Inverter power, P i (W) in watts is calculated by dividing the rated inverter power, RP (W) in watts and efficiency, E in percentage by 100. This is the simplest case, and if the inverter performs only this step, it is a square-wave inverter. This type of output is not very efficient and can be even detrimental to some loads. Everything in a solar system from the solar panel voltage output to the DC battery works based on DC. This piece focuses on practical math, climate effects, and sizing ranges you can use today. Calculating your solar panel requirements involves determining the wattage needed and estimating the solar panel output. But most appliances run on alternating current (AC).