Fraunhofer ISE tool: 20 GW of batteries would lift German solar value 35%
Serguey Asael Shinder2 min readThe Fraunhofer Institute for Solar Energy Systems ISE has released a free simulator that shows how extra battery storage would have changed prices on Germany's day-ahead electricity market, pv magazine reports. The tool runs on Fraunhofer's Energy-Charts platform and is updated daily.
How it works. The simulator takes the actual buy and sell bids from the daily German exchange auction and recalculates the price as if a battery fleet of the user's choosing had taken part — from 0 to 20 GW of power, with two to six hours of storage. Users can also choose whether power plants that submit block bids covering several hours respond to the changed prices, and whether neighbouring countries are included through market coupling. Results come in quarter-hour steps and can be downloaded, along with the batteries' charging and discharging, their state of charge, consumption and potential wind and solar feed-in.
What Fraunhofer found for 2025. The institute ran last year's data with an added 20 GW of two-hour batteries, with block bids but without cross-border trade. In that scenario, the average gap between the day's most and least expensive quarter-hour falls from €130/MWh to €53/MWh, a drop of 60%. Hours priced above €200/MWh fall from 169 to 20, and hours with negative prices from 575 to 271. For solar, the result that matters most is the market value, which rises by 35%, from €45.08/MWh to €61.02/MWh.
The extreme days show the mechanism. On 20 January 2025, the most expensive day of the year, the simulated batteries would have cut the evening peak from €583/MWh to €221/MWh. On 11 May 2025, the cheapest day, they would have soaked up midday power and lifted the price from minus €250/MWh to minus €20/MWh.
Fraunhofer's Energy-Charts project manager Leonhard Gandhi drew the limit himself: storage evens out prices but does not produce electricity, so it has to be planned together with reliable generation.
Why it matters
Germany's solar build-out has been undercutting its own revenue: more panels mean more midday hours at or below zero. A tool that lets anyone test how much storage changes that — on real bids rather than on a stylised model — makes the debate about battery targets measurable. The caveats are in the settings: the headline figures assume no cross-border trade, which in reality absorbs part of the same surplus.