How much energy could that system deliver?

Published by firstgreen on

Energy yield (E) in kilowatt-hour can be estimated using the following equation:

E = Cx  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.


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