I am Stefan Douw and I build Stekkerkompas myself. There was no good, honest Dutch calculator that works out solar, battery and heat pump together, so I made one. No team behind the scenes and no sales target: just someone who wanted to work it out properly and keep it honest.

You enter what you have and what you are considering, and the calculator works out the combined return. Solar, battery and heat pump affect each other, so I model them together rather than separately.

The figures are estimates, not a guarantee or financial advice. I deliberately use the honest middle, not a manufacturer's best-case numbers. Where a return is uncertain, battery trading especially, I show a range instead of a single figure.

How I calculate is laid out openly in the "How we calculate" box on the result and product pages, and every article lists its sources.

Everything runs in your browser. Your data stays on your own device and is not sent anywhere. See the privacy page for details.

Questions, spotted an error, or have a suggestion? Email info@stekkerkompas.nl.