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 seen as a huge promise for the future – a promise they have kept. Every year, their share of the electricity mix increases; in 2023, it was almost 14 per cent worldwide.

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

Rolls-Royce supplies large-scale storage solutions in the form of mtu EnergyPack QG units, which consist of modular capacity and power units that can be flexibly configured. An mtu large-scale battery storage system with a power output of 32.6 megawatts and a storage capacity of 65.2 megawatt hours is currently being built in Zeewolde, Netherlands. When the wind is blowing strongly and the turbines in the wind farm generate more electricity than the grid can absorb, the excess energy is stored in the battery systems. This prevents grid overload at times when a lot of electricity is available. Later, the storage units also supply green electricity to the grid when there is no wind but customers still need energy.

mtu EnergetIQ: The brain behind the hardware

An even larger mtu plant with a storage capacity of 132 megawatt hours is currently being built in Turkey. In both plants, the intelligent mtu EnergetIQ control system ensures that the plant can be used efficiently and thus profitably.

There is no question that this expertise will be in demand, and these figures prove it: experts estimate that up to 700 gigawatt hours of battery storage capacity could be built worldwide by 2035 – more than half of it in China. By 2050, a growth in capacities in the terawatt range is expected.

Gas-fired power plants: rapid energy generation

Batteries alone will not be enough to compensate for the fluctuations in solar and wind energy. Gas-fired power plants are also needed. These generate electricity using gas – and in the future, hydrogen. The British capacity market is considered one of the most modern in the world: power plant operators are paid to maintain capacities that they can then flexibly ramp up when needed. There are already over 500 mtu gas gensets in use in the UK – and that number is set to rise sharply. They are used in decentralised gas engine power plants and can ramp up to full load in just two minutes.

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.