The energy generated by solar panels is related to the sunlight the panel receives and the efficiency with which it generates electricity.
Solar insolation is the amount of light received at the earth's surface.
The standard unit is kWh/m2/day; ie the amount of energy radiated from the sun that hits an area of one square metre every day.
Solar panels can be compared by measuring their power output.
The "peak watt" (Wp) used to rate solar power is the power in watts produced by a solar module (group of solar cells) illuminated under the following standard conditions:
- 1000 watts per metre squared intensity of light
- 25 degrees centigrade ambient temperature
- a light spectrum that relates to sunlight passed through the atmosphere when the sun is at a 42 degree elevation from the horizon (air mass 1.5).
With day and night cycles, and the variation in insolation and cloud cover over the day, the average electrical power produced by a solar cell in a year will be approximately 15 - 20% of its peak watt rating.