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Do you need a battery?
A battery pays when you are out during the day and home in the evening, or when you want power in a blackout. Answer three questions to see which applies to you, what a battery costs and what it changes.
Answer the three questions to see the answer.
How it works
Without storage, households use 20 to 40% of what their panels produce; a battery typically doubles that (Fraunhofer ISE). Each kWh a battery moves from the grid to your evening is worth the price on your bill, about €0.24, instead of the €0.05 a surplus sells for.
When the grid fails, string and microinverter systems stop working; a hybrid inverter can keep running with a battery (ADENE and DGEG). A 5 kWh battery costs €3,500 to €4,500 (Bave Energy, whose page does not say whether VAT is included) and lasts 12 years on average (ADENE and DGEG).
Sources
- Fraunhofer ISE, Recent Facts about Photovoltaics in Germany, version of 26 August 2026 (self consumption without and with a battery)
- ADENE and DGEG, practical guide to individual self consumption, chapter I (panel efficiency about 22%, power warranty 97% in year one and 80% at 25 years, inverters, registration)
- Bave Energy, how much solar panels cost in Portugal in 2026, updated 5 June 2026 (battery prices; the page does not say whether VAT is included)
- Eurostat, household electricity prices (nrg_pc_204), Portugal, 2,500 to 4,999 kWh a year, all taxes included, second half of 2025
- Portal Energia, the surplus regime in 2026 (fixed price around €0.05 per kWh)
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