​A recent survey by BDEW suggests that German grid operators have approved 78 GW of grid-scale batteries. By contrast, around 2.5 GW are installed today and Modo Energy’s central forecast reaches 14.3 GW by 2030.

Duplicate applications, permitting delays and financing constraints make it unlikely that the full pipeline will be built. Even so, the scale of committed capacity leaves a wide range of plausible buildout paths, including periods where deployment runs ahead of market needs.

In that case, additional batteries compete for the same opportunities, compressing spreads and merchant revenues. Varying capacity growth by ±50% shows the stakes; overbuild cuts average day-ahead revenues by 17% by 2030, while underbuild lifts them by 11%.

This article is part of a series on revenue risk and fundamentals sensitivity:

• What 50% lower demand growth means for batteries
• How gas and carbon prices affect BESS revenues
• How BESS overbuild could cannibalise revenues

Sunk costs and policy deadlines drive overbuild risk

Securing a grid connection changes incentives. Once projects are well advanced, withdrawing means forfeiting time and capital already invested, while clear signals of overbuild only emerge once new capacity is operational and affecting prices.

Policy design reinforces this dynamic. Batteries commissioned before August 2029 receive a 20-year grid fee exemption, creating an incentive for developers to commission projects ahead of the deadline, even if market fundamentals would support slower deployment.

To quantify this risk, we test alternative BESS buildout paths around Modo Energy’s central forecast. Capacity growth is varied by ±50% to create overbuild and underbuild scenarios, alongside a 78 GW stress case.

Note that while the scenarios are symmetric in percentage growth terms, the absolute changes in installed capacity vary between overbuild and underbuild, shaping the scale of the impacts that follow.

Higher buildout means lower merchant revenues

Higher storage buildout translates directly into lower merchant revenues. Under the overbuild scenarios, average day-ahead revenues fall below the central case across the forecast horizon, while underbuild lifts revenues.