Compliment of the Month: TenneT explores the potential of Long Duration Energy Storage

In our 'Compliment of the Month' series, we highlight a party that is committed to accelerating the energy transition each month. For April, our appreciation goes to TenneT, which for the first time calculated the effects of Long Duration Energy Storage (LDES) in the 2025 Security of Supply Monitor, thus making an important contribution to understanding and safeguarding our future energy supply.

Contribution of Intraday and Multiday LDES to Security of Supply

LDES differs from conventional lithium-ion batteries in that it can store energy for days rather than just a few hours. TenneT has therefore added two types of LDES to the model: intraday LDES and multiday LDES. Intraday LDES is modelled with 16 hours of supply per megawatt of power, which equates to 16 MWh per MW that can be deployed at any time. Multiday LDES, in the form of Compressed Air Energy Storage (CAES), utilises underground salt caverns and can store energy for up to 84 hours without significant losses.

The calculation shows that intraday LDES supplies approximately 40% of its capacity in periods of shortage and multiday LDES even almost 90%. In comparison: short-cycle 2- or 4-hour batteries only use approximately 12% of their capacity in periods of shortage. Thanks to the longer storage cycles, LDES can therefore release much more “firm capacity” at times when conventional flexibility options reach their limits. This additional deployability translates directly into a lower LOLE (Loss of Load Expectation) and a reduced EENS (Expected Energy Not Served), as calculated in the Monitor.

Expected growth towards 2035

Because LDES systems can buffer and feed in excess wind and solar energy when production is low, they will play an increasingly important role. TenneT expects the installed LDES capacity to increase steadily until 2033 and then even further towards 2035. According to TenneT, this growth not only supports security of supply, but also helps to reduce dependence on fossil reserves and smooth out price fluctuations in the electricity market.

At the same time, TenneT emphasizes the challenges facing LDES. Initial capital costs are high and payback periods can be ten years or more, which deters private investors. Furthermore, the volatility of electricity prices leads to unpredictable revenues, making the business case seem unreliable. Public concerns about underground storage and the use of certain chemicals also play a role.

Recommendation and outlook

To overcome these obstacles, TenneT points to inspiring examples from abroad. The United Kingdom uses a Cap-and-Floor scheme that offers investors a guaranteed minimum and maximum income, thus limiting risks. Spain compensates with Capacity Payments for available capacity, regardless of actual deployment, which promotes investment and network stability. In Germany, projects receive subsidies, cheap loans and tax benefits, after which they compete on the free market and benefit from price volatility.

Based on these international examples, TenneT advises the Dutch government to also investigate incentive measures for medium and long-term energy storage, in addition to the well-known instruments such as gas-fired power stations, demand response and interconnection.