Calculate
What size solar system do you actually need? Enter your power bill (or annual kWh) and location to get the system in kilowatts, the panel count, and the roof area it takes.
Enter your usage to size a system.
Full cost & payback → Get installer quotes →Your system needs to generate about as many kilowatt-hours per year as you use (times your target offset). Divide that annual number by how much one kilowatt of panels produces where you live — roughly your peak sun hours × 365 × a derate factor of about 0.84 — and you get the system size in kW. Divide the watts by your panel wattage for the panel count.
Most roofs can hold more than a bill-offsetting system needs. If you're adding an EV or a heat pump later, size to 110–120% now — it's cheaper than a second install.