Innovative modular foldable concentrating solar energy system
I. Detailed description of the drawings
Fig. 1. Typical assembly of reflectors of the Cassegrain type
The classical optical concentrating system in the art (typical assembly of reflectors of the Cassegrain type), as shown in Fig. 1, comprises concentrating parabolic surface 1 with a focus (focal
line, in case of cylindrical surfaces) F coinciding with the focus
of the collimating parabola 2. The incident parallel light rays of
size a in Fig. 1 fall upon the reflective surface of the
concentrating parabola 1 and are concentrated at the focus (focal
line) F. The concentrating ratio a/b to the outgoing collimated
light beam can be changed by varying the parameter of the collimating parabola 2. By rotating the collimating parabolic
reflective surface 2 around the focus (focal line) F, the outgoing
light beam changes only its path, without changing the concentration of the collimated light rays. Some of the problems of this widely known system are: the first one is the need of cooling the collimating surface 2, which, as a rule, is much
smaller than the concentrating one 1. It can be resolved by
applying forced cooling, by thermally
coupling the collimating 2 to the
concentrating 1 parabolic surface as
well as by ensuring additional cooling
surface. The problem can also be
resolved by enlarging the area of the
collimating surface 2 to allow for
maintaining the heating within
permissible limits, as is shown in Fig.
2. The other problem is the
overshadowing of a portion of the
concentrating parabolic surface 1 and
a portion of useful incident light rays
is lost while the collimated surface 2
heats additionally. As it is shown in
the Fig. 3, this problem can also be
Fig. 2 is an embodiment of Fig. 1, but the
collimating parabolic surface 2 has the
area of size a, commensurate to the
aperture of the concentrating parabolic
surface 1. In this case, to realize the same
concentration of incident light rays, as in
Fig. 1, the parameter of the collimating
parabola of the surface 2 should be much
smaller than that in Fig. 1. In this way the
heating of the collimating parabolic
surface 2 is practically commensurate to
that of the concentrating parabolic surface
1 from Fig. 1. If needed, the area of the
collimating parabolic surface 2 can be
enlarged depending on the needed
dissipated heat power. This construction
allows such positioning of the collimating
parabolic surface 2 so that it is located at
a sufficient distance from the caustic point (line) F. In case the collimating parabolic surface 2 is located opposite to the
incident light rays both parabolic surfaces could be manufactured as a module. In this way the preciseness of the mutual location of both
is guaranteed in the
Fig. 3 shows a
of two identical
pairs of parabolas,
shown in Fig. 2,
with coinciding foci
(focal lines) F. The icollimating
parabolic surface 2
with focus (focal
line) F is mounted 1on the rear side
incident light rays)
parabolic surface 1
with a focus (focal
line) F. This type 2of positioning
greater space and
size of the
, as well as for 2
The outgoing light
beams are parallel
to each other and
each other, i.e. they
are summed up. In
this way the
incident light rays
of size 2a are transformed into the outgoing light beam of size 2b.
In this way optical concentrating systems of similar components can be assembled without restrictions as to the size. The system can fold down when necessary, as shown in Fig. 16. This approach remains the same with all other suggested constructions.
On first thought, the idea of folding and unfolding in working (erected) position such construction may seem heretical. But as shown in Fig. 4 and Fig. 5, this problem can be resolved in principle, especially where trough-
shaped surfaces are concerned. The elements, which have the reflective surfaces with the shape of the concentrating 1 and collimating 2 parabolas, are attached to the moving part 9, which can be moved away freely
along the slide-ways 8. Positioning can be performed with greatest precision by supports 10 and 11. Supports 10
and 11 are located on carriers 13 at the right places with the required precision and it is maintained during the positioning of the relevant elements. When the relevant element needs to be appropriately positioned, it has simply to be pressed to its relevant support with the appropriate force and the required precision of positioning
will be achieved. Bumpers 12 protect the construction against impact. The reflective surface components having the shape of all other couples of curves, described above, can also be located in this way.
The system in working (erected)
The system in
II. Detailed description of the animation
The animation could be started (of course, after unzipping it) by clicking on the file movie.exe. It needs Flash
player on your computer.
The scene 1 shows the well known and proven Cassegrain assembly of concentrating and collimating mirrors. There are several reasons this assembly not to be used for solar energy concentrating purposes: The collimating mirror is very quickly heated to the very big temperatures and will be melted, if the appropriate forced cooling will not be used (scene 2). But this technical decision is impractical for the aforementioned
purposes – it makes the device so expensive, that practically the system will be unsoldable. So that such technical solution must be found, which to ensure the passive cooling of the collimating mirror. The first step was shown in the scene 3 – if to the first concentrating module (consisting concentrating and collimating mirrors), the second one is added in such a way, so that the first collimating mirror is thermally connected to the second concentrating mirror. In this way the thermal problems could be avoided, the modules are equal, (relatively small to be precisely molded) and don’t disturb each other. The big concentrating mirror hides the collimating one. It seems that the problem could be resolved in this way. But as it often happens when you resolve one problem another one appears. One of these problems is the mutual disposition between the concentrating and collimating mirrors – it must be guaranteed with big preciseness. So that another solution is
searched, which to resolve all of the aforementioned and this problem together. One attempt is shown in the scene 4 – the surface of the collimating mirror is enlarged enough to be cooled passively and in the same way it continue to collimate the concentrating solar rays. But in this case it would hinder the incoming solar rays to reach the concentrating mirror from the next module. So that the collimating mirror must be hidden behind the concentrating one – scene 5.
Scene 6 shows the final module, which resolve all the problems. With such kind equal elements the concentrating system could be build as big as it is possible (scenes 7 and 8). After so many transformations the
final module remains still Cassegrain assembly of mirrors.
The problem with the strong winds and the other harsh environmental conditions could be resolved by folding down the whole system in the save position. In this way the big surface could be reduced several times and the big efforts, which the whole construction must to endure, would be avoided. The solution is shown in the scene 9 – the modules allow this folding. The working position of the modules is ensured by the relevant system of supports.
The next scene 10 shows how the system works – the concentrated solar rays are very close to the concentrated
area. In this way the construction of the whole system is additionally simplified.
The scene 11 shows how the big number of concentrating systems works in the village or a town. In solar days this system could satisfy the all the needs of the home and the excess of the accepted energy could be gathered in the common electric generator.
This is one of the cheapest ways for using solar energy with the existing technologies (for example, the final element is practically used by the Solargenix in the Cramer Junction, California) (Fig. 9-13). The modules could be build from the molded members in the described modified Cassegrain assembly form. The members can be molded in the similar (but very simplified) manner like the molded aspherical lenses, produced by Edmund Industrial Optics (http://www.edmundoptics.com/), Melles Griot Inc (http://www.mellesgriot.com/),
Newport Corporation (http://www.newport.com/), Rolyn Optics Company (http://www.rolyn.com/), etc. The
high efficient reflective folio manufactured by 3M, Alanod or other companies could be used for stretchening between molded and fixed members. In this way the final element can be build.
III. Brief review of the concentrating state-of-the-art solar energy concentrating systems
The basic concepts and ideas of photovoltaics using concentrated sun light (CPV) have been published and patented in the 70’s and 80’s of last century. So they are about as old as the basic principles of flat panel PV
technology. But existed CPV is not well suited for small industrial applications. In the beginning of terrestrial PV applications, about 30 % of solar cell production was used in industrial and consumer products like watches, pocket calculators, traffic applications, solar home systems etc., where often only a few W are necessary for p
electric powering and where tracking is not possible. So while these applications were historically a strong motor for the growth of PV production, CPV could not take part in this market section. CPV is also not well suited for grid connected roof systems. The application of PV modules in grid connected systems of a few kW size p
mounted on or integrated in the roof surface of private homes was and still is one of the biggest stimulus of the PV market due to support of several government programs world wide. Here again the small size of systems, the necessity of tracking (i.e. of moving parts) and the need they to withstand to the strong winds makes CPV not a good option.
CPV offers such a large variety of technical possibilities but R&D is still in the state of finding the best options. CPV systems promise a number of advantages if they are built with a size > 10 kW and at big enough p
fabrication volume (> 10 MW/y) as will be described below. p
Nowadays rooftop installation is currently becoming a practical goal for a new generation of CPV.
1. Solar lighting concentrating systems
Once concentrated, the solar energy could be used not only for producing electricity, but for heating and lighting. This method of lighting is already proved by the solar lighting system based on a design developed by Oak Ridge National Laboratory and built at Utah State University. The system captures the full-spectrum direct sunlight and delivers it directly instead of converting it into electricity and then into artificial light. The lighting system consists of a two-axis solar tracking system, a 1m parabolic mirror to concentrate sunlight, an elliptical secondary mirror to filter the infrared (IR) and re-direct the visible (typical assembly of reflectors of the Cassegrain type), and a fiber-optic bundle for transmission (see Fig. 6). An infrared-photovoltaic (IR-PV) array placed behind the elliptical mirror could be used to generate electrical power.
Pure visible light – without the uncomfortable infrared or the damaging ultraviolet – is conducted through the
optical fibers into the building.
System HSL 3000
The fibers could feed concentrated light from the system HSL 3000 into an acrylic rod, the non-electrical
equivalent of the fluorescent tubes between which it is sandwiched in the commercial hybrid lighting fixture.
The sunlight, which would otherwise continue in a straight line, is diffused outward into the room by means of
hundreds of tiny scratches on the surface of the rod.
Fig. 6. The solar lighting system concentrates
rays directed by primary and secondary
mirrors (Cassegrain assembly) to full-
spectrum output through a fiber optic bundle.
NI: Non-imaging. IR: Infrared
One HSL 3000 is capable of lighting
approximately 1000 square feet.
The HSL 3000 is scheduled for release
early in 2007, and is initially priced at
about $8,000 USD.
Although Sunlight Direct has not
specified the cost of installation – other
than to imply that it would involve extra
money you would not be paying if doing
it yourself – having professionals do the
work would obviously add to the price of
the system. Basing a rough guess on the
rates charged by other professional
trades, this could amount to an additional $1000 or more, depending on the size of the house and the number of
areas to be lighted. But the safety factor may make this worth the extra cost
Fig. 7. The HSL 3000, a hybrid lighting system
developed by Sunlight Direct, carries the actual light
of the sun indoors. The system’s 48-inch primary
mirror concentrates light into a secondary mirror,
which strips away the infrared and ultraviolet
components, and directs the visible light into the
receiver. A tracking system has two motors governed
by a GPS microprocessor, which can calculate the
position of the sun within half a degree.
Fig. 8. It’s hard not to fantasize about a kitchen console with
heat-tolerant optical rods of various thicknesses depending on
the volume to be heated. These could be inserted into anything
that requires to be boiled.
With the sun’s power focused, a lot of daytime food
preparation could be done without fuel.
Early designs of the hybrid system included thermal
photovoltaic cells to take advantage of the IR energy that
is not currently being used by the HSL 3000. This idea was abandoned due to the cost of these cells and the low power output, but might be revisited if the cost comes down. This might become an add-on in future. If so, the basic system should be designed so that additional features can be simply plugged in without having to re-tool or to modify the already-installed solar collector.
As you can see prof. Dely, this company uses the same principles, as they are used in my construction.
2. Solar thermal electric systems
Parabolic trough concentrating systems
Fig. 9. A parabolic trough
concentrator focuses solar radiation
onto a linear receiver when faced
directly at the sun
Each solar collector has a linear
parabolic shaped reflector that
focuses the sun’s direct beam
radiation on a linear receiver
located at the focus of the
parabola. The collectors track the
sun from east to west during the
day to ensure that the sun is
continuously focused on the
linear receiver. The solar field is
modular and is composed of
many parallel rows of solar
collectors aligned on a north-
south horizontal axis (Fig. 10).
The receivers convert energy from the sun into electricity by using concentrated solar radiation from the plant’s parabolic mirrors to increase the temperature of the thermo-oil heat transfer fluid (usually artificial oil) flowing through the receiver to 395ºC. This heated fluid is then used to turn water into steam, which drives a turbine and generates electricity (Fig. 11). In this way one of the cheapest electricity from the solar energy is generated. Parabolic trough technology is currently the most proven of the solar thermal electric technologies. The first large commercial-scale solar power plant has been operating in the California Mojave Desert since 1984 (SEGS I). The nine plants, which continue to operate daily, range in size from 14 to 80 megawatts (MW) and represent a total of 354 MW of installed electric generating capacity.
The new 64MW Nevada Solar One power plant will follows in the steps of the 354MW solar thermal power
plants and will use new technologies to
capture even more energy from the sun:
Amendment for expansion to 64 MW was
approved in June 5, 2005. In the February
11, 2006 SCHOTT officially introduced to
the public its new PTR 70? solar receiver,
which will lie at the heart of Solargenix’s
new power plant.
The SCHOTT receivers convert energy
from the sun into electricity by using
concentrated solar radiation from the
plant’s parabolic mirrors to increase the
temperature of the thermo-oil heat transfer
fluid flowing through the receiver.
Fig, 12. The aerial view of the 2.5 km? power plant in the California Mojave Desert.
Solargenics has been developed the Roof Integrated “Tracking” Solar Systems for mid and high temperatures applications to meet a wide range of energy needs: electricity generation, hot water and space heating, absorption
cooling. In fact the process is “co-generating” as it is shown in the fig. 13.
Fig. 13: The power roof generates temperatures up to 550ºC
The followed several pictures illustrated how some of the most important stages of the construction look like:
Parabolic dish concentrating systems
Fig. 14. A paraboloidal dish concentrator focuses solar radiation onto a
point focus receiver
The high concentration ratios achievable with dish concentrators
allow for efficient operation at high temperatures. Stirling cycle
engines are well suited to construction at the size needed for
operation on single dish systems and they function with good
efficiency with receiver temperatures in the range 650ºC to 800ºC.
To achieve good power to weight ratios, working gas pressures in
the range 5 – 20MPa are employed and use of either the high conductivity gases hydrogen or helium gives
improved heat transfer. The Advanco corporation
and McDonnell Douglas have produced 25kWe
dish Stirling units which have achieved solar to
electric conversion efficiencies of close to 30%.
This represents the maximum solar to net electric
conversion efficiency achieved by any solar
energy conversion technology.
Fig. 15. Solar Plant 1, 400 dishes producing steam.
The biggest distributed array / central plant solar
thermal power system that has been trailed is the
“Solarplant 1” system built in Southern California