Solar Photovoltaic Solutions

Usually, the lowest month kWh/m²/day value is the starting point. Sometimes, the average number of sun hours per day is taken to be equal to kWh/m²/day as shown in the graphs below. It is typically between about 5 and 6 kWh/m²/day). That is equivalent to 5 – 6 hours of 1000 W/m² sunlight every day for many geographical locations. However, the daily sun hours must be adjusted for other factors to obtain the actual energy generation capacity.

Some of these factors are presented as follows. The correction factors include:

1. 15% for temperature above 25 ˚C (for each degree over 25 ˚C the maximum power of the solar module is reduced by the value of the temperature coefficient). That value is in the range of –0.44% to –0.50% for crystalline silicon with best value of –0.38% for mono-crystalline silicon and –0.34% for amorphouse silicon while it is –0.25% for Cadmium Telluride thin films.
2. 5% for losses due to sunlight not striking the solar module straight on (caused by glass having increasing reflectance at lower angles of incidence).
3. 10% for losses due to not receiving energy at the maximum power point, MPP (not present if there is a MPPT controller).
4. 5% allowance for dirt, dusts or droplets from birds.
5. 10% allowance for the solar module being below specification and for ageing.

The total correction factor = 0.85 X 0.95 X 0.90 X 0.95 X 0.90 = 0.62

The actual energy generation capacity =  0.62 X W_p rating. That is, for every W_p capacity in the solar module, we can expect to get an average of 0.62 X W_p Wh/day during the lowest solar month (or design month).