Before a solar system is designed, before the first solar panel is installed, and well before we flip the switch on a solar array, we provide any home or business owner considering solar power with documentation that estimates the proposed system’s monthly and annual electricity production, and the resulting monetary savings. Have you ever wondered how we calculate your estimated power output and financial benefits of installing solar? If so, read on.

An organization called the National Renewable Energy Laboratory (NREL) is our resource for this information. NREL is funded through the United States Department of Energy, and focuses on data collection and tools to help in the research and development of renewable energy and energy efficiency. We use an NREL tool, the PVWatts® Calculator, to estimate the energy production and cost of energy of grid-connected photovoltaic (PV) energy systems.

The PVWatts® Calculator allows homeowners, small building owners, installers – like us – and manufacturers to easily develop estimates of the performance of potential PV installations. It’s a web-based, interactive tool that requires just a few simple inputs to create an accurate forecast of solar production. PVWatts® uses “typical year” weather data to represent the long-term solar resource at the selected location. The calculator automatically identifies appropriate data for a system based on the address provided for its location.

To represent the system’s physical characteristics, PVWatts® requires values for inputs including system DC size, module type, array type, system losses (due to factors such as shading, dirty panels, wiring losses, inverter efficiency, etc.), and the array tilt and azimuth angle (“azimuth” is the compass angle of the array; due south is the best azimuth for maximum annual solar energy harvest in the northern hemisphere).

Analyzing system production and financial returns from a solar array can get more complicated (well, we think it’s more fun!) from there, but we won’t bore you with those details here. Using PVWatts®, our estimates of output and savings have been remarkably accurate – we do check back regularly and the PVWatts® Calculator has shown itself to be a reliable, trusted tool.

Have any questions for us? Give us a call or email us at and we’ll be happy to help!

Continue Reading
« | »