Methodology and sources

Every number on this site comes from a formula you can check. Here it is.

Generation

Yearly generation = panel kWp × site yield × orientation factor × (1 − clipping loss). Site yield is kWh per kWp per year for an optimally tilted, south-facing array, taken from the EU's PVGIS (SARAH3, 14% system loss) for Germany and the Netherlands, and derived from NREL PVWatts for US states. The orientation factor scales that optimum for how the panels are mounted; a vertical south-facing balcony railing is about 0.70–0.72 of optimal. Clipping starts when panel power exceeds inverter power by more than 20%.

Self-consumption

A plug-in kit only saves money on power you use while the sun shines, so the share you use yourself depends on how big the kit is compared with what your home uses. We estimate it as 1 ÷ (1 + 2.1 × f × r^1.2), where r is yearly generation divided by yearly consumption, and f is 0.7 when someone is mostly home in the day, 1 when partly and 1.5 when rarely. A two-person home using 2,400 kWh a year uses about 69% of a 900 W balcony kit and about 53% of an 1,800 W one. The curve is our own simplification, calibrated to a published reference case (HTW Berlin figures reported by Cleanthinking: a 2,100 kWh home uses about 70% of an 800 W kit). If you do not enter your own yearly use, we take a typical figure for your household size and country; those typical figures are our own estimates from national averages, not taken from an official table, so entering your own figure gives a better answer. A battery moves part of the exported energy into evening use (280 cycles a year at 83% round-trip efficiency), capped at 95%. The range on every result is ±7 points of self-consumption.

Kit prices and suggested size

The price next to the slider is a real one: the cheapest complete kit we found on sale in your country that delivers at least the power you chose, with or without a battery. Kits are sold in a few sizes, so the price climbs in steps. Often a bigger kit costs only a little more, and sometimes the same. We read the prices from the shops' own pages between 5 and 13 November 2026, some of them during sale weeks. They change often, and mounts and delivery are extra. The slider stops at the largest kit we found that is allowed where you live. Where no complete kit is on sale, we say so and show an estimate instead.

For the suggestion we compare those real sizes. Starting from the smallest kit that pays for itself within 5 years, we move up to the next size as long as its extra cost comes back within 5 years from the extra power you would use. A bigger kit always generates more, but more of it goes to the grid unpaid, so each step up earns less than the one before. If no kit pays back within 5 years, we show the size that pays back fastest and say so.

The product list under a result shows kits with at least the power you chose, cheapest first. If a brand we have an affiliate deal with sells a matching kit, its cheapest one is always in the list, in its place by price, and it is labelled as an affiliate link.

Savings and payback

Savings = self-used kWh × your retail price + exported kWh × feed-in. Where net metering still applies (Netherlands until 1 January 2027), exported energy is credited at the retail price until that date. Panels degrade 0.5% a year. The optimistic end assumes power prices rise 2% a year, the conservative end assumes flat prices. Payback is the first year cumulative savings exceed the kit price. We stop at 25 years.

What we leave out

• Installation costs, if you pay someone to mount the kit.
• Subsidies. Some cities and states pay part of the kit; check locally, it only shortens payback.
• Inflation on the kit price itself and interest you could earn instead.
• Your real load profile. Nothing beats a smart plug and a month of data.

Rules

Wattage caps, registration steps and tenant rights come from the law, the regulator or a national consumer body, and each country or state page links its sources with the date we checked them. Anything we could not confirm from an official page is listed on that page under "Still being confirmed".

Prices

Average household electricity prices come from national statistics (BDEW for Germany, CBS for the Netherlands, EIA for the US) and are refreshed monthly. Kit prices are read from the maker's shop and refreshed monthly; the date is on every kit.

Found an error? Email info@plugpayback.com and we will check it.