Free calculator

Rooftop solar calculator

Find the right size for your electricity use, with its cost, savings and payback. Fill in the main boxes. Everything else has sensible defaults.

Sun rising over solar panels
1. Location
Pick from the list, or press Search to look up any place in the world. Live search needs an internet connection. Place search © OpenStreetMap contributors. Sunlight: NASA POWER.
2. Your home
Find it on your bill. It is often called "units".
Planning average for the country. Replace it with your area value.
Heat, dust, shade and wiring. 20 is a common planning figure.
3. Electricity prices
Used for power you consume yourself.
Check your utility. Net metering rules differ by area.
Without a battery, usually 20 to 40 if you are out in the daytime.
4. System cost
Filled from country defaults. Replace with real quotes.
Permits, design and interconnection.
5. Battery (optional)
Set to 0 to hide the comparison.

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Simple estimate. Subsidies, tax credits, yearly output loss, price rises and upkeep are not included.

This is a planning estimate, not financial or engineering advice. Get a roof survey and a written quote from an installer before you decide.

Other sizes

SizeYearly kWhCoversYearly saving
How these numbers are calculated
  • Sunlight comes from NASA POWER when you pick a place. Otherwise it is one planning average for the whole country, so replace it with your area value if you have one.
  • The recommended size is matched to your yearly electricity use, after system losses.
  • Savings are the solar power you use at home at your price, plus exported power at the export price.
  • Payback is a simple estimate: system cost divided by yearly saving.
  • Not included: subsidies, tax credits, yearly output loss, price rises and upkeep.

Inputs used