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A question, found a mistake or have an idea for the calculator? Let us know. We usually reply within a few working days.

About us

Everyone in the Netherlands deserves honest, number-based insight into their energy bill for 2027. Nothing more, nothing less.

For everyone the calculator remains free and independent: no account, no ads, no tracking, and no supplier or installer that can pay to rank higher.

Truly independent calculations. We don’t sell batteries, solar panels or contracts, we don’t refer you to anyone and we don’t favour any brand. We calculate with real hourly prices and market data. If your payback time comes out at 15 years, we simply tell you so. Honesty is the best policy. For the same reason, the dashboard is switched off for commercial use: only community organisations, such as a local energy advice desk, can get a licence. What to look for in a comparison site?

We are considering making the code public (open source), so that anyone can check how the calculator works. The data is already open: rates, grid charges and battery prices come from our project energieprijzen-nl on GitHub.

Who makes this?

I'm Zhi Zheng, a graduate econometrician with more than ten years of experience in IT and process improvement. With the neighbours, at work and on the side of the football pitch, the talk kept turning to home batteries. My wife wanted a simple answer: how quickly does a battery like that pay for itself? At the same time I was looking for a good example of what you can build with AI.

It started with a few simple sums. It soon became clear what was missing: VAT, the sun behaving differently than in the model, fixed costs that did not match the bill. After many iterations it became this calculator, built with the help of AI. Many comparisons look at just one part, while solar panels, battery, contract, car and heat pump together determine the bill. Here everything is calculated together.

At first I had a licence for professionals in mind. Now my main aim is to show as many people in the Netherlands as possible what a choice does to their electricity bill, and so contribute to the energy transition.

Energie27 is a CSR project (corporate social responsibility) of SynerZhi Consultancy B.V. from Almere, Zhi Zheng's company.