About this site

This site starts from a question forums have answered for years without a calculation: how big should the battery be? In the threads we read, answers range from 5 to 12 kWh or say «none at all», without using the data of the person asking. Here you calculate with your own figures and with public profiles whose sources are on every page. The site signs with its own name; who runs and provides it, with the details the law requires, is stated in the legal notice.

How we test and choose

We have not measured batteries or heat pumps ourselves, and we say so on every page. The calculators use public data with a link and a date: the BDEW H25 standard load profile, hourly solar output from PVGIS (European Commission), HTW Berlin laboratory measurements of batteries and Fraunhofer ISE field measurements of heat pumps. The formulas are checked with automated tests, and the assumptions are written under every result. We calculate energy and running costs, not returns, incentives or loans, and we give no installation advice. Advertising links sit apart from the result and never change it.