A 400-watt panel can generate roughly 1. 5 kWh of energy per day, depending on local sunlight. household's 900 kWh/month consumption, you typically need 12–18 panels. Output depends on sun hours, roof direction, panel technology, shading . In California and Texas, where we have the most solar panels installed, we get 5. Solar panel effectiveness depends on external factors such as amount of sun every day, and internal factors such as the efficiency and quality of panels. For the latter, there are ways to improve solar panel efficiency which we urge our readers to look at. Whether you. Most residential panels in 2025 are rated 250–550 watts, with 400-watt models becoming the new standard. Increasing panel count or choosing higher wattage.