Once you have prioritized your municipal sites for solar, you can roughly estimate the solar capacity (in kilowatts [kW]) and energy (in kilowatt-hours [kWh]) production potential by using free software such as NREL’s System Advisor Model (SAM) or PVWatts Calculator. SAM is a detailed program that determines the capacity and energy of a solar system by taking into account solar tilt, ground cover ratio, and type of PV module. PVWatts, on the other hand, is a simpler online tool that estimates the capacity and energy available from a user drawn area at a specified location. A quick rule of thumb for commercial rooftop solar is that roughly 70% of a roof can be utilized for solar panels, of which a system size is 10 W/ft2 (for 20 degree tilted systems) to 16 W/ft2 (for horizontal systems). For ground-mounted systems, five acres of land is typically needed to reach a capacity of 1 MW (4-5 W/ft2).
Next, refine each site’s system capacity based on these two important local regulations: