When the wind falls silent and the sun goes to sleep

The share of wind and solar energy in the global electricity mix is increasing. But wind and sun do not only provide too little energy in the so-called dark doldrums. This is where battery storage and gas-fired power plants come into play – two different technologies that keep our power grid stable even in critical times.

Solar and wind energy have long been considered a huge promise for the future—a promise they have kept. Their share of the electricity mix is increasing every year, reaching over 15 percent worldwide in 2024.

However, the higher the proportion of wind and solar energy in the grid, the greater the importance of a word that was only added to the Duden dictionary in 2016: dark doldrums. It refers to times when the wind and sun do not provide any energy because it is either dark or there is no wind because it is calm.‘

Solar and wind power are volatile, and the peaks in power generation do not always coincide with the peaks in demand. To balance out these fluctuations and to be able to use the electricity generated at all times, more energy storage is urgently needed. For longer periods of dark doldrums, additional capacity reserves are needed,’ said Andreas Görtz, who heads the sustainable solutions business at Rolls-Royce's Power Systems division.

Two technologies will play a crucial role here: battery storage and gas-fired power plants.

mtu EnergyPacks: Storing green energy

On sunny or windy days, when the sun and wind generate more energy than is actually needed, battery systems such as the mtu EnergyPack QG store the surplus energy. This stored energy can be fed back into the grid later. In the event of sudden demand peaks or unexpected outages, battery storage systems can also react quickly and provide additional power at short notice.

But battery storage systems have even more advantages: they can supply or absorb energy in fractions of a second to compensate for fluctuations in the grid frequency. This is crucial to ensuring the stability of the power grid. By flexibly feeding energy into the grid, they help to smooth out peaks and reduce the load on grid components.

mtu battery energy storage system: modular units, flexibly scalable

With the mtu EnergyPack QG, Rolls-Royce supplies large-scale storage solutions consisting of modular units for capacity and power that can be flexibly configured. A large-scale mtu battery storage facility with an output of 291 megawatts and a storage capacity of 582 megawatt hours is currently being built in Lithuania. The battery systems store surplus electricity from renewable energies and feed it back into the power grid when demand increases, balancing the system and ensuring a reliable power supply.

mtu EnergetIQ: The brain behind the hardware

A central component of the Rolls-Royce solution is the EnergetIQ Manager. This controls groups of energy sources and storage facilities as well as energy distribution along the entire path from generation to the consumer.

There is no question that this expertise will be in demand, as these figures prove: For example, the research and analysis company BloombergNEF expects that by 2035, energy storage facilities in the double-digit terawatt hour range will be built worldwide, a significant portion of them in China. International energy studies unanimously predict that capacity will expand further into the terawatt range by 2050.

Gas-fired power plants: rapid energy generation

However, batteries alone will not be sufficient to compensate for fluctuations in solar and wind energy. During periods of low sunlight and wind, it is often necessary to bridge gaps of several weeks. This is where gas-fired power plants come into play, generating electricity from gas. Rolls-Royce supplies turnkey plants for this purpose with capacities ranging from 5 to several hundred megawatts, depending on requirements. Thanks to preconfigured, factory-tested modules with capacities of 10, 20, and 30 megawatts, the power plants can be connected to the grid within 12 to 18 months of ordering.

Hydrogen: long-term storage with the potential to keep the grid stable

The power plants are still running on gas, but mtu engines are H2-ready. That means they can be retrofitted with a special kit to make hydrogen engines. ‘There is no demand for that yet, but as soon as green hydrogen is available in larger quantities, our customers will be able to use our engines to generate energy with zero carbon emissions,’ explained Tobias Ostermaier, who heads the PowerGen business at Rolls-Royce. Hydrogen could then be used for long-term storage. Hydrogen power plants in combination with electrolysers and a well-developed hydrogen infrastructure would become an important element of grid stability.

Even better in combination: battery storage and gas power plants working together

More and more often, battery storage and gas engines are being used together – in microgrids that enable a self-sufficient energy supply. In these, the base load is usually provided by renewable energy sources such as solar panels. If no solar power is available, the batteries, in which surplus energy has been stored, take over. Such a microgrid will look familiar to many homeowners. This microgrid can be expanded to include a diesel, gas or hydrogen-powered generator. These are always on hand as a reliable source of energy, thus making the microgrid a dependable energy network.

‘We are still in the early stages, but it is fascinating to see how our products are helping to make an almost 100 percent carbon-neutral energy supply possible,’ says Tobias Ostermaier.