Solar photovoltaic energy
For correct sizing of PV systems, the user needs to estimate the demand on the system, as well as
acquiring information about the solar insolation in the area (approximations can be made if no data is
readily available). It is normally assumed that for each Wp of rated power the module should provide
0.85watt hours of energy for each kWhm-2 per day of insolation (Hulscher 1994). Therefore if we
consider a module rated at 200 Wp and the insolation for our site is 5 kWhm-2 per day (typical value
for tropical regions), then our system will produce 850Wh per day (that is 200 x 0.85 x 5 = 850).
Figure 2: Components of a typical off-grid PV system. Illustration: Neil Noble / Practical Action.
Some benefits of photovoltaics
No fuel requirements - In remote areas diesel or kerosene fuel supplies are erratic and often
very expensive. The recurrent costs of operating and maintaining PV systems are small.
Modular design - A solar array comprises individual PV modules, which can be connected to
meet a particular demand.
Reliability of PV modules - This has been shown to be significantly higher than that of diesel
Easy to maintain - Operation and routine maintenance requirements are simple.
Long life - With no moving parts and all delicate surfaces protected, modules can be
expected to provide power for 15 years or more.
National economic benefits - Reliance on imported fuels such as coal and oil is reduced.
Environmentally benign - There is no pollution through the use of a PV system - nor is there
any heat or noise generated which could cause local discomfort. PV systems bring great
improvements in the domestic environment when they replace other forms of lighting -
kerosene lamps, for example.