|Title of Invention||
SOLAR ELECTRICITY GENERATOR SYSTEM
|Abstract||The invention relates to a solar electricity generator system comprising a generally planar optical concentrator lens (2) in two-axis tracking of solar radiation, generally U-shaped troughs (1) floating on a layer of water, said troughs (1) being arranged in banks closely positioned to each other so as to maximize their areal coverage, said troughs (1) being tiltable around a horizontal geometric axis (7), said lens (2) positioned across the open side of a said trough (1), a photovoltaic cell (4') receiving concentrated solar radiation from said lens (2). The said cell (4') is placed together with a heat conducting device (50) within a protrusion at the area (5') of a said trough (1) opposite said lens (2), said device conducting the heat of said photovoltaic cell (4') into said layer of water (5), and the system further comprising a homogenizing glass rod (50) positioned between said lens (2) and said photovoltaic cell (4').|
|Full Text||SOLAR ELECTRICITY GENERATOR
FIELD OF THE INVENTION
The invention refers to photovoltaic solar power plants of large size.
BACKGROUND OF THE INVENTION
The invention refers to devices for the direct conversion of solar energy into electric-
ity, in contrast to indirect conversion involving elevated-temperature intermediary processes
producing mechanical torque that is applied to rotary electrical generators. Large solar elec-
tricity generators are known to be currently operating in California. All of the largest first con-
centrate sunlight into high-temperature heat and thereafter, with methods known from com-
bustion-heated power-stations, partially into electricity, the rest waste heat All currently op-
erating solar power plants with utility-significant electrical-output cover huge tracts because
their areal yield is below 3%. Their high cost and considerable height lead to wide east-west
separation of concentrator modules. Their high cost is due to the masses of metal required
for the wind-loads generated by the height while the height ironically enough, is required in
order to extend the number of hours per day that each module operates without being shad-
owed by its southern neighbors. Additional cost factors accrue from the high maintenance
labor involved in solar thermal electrical generation.
Large-scale photovoltaic plants have only recently become economically viable due
to the steadily decreasing photovoltaic-cell costs and steadily increasing cell efficiency. But
without concentration, covering huge tracts of land with banks of one-sun cells will result in
large masses of exotic metals being deployed across the landscape, necessarily in large
panels that require their own wind-resistant structures. The present invention offers great
improvements over this prior art, due to the efficiency-advantages of concentrating sunlight
on PV cells.
Theoretically, some photovoltaic cells could convert nearly 50% of the irradiation di-
rectly into electricity, and practically nearly 40% has already been achieved in laboratory
tests, but both of these are for solar concentration. The prior art of solar concentration,
however, leads back to the same excessive land utilization, due to the requirement for mod-
ules to be separated. The air-cooled PV concentrators of the prior art are still expensive
enough as to require all-day operation for practical payback, because their concentrations
are only in the tens.
The prior art suffers from impracticaily excessive land utilization, which is expressed
by their low areal solar efficiency, defined as electricity out divided by sunlight hitting all the
land needed by tine installation. The present invention offers an environmentally benign sys-
tew of solar electricity generation that improves upon the aforementioned prior art with a
compact, maintainable, resource-modest design that is easy to manufacture and install. By
covering 87% of the set-aside land rather than 5%, far less acreage must be set aside per
billion watts produced. The present invention offers highly scalable, compact solar-electricity
installations with improved logistics of installation, maintenance, and control and improved
economics of manufacturing and payback.
SUMMARY OF THE INVENTION
The invention therefore uses concentrated photovoltaic conversion of sunlight, in
two-axis tracking of its direct component, optically focused to high concentration (about 400
in the preferred embodiment described herein) and kept to high efficiency by integral water
As disclosed further, the following measures are taken to approach levels of areal
efficiency an order of magnitude above the prior art.
1. The optically active aperture will be a large fraction (near 90% areal utilization) of
the ground surface. A novel two-axis tracking configuration is herein disclosed
that attains this.
2. The irradiation on the photovoltaic cells will be several hundred suns, for operat-
ing efficiency to approach ideal limits, but not so high (thousands of suns) as to
shorten reliable lifetime.
3. The conversion will be performed by multi-junction cells, because their compo-
nent layers can each specialize in a portion of the solar spectrum, which is the
underlying reason for the aforementioned high ideal conversion efficiencies.
4. The highly non-uniform distribution of concentrated flux at the small round focal
spot (thousands of suns) will be distributed more equably over the larger, square
photovoltaic cell. Because lens focal length varies with wavelength, the focal
spot is spectrally non-uniform as well, with substantially wider focal spots at
400nm and 1100 nm, than at the flux-weighted median refractive index of 1.492.
Series-connected multi-junction cells, however, work best when the entire cell
has the same spectral balance of concentrated solar flux received.
5. Because efficiency declines with temperature elevation, there will be a heat sink
to remove fierce levels of unconverted solar heat, effective enough that the tem-
perature difference between the bottom of the photovoltaic cell and the heat sink
is only a few °C. At hundreds of suns, this means water cooling.
6. Two-axis tracking of the direct component of solar-radiation will be cost-
effectively implemented while retaining low overall height.
A further requirement for competitive large-scale solar electricity production is
the enhanced cost-effectiveness over prior-art solar-energy conversion
systems. The present invention makes this possible by:
a) Reduced material mass per watt, by using the buoyancy of the
concentrators to support horizontal tracking by floating on the
b) Minimal height of the system (literally knee-high) so that there is
little vulnerability to the extremes of wind,
c) Use of small photovoltaic cells, for which the transfer of the solar
electricity requires only short leads to a low-resistance common
d) Shortfocal-length concentrating lenses and kaleidoscopic mixing
rods, combined with natural-convection water-cooling, assure
The invention fulfills all these requirements by the features of the invention.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 shows a cross-section through two troughs
Figure 2 shows a top-view of the skeleton of a platform.
Figure 3 shows part of a solar farm.
Figure 4 shows the position of two troughs at low sun elevation.
Figure 5 shows the view of a trough from above.
Figure 6 shows an end wall of a trough.
Figure 7 shows the suspension of two troughs.
Figure 8 shows the bearing for the troughs.
Figure 9 shows the electricity collector.
Figure 10 shows the profile of the focal-area of a pencil or rays.
Figure 11 shows the use of a radiation-homogenizer
Figure 12 shows the same arrangement with of a radiation-homogenizer.
Figure 13 shows a radiation-homogenizer whose entrance plane is larger than its
Figure 14 shows the same radiation-homogenizer with eccentric focus
Figure 15 shows the heat dissipation from a movable radiation-homogenizer by
Figure 16 shows the heat dissipation by a heat pipe.
Figures 17a, 17b, and 17c show an elongated heat pipe.
Figure 18 shows a lifting device for the troughs.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
Figure 1 shows in schematic presentation a vertical section through concentrators
positioned in troughs 1, covered by lenses 2 which concentrate parallel monochromatic rays
3 at focal spot 4. The troughs are supported on water body 5. The troughs are kept at a dis-
tance of only a few millimeters from each other by traverses 6. For tracking in solar eleva-
tion, the troughs can pivot around the horizontal geometric axis 7. The pivoting is controlled
by sun-tracking sensors and is based on pneumatically driven balancing torques. By pump-
ing water from ballast compartment 8 into ballast compartment 9, the two of which pneu-
matically inter-communicate via tube-shaped traverse 6, a buoyancy-torque makes each
trough pivot upward to keep lens 2 aimed directly at the climbing sun, until it has reached its
highest position at noon. Thereafter blower 10 creates positive pressure in ballast compart-
ment 9 through traverse 6, so that water flows back from ballast compartment 9 into ballast
compartment 8. This causes the trough during the afternoon hours to pivot the lens down-
ward. The angle of traverse is proportional to the positive or negative pressure.
Figure 2 shows skeleton 20 of a floating platform with multiple troughs 21, each
comprising 12 concentrator lenses. The skeleton 20 comprises floating ring 22, which forms
a unit with floating traverses 6' and vertically joins members 23 to traverses 6'. Vertical
bearing 24 is arranged in the center of the platform and is connected to the ground. Ring 22
can have teeth 28 (as on a tooth-belt) that will be turned by disc 29, which is driven by an
electric motor. The platform revolves around the vertical axis of the platform at the azimuthai
angular velocity of the sun, controlled by a sun finder. Concentrating lenses 2' thus point at
the sun in both horizontal and vertical axes. During the night the platform turns back into the
morning position, but on breezy nights with the troughs aimed into the wind for enhanced
cooling of the water.
Figure 3 shows a group of platforms of a solar farm arranged in a close-packed man-
ner suitable for any number of platforms. In such a case of multiple platforms, azimuihai-
tracking drive will be done by pneumatic-tire guiding-wheels 30 arranged interstitially be-
tween three platforms. Each fifth such wheel 31 is driven by an electric motor, the torque of
which is transferred to outer rings 22'. Also in this case the rings 22' can have teeth to en-
gage the teeth of guides 30. Footbridges 34 run above guides 30 to allow personnel access
for maintenance. Below each platform 20' of the solar farm there is a shallow body of water,
upon which it floats. This enclosed pond is protected from evaporation by layer of oil atop it
Into this water layer the waste heat of the photovoltaic cells is conducted. The cooling of the
water layer is done by its exposure to the outside air. During hours when the sun is too low,
and especially at night, platform 20 will be turned so the trough rows face into the direction of
the wind, giving it good access to the pond water.
Such a solar farm can also be placed on natural bodies of water. If the bottom of a
lake is too deep, the axes 33 of the guiding wheels 30 will be connected to each other by
rods and the combined guiding wheels 30 will be attached via anchor apparatus to the bot-
tom. Also, numerous industrial installations have large aeration ponds suitable for dual use
with the present invention, as long as the troughs are made of a low-corrosion material.
Figure 4 shows troughs 1 in transverse cross-section, to show their interiors, where
the conversion of the sun's irradiation takes place. These troughs float on water layer 5 At
low sun elevations trough V displaces an amount of water defined by dotted line 40 and
those portions of trough-walls 54 lying below it At each elevation angle geometric circle 41
has tangentto the plane of the water surface. Dotted lines from 40 through 42 define that
plane at higher solar elevations, all of them tangent to circle 41. The distance 61 of the
troughs 1 and 1' from each other results from the width of the lenses 2" plus a gap of mini-
mal width between the troughs. At elevation angle shown of 24°, rim 47 of protruding guard
frame 48 touches the protruding part 49 of the adjacent trough. Relative to bisecting line 45,
optical axis 46 of lens 2 is moved downwards. This optical axis intersects the center of the
entrance plane of radiation-homogenizer 43. The highly concentrated pencil of concentrated
solar rays will enter rod 43 and by loss-free total internal reflection make its way to photo-
voltaic cell 4'. Due to the kaleidoscopic action of these internal reflections, the spatial distri-
bution of the sunlight on 4' will having become more even. Photovoltaic cell 4' is in good
thermal contact with extruded rod 50, positioned to stay below water surface 5' at all solar-
elevation angles of trough 1'. At one end, hose 52 opens to the outside air and on the other
end it is closed. Wire grid 53 runs parallel to peripheral ray 39 and prevents hose 52 from
entering the pyramid within rays 39 of the concentrator lens.
In response to meteorological increases in air pressure, hose 52 fills with outside air.
This measure ensures that the compartment enclosed by lenses 2', walls 54 and 55, and the
end wall always has the same air-pressure as the outside air, minimizing uncontrolled air-
exchange with ambient To dry the air entering the interior, a recycling dessicator is provided
in canister 37 on hose 52. Dry interior air is essential because multi-junction-cells are hygro-
Figure 5 shows a view of the trough from the side facing the sun. At end plates 56
and 56' the troughs have stub-shafts 57, and can be tilted thereupon around horizontal geo-
metric axis 58. The position of the axis 58 is chosen for zero buoyancy-torque at ail opera-
tional tilting angles. Lens 2' has on its inner side a multiplicity of refracting grooves 59 in the
central half of the lens and peripherally about it are TIR grooves 60, enabling the short focal
length required by such a zero-torque trough-shape. As shown in Figure 4, only with such a
short focal length, as represented by dotted line 46, can inter-trough distance 61 be barely
larger than the trough's width, for close to 100% fiil-factor. Since the troughs are supported
by floating in water, their walls need less materia* thickness than would be necessary to pre-
vent twist deformation when out of the water. In order to save on the expense of corrosion-
resistant wall material, diagonal bracing wires 62 form an 'X on each lens, ensuring trough
stiffness, which is required for all the homogenizer rods to line up on their respective foci.
Up to twelve Lens-Rod-Cell-Units are installed per trough. Guard-frame 48 in Figure
4 prevents lens 2" from submerging in water-surface 5' at the lowest solar elevation
Figure 6 shows a view on the end plate 56 of a trough with guard-frame 48 and stub-
Figures 7 and 8 show two troughs with end plates 56 and 56' with stub-shafts 57"
which are supported by ball-bearings. Wall 70 projects between end plates 56 and 56', and
ball bearings 66 and 67 are mounted on it, as well as electricity collectors 71 and 71'. Wall
70 is part of extruded tube 70; most of which lies below water surface 5'. This tube 70' cre-
ates a buoyancy force that is transferred via ball bearings 66 and 67 to stub shafts 57' and
57', thereby supporting troughs 69 and 69'. Extruded tubes 70' are connected to platform-
ring 22' of Figure 1 via supports 75.
Figure 8 shows extruded tube 70' running perpendicular to longitudinal axis 58 (figure
5) of the troughs. At wall 70, ball bearings 67 and 67' and electricity collectors 71 and 71' are
Figure 9 shows a cross-section through stub-shaft 57" with ball bearings 66 and 67
and electricity collector 71, in which contact-body 76 is pressed against slide-ring end 78 by
spring 72. Slide-ring end 78 needs to extend only an angle at the center of about 70°, so that
the weight of the trough on contact body 76 keeps it in firm contact with slide-ring end 78 at
all angles of elevation. The slide-ring ends are series-connected with photovoltaic cells 4'
(figure 4) so that opposite electric polarities are attained at opposite ends of the trough. De-
pending on the desired trough output-voltage, the multiple photovoltaic cells can be con-
nected in series for the highest voltage or in parallel for hydrogen-hydrolysis or a combina-
tion of both for intermediate voltages. Similar series-parallel choices will determine how
trough voltages combine for a desired platform voltage, when the power is conducted to the
outside via a highly flexible cable.
The key component of radiation-homogenizer is described in Figures 10 to 14.
Figure 10 is intensity plot 100 of the focal spot of the concentrating lens, with peak
101 of many thousands of suns and the remaining cell area dark. Such excess flux density
will destroy the cell. Instead, a uniform distribution across the ceil will result in 460 suns of
geometric concentration, near the cell optimum.
Figure 11 depicts radiation-homogenizer rod 80 receiving at end 81 the focused ra-
' diation of lens 2. Radiation-homogenizer rod 80 is made of glass of the highest volume
transmissivity across the operational solar spectrum, to minimize absorptive heat loads
therein. Most common glasses have solar absorption bands sufficiently dense as to add an
unacceptable heat load to the cell. Figure 12 shows a side view of the same, with slanted
side 84 of rod 80 extending to thermally conductive heat-sink bar 85. This slant is necessary
to keep bar 85 submerged at all solar elevation angles.
Figures 13 and 14 show radiation-homogenizer 80 with walls 86 and 87 and
87'slanting inward towards bottom surface 82. Figure 13 shows rays at middle 130 of en-
trance plane 131, while in figure 14 rays off center. Exit surface 82 is in optical contact with
photovoltaic cell 83 via optical-adhesive layer 83a. The lower side of photovoltaic cell 83 is
connected to metal layer 85a of a material of thermal expansion coefficient close to that of
the cell. This metallic layer is soldered to heat sink 88 before the cell and rod are bonded to
This same optical device, the homogenizing, rod, performs three functions:
a) Loss-free redistribution over the rectangular exit surface of the highly nonuniform
concentrated solar radiation flux, which forms a circular spot on the entry surface.
b) Loss-free deflection of the total radiation flux by tilting the rod up to 20° about its
entry face, in order to keep the heat sink submerged.
c) Providing an expanded entry surface (30% wider than the cell) large enough to
collect all the focused sunlight even at a 1 ° error in elevation tracking
Figure 15 shows the arrangement in which radiation-homogenizer rod 145'" is en-
closed by tube 155, which makes sole contact to rod 145'" via sharp edges that scatter very
little concentrated sunlight Tube 155 is connected to metal base 156, which forms narrow
gap 157 with heat sink 154. Gap 157 is filled with mercury, a supply of which is in bellow
Figure 16 shows an evacuated heat pipe surrounded by bellow 158'. Wick 160 ab-
. sorbs condensate fluid. Spacer 161 prevents heat absorbing pianes 156' and 154' from be-
ing moved together by outside air pressure.
Figure 17a shows a side-view of a trough with the stub-shaft 57". Photovoltaic cell 4'"
is placed in protrusion 165 and is in thermal contact with heat pipe 166, the longitudinal
extension of which runs perpendicular to endplate 56" down the entire length of the trough,
from its first photovoltaic ceil to the last. Figure 17c shows absorbent wick-layer 167 posi-
tioned within heat pipe 166, from whose section 169 the heat transfer fluid, for instance wa-
ter, evaporates. The vapor flows through compartment 170 to wall 171 which stays below
water surface 5'" at all operational solar-elevation angles. At this wail the heat transfer fluid
condenses and will be conveyed by capillary forces of wick-layer 167 back to photovoltaic
cell 4"and its waste heat. Heat pipe 166 is air-tight and evacuated except for a small amount
Figure 17b shows a second trough, which like the first can be tilted down to an eleva-
tion angle of 20°.
As an alternative to the aforementioned pneumatic tracking, Figures 17a and 17b,
show a mechanical method for collectively tilting the lens-photovoltaic-units..
In Figures 17a and 17b, heat pipes 166 of the troughs have eyelets 172 at which
rope 178 is fixed. In order to tilt the troughs around their horizontal axis to lower elevation
angles, rope 178 will be moved by a linear motor in the direction of arrow 180. The adjusting
force for a tilting to higher elevation angles comes from the screw-springs 181 which are
connected.to the platform skeleton.
Figure 18 shows a trough in longitudinal view 182 and cross-sectional view 183. At a dis-
tance 184 of about a quarter of the total length a handle 185 is positioned. Via a crane, not
shown, the rectangular tube 186 will be lowered between the two handles 185. Thereafter
tongues 187 extend from the tube 186. Now the trough with the stab-shafts 57'", whose tor-
sion rigidity is low since it normally floats on water, can be lifted out of its bearings as shown
in Figure 9.
1. Solar electricity generator system comprising a generally planar optical
concentrator lens (2) in two-axis tracking of solar radiation, generally U-
shaped troughs (1) floating on a layer of water, said troughs (1) being
arranged in banks closely positioned to each other so as to maximize
their areal coverage, said troughs (1) being tiltable around a horizontal
geometric axis (7), said lens (2) positioned across the open side of a said
trough (1), a photovoltaic cell (40 receiving concentrated solar radiation
from said lens (2), characterized in that said cell (40 is placed together
with a heai.conducting device (50) within a protrusion at the area (50 of
a said trough (1) opposite said lens (2), said device conducting the heat
of said photovoltaic cell (40 into said layer of water (5), and the system
further comprising a homogenizing glass rod (50) positioned between
said lens (2) and said photovoltaic cell (40)
2. The system as claimed in' claim 1, wherein said rod having a longitudinal
axis and comprising two opposing surfaces and multiple longitudinal
planar walls of sufficient length to mix the concentrated solar radiation
both spatially and spectrally sufficiently thorough so as to improve the
radiant utilization performance of said photovoltaic cell, one of said
surfaces receiving said concentrated sunlight and the opposing surface
being in optical contact with said photovoltaic cell.
3. The system as claimed in claim 1, wherein the protrusion is tilted with
respect to the direction of said solar radiation.
4. The system as claimed in claim 2, wherein said longitudinal axis of said
homogenizing rod is tilted with respect to the direction of said
concentrated solar radiation.
5. The system as claimed in claim 4 wherein said tilt is in a downward
direction, said downward direction defined during tracking-operation at
the lowest solar altitude.
6. The system as claimed in claim 2, wherein at least one of said
longitudinal walls is not parallel to said longitudinal axis, so that said rod
tapers in the direction of said concentrated solar radiation.
7. The system as claimed in claim 2, wherein associated with said
homogenizing rod are structural support means making only point or line
contacts with said rod.
8. The system as claimed in claim 7, wherein said structural support means
comprises a tube with internal diameter equal to the diagonal dimension
of said rod.
9. The system as claimed in claim 1, comprising a large shallow circular
pond, said pond contains multiple banks of linear troughs closely
positioned so as to maximize their areal coverage close to 100% fill-
factor, said troughs being covered by lenses having on their inner side
refracting grooves in the center-region and peripherally reflecting grooves
enabling a short focal length.
10. The system as claimed in claim 1, wherein said water is covered by an
anti-evaporative means comprising a thin layer of an immiscible fluid of
lower density than water, said fluid having sufficiently low vapor pressure
for practical periods of persistence.
11. The system as claimed in claim 1, wherein said heat conducting device
comprises a heat pipe in thermal contact with said water.
12. The system as claimed in claim 1, wherein buoyancy-balancing weight
and a buoyancy-balancing torque about said shafts is exerted by
distributed weights positioned eccentric to the center of gravity of said
13. The system as claimed in claim 12, comprising chambers within said
linear troughs and means of transferring air between said chambers.
14. The system as claimed in claim 13, wherein said air-transfer means
comprises an air-blower and pipes connecting said blower to the upper
portions of said chambers.
15. The system as claimed in claim 1, comprising electrical conducting means
to convey solar-generated electricity out of said troughs wherein said
electrical conducting means comprise a conducting strip and a brush
means being in contact with said conducting strip.
16. The system as claimed in claim 13, comprising a floating frame holding
said banks of linear troughs, wherein structural elements of said floating
frame comprise air ducts.
17. The system as claimed in claim 1, wherein said troughs comprise air-
sealing means for mounting said concentrating lenses.
18. The system as claimed in claim 17, wherein said troughs comprise air-
19. The system as claimed in claim 17, wherein said troughs comprise a
bellows system to equalize interior and exterior air pressure.
20. The system as claimed in claim 1, wherein walls of the troughs have less
material thickness than would be necessary to prevent twist deformation
when out of the water.
21. The system as claimed in claim 1, wherein each trough has two end-walls
with stub-shafts and a U-shaped-wall, the position of the axis being
chosen for zero-buoyancy-torque at all operational tilting angles.
22. The system as claimed in claim 1, wherein the current of the photovoltaic
cell will be used for producing hydrogen by hydrolysis.
The invention relates to a solar electricity generator system comprising a
generally planar optical concentrator lens (2) in two-axis tracking of solar
radiation, generally U-shaped troughs (1) floating on a layer of water, said
troughs (1) being arranged in banks closely positioned to each other so as to
maximize their areal coverage, said troughs (1) being tiltable around a horizontal
geometric axis (7), said lens (2) positioned across the open side of a said trough
(1), a photovoltaic cell (4') receiving concentrated solar radiation from said lens
(2). The said cell (4') is placed together with a heat conducting device (50)
within a protrusion at the area (5') of a said trough (1) opposite said lens (2),
said device conducting the heat of said photovoltaic cell (4') into said layer of
water (5), and the system further comprising a homogenizing glass rod (50)
positioned between said lens (2) and said photovoltaic cell (4').
|Indian Patent Application Number||471/KOLNP/2004|
|PG Journal Number||12/2009|
|Date of Filing||08-Apr-2004|
|Name of Patentee||LAING, NIKOLAUS, JOHANNES|
|Applicant Address||KLINGELBRUNNENWEG 4, 71686 REMSECK|
|PCT International Classification Number||H01L 31/052, 31/042|
|PCT International Application Number||PCT/EP2002/011309|
|PCT International Filing date||2002-10-09|