Typically, a residential solar system ranges from 3,000 to 10,000 watts (3 to 10 kW) to cover most or all electricity needs, with precise sizing tailored to individual usage and location. Wattage is measured in watts (W), and 97% of solar panels fall in the 400+ W power range in 2026. We'll use 430-watt panels in these calculations because it's the. While it varies from home to home, US households typically need between 10 and 20 solar panels to fully offset how much electricity they use throughout the year. The goal of most solar projects is to offset your electric bill 100%, so your solar system is sized to fit your average electricity use. Wattage refers to the amount of electrical power a solar panel can produce under standard test conditions (STC), which simulate a bright sunny day with optimal solar irradiance (1,000 W/m²), a cell temperature of 25°C, and clean panels. You should also consider the age of your roof and how long until it will need replacement.