Solar cells, usually in the form of thin films or wafers, are 
  semiconductor  devices  that  convert  3-25 per cent  of  the 
  incident  solar energy into DC electricity, with efficiencies 
  depending  on  illumination-spectrum  intensity,  solar- cell 
  design, materials and temperature.  A solar cell behaves much 
  like a low-voltage (about 0.5 volts) battery, whose charge is 
  continuously  replenished at a rate  proportional to incident 
  illumination.  Connection of such  cells into series-parallel 
  configurations  allows the  design of solar  panels with high 
  currents  and  voltages  as  high  as several kilovolts.  The 
  extraordinary simplicity of a solar-voltaic system would make 
  it a highly desirable energy system, both in developing areas 
  and in industrialized nations.The attractions of photovoltaic 
  arrays  include  the  absence  of  moving  parts,  very  slow 
  degradation of properly sealed cells, possibility for modular 
  systems at sizes from a few  watts to megawatts, and  extreme 
  simplicity of use.

  Until now, however, high costs of development and fabrication 
  of  solar  arrays  have  discouraged  widespread  application. 
  There  is  evidence  that ,  with  appropriate  technological 
  development and mass production techniques, the cost of solar 
  arrays  can  be lowered to the point  where a complete system- 
  solar  conversion ,  power  conditioning   and   transmission/
  distribution - can  compete  on a lifecycle  cost  basis with 
  other  large-scale energy-system alternatives, and perhaps be 
  even useful in small-scale applications in remote rural areas.