Solar radiation collection with high concentration level, high optical efficiency and spectrum splitting.

The major cost item in photovoltaic solar panels is the amount of photovoltaic material used. A concentrator reduces the amount of material used by concentrating the photons to fall on a much smaller area. If the geometric concentration level is 500, then the amount of material required is reduced by a factor of 500. As the concentration level increases the accuracy of tracking to keep the light focused on the solar cell is also increased. Optical efficiency also decreases as the concentration level is increased.

 

Concentration with refraction Concentration with reflection

Fresnel lens are commonly used to focus the photons. The cell is placed between the fresnel lens and the focus. If the area of the fresnel lens is A and the area of the cell is R, then the concentration level C is A/R. At concentration level C the cell is placed F/sqrt(C) distance from the focus, where F is the focal length. There are losses every time light is refracted or reflected. To simplify discussion these losses are not considered here.

Front Focus 

Ray-trace of 400x concentration at front focus with the cell radius 85% bigger. The cell has to be 242% bigger to capture 99% of the photons. The hot spot at the center is more than 2000x. The acrylic fresnel lens is 395mm x 395mm, with F/D of 0.835, 395 grooves, refraction index of 1.49 and Abbe number of 55.3 Ray-trace of 400x concentration at back focus with the cell radius 54% bigger. The cell has to be 136% bigger to capture 99% of the photons. The high spot at the center is greater than 400,000x and approaches infinity as the spot gets smaller. 

However as photons converges to the focus point, it tends to cross itself, creating hot spots. Shorter wavelength (UV) photons are more refracted than longer wavelength (infra-red) photons causing the shorter wavelength photons to be more focused to the center and the longer wavelength photons are diffused away from the center. 

At the back focus, the longer wavelength photons are  concentrated at the center and the shorter wavelength photons are diffused over a large area.

Various technologies (secondary optical elements, secondary flux modifiers, homogenizer, TIR-R Total Internal Refraction and Refraction) are used to make the concentrated light more uniform in intensity and color. 

Heat is produced when the energy of the photon exceeds the band gap of the photovoltaic material. Solar cells lose efficiency for each oC rise in temperature. More electricity and less heat are produced if the band gap of the photovoltaic material and the energy of the photon are matched closely. The energy of the photon is a function its wavelength. 
                       

Multi junction devices are more efficient because they capture a larger portion of the solar spectrum by layering single junction cells of decreasing band gap. The top layer has the highest band gap. The theoretical efficiency (before optical and other losses) increases as the number of junctions is increased, reaching 86% for infinite number of junctions. A severe limitation of MJ cells is that the photocurrent produced by each layer must be matched because each layer is connected in series and the maximum current is limited by that produced by the weakest layer. Another limitation of MJ cells is that each layer must be optically transparent to allow the photons that it cannot use to pass to the layer below.

The methods described here aim to achieve high concentration level with minimal optical loss and more uniform intensity. These methods capture the concentrated shorter wavelength photons at the front and the concentrated longer wavelength photons at the back. This method uses fresnel lens to split the solar spectrum and capture more of the photons with three separate solar cells. The first cell at the front focus will capture more of the shorter wavelength photons and less of the longer wavelength photons. In the middle cell after the focus, the longer wavelength photons are now more focused to the center and the shorter wavelength photons to the edge. The middle cell has a hole in the center to pass the red and infra-red photons to the third cell behind it.

Silicon can be used as the photovoltaic material for all three cells. The light at the first solar cell will be quite uniform in colour, therefore 3J cells can be used at the front focus. For the second solar and third cells higher band gap materials are placed at the edge, using lower band gap materials as you move towards the center. 

The heat load is now separated into three areas, with the third cell having the heaviest heat load because of the infra-red. Cooling is achieved by attaching liquid cooled copper heat sink to the back of the cells. The cells and the heat sink will need to be insulated from the environment to protect them and the environment. The heat sink for the front cell must be tapered to be smaller towards the focus. The heat sink for the middle cell is hollow, the hole is bigger towards the third cell. The front coolant tubes must present a flat surface to the front to reduce reflection losses. The concentrated infra-red at the third cell can be feed instead to a photovoltaic cavity converter or to drive high temperature chemical reactions.

Mirrors can be placed on the heat sink behind the first and second solar cell to reflect back light from the second and three solar cells to increase efficiency further.

To make use of convection the coolant will enter from the bottom of the heat sink and exit from the top. The coolant will pass through the front blue cell first, followed by the middle green cell, then the third infra-red/red cell. The electrical connections must be behind or inside the coolant tubes.

 

Light concentrated by reflectors also have the same problem with non-uniform intensity that is also solved by using the light at both the front and back focus. Reflective concentrators produces uniform color flux, which makes them more suitable for use with MJ (Multijunction) cells.

This method also applies to line focus fresnel lens instead of the point focus fresnel lens as described. The light pattern falling on the solar cells depends on the material of the fresnel lens, focal length, refraction index, Abbe number, number of grooves and the concentration level. Less grooves means less tip losses. This method applies to both imaging and non-imaging optics.

The light intensity and colour at each of the focus planes can be calculated using an appropriate algorithm. At each focal plane, the program can calculate the light intensity and colour as a function of the distance from the centre of the solar cell. This may be used to determine the width/radius for each slice forming the solar cell, so the energy falling on each slice is equal. The program may implement the algorithms described in Proceedings of SPIE - Volume 3781, ‘Fresnel lens solar concentrator design based on geometric optics and blackbody radiation equation’ by Michael D. Watson and Robert R. Jayroe, Jr., October 1999, pp. 85-93. This program can also calculate the concentration level for each focus plane so that the light intensity does not exceed a nominated intensity level at any of the slice. The program can also calculate the concentration level for a given solar cell radius at each focal plane.

For a particular lens, the optimum concentration level for the middle cell is when mostly infra-red and red light falls on the third cell. The optimum concentration level can be increased by using higher focal length, higher refraction index material for the fresnel lens or less color dispersive (higher Abbe number) material for the fresnel lens.

The ratio between electricity produced and the quality / temperature of the thermal energy produced can be actively controlled by regulating the flow rate of the coolant.
 

Ray-trace using an acrylic Fresnel of 1000 x 1000 x 2 mm, a focal length of 1000 mm, a groove pitch of 0.2 mm, a refractive index of 1.49 and an Abbe number of 55.3 (BHPA1000-2 from http://www.bhlens.com/fresnel_lens.aspx). The spokes on the second cell show how much of the light (2.5%) misses that solar cell. Example of a three cells solar collector. Looking down, fresnel lens is at front and the solar cells at the back

The program calculates the parameters so that about a third of the energy falls on the first cell. The two cells are divided into 36 slices and the intensity of each slice is limited to about 100x. The width of both cells is 150mm. The intensity of the light at the center 5% of the second cell is very low and that region cannot be used.

The result of the calculations are as follows:

Total available energy 888 Watts
Acrylic Fresnel Lens width 1000 mm, focal length 1000mm (f/1), 2500 grooves
887.65W/m2 ASTM G-173-03 Direct Normal solar spectrum
Refraction index 1.492 at 589.2nm
Cauchy Equation n(nm) = 1.4779 + 5049.6 / nm ** 2 – 6.9486e7 / nm ** 4
Sun half angle 0.26657 degree
‘Slice’ is the slice number. 1 is the inner most slice.
‘Radius’ is the radius of the slice.
‘Power’ is the maximum energy that is available at that slice.
‘Tot W’ is the cumulative energy in Watts.
‘Tot %’ is the cumulative energy in percentage.
'QEff %' is the quantum efficiency.
‘Ix’ is the Light intensity for that slice. 1 means 1 sun concentration level.
‘Ax’ is the average concentration level for all cells. Area of Input/Area of all cells.
‘Area’ is the area of the slice.
‘UV’, ‘Blue’, ‘Green’, ‘Red’, ‘NIR’ (Near Infrared) and ‘IR’ (Infrared) is the percentage energy contribution of these wavelengths.

fresnelx w1000 g2500 l1000 r12 c11:75 c36:75 e97.5
 887.65W/m2 refractive index at 589.2nm(1.492) m(20), eff(97.500%) SunHalfAngle(0.26657o)
Total input energy 888 Watts
Acrylic Fresnel Lens Width 1000mm x 0.150mm, Area 1.00m2, Focal Length 1000mm (f/1.000), 2500 grooves
Slice  Radius   Power    Tot   Tot  QEff       Ix      Ax     Area    UV  Blue Green   Red   NIR    IR
                                                                      390   492   622   760  1110  4000
           mm       W      W     %     %                       cm2     %     %     %     %     %     %
   0           887.65    888 100.0  50.8      1.0       1 10000.00   5.6  13.0  19.6  18.2  27.5  16.0

Cell 1 Concentration Level 4.267x, distance from lens 515.921mm, 0.5159f, nominal radius 273.113mm
   1    9.029   24.04     24   2.7  50.8    105.8     106     2.56   5.9  13.4  19.7  18.1  27.2  15.6
   2   15.611   24.04     48   5.4  50.7     53.2      71     5.10   5.9  13.4  19.7  18.2  27.0  15.7
   3   22.193   24.04     72   8.1  50.8     34.6      53     7.82   5.9  13.4  19.7  18.2  27.2  15.7
   4   28.784   24.04     96  10.8  50.8     25.7      42    10.55   5.9  13.4  19.7  18.2  27.1  15.7
   5   35.376   24.04    120  13.5  50.8     20.4      34    13.29   5.9  13.4  19.7  18.1  27.2  15.7
   6   41.973   24.04    144  16.3  50.8     16.9      29    16.03   6.0  13.4  19.7  18.1  27.1  15.7
   7   48.570   24.04    168  19.0  50.8     14.4      26    18.77   6.0  13.4  19.7  18.1  27.1  15.7
   8   55.172   24.04    192  21.7  50.8     12.6      23    21.52   6.0  13.4  19.7  18.1  27.1  15.7
   9   61.777   24.04    216  24.4  50.8     11.2      20    24.27   6.0  13.4  19.7  18.1  27.1  15.7
  10   68.386   24.04    240  27.1  50.8     10.0      18    27.03   6.0  13.4  19.7  18.1  27.1  15.7
  11   75.000   24.04    264  29.8  50.8      9.1      17    29.79   6.0  13.4  19.7  18.1  27.1  15.6
  
Cell 2 Concentration Level 42.618x, distance from lens 1153.181mm, 1.1532f, nominal radius 86.423mm
  12   16.771   24.04    288  32.5  45.3     30.7      18     8.84   0.0   0.0   0.1  10.9  46.0  43.0
  13   19.151   24.04    313  35.2  53.3    100.8      19     2.69   0.0   0.0  12.6  23.4  39.0  24.9
  14   21.232   24.04    337  37.9  52.4    102.6      20     2.64   0.0   2.8  19.8  20.6  34.6  22.3
  15   23.179   24.04    361  40.6  51.8     99.7      21     2.72   0.0   7.8  18.7  19.4  32.8  21.3
  16   25.048   24.04    385  43.3  51.3     95.6      22     2.83   0.3  10.0  18.0  18.8  31.9  20.9
  17   26.861   24.04    409  46.0  50.8     91.6      23     2.96   1.8  10.1  17.5  18.4  31.4  20.8
  18   28.629   24.04    433  48.8  50.5     87.8      24     3.08   2.8   9.8  17.2  18.1  31.2  20.9
  19   30.364   24.04    457  51.5  50.3     84.3      25     3.21   3.3   9.6  16.9  17.9  31.1  21.2
  20   32.067   24.04    481  54.2  50.1     81.1      26     3.34   3.4   9.5  16.6  17.7  31.2  21.6
  21   33.740   24.04    505  56.9  49.9     78.3      27     3.46   3.4   9.3  16.4  17.6  31.3  22.1
  22   35.379   24.04    529  59.6  49.6     76.1      28     3.56   3.3   9.1  16.1  17.4  31.4  22.8
  23   36.977   24.04    553  62.3  49.2     74.5      28     3.63   3.2   8.8  15.8  17.2  31.4  23.5
  24   38.531   24.04    577  65.0  48.7     73.5      29     3.69   3.1   8.6  15.4  16.9  31.4  24.7
  25   40.028   24.04    601  67.7  47.9     73.3      30     3.70   3.0   8.3  14.9  16.5  31.2  26.2
  26   41.472   24.04    625  70.4  47.3     73.3      31     3.70   2.9   8.0  14.4  16.1  31.2  27.5
  27   42.888   24.04    649  73.1  47.6     72.2      31     3.75   2.8   7.8  14.2  16.0  31.9  27.3
  28   44.427   24.04    673  75.8  53.4     64.1      32     4.22   3.0   8.4  15.5  17.6  36.5  18.9
  29   46.095   24.04    697  78.5  60.6     57.1      32     4.74   3.3   9.1  16.9  19.4  42.4   8.9
  30   47.955   24.04    721  81.3  66.0     49.3      33     5.50   3.6  10.2  18.9  22.1  45.0   0.1
  31   50.119   24.04    745  84.0  61.4     40.6      33     6.67   4.2  11.8  22.1  26.5  35.4   0.0
  32   52.628   24.04    769  86.7  57.8     33.4      33     8.10   4.8  13.7  25.9  31.9  23.7   0.0
  33   55.719   24.04    793  89.4  53.7     25.7      33    10.52   5.9  16.8  32.3  40.0   5.1   0.0
  34   59.699   24.04    817  92.1  49.9     18.8      32    14.43   7.5  21.4  42.3  28.8   0.0   0.0
  35   65.348   24.04    841  94.8  45.9     12.2      30    22.19  10.5  30.2  55.1   4.2   0.0   0.0
  36   75.000   24.04    865  97.5  41.4      6.4      28    42.55  17.3  50.6  32.1   0.0   0.0   0.0
 
  

Another example using a 4 x 4 array of 1500mm x 1500mm Fresnel lenses of four different types to construct a 36m2 Fresnel lens system with a focal length of 5012mm. The solar cell 1 consist of 48 circular slices of silicon. The 48 slices are connected in series from the centre to the edge to produce 28.8 volts. Increased voltage (or lower current) may be generated by increasing the number of slices. The width of each slice is made proportional to the light energy expected at its distance from the centre, so that the current produced by each strip is the same. Slice 35 and 36 are not used because the light intensity is too low and too much material will be required to collect it.

All the solar cells are placed on an aluminium oxide ceramic base that is bonded to a copper heat sink. The second and third cell will be constructed similarly. Such a cell can be constructed on a single 150/200 mm wafer with current microelectronic batch fabrication processes, such techniques are described in US patent 3,994,012 to Raymond Warner, Jr. 

At the effective concentration level of 415, the optical efficiency is 93.5%.

The results of a simulation of the light intensity and distribution for 36 slices instead of 144.

fresnelx w6000 g6000 l5012 r13 R25 c12:75 c24:100 c34:100 e99 i1
 887.65W/m2 refractive index at 589.2nm(1.492) m(20), eff(99.000%) SunHalfAngle(0.26657o)
Total input energy 31955 Watts
Acrylic Fresnel Lens Width 6000mm x 0.405mm, Area 36.00m2, Focal Length 5012mm (f/0.835), 6000 grooves
Slice  Radius   Power    Tot   Tot  QEff        Ix      Ax     Area    UV  Blue Green   Red   NIR    IR
                                                                       390   492   622   760  1110  4000
           mm       W      W     %     %                        cm2     %     %     %     %     %     %
   0 3385.138 16247.27  16247 100.0  50.8   6000.0   6000.0 360000.00   5.6  13.0  19.6  18.2  27.5  16.0 1.12eV 100% 0.70eV  50%

Cell 1 Concentration Level 350.133x, distance from lens 4744.148mm, 0.9466f, nominal radius 180.909mm
   1   24.962  446.81    447   2.8  40.7    505.7    505.7    19.58  52.6  10.9  11.0   8.4  11.2   5.9 3.09eV 115% 1.13eV  58%
   2   28.994  446.82    894   5.5  46.5   1448.5    749.7     6.84  24.7  17.2  17.4  13.4  17.9   9.5 1.38eV 103% 0.93eV  56%
   3   33.148  446.81   1340   8.3  47.1   1220.9    860.4     8.11  22.1  17.7  18.0  13.9  18.5   9.8 1.38eV 103% 0.93eV  55%
   4   37.401  446.82   1787  11.0  47.5   1050.2    901.1     9.43  19.9  18.3  18.4  14.3  19.0  10.1 1.38eV 102% 0.70eV  54%
   5   41.722  446.85   2234  13.8  47.8    921.9    905.2    10.74  18.5  18.9  18.6  14.5  19.3  10.3 1.38eV 102% 0.70eV  54%
   6   46.143  446.82   2681  16.5  48.2    811.2    888.1    12.20  16.0  19.9  19.0  14.8  19.8  10.5 1.38eV 102% 0.70eV  54%
   7   50.662  446.83   3128  19.3  48.6    720.6    859.5    13.74  13.1  21.4  19.4  15.1  20.2  10.8 1.37eV 101% 0.70eV  54%
   8   55.306  446.81   3575  22.0  49.0    640.2    824.2    15.46   8.9  23.7  20.0  15.5  20.8  11.1 1.34eV 101% 0.71eV  54%
   9   60.030  446.81   4021  24.8  49.3    578.5    787.1    17.11   3.5  28.3  20.2  15.7  21.1  11.2 1.34eV 101% 0.71eV  54%
  10   64.872  446.82   4468  27.5  49.6    521.0    748.8    19.00   0.6  29.6  20.7  16.1  21.6  11.5 1.34eV 101% 0.71eV  53%
  11   69.873  446.81   4915  30.3  50.1    467.7    710.0    21.17   0.6  27.3  21.4  16.6  22.3  11.9 1.34eV 100% 0.71eV  53%
  12   75.000  446.81   5362  33.0  50.5    424.3    672.3    23.34   0.5  25.8  21.8  16.9  22.7  12.1 1.14eV 100% 0.70eV  50%

Cell 3 Concentration Level 152.594x, distance from lens 5417.735mm, 1.0810f, nominal radius 274.036mm
  13   29.125  446.82   5809  35.8  36.1    371.5    632.9    26.65   0.0   0.0   0.0   0.7  42.0  57.3 0.73eV 184% 0.70eV  17%
  14   36.981  446.81   6255  38.5  44.2    606.8    630.9    16.32   0.0   0.0   0.0  11.9  44.2  43.8 0.73eV 137% 0.70eV  31%
  15   43.569  446.81   6702  41.3  36.7    593.9    628.3    16.67   0.0   0.0   0.3  15.2  32.7  51.8 0.73eV 166% 0.70eV  35%
  16   49.155  446.82   7149  44.0  32.7    608.4    627.0    16.27   0.0   0.0   2.5  12.7  28.3  56.6 0.73eV 206% 0.70eV  35%
  17   53.873  446.80   7596  46.8  41.4    648.3    628.3    15.27   0.0   0.0   4.9  13.8  35.9  45.4 0.78eV 161% 0.70eV  26%
  18   58.093  446.81   8043  49.5  42.7    666.9    630.3    14.84   0.0   0.0   2.3  12.9  39.4  45.4 0.93eV 182% 0.71eV  15%
  19   61.955  446.83   8490  52.3  60.9    679.8    632.7    14.56   0.0   0.0   0.0  11.2  63.1  25.7 1.01eV 133% 0.70eV   4%
  20   64.981  446.83   8936  55.0  83.9    820.4    640.0    12.07   0.0   0.0   0.0   4.7  93.0   2.4 1.11eV 104%
  21   68.276  446.80   9383  57.8  87.7    717.5    643.4    13.80   0.0   0.0   0.0   0.2  99.8   0.0 1.15eV 103%
  22   73.137  446.80   9830  60.5  84.9    458.5    631.8    21.59   0.0   0.0   0.0   0.0 100.0   0.0 1.21eV 108%
  23   80.276  446.81  10277  63.3  80.9    287.7    600.6    34.41   0.0   0.0   0.0   0.0 100.0   0.0 1.29eV 115%
  24   99.971  446.80  10724  66.0  75.6     88.8    484.2   111.52   0.0   0.0   0.0   0.7  99.3   0.0 1.40eV 124%

Cell 2 Concentration Level 313.033x, distance from lens 5295.280mm, 1.0565f, nominal radius 191.329mm, Center hole radius 30.582mm
  25   33.686  446.82  11170  68.8  62.9   1579.9    467.0     6.27   0.0   0.0   9.8  27.9  54.3   8.0 1.46eV 130% 0.70eV  11%
  26   37.121  446.82  11617  71.5  61.7   1295.7    478.8     7.64   0.0   0.0  12.7  34.8  45.6   7.0 1.51eV 134% 0.70eV  10%
  27   41.108  446.83  12064  74.3  60.4   1010.5    488.3     9.80   0.0   0.0  16.7  49.1  28.5   5.7 1.56eV 139% 0.70eV   9%
  28   45.597  446.80  12511  77.0  58.9    809.6    495.3    12.23   0.0   0.0  20.8  73.5   0.7   5.0 1.62eV 144% 0.70eV   8%
  29   50.820  446.82  12958  79.8  57.2    625.8    498.9    15.82   0.0   0.0  26.3  69.3   0.0   4.4 1.68eV 150% 0.70eV   8%
  30   56.860  446.82  13404  82.5  57.0    484.5    498.4    20.43   0.0   0.6  33.1  64.8   0.0   1.4 1.74eV 155% 0.70eV   3%
  31   63.983  446.82  13851  85.3  55.5    366.1    492.7    27.04   0.0   3.3  39.7  56.5   0.0   0.6 1.81eV 161% 0.70eV   2%
  32   72.861  446.81  14298  88.0  53.6    259.4    479.2    38.17   0.0   7.0  51.2  41.7   0.0   0.1 1.88eV 167% 0.70eV   2%
  33   84.314  446.82  14745  90.8  51.4    175.1    455.3    56.55   0.0  12.1  77.3  10.6   0.0   0.0 1.96eV 174% 0.70eV   2%
  34  100.002  446.81  15192  93.5  49.0    109.0    416.3    90.84   0.0  19.7  80.3   0.0   0.0   0.0 2.04eV 181% 0.70eV   2%
  35  124.215  446.81  15639  96.3  46.4     58.0    353.9   170.56   0.0  32.7  67.3   0.0   0.0   0.0 2.14eV 190% 0.70eV   2%
  36  176.046  446.80  16085  99.0  43.1     20.2    242.8   488.92   0.0  67.5  32.5   0.0   0.0   0.0 2.30eV 204% 2.28eV   1%
  37  676.309  161.59  16247 100.0  39.3      0.3     24.2 13395.79   5.8  94.2   0.0   0.0   0.0   0.0 2.57eV 228% 1.09eV   4%

  

   

4 x 4 array of fresnel lens constructed from 4 different fresnel lens.
HMJ (Horizontal Multijunction) cell with 12 slices. No front surface grid, front or back contact, bus bar or bypass diode is required. Expected efficiency of 20% at 100x to 2500x concentration. High voltage/low current. Wafer size solar cell (100mm to 450mm diameter) 

Initial application will be in solar farms in regions with high direct insolation to efficiently supply loads up to 7000km away with underground high voltage DC (HVDC) transmission lines. With this method, the major cost item is shifted from the solar cells to the fresnel lens. The cost of the fresnel lens can be reduce by making them as thin as possible. 

The land below this type of solar concentrator can still be used, because the diffused background light cannot be focused.  Example of such land are parks, car parks, over roads (when we stop using pollution causing cars), cycle ways, schools, shops, residential  and degraded land. This method will very efficiently in extracting the direct UV and Infra-red radiation. Concentrated solar power can be very dangerous, take care. Wind load will become a problem as the size of the fresnel lens gets bigger and higher.

27th August 2008
Philip Wong BSc BE(UNSW)
Phone/fax: 61 2 9805 0356
Mobile: 04 0404 0968 (Australia)
Sydney, Australia
ioserver@ioserver.com 

Fresnelx Calculates intensity and colour distribution of solar radiation falling on up to three surfaces. Run "fresnelx x" to see available commands.
Concentrated Solar Thermal Power with Point Focus Fresnel lens and reflector
Bifacial concentration on VMJ (Vertical Multijunction) solar cells
Spectrum splitting concentration on to three solar cells

Lens

Fresnel Lens Manufacturer. bhlens.com
Fresnel Lens Manufacturer. fresneloptic.com
Fresnel Lens Manufacturer. ntkj.co.jp 2.9m x 5m lens
Fresnel Lens Distributor. 3dlens.com

Cells

Photovolt VMJ cell (100x to 2500x, 20% efficiency silicon solar cells) $5/cm2
AZUR concentrator cells $21/cm2
EMCORE 3J Concentrator cells $8/cm2
QuantaSol
Spectrolab Terrestrial Concentrator cells $10/cm2
Sunpower. Their 26% efficiency 250x silicon concentrator cells are no longer available $6/cm2
1 Sun Silicon Solar Cells WB-28 100mm round $0.06/cm2
Indium Gallium Nitride Solar Cells
Multiple band gaps Semiconductors 

Photovoltaic Concentrators

Amonix
Arima Eco Energy
Concentrix Solar, GmbH
Energy Innovations
Entech
GreenVolts
Isofoton
Opel International Inc
RoseStreet Labs Energy, Inc. Full spectrum concentrator.
Solar Systems (Australia)
sol3g
Soliant Energy
SolFocus
Whitfield Solar

Concentrated Solar Power (Thermal)

Ausra (CLFR - Compact Linear Fresnel Reflector)

Tracking

Inspira
Precise Tracking. Precision Solar Technologies
Solar Tracker tracker.cat
Celestron 80mm Refracting Telescope, available for AUD$449 from my local electronic store that can track stars that are light years away with open loop tracking.

References

Energy and aesthetics of building integrated RES (renewable energy sources)
Nonimaging Fresnel lens for solar concentration
Novel Materials and Devices for Sunlight Concentrating Systems IBM Research
Photovoltaic semi-conductor devices. Raymond M. Warner, Jr.
The fresnel lens concept for solar control of buildings
The Solar Race. A multidisciplinary team works fervently to make solar building technology more powerful than ever.
A simple analytical treatment of edge-illuminated VMJ silicon solar cells. N.H. Rafat, Solar Energy, Volume 80, Issue 12, December 2006, Pages 1588-1599

Optical Design software. optenso.de
Persistence of Vision Raytracer
Reference Solar Spectral Irradiance: ASTM G-173

Swiftech MCP655 12VDC Water Pump, 50,000 hour MTBF, 20L/Min, 60oC
EBP Electric Booster Pump, 12VDC, 15L/Min, +120oC

Online Emachineshop. 

Last updated: 21 March 2013