Charge cheap. Discharge expensive. Keep the difference.

It estimates how much a battery at an EV charging site could save in a year through energy shifting. The battery charges when day-ahead electricity prices are low and powers the chargers when prices are high. The estimate runs on 12 months of real day-ahead prices for the price zone you choose.

No. It is built for operators who are considering a battery for a charging site and want to see whether it makes sense, and roughly what size it should be. You enter your chargers and the battery size you want to test, and the calculator does the rest.

Energy shifting means buying electricity when it is cheap, storing it in a battery and using it when electricity is expensive. It is also called price shifting or energy arbitrage. At a charging site, the battery charges in low-price hours and supplies the chargers during price peaks, so the operator buys less energy at peak prices. The saving is the price difference between those hours, minus the energy lost in the battery.

The calculator covers 29 day-ahead price zones in 17 European countries: Denmark, Sweden, Norway, Finland, Germany, Luxembourg, the Netherlands, Belgium, France, Spain, Portugal, Italy, Switzerland, Austria, Poland, the Czech Republic and Ireland. Countries with several price zones, such as Denmark, Sweden, Norway and Italy, list each zone separately, because prices differ between them.

The prices are day-ahead auction results from the ENTSO-E Transparency Platform, the public data platform of Europe’s transmission system operators, at 15-minute resolution. For Ireland, the prices come from the SEMOpx day-ahead market, via kilowatt.ie. The yearly figure simulates every day from 1 October 2025 to 30 September 2026 in a row.

For each day, it compares every 15-minute price with that day’s average:

Cheap periods are at least 20% below the average. The battery charges then, using only the grid capacity the chargers aren’t using.

Expensive periods are at least 20% above the average. The battery discharges then to power the chargers.

The simulation also keeps the battery between 5% and 95% charge, assumes 95% round-trip efficiency, and limits the battery to two full cycles a day by default.

A battery saves the most at sites where the gap between cheap and expensive hours is large, and where the chargers are busy when prices peak. The site also needs spare grid capacity in the cheap hours, so the battery can recharge. Price gaps vary by zone and season, which is why the calculator shows a summer and a winter day separately.

The battery can only recharge with the grid capacity left over after the chargers. At a busy charging site with a tight grid connection, there is less room to charge in cheap hours, which lowers the saving. By default the calculator sets the grid connection to the chargers’ combined power, and you can change it under Advanced settings.

The estimate only covers the day-ahead spot price. Grid tariffs, taxes and VAT are left out, and so are Boost and peak shaving. Time-of-use grid tariffs and capacity charges can change the value of a battery considerably, so the result for a real site may be higher or lower.

Boost uses part of the battery to give drivers full charging power even when the site’s grid connection is maxed out. The calculator keeps a reserve for Boost, 20% of the battery by default, and energy shifting never uses that reserve. Any value from Boost comes on top of the energy shifting saving shown in the calculator.

The estimate is indicative, not a quote. It uses real market prices but a typical charging profile, while every site’s load, tariff and battery are different. For a figure you can plan with, request a personalised site analysis.

FLEXECHARGE runs the simulation on your charging site’s real situation: your charging load, energy contract, grid tariff and grid connection. The analysis also covers Boost and peak shaving, which the calculator leaves out. If you have charging data at 15-minute resolution or finer, ideally covering a full year, we use it for the most reliable result.