04What happens when supply runs tight?

Storage: the batteries that live off the spread

How much does a battery earn from the daily price swing, and how fast are batteries arriving?

Grid batteries charge when power is cheap and sell into the evening peak. Large batteries in Germany grew from about 0.6 GW at the end of 2021 to about 4.4 GW so far in 2026, according to Germany's register of power plants (the Marktstammdatenregister). Home batteries add roughly 24 GWh of storage (energy, where GW measures power) that never sees a market price.

As storage grows it narrows the spread it earns from. The view illustrates that effect with a model and states its inputs.

A model battery (1 MW, 2 MWh, returning 85% of the energy it stores) run over ENTSO-E day-ahead prices, and the German battery fleet from Germany's official register of power plants (the Marktstammdatenregister).

1 · A day in the life of a battery

average day-ahead price, charge and discharge

The day-ahead price is the wholesale price agreed the day before delivery. On average (line) it dips at midday, when solar output peaks, and rises in the evening. A 2-hour battery charges in the cheapest hours (bars below zero) and discharges into the evening peak (bars above).

An upper bound. The captured figure assumes perfect foresight and 85% round-trip efficiency. Real batteries earn less: they cannot see prices in advance, they wear with use, and each new battery narrows the spread.

2 · Where storage is being built in Germany

Germany is two storage markets. Home batteries hold most of the energy; they sit behind a household meter and never see a market price. The large-scale fleet that trades the spread is young and small next to it. Every unit is in the national register, so this is a count.

3 · Storage and the spread

monthly 2-hour spread (TB2) · €/MWh

A battery earns from the gap between the day's two cheapest and two dearest hours (the 2-hour spread, TB2). The wider that daily spread, the more a battery can earn by charging cheap and selling dear.

4 · More storage, thinner spread

modelled, illustrative

Buying cheap to sell dear limits itself: each battery chasing the same daily price swing helps flatten it. This model shows how the spread, and the revenue per MW, shrink as battery capacity grows. It illustrates the effect from stated inputs.

5 · Has storage narrowed the spread yet?

measured · one point per year

The model above says more batteries mean a thinner spread. Here is what the record shows so far: the large-scale fleet at each year-end against the average 2-hour spread that year.

Questions

How much battery power is running in Germany?

About 4.4 GW of large batteries so far in 2026, up from about 0.6 GW at the end of 2021, according to Germany's register of power plants (the Marktstammdatenregister). Home batteries add roughly 24 GWh of storage, a measure of energy where GW measures power; they never see a market price.

How does a grid battery make money?

It charges when power is cheap and sells into the evening peak, so it earns from the daily spread: the gap between the day's cheapest and dearest hours. As more storage is built it narrows the spread it earns from; the page illustrates that effect with a model and states its inputs.

How these numbers are made: The canonical hourly grid, The daily spread (TB1 and TB2), The perfect-foresight arbitrage bound, The battery fleet from the register.

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