What you'd save by shifting load to the cheapest hours

How shifting a load saves money

Most households pay one price for every kilowatt-hour, whatever the hour. A dynamic tariff charges each hour at the wholesale price plus the fixed parts of the bill, and since 2025 every German supplier has had to offer one to customers with a smart meter. On such a tariff, power on a sunny midday or a windy night costs less than power at the evening peak. A load that can wait, such as an electric car, a heat pump with a hot-water tank or a home battery, can then be set to run in the cheapest hours.

The saving depends on how much energy the load can move, how far apart the cheap and dear hours are, and how often the cheap hours come round. An electric car that charges every night has plenty of energy to move and a long window in which to move it. A heat pump has to run when the house is cold, so less of its demand can wait. The daily gap between cheap and dear hours is charted on The Spread. It differs a good deal between bidding zones, so the calculator lets you switch zone.

The calculator knows every price in advance and always picks the cheapest hours. Real controllers plan with less certainty. The next day's prices are published early in the afternoon before, but a controller still has to guess how much the car or the house will need, so it catches most of the cheap hours and misses some.

In most household tariffs the network charges, taxes and levies are the same in every hour, so shifting a load saves on the energy part of the bill alone. Some owners of heat pumps or home car chargers with a smart meter can choose network charges that change by time of day. Electricity Bill Breakdown shows how large the energy part is, and Storage shows the same trade made at grid scale.