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Solar against other places for your savings
Put the price of a system next to a bank deposit at 1.62%, savings certificates at 2.5% plus premiums and 10 year Treasury bonds at 3.54%, after the 28% tax on interest. Solar's return is the bill you no longer pay, which is not taxed, but it depends on how much of the production you use and on the price of electricity.
Equivalent yearly return, after tax
- 7.5%
Solar, a 2.5 kWp system for about €4,400
Over 25 years. It is the bill you no longer pay, which is not taxed; it depends on how much of the production you use and on the price of electricity, and the money stays on the roof.
Payback: 9 to 12 years
- 2.5%
10 year Treasury bonds
Gross rate of 3.54% (ECB, August 2026), less 28% tax.
- 2.4%
Savings certificates, series F
Base rate of 2.5% in October 2026 plus the permanence premiums, over the 15 year term, less 28% tax.
- 1.2%
Term deposit up to one year, renewed
Gross rate of 1.62% (ECB, August 2026), less 28% tax.
On these numbers, solar returns more than all three alternatives, as long as you use the assumed share of the production and electricity prices do not fall.
How it works
Rates: new household deposits up to one year, 1.62% (ECB, August 2026); savings certificates series F, 2.5% base in October 2026 plus the permanence premiums; 10 year Treasury bonds, 3.54% (ECB, August 2026). Interest is taxed at 28%. Each rate is held for the whole period, which no one can promise.
Solar: the yearly saving from the savings calculator model, with output falling from 97% in year one to 80% in year 25, the minimum ADENE and DGEG say a panel should guarantee. Surplus income up to €1,000 a year is outside IRS. A battery is replaced after 12 years, its average life. Electricity prices are held flat, which is the cautious case.
Sources
- European Central Bank, bank interest rates, Portugal, household deposits up to one year, new business, August 2026
- ECO, savings certificates (Certificados de Aforro, series F) pay the maximum base rate of 2.5% in October 2026, with the permanence premiums, 25 September 2026
- European Central Bank, long term interest rate for convergence purposes, Portugal (10 year government bonds), August 2026
- Portal das Finanças, CIRS article 71 (28% flat rate on interest)
- Portal das Finanças, CIRS article 12 (surplus sale income up to €1,000 a year is outside IRS)
- 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)
- 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)
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