Thousands of American homeowners decide to go solar every year. Residential and commercial solar systems are usually sized by customers, measured in watts or kilowatts (instead of number of panels).
A watt is a unit of power, measured by taking energy over time. When you receive your solar system quote, you are usually seeing all sizes in Direct Current (DC) watts. However when the contract is signed and the utility applications are being submitted, the same customer might see Alternating Current (AC) watts instead on the utility form. On the other hand solar inverters are sized in AC Watt terms. So needless to say, this can be very confusing!
The difference between DC and AC watts seems technical, but is important. DC watts and AC watts are different sizes, which can mean different sized solar systems. A rule of thumb — DC system size is related to the power rating of the solar panels, while AC system size is related to the power rating of the inverter. Different jurisdictions and utilities require standard measurements. This article is meant to help homeowners understand this important difference.