The Solar Cell system converts the inexhaustible energy of sunlight into electric energy, thereby saving fossil fuel resources.
Currently, electricity can be generated by means of solar cells at 120 to 130 W per square meter (25 deg.C ; 1,000 W/m2).  On-going technological advances are expected to further improve the power generation efficiency

 

 

The amount of solar radiation varies with time in a day.  The figure below shows the changes in solar radiation and in electric power produced by a 20 kW Solar Cell system installed in the UNEP International Environmental Technology Centre Osaka, in a clear day in April.  It is found from this figure that this system generates electricity from 7:00 a.m. to around 7:00 p.m., and that the power generation values have a nearly normal distribution against the time axis

 

 

The following figure shows the changes in setup cost and in power generation cost calculated on the basis of the setup cost.  The current power generation cost is about 100 yen/kWh, nearly four times as high as electricity rates.
(Annual power generation: 1,000 kWh
Service life: 20 years
Interest rate: 4%/year
Maintenance cost: 10,000 yen/year)

source  

http://www.gec.jp/ESB_DATA/EN/Tech/html/esb-131.html