How much power will my solar panels make, and is a battery worth it?
Got a quote for solar panels or a home battery and not sure if the math works? Pick your country and city (the calculator knows yields for 100+ locations), enter the system size in kWp (how many panels you'll fit on the roof), your annual home electricity use, and your price per kWh. In a few seconds you see concrete numbers: annual production, how much you'll use on the spot (self-consumption), how much goes to the grid, and annual savings in your currency.
Sun-yield data comes from PVGIS (European Commission) and Global Solar Atlas (World Bank / Solargis), the same sources professional installers use to design real systems. Self-consumption ratios come from research by Fraunhofer ISE and NREL: not made-up numbers, but the figures actual energy engineers work with.
Simple mode: type 4 numbers, get the answer. Advanced mode adds a monthly chart (you'll see why solar "doesn't work" in December), battery backup runtime during a power cut, payback period, and a separate feed-in tariff for energy you sell back to the grid.
How to use it
- Pick a country from the list, the calculator shows the typical annual yield (how many kWh per year 1 kWp of panels makes there). Poland is around 1050 kWh/kWp, Spain 1600, Norway 850.
- If your country has a city list (e.g. Germany, US, Australia), pick the closest one. Phoenix (1900) vs Seattle (1100) is a 70% difference, so the city matters a lot.
- Enter the system size in kWp ("kilowatt-peak", panel power under perfect conditions: noon, clear sky). Typical values: 3-5 kWp for an apartment / small home, 5-10 kWp for a single-family house, 10-20 kWp if you also run a heat pump and an electric car.
- Enter annual electricity use in kWh: find it on your bill, "annual usage" line. Average: 2,000 kWh for an apartment, 4,000 for a 4-person family, 6,000-10,000 for a heat-pumped house.
- Pick battery capacity: 0 (panels only, no battery), 5 kWh (small, covers an evening), 10 kWh (typical home battery), 15 kWh (large, with outage backup in mind). The calculator estimates self-consumption from research, bigger battery = more energy used on site.
- Enter your price per kWh: what you pay your utility. The calculator shows annual savings in your currency.
- Advanced mode: toggle at the top. Adds: a monthly chart (production vs use), battery runtime during an outage (e.g. fridge + lights = 0.3 kW: how many hours?), payback period (enter system cost), and a separate feed-in tariff for energy sold to the grid (often 30-70% of the buy price, varies by country and program).
- Every change recalculates instantly. Experiment: bigger battery vs more panels, sunnier city vs default, quickly see where the real savings are.
When this is useful
Six typical situations where the calculator gives you concrete numbers instead of a salesperson's promises:
- Before signing with an installer. The salesperson says: *"6 kWp will produce 6,500 kWh and cover 80% of your home"*. Run your numbers and see: 5,500-6,500 kWh is realistic (depends on city and roof tilt), but 80% coverage with no battery is misleading; realistically you'll get 30-40% self-consumption. Now you know whether you need a battery or whether the installer is rounding for marketing.
- Checking if a battery makes sense. A 10 kWh battery costs $1,500-2,500 in hardware (Pylontech, Growatt, BYD, EG4) but $6,000-12,000 installed turn-key. Without battery, self-consumption is ~30%; with battery it climbs to ~65%, an extra 1,000-1,500 kWh/year consumed at home instead of exported cheaply (annual extra benefit ~$300-500). Payback at hardware-only cost ($2k): 4-7 years. At turn-key price ($10k+): 20-30 years, often longer than the warranty. Hardware-only + certified electrician usually wins on numbers.
- Year-one audit. Your system is one year old, the meter says 5,800 kWh produced. Is that good? Run the numbers → forecast was 6,200. You're 6% short, within tolerance (cloudy year, dust). A 20%+ drop is a red flag: shaded module, inverter fault, call service.
- Sizing for a heat pump + electric car. Add the heat pump (+3,000 kWh/year) and EV (+3,000 kWh if charged at home). Total: 10,000 kWh. The calculator shows that 5 kWp won't cover it: you need 8-10 kWp for a yearly balance. Without a battery you'll still pull a lot from the grid in winter, but annual figures balance out.
- Comparing offers from different installers. Company A: 8 kWp + 10 kWh battery for $25k. Company B: 10 kWp without a battery for $18k. The calculator shows annual savings for both, and you may discover B saves the same (more production offsets the missing battery) at lower cost. Decision on numbers, not on a sales pitch.
- Checking how long you'll last in a blackout. Storm, grid down for 6 hours. Fridge + router + lights (0.25 kW) gives ~33 hours of runtime on a 10 kWh battery. Adding electric heating (+2 kW) cuts it to only 4 hours. Now you know what not to plug in during an outage.
For the matching pieces: compare your savings against live tariffs in the live electricity prices feed, size DIY battery banks in the battery pack calculator, and for office / server UPS sizing use the UPS runtime calculator.