You will need to work with your installer to evaluate your electricity usage so that your solar electric system can be appropriately sized. Monthly utility bills include a summary of how much power you have used each month for the past year. The installer will need a recent bill to determine an appropriate system size based on your power needs, site characteristics, and budget.
Utilities charge residential customers for electricity consumption, measured in kilowatt-hours (kWh), which is shown on the electric bill. As an example, if a 40-watt light bulb is turned on for 100 hours, a total of 4,000 watt-hours or 4 kWh of electricity would be consumed. The average New England household uses 7,536 kWh measured in kilowatts (kW), the equivalent of 1,000 watts.
The actual electricity generated by a solar electric system is a function of its size, efficiency, sun exposure, and a variety of other factors discussed on this page. The average residential solar electric system size in Massachusetts is around 7 kW. In Massachusetts, a 1kW solar electric system will produce approximately 1,100 kWh of electricity per year, which means that a 7-kW system will produce roughly 7,700 kWh per year. This example system could therefore produce enough electricity to cover 100% of the electricity consumption for an average New England household.