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The road to energy independence
Most homes stop at the second or third step, and that is often the right place to stop. Each step below says what it changes, what it costs and when it is worth taking. Pick the step you are at to see the next one.
Next step
Know your consumption
What it changes: A year of bills, or E‑REDES's 15 minute readings, show how much you use and when. ADENE and DGEG ask designers to start there when sizing a system.
What it costs
Free.
Panels sized to your consumption
What it changes: A grid tied system sized so production comes close to consumption, as ERSE asks. Without a battery you use 20 to 40% of what it produces (Fraunhofer ISE); the rest is sold as surplus.
What it costs
€5,500 to €7,500 with VAT for 4 kWp, turnkey (4gnews, from DGEG certified installers).
Work out the savingMove consumption into the sunny hours
What it changes: Run the washing machine, the dishwasher and the water heater while the panels produce. Each kWh used at noon instead of sold is worth about €0.19: the bill price less the surplus price.
What it costs
Next to nothing: the machines' own timers are enough.
A hybrid inverter, ready for a battery
What it changes: Not every inverter takes a battery (ADENE and DGEG). Choosing a hybrid now keeps the next two steps open.
What it costs
Ask the installer to price a string inverter and a hybrid side by side.
See what to ask in a quoteA battery
What it changes: Typically doubles the share of production you use (Fraunhofer ISE), moving the day's surplus into the evening. It lasts 12 years on average (ADENE and DGEG).
What it costs
€3,500 to €4,500 per 5 kWh (Bave Energy). It rarely pays for itself on savings alone.
Do you need a battery?Power in a blackout
What it changes: With a hybrid inverter, a backup function and a battery, the house keeps its essentials when the grid fails; string and microinverter systems stop (ADENE and DGEG). The Iberian blackout of 28 April 2025 made this the first question for many households.
What it costs
The battery, plus the inverter's backup function and a panel for the essential circuits. Ask for the price in writing.
How it works
The shares of production a household uses come from Fraunhofer ISE: 20 to 40% without storage, typically doubled with a battery. The blackout facts come from the ADENE and DGEG guide, system prices from 4gnews, battery prices from Bave Energy and the sizing duty from ERSE.
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)
- 4gnews, home solar prices in 2026 from DGEG certified installers in Lisbon, Porto and Coimbra, turnkey, 23% VAT included, 30 July 2026
- 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)
- ERSE, self consumption FAQ (FAQ do regime de autoconsumo), May 2025 (duties of the owner and the installer)
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