Are dynamic electricity tariffs reasonable for EV?

A dynamic electricity tariff is a flexible pricing model where the cost of electricity changes hourly or in 15-minute intervals based on live exchange rates. In Europe the EPEX (European power exchange EPEX SPOT SE) is responsible for the day-ahead-trading. This dynamic tariff allows consumers to save money by shifting high-energy tasks to times when renewable energy is abundant and prices drop. In Germany, energy suppliers are legally required to offer at least one dynamic tariff option to household customers and some of them are advertising with “Save up to 35% compared to fixed price tariffs!”. But is this advertisment valid for a regular customer? Lets see…

Why pondering about dynamic tariffs and where to get a good databasis?

Since July 2026 I’m an owner of an electric car and I was curious if I could reduce my monthly energy-bill using such a dynamic electricity tariff as advertised. But the online-calculators are quite generic and I was not able to find a decent tool that fits all my needs as I wanted a calculation over a full year. As an electrical engineer, it is therefore mandatory to write such a tool myself And guess what: compared to the standard tariff, such a dynamic electricity tariff is not cheaper under all circumstances, but one step after another.

I wanted to calculate which tariff is cheaper based on my own energy demand of the year 2025. In my home I got a PV-system with around 10kW peak, a battery with an energy of 14kWh and we are 8 people with 3 fridges, 6 WiFi-Accesspoints and a couple of other electric devices like in other houses. So we have a quite high base-load of around 250 to 300W and several energy-peaks up to 4kW within a regular day. Since a couple of years I’m recording the different loads and energy-sources with an InfluxDB/Grafana-combination, so I got a pretty good idea what happens within my house:

In yellow the power of our PV-system is shown, the power-demand of our house is shown in orange, the battery-power in blue and…