From Open Energy Information

PVWatts Calculator is an interactive web application developed by the National Renewable Energy Laboratory (NREL) that allows homeowners, installers and manufacturers to easily develop estimates of the performance of potential PV installations at specific locations. The calculator estimates the electricity production of a grid-connected roof- or ground-mounted photovoltaic system based on a few simple inputs. To use the calculator, you type the address or geographic coordinates of the system's location, specify the system size and array orientation, and provide some information about the system's cost and electricity rates. PVWatts calculates estimated values for the system's annual and monthly electricity production, and for the monetary value of the electricity.


Important Note. The PVWatts Calculator is suitable for very preliminary studies of a potential location for a photovoltaic system that uses crystalline silicon photovoltaic modules. The production estimates that PVWatts calculates do not account for many factors that are important in the design of a photovoltaic system. If you are using PVWatts to help design a system, you should work with a qualified professional to make the final system design based on an assessment of the system location and using more detailed analysis and design tools.

PVWatts calculates the electricity production of a photovoltaic system with crystalline modules using an hour-by-hour simulation over a period of one year. It also estimates the cost and value of the electricity produced by the system. You provide an address, zip code, or geographic coordinates of the system's location, and PVWatts Calculator automatically identifies solar resource data for you to choose from. To represent the system's physical characteristics, PVWatts requires values for five inputs: The system's DC size, array type, a DC-to-AC derate factor, tilt angle, and azimuth angle. PVWatts makes cost of electricity estimates based on whether the system is on a residential or commercial property, its installation cost, and the retail cost of electricity.


The National Solar Radiation Data Base is used by the tool for several of the calculations and can be used for finding local inputs. [2]


  1.  "PVWatts"
  2. 2.0 2.1  "National Solar Radiation Data Base"