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Innovative modular foldable concentrating solar energy system

By Ruby Rogers,2014-12-13 16:23
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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 cas..

    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

    resolved.

    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

    parabolic surfaces

    is guaranteed in the

    process of

    manufacturing.

Fig. 3 shows a

    system comprising

    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

    (invisible for

    incident light rays)

    of the

    concentrating

    parabolic surface 1

    with a focus (focal

    line) F. This type 2of positioning

    provides for

    greater space and

    size of the

    collimating

    parabolic surface

     , as well as for 2

    adding of

    additional

    dissipating surfaces.

    The outgoing light

    beams are parallel

    to each other and

    practically touch

    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.

Fig. 4

The system in working (erected)

position

    Fig 5.

    The system in

    the save

    (folded)

    position

    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

    Introduction

    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).

     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.

     Fig. 11.

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

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