, since the purpose of a heliostat in a solar energy
collection scenario is generally to change angles so as to reflect
incoming sunlight to a solar energy collector, a perpendicular
orientation relative to incoming sunlight is rarely, if ever,
useful. As the heliostat is angled away from perpendicular, the
effective amount of surface area (and therefore also the amount of
reflected solar energy) decreases.
[0028] One factor for determining an optimum heliostat field layout
is the cosine efficiency of the heliostat. In some implementations,
this efficiency can depend on the Sun's position, the location of
the individual heliostat relative to the receiver tower, or a
combination of both. The heliostat is positioned by the tracking
mechanism so that its surface normal bisects the angle between the
Sun's rays and a line from the heliostat to the tower. The
effective reflection area of the heliostat is reduced by the cosine
of one-half of this angle (e.g., angle .theta..sub.i shown in FIG.
1A). This may be visualized by considering heliostats at two
positions in a field as shown in FIGS. 1A-1C.
[0029] FIGS. 1A-1C illustrate examples of the cosine effect for two
heliostats 110 and 120 located on opposite sides of a solar energy
receiver to 125 in a solar energy collection facility 100. A solar
energy receiver 130 is mounted atop the receiver tower 125 to
receive solar energy reflected by the heliostats 110 and 120. To
simplify the example, the facility 100 is shown in a substantially
noontime configuration (e.g., the Sun 102 is at its peak south of
the facility 100).
[0030] The heliostat 110 has a small cosine loss (e.g., compared to
the heliostat 120) since its surface normal is almost pointing
toward the receiver 130, resulting in an effective reflective area
112. The heliostat 120 has a larger cosine loss and a smaller
effective reflective area 122 because of the position it must
assume in order to reflect the Sun's 102 rays onto the receiver
130. It should be noted that in some implementations, the most
efficient heliostats may be located opposite the Sun 102 relative
to the receiver 130.
[0031] In the illustrated example, the heliostat 120 is located in
a south field (e.g., south of the solar energy receiver 130), and
the heliostat 110 is located in a north field (e.g., north of the
solar energy receiver tower 130). Generally speaking, in the
northern hemisphere the Sun 102 appears to move across the sky in
an arc that is to the south of overhead. In the examples used
throughout this document, the terms north field and south field
will generally be given in relation, but are not limited to,
implementations in the northern hemisphere where the Sun's path is
southward of overhead. It should be noted that any of the examples
given in this document can also be applied to southern hemispheric
applications where the Sun's path is generally north of overhead.
In such implementations, the terms "north" field and "south" field
can be transposed to implement functionality similar to that
described for northern hemispheric implementations.
[0032] An expression for calculation of the cosine of this half
angle has been developed as the following equation:
cos 2 .theta. i = ( z 0 - z 1 ) sin .alpha. - e 1 cos .alpha. sin A
- n 1 cos .alpha. cos A [ ( z 0 - z 1 ) 2 + e 1 2 + n 1 2 ] 1 / 2
##EQU00001##
[0033] Where .alpha. and A are the Sun's altitude and azimuth
angles, respectively, and z, e, and n are the orthogonal
coordinates from a point on the receiver 130 at the height of the
heliostats' 110 and 120 mirrors. An angle 114 represented by
.theta..sub.i is the angle between a Sun ray 116 and a surface
normal 118. Similarly, an angle 114 also represented by
.theta..sub.i is the angle between a Sun ray 116 and a surface
normal 118.
[0034] FIG. 2 is an example of a fixed (i.e., static) assignment of
heliostats and solar energy receiver in a solar energy collection
facility 200. In the illustrated example, a collection of
heliostats 210 is grouped into a collection of north fields
230a-230c and a collection of south fields 240a-240c. Each of the
north fields 230a-203c and each of the south fields 240a-240c are
permanently assigned to direct solar rays to one of the receivers
220a-220c. For example, the north field 230a and the south field
240a are assigned to direct solar rays to the receiver 220a.
Similarly, the north field 230b and the south field 240b are
assigned to the receiver 220b, just as the north field 230c and the
south field 240c are assigned to the receiver 220c. When a
heliostat is assigned to a receiver, reflective surfaces on the
heliostat are positioned to direct solar rays to the receiver. In
some examples, the reflective surfaces move throughout the course
of a day to track the movement of the Sun across the sky.
[0035] Equation 1 can be used to show that for northern hemispheric
implementations, heliostats located opposite the Sun relative to
the receiver can be the most efficient. In the example of the
facility 200, the heliostats 210 in the north fields 230a-230c can
generally have lower cosine losses than the heliostats 210 in the
south fields 240a-240c. In the morning, the heliostats 210 located
west of their associated receivers 220a-220c will generally have
higher efficiencies than those located east of the receivers
220a-220c. The opposite occurs in the afternoon, giving the east
and west heliostats 210 an average efficiency in between the high
and the low.
[0036] FIGS. 3A-3C illustrate example configurations of a solar
energy collection facility 300 that improve solar energy collection
efficiency. In particular, these configurations can reduce the
cosine effect on a collection of heliostats 302 as the Sun moves
across the sky. Sunlight shines on the facility 300 in a direction
generally indicated by arrows 310. As such, FIG. 3A represents the
facility 300 as it generally is configured in the morning (e.g.,
the Sun is shining out of the southeast). Likewise, FIG. 3B
represents the facility 300 as it generally is configured around
noon (e.g., the Sun is approximately due south) and FIG. 3C
represents the facility 300 in the afternoon (e.g., the Sun is
shining out of the southwest).
[0037] Referring to the morning configuration illustrated by FIG.
3A, the heliostat assignments are depicted by boundaries shown in
broken lines. In the example shown, the boundaries 304a-304d follow
paths roughly parallel to the Sun's rays, as indicated by the
arrows 310. As such, the heliostats 302 between the boundaries 304a
and 304b form a heliostat grouping 320a that is roughly aligned
along the direction of the Sun's rays and are assigned to reflect
solar energy toward a solar energy receiver 330a. The approximate
direction of the reflected solar energy is represented by arrows
350. Similarly, a heliostat field 320b and a heliostat field 320c
are also organized roughly parallel to the Sun's rays to reflect
solar energy toward solar energy receivers 330b and 330c
respectively.
[0038] As the Earth rotates, the Sun appears to move across the
morning sky and reaches its solar apex around noon. Referring now
to FIG. 3B, the heliostats 302 between boundaries 304e and 304f
form a heliostat grouping 320d that is assigned to the receiver
330a, i.e., solar energy shining upon the grouping 320d is
reflected to the receiver 330a. Similarly, the heliostat grouping
320e is between boundaries 304f and 304g and assigned to reflect
sunlight toward the receiver 330b, and the heliostat grouping 320f
is between boundaries 304g and 304h and assigned to reflect
sunlight toward the receiver 330c. As such, the heliostat groupings
320d-320f assigned to the receivers 330a-c at mid-day are different
than the heliostat groupings assigned to the receivers 330a-c in
the morning. The heliostat assignments can change throughout the
course of the day such the boundaries roughly align to the incoming
solar radiation and therefore improve the overall cosine efficiency
of the facility.
[0039] Referring now to FIG. 3C, the heliostats 302 between
boundaries 304i and 304j form a heliostat grouping 320g. Sunlight
falling upon the grouping 304g is reflected to the receiver 330a.
Similarly, the heliostat grouping 320h between boundaries 304j and
304k is assigned to reflect sunlight toward the receiver 330b, and
the heliostat grouping 320i between boundaries 304k and 3041 is
assigned to reflect sunlight toward the receiver 330c. As such, the
heliostat groupings 320g-320i utilize different groupings of the
heliostats 302 compared to the groupings illustrated in FIGS. 3A
and 3B to roughly align the groupings 320g-320i parallel to the
incoming solar radiation and therefore improve the overall cosine
efficiency of the facility in the afternoon. In the particular
example shown, three different heliostat assignments are depicted
in the morning, mid-day and afternoon. However, it should be
understood that the assignments of the heliostats to the receivers
can be changed at many times during the day, and the example shown
is simplified for illustrative purposes.
[0040] FIG. 4 is a schematic representation of the Sun's position
in the sky throughout an example day. In particular, FIG. 4 can be
used to illustrate an example of how the Sun's position can
influence the assignment of heliostats in a solar energy collection
facility, such as the facility 100 of FIG. 1A or the facility 300
of FIGS. 3A-3C. An individual configuration of heliostats generally
has a high cosine efficiency at one time of the day, and gradually
diminishing efficiencies on either side of that time.
[0041] In some implementations, such as those illustrated by FIGS.
3A-3C, a solar energy collection facility may create multiple peak
cosine efficiency times by varying how heliostats are assigned to
receiver towers. Two, three, four, or more different configurations
of heliostats and receivers may be defined and implemented for
different periods of the day. For example, one configuration may
have a peak cosine efficiency at mid-morning, another configuration
may have a peak cosine efficiency at noon, and another
configuration may have a peak efficiency at mid-afternoon. In some
implementation, between the peak efficiency times may be times at
which the cosine efficiencies of two timewise adjacent
configurations may be substantially equal. For example, a morning
configuration that had a peak cosine efficiency around 7 am and a
mid-day configuration that peaks around 12 pm may have
substantially equal cosine efficiencies around 8:30 am. In some
implementations, such times may be chosen to trigger transitions
from one heliostat field configuration to the next.
[0042] In some implementations, the arc 405 may change throughout
the year. For example, in the northern hemisphere the Sun generally
rises earlier in the morning, rises higher overhead at mid-day, and
sets later at night in the summer than it does in the winter. As
such, the specific configurations of the heliostats, the times at
which they are used, the times at which configurations are changed
over, or combinations of these and/or other factors may be used to
anticipate the optimal organization of solar energy collection
facilities throughout the year.
[0043] In some implementations, the configuration of a heliostat
field may be substantially variable throughout the day. For
example, rather than defining a finite number of configurations
(e.g., the three illustrated by FIGS. 3A-3C), the receiver
assignments of individual heliostats may be chosen and re-chosen
dynamically throughout the day and year in order to optimize cosine
efficiencies and/or totalized power reflected to the receivers.
[0044] Generally speaking, solar energy receivers can operate most
efficiently for a given amount of received reflected solar energy.
Furthermore, this operational efficiency may not be linearly
proportional to the amount of reflected energy received. For
example, in a combination of ten heliostats and two receivers on a
Sunny day, five heliostats may reflect enough light to cause a
single receiver to operate at or near its peak operational
efficiency (e.g., 100%). Therefore the total output of the
combination may be 200%. However, on an overcast day, for example
where the amount of light is reduced by a third, the output of each
may only be 40% (e.g., 80% total). In some implementations, a
greater total output may be realized by completely shutting down
some receivers and reassigning the corresponding heliostats to the
remaining receivers. For example, on the aforementioned overcast
day, one receiver may be sacrificed and all ten heliostats may be
reassigned to the remaining receiver, causing enough light to be
reflected to the remaining receiver to cause it to operate closer
to peak operational efficiency. By operating a single receiver at
100% output, a greater total output may be realized than would be
possible by running both at 40% output (e.g., 80% total).
[0045] Similarly, during times of the day when the sunlight is less
intense, e.g., early morning and late afternoon, shutting in some
receivers (i.e., not directing sunlight to some of the receivers)
and redirecting the sunlight to the remaining activated receivers
can improve the overall output of the solar energy collection
facility. Referring again to FIG. 4, the area 420 schematically
represents the time of day in the early morning when the sunlight
is less intense at a given location for a given day. In the example
shown, the sunrise is at approximately 6:00 am and the sunset is
approximately 6:00 pm, although these times vary considerably with
the particular location on Earth and time of year. During the time
period represented by 420, some of the receivers can be closed-in
(i.e., inactivated) and the heliostats can be assigned to the
remaining receivers that are activated.
[0046] FIGS. 5A-5C show example configurations of heliostat
assignments to concentrate available solar energy under varying
daylight conditions. For example, in the morning configuration
illustrated by FIG. 5A, a collection of receivers 505 have been
closed-in (i.e., are inactivated) and the heliostats 515 have been
assigned to reflect light upon a collection of receivers 510 that
are activated. In the illustrated example, thirty six of the
heliostats 515 have been assigned to each of the receivers 510.
When compared to the morning configuration illustrated by FIG. 3A
in which eighteen heliostats are assigned to each receiver, the
configuration of FIG. 5A assigns a greater number (e.g., 36 of the
heliostats 515 to the activated receivers 510 to compensate for the
reduced amount of available morning sunlight during the time period
420.
[0047] Referring again to FIG. 4, during the time period
represented by 430, the optimal heliostat assignment may be to
activate all of the receivers, i.e., to re-activate the subset of
receivers 505 that were closed-in during the time period 420.
Referring now to FIG. 5B, heliostat assignments for a given time
during the time period 430 are shown, in this particular example at
a given time of mid-day. All of the receivers 505 and 510 are
activated and the heliostats 515 have been reassigned such that
eighteen of the heliostats 515 are assigned to each of the
receivers 505 and 510. Various different heliostat assignments can
be used during the time period 430 when all of the receivers are
activated.
[0048] FIG. 5C represents the facility 500 in a late afternoon
configuration, when the sunlight intensity has again decreased, and
corresponds to a time during time period 440 shown in FIG. 4.
Similar to the morning configuration shown in FIG. 5A, the
receivers 505 have been sacrificed, and those receivers' 505
heliostats 515 have been reassigned to the receivers 510 to
increase the total amount of solar energy reflected onto the
receivers 510 to compensate for the reduced amount of available
sunlight. In the illustrated example, thirty six of the heliostats
515 are assigned to each of the receivers 510. In the particular
example shown, the same subset of receivers 505 was closed-in
during the morning period 420 and the afternoon period 440.
However, it should be understood that different subsets of
receivers can be closed-in at different times of the day, and that
the subset of closed-in receivers can be more or less than 1/2 of
the total number of receivers and that the number of receivers
closed-in can vary during the day as well. For example, during the
time period 420, some of the closed-in receivers can be reactivated
before others, allowing for a gradual start-up of all of the
receivers in the field as the morning goes on. A similar gradual
shutting-in effect can be taken toward the end of the day (i.e.,
during time period 440.
[0049] In the example described above, some of the receivers were
closed-in during the certain times of the day based on predictable
factors, i.e., the predicted sunlight intensity based on the
location and time of year. In other implementations, some of the
receivers can be closed-in during certain times of the day to
account for unpredictable factors, e.g., changes in the weather
that affect the sunlight intensity. For example, in a large solar
energy collection facility, a passing cloud bank may reduce the
amount of light that shines on a portion of the heliostat field.
One possible way to reduce the impact of such unpredictable
lighting conditions is by dynamically sacrificing some receivers
and reassigning those receivers' heliostats among the remaining
active receivers.
[0050] In some implementations, one or more sensors may be used to
measure the amount of available sunlight at some or all of the
receivers and/or heliostats in the facility 500. The measurements
from the sensors can be used to dynamically re-assign the
heliostats and potentially to close-in some of the receivers to
account for reduced sunlight intensity. The measurements can be
also used to later reactivate some or all of the closed-in
receivers, for example, after a cloud bank has passed or clouds
have dissipated.
[0051] FIG. 6 is a flow diagram of an example process 600 for
assigning and reassigning a collection of heliostats among a
collection of solar energy receivers in a solar energy collection
facility. In some implementations, the process 600 may be used by
the facilities 100, 300, and/or 500 to reconfigure the assignment
of heliostats among receivers.
[0052] In some implementations, in addition to the Sun's daily and
seasonal movement in the sky, other less predictable factors may
affect the amount of solar energy collected by a receiver tower.
For example, overcast skies, fog, rain, smoke, and airborne dust
can variably reduce the amount of sunlight that shines upon a
heliostat field. In another example, materials (e.g., snow, ice,
dust, ash) or mechanical malfunctions can unexpectedly impede or
prevent heliostats from properly reflecting solar energy until the
heliostats can be cleaned or repaired. In such cases, the total
amount of energy provided to a receiver may be less than what is
needed to efficiently operate the receiver. In some
implementations, the number of receivers, and the heliostats
assigned to them, may be dynamically reconfigured in response to
variations in the amount of solar energy received at the
towers.
[0053] Initially, an initial heliostat assignment is imposed to the
solar energy receiver towers (Step 610. In some implementations,
the initial assignment may be determined using predictable patterns
of the Sun's movement for various times of the day and/or various
times of the year. In some implementations, the initial assignment
may be determined using predicted weather conditions. For example,
during the dark hours of the early morning a weather forecast may
be used to anticipate that the sky will be cloudy and overcast at
sunrise, and the heliostat assignment may be configured prior to
sunrise in a way that may anticipate and/or compensate for the
reduction in sunlight caused by the clouds at dawn.
[0054] Solar energy levels are monitored, e.g., at some or all of
the active receiver towers (Step 620. If the solar energy levels at
one or more receivers are less than a first threshold ("Yes" branch
of Step 630, then a subset of the active receivers is inactivated
(Step 640. A modified heliostat assignment is then imposed to the
active receivers (Step 650. For example, when one or more receivers
are receiving an insufficient amount of reflected light to operate
efficiently, a controller may deactivate some receivers and direct
the heliostats that were assigned to direct light toward those
receivers to reflect their light to one of the remaining (e.g.,
active) receivers to increase the amount of solar energy being
provided to those towers. Solar energy levels at some or all of the
active receivers continue to be monitored (Step 620.
[0055] If, however, the solar energy levels at one or more
receivers are not less than a first threshold ("No" branch of Step
630, then a second determination is made, i.e., whether the solar
energy levels at some towers exceeds a second threshold (Step 660.
If at the solar energy levels at some of the active receivers does
not exceed a second threshold ("No" branch of Step 660, then
monitoring of solar energy levels at the active receivers continues
at (Step 620. However, if the solar energy levels at some of the
active receivers exceeds the second threshold ("Yes" branch of Step
660, then some or all of the inactive receivers are reactivated
(Step 670, and a modified heliostat assignment is imposed to the
active receivers (Step 650. For example, when a receiver is
provided with more solar energy than it can efficiently or
effectively use, a controller may bring an additional receiver
online to receive the excess energy. The controller may reassign
one or more heliostats from the oversupplied receiver to the
additional receiver by directing the reassigned heliostats to
reflect their sunlight to the additional tower. Solar energy levels
at the active receivers continue to be monitored (Step 620.
[0056] FIGS. 7A-7B illustrate example configurations of heliostats
and solar energy receivers in all north field configuration 700. In
some implementations, heliostats located on roughly the opposite
side of a solar energy receiver from the Sun may exhibit lower
cosine losses than those seen at heliostats located between the
receivers and the Sun. For example, heliostats located opposite of
the Sun (e.g., in north fields) may reflect the incoming solar
energy to the receiver at angles that are closer to their surface
normals as compared to heliostats located between the receiver and
the Sun (e.g., in south fields).
[0057] In some implementations, the overall cosine losses of a
heliostat field may be reduced by arranging heliostats and
receivers, such that a majority or substantial entirety of the
heliostats are configured in north field arrangements (e.g.
opposite the receivers from the Sun). Furthermore, by dynamically
altering the assignment of heliostats to receivers during the day,
still lower cosine losses may be achieved. Referring to FIG. 7A,
the configuration 700 is illustrated in a morning arrangement. A
collection of heliostats 705 is assigned to a collection of solar
energy receivers 710 that are located between the heliostats 705
and the incoming sunlight, the general direction of which is
indicated by a collection of arrows 730. Similarly, a collection of
heliostats 715 are assigned to a collection of solar energy
receivers 720 that are also located between the heliostats 715 and
the incoming sunlight.
[0058] Since the Sun rises in the east, the morning sunlight falls
upon the configuration 700 from a southeast direction as indicated
by the arrows 730. In addition to taking advantage of the lower
cosine losses offered by a substantially north field arrangement of
the heliostats 705, 715, even lower cosine losses may be achieved
by dynamically reconfiguring the assignment of the heliostats 705,
715 to the receivers 710, 720 as the day progresses. For example,
as illustrated by FIG. 7A, the heliostats 705, 715 are assigned in
groups that are roughly opposite the receivers 710, 720, from the
incoming sunlight. For example, a group of heliostats 740 is
configured in a modified north field configuration behind, and
assigned to reflect their solar energy to, a receiver 750.
[0059] Referring now to FIG. 7B, the configuration 700 is assigned
in an afternoon arrangement. The arrows 730 generally indicate the
southwest origin of the afternoon sunlight. The configuration 700
has been reorganized from its morning arrangement to better align
and group the heliostats 705, 715 with the receivers 710, 720 to
reduce cosine losses. In the illustrated example, the receiver 750
has a group of heliostats 760 assigned to reflect light to it, and
the group 760 is organized in a modified north field configuration
where the heliostats 705 in the group 760 are located roughly
opposite the receiver 750 from the incoming sunlight.
[0060] FIG. 8 is a block diagram of an example heliostat field
system 800. In various implementations, the system 800 may be the
facilities 100, 300, 500, or 700. The system 800 includes a
collection of heliostats 805 arranged as a heliostat field 810. In
some implementations, the heliostat field 810 may represent a
so-called north field or south field of a solar energy collection
facility. The system shown is simplified for illustrative purposes
and may include many dozens, hundreds or even thousands of
heliostats 805 and many dozens, hundreds or even thousands of
receiver towers.
[0061] The heliostats 805 are each able to vary the direction in
which their one or more reflective surfaces are pointing. As such,
the heliostats 805 can be pitched and angled so as to selectably
reflect incoming sunlight, represented by arrows 815, to either a
solar energy receiver tower 820a or a solar energy receiver tower
820b. Arrows 825 represent the reflected sunlight. The solar energy
receiver towers 820a and 820b each include a solar energy receiver
830a and 830b respectively. The solar energy receivers 830a, 830b
are configured to receive solar rays reflected by the heliostats
805. The heliostats' 805 pitches and angles can be varied
throughout the day to track the Sun as it appears to move across
the daytime sky in order to maintain their reflective relationship
with a selected one of the receivers 830a, 830b to which they are
assigned to direct solar rays.
[0062] The heliostats 805 are communicably connected to an
assignment control system 835, e.g., by communication lines 840. In
some implementations, the communication lines 840 may conduct power
to the heliostats 805 (e.g., to energize their pitch and angle
mechanisms). In some implementations, the communication lines 840
may be supplemented or replaced by wireless communication links
between the heliostats 805 and the assignment controller 835. The
assignment control system 835 communicates with the heliostats 805
to assign each of the heliostats 805 to direct solar rays to two or
more different receiver towers (e.g., the receiver towers 820a,
820b) at two or more different times of day, wherein each of the
heliostats 805 directs solar rays to one of the receiver towers
820a, 820b at a time. The assigning can be based on estimated
efficiencies of the heliostats 805 in directing solar rays to the
receiver towers 820a, 820b determined for a plurality of times of
day, and/or based on actually efficiencies.
[0063] In some implementations, the assignment control system 835
may be configured to assign the heliostats 805 to direct solar rays
to a subset of the receiver towers 820a, 820b, such that the
remaining receiver towers are closed-in, e.g., based on estimated
levels of solar ray intensity at different times of the day. For
example, in the early morning or late afternoon the assignment
control system 835 may reassign the heliostats 805 normally
assigned to the receiver tower 820b to the receiver tower 820a.
Optionally, the assignment control system 835 can command the
receiver tower 820b to close-in. In some implementations, a
receiver tower closes in by closing shutters to block a receiver
face (which may include a receiver aperture, for example, for a
cavity style receiver) that is adapted to receive the solar rays.
In other implementations, the receiver tower doesn't actually
undergo a change at all, other than that no heliostats are assigned
to direct solar rays to the receiver. In some implementations, an
engine coupled to the receiver to generate power is powered down.
Other steps to deactivate a receiver can be taken, and these are
but some examples. In some implementations, the assignment control
system 835 may be configured to assign the heliostats 805 to direct
solar rays to the receiver towers 820a, 820b, such that the
closed-in receiver towers are reactivated, based on the estimated
levels of solar ray intensity at different times of the day.
[0064] A heliostat tracking control system 845 is configured to
control the positioning of one or more reflective surfaces included
on each of the heliostats 805 based on a position of the Sun and
which of the receiver towers 820a, 820b the heliostat 805 is
assigned to direct solar rays toward. In some implementations, the
controller 845 may substantially control the pitch and angle of the
heliostats 805 to control the direction in which their light is
reflected. In some implementations, the heliostat tracking control
system 845 is implemented as a controller at each of the individual
heliostats 805. That is, the heliostats 805 may include processors
that substantially independently determine and control the pitch
and angle of the heliostats reflectors based on an assignment sent
from the assignment control system 835.
[0065] A solar energy level monitoring system 850 is configured to
monitor, for each of at least some of the receiver towers 820a,
820b, a level of solar energy absorbed by the receivers 830a, 830b,
mounted on the receiver towers 820a, 820b. In some implementations,
the solar energy level monitoring system 850 further includes (or
alternatively includes) a collection of solar energy sensors 855
that sense the intensity and/or direction of incoming sunlight.
[0066] In some implementations, the assignment control system 835
may be configured to assign the heliostats 805 to direct solar rays
to a subset of the receiver towers 820a, 820b, such that the
remaining receiver towers are closed-in when at least some of the
monitored levels of solar energy are below a predetermined first
threshold value. For example, the solar energy monitoring system
850 may detect that received solar energy levels at both of the
receivers 830a and 830b is below a predetermined threshold value
(e.g., based on the efficiencies of the receivers 830a, 830b for
different amounts of received solar energy), and the assignment
control system 835 may use this information to close-in the
receiver tower 820a and reassign additional ones of the heliostats
805 to the receiver tower 820b. In another example, the solar
energy monitoring system 850 may monitor the solar energy sensors
855 and determine that the intensity of incoming sunlight has
fallen below a threshold value (e.g., a cloud bank is reducing the
amount of sunlight shining on some of the heliostats 805, and the
assignment control system 835 may use this information to reassign
the heliostats 805 among the receiver towers 820a, 820b.
[0067] The assignment control system 835 may, in some
implementations, assign the heliostats 805 to direct solar rays to
the receiver towers 820a, 820b, such that the closed-in receiver
towers are reactivated, when at least some of the monitored levels
of solar energy are above a predetermined threshold value (e.g.,
inactive receiver towers 820a, 820b, may be reactivated to take
advantage of additional available solar power). In some
implementations, the solar energy sensors 855 may sense and/or
track the position of the Sun, and provide that positional
information to the heliostat tracking controller 845. In some
implementations, a number of the solar energy sensors 855 may be
located throughout the heliostat field 810 to provide the solar
energy monitoring system 850 with solar energy intensity
information for various locations across the heliostat field
810.
[0068] To determine various assignments of the heliostats 805 and
the receiver towers 820a, 820b to reduce inefficiencies, e.g.,
cosine losses, in some implementations the assignment control
system 835 may use the information it receives from the solar
energy monitoring system 850, along with time and date information,
weather forecast information, astronomical information (e.g.,
seasonal arcs of the Sun, sunrise and sunset information,
predictions for solar eclipses), and combinations of these and/or
other types of information. In some implementations, the assignment
controller 835 may use a combination of time and date information
along with astronomical information to determine an initial
assignment. For example, just before dawn, the assignment
controller 835 may prepare the system 800 to collect the morning
sunlight by assigning the heliostats 805 to the receivers 820a,
820b in a morning configuration such as that illustrated in FIG.
3A.
[0069] In some implementations, the assignment controller 835 may
use weather information, forecasts, sensed solar energy intensity
information (e.g., from the sensors 855, received solar energy
information (e.g., from the receivers 830a, 830b), or combinations
of these and or other types of information that may be variable or
substantially unpredictable to dynamically modify the assignments
of the heliostats 805 and the receiver towers 820a, 820b. For
example, smoke from a forest fire may unexpectedly block out a
portion of the light that would normally shine on the heliostats
805, and the assignment controller 835 may respond to the reduced
amount of light by shutting in the receiver tower 820a and
signaling the heliostats 805 normally assigned to the receiver
tower 820a to consolidate their reflected light upon the remaining
receiver tower 820b. In another example, a malfunction may cause
the assignment controller 835 and/or the heliostat tracking
controller 845 to lose communication with and control of parts of
the heliostat field 810, rendering some of the heliostats 805 in
that field 810 substantially unable to maintain their reflective
relationship with the receivers 830a, 830b. The assignment
controller 835 may respond by consolidating the solar energy
reflected by the remaining, operational heliostats 805 onto a
single one of the receivers 820a or 820b.
[0070] In some implementations, the heliostats 805 focus the Sun's
energy onto receivers 830a, 830b to heat a working fluid, e.g.,
water, air or molten salt. The working fluid can travel through a
heat exchanger 860 to heat water, produce steam, and then generate
electricity through a turbine 870 connected to a generator 880. In
some implementations, the heliostats 805 focus the Sun's energy
onto receivers 830a, 830b to heat air or another gas. The heated
gas is then expanded through the turbine 870, which turns a shaft
to drive the generator 880. The electricity can be conducted, e.g.,
by wires 890, to a utility grid, or some other point where the
electricity can be distributed or consumed. In some
implementations, some of the electricity may be consumed by the
system 800 itself, e.g., by the assignment controller 835 and/or by
the heliostats 805 in order to move to track the Sun and/or to move
based on a new receiver assignment. In some implementations, the
heat exchanger 860, turbine 870 and generator 880 can be
implemented on a per-receiver tower basis and can be included at
each receiver tower. Alternatively, a heat exchanger, turbine and
generator can be positioned to service a subset of the receiver
towers.
[0071] In some implementations, the receiver can be configured to
move, e.g., rotating about a vertical axis, translating or both.
Moving the receiver may enhance solar energy received at the
receiver and reduce cosine losses. FIG. 9 is a schematic
representation of an example receiver 904 mounted on a receiver
tower 902 in a heliostat field that includes multiple heliostats
918 and 920. Although six heliostats are shown, in practice, many
more heliostats can be used in a field, in some examples, in the
hundreds or even thousands. The receiver 904 includes a receiver
face 905 that is configured to receive solar energy reflected from
multiple heliostats that are assigned to direct solar rays to the
receiver 904. It should be understood that in some implementations,
the receiver face 905 includes a surface that is configured to
receive the solar energy, and in other implementations, e.g., a
cavity receiver, the receiver face 905 includes an aperture behind
which is formed a cavity. The surface of the cavity receives the
solar rays that are incident on the aperture formed in the receiver
face 905. Other configurations of receiver are possible. The
receiver 904 can be mounted on the tower 902 with a mount 906 that
is configured to allow the receiver 904 to rotate about the axis
908 in the directions indicated by the arrow 910, e.g., with a
thrust bearing although other configurations of mount can be used.
The receiver face 905 can thereby be selectively reoriented to face
in different directions.
[0072] By way of example, in the Northern hemisphere, during the
morning when the Sun is in the east, it may be more efficient to
have the heliostats 920 that are positioned west of the receiver
904 direct solar energy to the receiver 904, and the receiver face
905 can be positioned to face toward the heliostats 920. In the
afternoon, when the Sun is in the west, the receiver face 905 can
be repositioned to face toward the heliostats 918 that are
positioned to the east of the receiver 904. Therefore, during the
course of the day, the heliostats that are assigned to direct solar
energy to the receiver 904 can change along with the direction that
the receiver face 905 is facing. Other heliostat assignments are
possible, for example, heliostats can be positioned to the north
and south of the receiver 904 and the heliostat assignment can be
changed throughout the day based on position of the Sun and/or
environmental conditions, along with movement of the receiver face
905, so as to optimize the solar energy received by the receiver
face 905. In some implementation, the heliostats that are assigned
to direct solar energy to the receiver 904 do not change, but the
position of the receiver face 905 does change to optimize the solar
energy received.
[0073] In some implementations, the receiver 904 can also be
pivoted about a horizontal axis to change the elevation of the
receiver face 905. That is, the position of the receiver face 905
can be adjusted to point downwardly or upwardly.
[0074] The receiver tower 902 is typically secured to the ground
916. For example, the tower 902 can be a pole that is mounted
several feet down into the Earth, to provide for a secure and rigid
attachment. In some implementations, the tower 902 itself can be
movable. The tower 902 can be mounted on a mounting assembly 912
that is configured to rotate the tower 902 about the axis 908 in
the directions of the arrow 910. In some implementations, the
mounting assembly 912 can be configured to translate the tower 902
to move to different positions within the field, for example, in
the direction of the arrows 914, although other directions are also
possible. The entire tower 902 can thereby be moved to reposition
the receiver 904 and to reorient the receiver face 905. The tower
902 can be moved to better position the receiver face 905 with
respect to either a fixed set of heliostats that are assigned to
direct solar energy to the receiver face 905, or with respect to a
dynamically assigned set of heliostats, i.e., a set of heliostats
that can change over time to accommodate for the position of the
Sun and/or environmental conditions.
[0075] In some implementations, a controller that is either local
at the receiver 904 or is remote to the receiver 904, can provide
signals to instruct one or more actuator assemblies to move the
receiver 904 relative to the tower 902 (e.g., rotate about axis 908
and/or to move the tower 902 relative to the ground 916. The
adjustments to the position of the receiver face throughout the day
can occur at predetermined intervals or can be continuous. In some
implementations, communications between the controller and the one
or more actuator assemblies can be over a wired communications
system, e.g., an Ethernet network, an I2C network, an RS232/RS422
connection, or other appropriate wired connection. In another
example, the communications ca be over a fiber optic connection. In
another example, the communications can be over a wireless network,
e.g., a wireless Ethernet (e.g., 802.11 network, a ZigBee network,
a cellular network, or other appropriate wireless network. In some
implementations, multiple estimated efficiencies of the receiver in
receiving solar rays at the receiver face from the set of
heliostats at multiple different times of day can be determined.
The controller can control the adjustment of the position of the
receiver face based on the estimated efficiencies for the receiver
at the multiple times of day. In some implementations, the
controller can control adjustment of the position of the receiver
face based on a level of solar energy absorbed by the receiver,
which can be measured by one or more sensors positioned at the
receiver or elsewhere. In some implementations, the controller can
control adjustment of the position of the receiver face based on
estimated levels of solar ray intensity at different times of the
day and/or on different days of the year. In some implementations,
the controller can control adjustment of the position of the
receiver face based on the azimuth direction of the Sun. That is,
the receiver face can be adjusted to approximately the same
direction as the azimuth direction of the Sun. The adjustments can
be based on the estimated azimuth direction of the Sun (e.g.,
estimated based on the location of the receiver, the time of day
and the time of year), or based on the actual azimuth direction of
the Sun (e.g., which can be determined based on one or more sensor
measurements).
[0076] Referring again to FIG. 8, in some implementations, the
controller can be the assignment control 835, which can be further
configured to control movement of one or more receivers, e.g.,
receivers 830a and 803b, which can be configured in a manner
similar to receiver 904 shown in FIG. 9. Movement of the receivers
can be based on information from one or more sensors, e.g., sensors
855 and/or sensors positioned on the receivers, and/or based on
predictable conditions, such as the position of the Sun and/or
based on unpredictable conditions, such as the weather.
[0077] An actuator assembly can be positioned at or near the mount
906 to drive the receiver 904 about the axis 908. A second actuator
assembly can be positioned at or near the mounting assembly 912 to
move the receiver tower 902 either in rotation and/or relative to
the ground 916. The actuator assemblies can include one or more
motors, bearings and/or wheels or tracks, depending on the type of
movement being imposed. Other configurations of actuator assembly
are possible, and the ones described are illustrative and
non-limiting.
[0078] In some implementations, a cost-benefit analysis can be used
when determining whether to change a heliostat-receiver assignment.
Heliostats generally do not have fast rates of movement, as they
move to track the Sun and therefore move at a relatively low rate
of speed throughout the day. As such, the time to reorient a
heliostat to point toward a different receiver may take several
minutes, for example, 15 minutes. While the heliostat is in
transition during the reorientation process, there is a loss of
energy from that heliostat, i.e., a cost is incurred. In
determining whether to re-orient a heliostat to point toward a
different receiver, the expected benefit of the reorientation can
be compared to the cost of reorientation. The benefit can be a
function of the duration of sunlight remaining in the day, the time
the heliostat will be pointed toward the new receiver and the
sunlight expected to be received over the day.
[0079] The following is an illustrative example of a cost-benefit
analysis. In the example, the benefit of a reorientation of the
heliostat is expected to be a 10% improvement over the current
output being 900 watts per square meter. At a 25% conversion
efficiency for two hours, the benefit can be calculated as
follows:
Benefit=0.10.times.900 Watts/m.sup.2.times.2 hours=45 Watt
hours
[0080] The cost (i.e., the energy not captured) of reorienting the
heliostat can be calculated as below, where in this example the
time to move the heliostat is 15 minutes.
Cost=0.25.times.900 Watts/m.sup.2.times.15/60 hr=56.25 Watt
hours
[0081] In this example, the cost exceeds the benefit (i.e., 56.25
exceeds 45, and therefore based on the cost-benefit analysis, it
does not make sense to reorient the heliostat. A similar evaluation
can be used to decide whether to move flux from a first receiver,
e.g., receiver A, to either of two other receivers, e.g., receivers
B and C. Based on the evaluation, the heliostat may be reoriented
to point toward receiver C because the heliostat can be orientated
to point toward receiver C faster than reorienting to point toward
receiver B, even if receiver C's power output is not as optimal as
receiver B (although both have better power output than receiver
A).
[0082] In some implementations, flux distribution at the receivers
can be used in determining whether to reorient heliostats to point
toward particular receivers. Assigning a heliostat to point toward
a first receiver, e.g., receiver A, may have beneficial (or less
detrimental) effects than if the heliostat is pointing toward a
second receiver, e.g., receiver B. Receivers can be a costly point
of failure in a solar thermal power conversion system. For example,
receiver melting can be an expensive failure that is preferably
avoided. Receiver life is a function of fatigue, and fatigue is
worsened by significant stresses that can be caused by thermal
expansion and/or differential thermal expansion. The flux
distribution within a receiver impacts the temperature of receiver
materials, which impacts absolute temperatures and temperature
gradients. For example, a receiver with large flux variations can
have uneven heating. Such a receiver would therefore have to be
operated at a lower working fluid temperature operating point, to
avoid peak temperatures approaching melting or temperature profiles
that disproportionately shorten receiver life due to fatigue.
Operating a thermal receiver at a lower working fluid temperature
will lower the efficiency of the power conversion system.
Accordingly, it may be preferable to pull some of the flux (e.g.,
the most peaky flux) out of receiver B and distribute this heat
into one or more other receivers, e.g., receiver A. Doing so may
allow the receiver B to operate at a higher working fluid
temperature, and therefore produce output power more efficiently.
The additional flux thereby added to the other receiver(s), e.g.,
receiver A, can add some power output as well, with less impact on
working fluid temperature requirements. As a result, the total
electrical power output of the field can increase.
[0083] FIG. 10 is a schematic diagram of an example of a generic
computer system 1000. The system 1000 can be used for the
operations described in association with the process 600 according
to one implementation. For example, the system 1000 may be included
in either or all of the controllers 835, 845, the sensors 855, or
in the heliostats 110, 120, 302, 515, 705, 715, and 805.
[0084] The system 1000 includes a processor 1010, a memory 1020, a
storage device 1030, and an input/output device 1040. Each of the
components 1010, 1020, 1030, and 1040 are interconnected using a
system bus 1050. The processor 1010 is capable of processing
instructions for execution within the system 1000. In one
implementation, the processor 1010 is a single-threaded processor.
In another implementation, the processor 1010 is a multi-threaded
processor. The processor 1010 is capable of processing instructions
stored in the memory 1020 or on the storage device 1030 to display
graphical information for a user interface on the input/output
device 1040.
[0085] The memory 1020 stores information within the system 1000.
In one implementation, the memory 1020 is a computer-readable
medium. In one implementation, the memory 1020 is a volatile memory
unit. In another implementation, the memory 1020 is a non-volatile
memory unit.
[0086] The storage device 1030 is capable of providing mass storage
for the system 1000. In one implementation, the storage device 1030
is a computer-readable medium. In various different
implementations, the storage device 1030 may be a floppy disk
device, a hard disk device, an optical disk device, or a tape
device.
[0087] The input/output device 1040 provides input/output
operations for the system 1000. In one implementation, the
input/output device 1040 includes a keyboard and/or pointing
device. In another implementation, the input/output device 1040
includes a display unit for displaying graphical user
interfaces.
[0088] Various implementations of the systems and techniques
described here may be realized in digital electronic circuitry,
integrated circuitry, specially designed ASICs (application
specific integrated circuits), computer hardware, firmware,
software, and/or combinations thereof. These various
implementations may include implementation in one or more computer
programs that are executable and/or interpretable on a programmable
system including at least one programmable processor, which may be
special or general purpose, coupled to receive data and
instructions from, and to transmit data and instructions to, a
storage system, at least one input device, and at least one output
device.
[0089] These computer programs (also known as programs, software,
software applications or code) include machine instructions for a
programmable processor, and may be implemented in a high-level
procedural and/or object-oriented programming language, and/or in
assembly/machine language. As used herein, the terms
"machine-readable medium" "computer-readable medium" refers to any
computer program product, apparatus and/or device (e.g., magnetic
discs, optical disks, memory, Programmable Logic Devices (PLDs))
used to provide machine instructions and/or data to a programmable
processor, including a machine-readable medium that receives
machine instructions as a machine-readable signal. The term
"machine-readable signal" refers to any signal used to provide
machine instructions and/or data to a programmable processor.
[0090] To provide for interaction with a user, the systems and
techniques described here may be implemented on a computer having a
display device (e.g., a CRT (cathode ray tube) or LCD (liquid
crystal display) monitor) for displaying information to the user
and a keyboard and a pointing device (e.g., a mouse or a trackball)
by which the user may provide input to the computer. Other kinds of
devices may be used to provide for interaction with a user as well;
for example, feedback provided to the user may be any form of
sensory feedback (e.g., visual feedback, auditory feedback, or
tactile feedback); and input from the user may be received in any
form, including acoustic, speech, or tactile input.
[0091] The systems and techniques described here may be implemented
in a computing system that includes a back end component (e.g., as
a data server), or that includes a middleware component (e.g., an
application server), or that includes a front end component (e.g.,
a client computer having a graphical user interface or a Web
browser through which a user may interact with an implementation of
the systems and techniques described here), or any combination of
such back end, middleware, or front end components. The components
of the system may be interconnected by any form or medium of
digital data communication (e.g., a communication network).
Examples of communication networks include a local area network
("LAN"), a wide area network ("WAN"), and the Internet.
[0092] The computing system may include clients and servers. A
client and server are generally remote from each other and
typically interact through a communication network. The
relationship of client and server arises by virtue of computer
programs running on the respective computers and having a
client-server relationship to each other.
[0093] While this specification contains many specific
implementation details, these should not be construed as
limitations on the scope of any invention or of what may be
claimed, but rather as descriptions of features that may be
specific to particular embodiments of particular inventions.
Certain features that are described in this specification in the
context of separate embodiments can also be implemented in
combination in a single embodiment. Conversely, various features
that are described in the context of a single embodiment can also
be implemented in multiple embodiments separately or in any
suitable subcombination. Moreover, although features may be
described above as acting in certain combinations and even
initially claimed as such, one or more features from a claimed
combination can in some cases be excised from the combination, and
the claimed combination may be directed to a subcombination or
variation of a subcombination.
[0094] Similarly, while operations are depicted in the drawings in
a particular order, this should not be understood as requiring that
such operations be performed in the particular order shown or in
sequential order, or that all illustrated operations be performed,
to achieve desirable results. In certain circumstances,
multitasking and parallel processing may be advantageous. Moreover,
the separation of various system components in the embodiments
described above should not be understood as requiring such
separation in all embodiments, and it should be understood that the
described program components and systems can generally be
integrated together in a single software product or packaged into
multiple software products.
[0095] A number of embodiments have been described. Nevertheless,
it will be understood that various modifications may be made
without departing from the spirit and scope of the invention.
[0096] In addition, the logic flows depicted in the figures do not
require the particular order shown, or sequential order, to achieve
desirable results. In addition, other steps may be provided, or
steps may be eliminated, from the described flows, and other
components may be added to, or removed from, the described systems.
Accordingly, other embodiments are within the scope of the
following claims.
* * * * *