Depending on how efficiently and well it works, it could be anywhere from 10 to 40 watts. A good inverter transforms more sunlight into electricity, requiring less extra power. Consequently, inverter sizes vary greatly. Additionally, you'll learn what appliances you can power and how you can select. This is the amount of energy in Wh (watt-hours) that the solar panels should be capable of producing daily. If left blank, the calculator will use the daily energy consumption calculated in the previous step. If. Let's say you have a 6kW solar array (twenty 300-watt panels). Your inverter needs to handle that 6kW of DC power, regardless of whether your home uses 2kW or 10kW at any given moment.