Savings assume the post-2027 world: salderen (net metering) has ended and feed-in is low. Until then salderen still applies, so a battery’s solar self-use value is near zero in the first years.

Battery trading income is the largest unknown. We model €70 per usable kWh per year, central, with a €40–€95 range. Battery payback and ROI move a lot with it, and the income is taxed and tends to fall as more batteries join the market.

Prices include 21% VAT, except solar panels (0% VAT for homes since 2023). Heat-pump payback is shown after the ISDE subsidy (per model). A home battery’s 21% VAT can sometimes be reclaimed by registering as an energy trader, but that is admin-heavy and not included here, so a battery may be cheaper than shown.

Lifetime return and ROI are in today’s euros (discounted 4%/yr); payback is in calendar years.

We assume real energy-price rises of 1%/yr for electricity and 4%/yr for gas, and equipment lives of 15 yr (battery), 25 yr (solar) and 18 yr (heat pump).