Plug-in solar with battery 2026: what the storage adds
A 1,800 Wp balcony system (Balkonkraftwerk) in Munich covers 58 % instead of 35 % of its output at home with a 2 kWh battery and saves €168 more a year. At an extra €900, the battery pays for itself in 5.3 years.
Checked by Radif Partners · Editorial policy · How we calculate
Extra saving from the battery
€168 a year
self-use 35 % → 58 %
| Output before the inverter | 2,047 kWh |
|---|---|
| used at home without battery | 713 kWh · 35 % |
| clipped without battery (800 VA) | 457 kWh |
| used at home with 2.0 kWh | 1,178 kWh · 58 % |
| Extra saving per year | €168 |
| Battery payback | 5.3 years |
Step-by-step calculation
- The battery sits on the DC side: at midday it stores what the home does not use, including the part above 800 VA that the inverter would otherwise clip.
- In the evening it supplies what the home needs, up to the inverter limit; about 90% round trip.
- Extra saving = extra self-used kWh × 36.2 ct; power fed in from a plug-in system earns nothing.
Estimate based on average weather 2005 to 2023 (PVGIS) and metered household loads. A single year can differ by a few per cent. How we calculate
A plug-in solar system with a battery only saves more if there is power left over at midday that nobody in the home would use. The calculator therefore runs the same system twice: once without storage and once with the capacity you choose, each time with the PVGIS yield for your postcode and the consumption of metered households from HTW Berlin. In the Munich example, 1,800 Wp facing south at 35° produce 2,047 kWh before the inverter. Without a battery, a household using 2,500 kWh uses 713 kWh of it, and 457 kWh are lost at the 800 VA limit. With 2 kWh, self-used power rises to 1,178 kWh, because the battery also absorbs part of the peak above 800 VA. That is €168 of extra saving a year at 36.2 ct per kWh. An 800 Wp kit gains only €100 with the same battery: storage pays mainly when there is plenty of panel capacity.
What the battery shifts on a balcony
A plug-in system produces most at midday, while a household uses power in the morning and evening. Without storage the surplus flows into the grid unpaid, and whatever the panels deliver above 800 VA is clipped by the inverter. The calculator assumes a battery on the direct-current side: it charges with the surplus, including that peak, and releases it in the evening up to the inverter limit. Some energy is lost in each direction, leaving about 90 % for the round trip. The simulation sets charging and discharging power at 0.5 kW per kWh, at least 0.8 kW.
Yield comes from PVGIS for your postcode, consumption from the quarter-hour profiles of 74 households (HTW Berlin). The result is not an average but a full year with dull weeks, holidays away and bright summer evenings.
Battery sizes compared
| Battery | Used at home | Share | Clipped | Saving/year |
|---|---|---|---|---|
| none | 713 kWh | 35 % | 457 kWh | €258 |
| 1 kWh | 993 kWh | 49 % | 409 kWh | €360 |
| 1.5 kWh | 1,093 kWh | 53 % | 363 kWh | €395 |
| 2 kWh | 1,178 kWh | 58 % | 332 kWh | €426 |
| 3 kWh | 1,300 kWh | 63 % | 285 kWh | €470 |
| 4 kWh | 1,367 kWh | 67 % | 252 kWh | €495 |
The first kilowatt-hour of capacity earns the most, each further one less. Between 2 and 4 kWh the gap here is just €68 a year. The reason is winter: from November to February the output is rarely enough to fill the battery at all.
When the extra cost pays off
Payback is the extra price of the battery divided by the extra saving, not by the whole saving of the system. At €900 and €168 a year that is 5.3 years. Compare this with the manufacturer's warranty on the cells: if payback is longer, the battery only pays if electricity prices rise. It earns most with high panel capacity, an open south-facing spot and a home that is empty during the day. If you start with 800 Wp, first check in the guide to 800 and 2,000 watts whether more panels are possible.
Rules that stay the same with a battery
For plug-in solar devices (Steckersolargeräte), section 8(5a) EEG sets a maximum of 2,000 watts of panel capacity and 800 volt-amperes of inverter output; the calculator uses that output limit. No VAT is charged on batteries supplied for photovoltaic systems (section 12(3) VAT Act). Registration in the market data register is covered in registering plug-in solar; technical questions are answered by the Federal Network Agency. If you want to export nothing at all, see zero export.