How much energy could that system deliver?
Energy yield (E) in kilowatt-hour can be estimated using the following equation:
E = CR x GHIa x D
In this equation:
- CR is the potential installed capacity of the solar PV rooftop system.
- GHIa is the global horizontal irradiation over a 1-year period in kWh/m2. Values can be obtained from a national or regional solar map or any resource databases.
- D is the derating factor for converting direct current (DC) to alternating current (AC). The derating factor generally ranges between 0.6 and 0. A typical derating factor of 0.77 can be used here.
To further illustrate how to calculate energy yield, we provide an example using the Firstgreen rooftop solar power project’s estimations.
Illustration:
Estimated Capacity of and Energy Delivered by the Firstgreen Rooftop PV Project
The Firstgreen team examined the roof plans for a building and found the installable area was 500 square meters. Using specifications of readily available modules (rated at 330 peak Watts [Wp] and sized 1 meter by 2 meter), the initial estimated photovoltaic (PV) system capacity was:
= 66 kilowatts-peak (kWp)
According to a regional solar map, the global horizontal irradiance (GHI) for New Delhi is about 5.2 kilowatt-hours per square meter per day (kWh/m2/day), equal to 1,898 kWh/m2. Using a typical value of 0.77 for the derating factor, Firstgreen estimated the annual yield of the rooftop PV system to be:
E = 66 x 1898 x 0.77 = 96,456 kWh or 96.5 MWh