How Does OpenSolar Calculate System Output?

Note: You can manually scale the output of your systems. Find out how to do so here. 

PV Watts

Currently, system generation output is calculated using PVWatts Version 6, with hourly resolution.

A brief summary of some of the inputs we use are shown here but for more information on PVWatts methodology, see here.

Weather Data

• PVWatts utilises hourly typical meteorological year (TMY) data (8760 data points) of:
  • Direct normal irradiance (DNI) and diffuse horizontal irradiance (DHI) [W/m2]
  • Ambient dry bulb temperature [˙C]
  • Wind speed at 10m above the ground [m/s]
  • Albedo = 0.2 for all hours of the year for TMY2 data files and uses hourly value provided in TMY3 files
• No adjustments are made for leap years or daylight saving times.

Sun Position

• PVWatts calculates the sun position every hour, finding the azimuth and solar zenith angles which are then later used to determine the insolation falling on the PV array.

Plane-of-ARRAY (POA) Irradiance

• The POA irradiance is calculated hourly throughout the year, taking in the effects of the sun’s azimuth and altitude angle, as well as the module tilt and azimuth to accurately calculate the insolation on the PV module throughout each day.

System Losses and Derating

A summary of the default PVWatts derating can be seen in the following table:

Note:

• If a microinverter is used then the mismatch loss given above will be reduced to 0%, giving a total of 12.32%. 
• If a DC optimiser is used, then the mismatch loss will go to 0% and you will be able to enter in the DC optimiser efficiency. You can find out how to add DC optimisers in Studio here at the bottom of the Inverters and Stringing section. 
• Losses due to inverter efficiency are based on the CEC/Euro efficiency ratings of each inverter model.
• Shading losses can also be configured manually within Studio (see how in this article)

Note: You can manually scale the output of your systems. Find out how to do so here.