Solar System Size Calculator
Find the exact kW system size, panel count, and roof space you'll need — sized to your real usage and local sunlight.
How Many Solar Panels Do You Need to Power a House?
To determine what size solar system you need, you first need to look at your average energy consumption. An average residential home using 900 kWh per month usually requires between 15 and 25 solar panels (around a 6kW to 8kW system size). Quoting system cost before sizing is like asking "how much is a car" without saying how many seats you need. This calculator flips the order: usage and live satellite sunlight first, size second, cost later.
The math on how to size a solar system is straightforward: take your monthly kWh usage, convert it to a daily number, then divide by your area's peak sun hours — the average number of hours per day the sun delivers roughly 1,000 watts per square meter. A home using 30 kWh a day in a city with 5 peak sun hours needs roughly a 6kW system before accounting for real-world losses.
Choosing Your Offset Percentage & Panel Count
100% offset means the system is sized to fully cancel your average bill over a year. Once you have a kW target, the number of solar panels needed for a house falls out automatically from panel wattage. Higher-wattage panels mean fewer panels for the same output, which matters most on roofs with limited usable area.
Why Your System Might Produce Less in December Than in July
The kW number this calculator gives you is sized against an annual average of peak sun hours, not a single day. In practice, production swings by season — a system in a place with real winters can produce 40-50% less power in December than in June, purely from shorter days and a lower sun angle.
Frequently Asked Questions
How many solar panels do I need to power a house?
An average house needs between 15 and 25 solar panels to power 100% of its electricity needs. The exact number depends on your monthly kWh usage, panel wattage (e.g., 400W), and local peak sun hours.
What size solar system do I need?
To determine what size solar system you need, divide your daily electricity usage (kWh) by your area's peak sun hours and multiply by an 85% system efficiency factor. Enter your monthly bill into the calculator above to get your exact system size in kW.
How do I know how to size a solar system accurately?
Accurate solar system sizing requires matching your daily energy requirement against live peak sun hours at your exact geographic location, rather than using generic regional averages.
How much roof space does a typical solar system need?
A standard residential panel is roughly 17.5 square feet. A 6kW system with 400W panels needs about 15 panels, which works out to roughly 260 square feet of usable, unshaded roof space.
Is this calculator using real, live data?
Yes. Every calculation fetches current peak sun-hour data live from NASA's POWER satellite database for your exact coordinates, rather than pulling from a static lookup table.