FIGURE 3. - SSPS DIMENSIONS Since 1965, the solar cell weight has decreased substantially. With the development of blanket-type construction for solar cell arrays, this weight is projected to drop to 4 kg/kW by 1975. The use of solar energy-concentrating mirrors can reduce the solar collector weight to about 1 kg/kW if 100-micron thick silicon solar cells are used, and to even less if gallium arsenide solar cells are used. c. Electrical Interconnections Because solar cell arrays with large areas will be required (e.g., one of the two solar arrays for the SSPS is about 5 km by 5 km), the satellite structures must be designed to combine mechanical and power distribution network functions to achieve high-voltage DC output. In the very large arrays, solar cells can be connected in series to produce any voltage desired. With existing solar cells, a series string can be assembled to build up the voltage to 50 kV or more. Development of the vertically illuminated, multijunction solar cell could product solar cells of high-voltage output. In such a solar cell, there may be a thousand junctions in series for each 1-cm wide cell. Thus, each cell may put out several hundred volts instead of the 0.5 volt from present solar cells. This type of cell will make it easier to build up a high voltage with a small number of cells, and thus allow most of the circuit to be in parallel and to be less susceptible to losses from open circuits. This arrangement also would preclude the loss of a total string of solar cells because of the loss of any one link.
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