What part can gas engines play in the energy transition?

The term “power plant strategy” already has a great chance of making it onto the shortlist for the 'Word of the Year' award in Germany, and maybe even winning. At the beginning of February, the German government published its key points on this. Since then, there has been heated debate. The central question is: How can we make the transition to climate neutrality in Germany and secure the energy supply at the same time – and do so efficiently, CO2-reduced and affordably? mtu gensets from Rolls-Royce are set to play their part. Dr. Daniel Chatterjee, Director Corporate Sustainability, Technology Management & Regulatory Affairs, and Michael Stipa, Vice President Strategy, Business and Product Development Stationary Power Generation at Rolls-Royce's Power Systems business unit, explain their role in the energy transition.  

Dr. Chatterjee, let's start from scratch: What actually is this power plant strategy?

Chatterjee: Well now, by 2030 at least 80% of the electricity consumed in Germany is to be derived from renewable sources – primarily from wind and solar power plants. At the same time, coal-fired power stations are to be withdrawn from the grid, although some plants will still be needed to secure supply around the clock, especially when the wind is still or the sun's not shining. The German government's power plant strategy now envisages gas-fired power stations generating electricity using eco-friendly hydrogen to fill this gap in the foreseeable future. The federal government is looking to put up to ten gigawatts of gas-fired capacity out to tender. It intends to fast-track the planning and approval of these plants and subsidize them from the Climate and Transformation Fund.   The new gas power plants will be facing a number of complex challenges: They will form a “resilience backbone” to compensate fluctuations in the weather affecting power generation from renewable energies. So they'll be kicking in during the so-called 'dark doldrums'.  

Electricity demand in Germany is set to increase dramatically over the next few years…

Chatterjee: Quite right. Private households are also sharpening power demand, for example due to the increasing prevalence of electric cars and heating systems. The Grid Development Plan of the four transmission system operators confirmed by the Federal Network Agency foresees a doubling of electricity demand over the next twenty years. And consumption patterns are also changing. Electric cars in particular are mostly charged after sundown.

In its power plant strategy, the German government has now resolved to build new gas-fired power plants to pave the way for a secure, climate-neutral electricity supply. Why the focus on gas?

Chatterjee: Compared to lignite or hard coal, gas combustion produces significantly fewer CO2 emissions, nitrogen oxides and soot particles. But there's also a wider perspective here: Although we're still very much reliant on gas at present, blue and green hydrogen will also be available in the future. And the idea is to use them in existing gas power plants. Using green hydrogen, i.e. produced from renewables, our electricity supply would then be completely climate-neutral. But it's not just about the environmental footprint:   Gas power plants are much more flexible than coal-fired plants in terms of start-up intervals and load cycles – and this is crucial, as gas power plants are primarily intended as backup and grid support in the long-term. In future, they'll have to be ramped up and down much more frequently and at much shorter notice.  

Michael Stipa, two different types of gas technology seem viable: Gas turbines and internal combustion engines. Which technology makes more sense?

Stipa: That naturally depends very much on the application. Gas and steam power plants are more at home when a lot of electricity needs to be generated over longer periods – mostly operating at full load and ramping up infrequently, they are more efficient than gas engines, and therefore also the more cost-effective technology. But demand is set to change in the future. The amount of electricity generated has to be constantly adapted to meet actual demand. We therefore need a more versatile solution, and that's where gas engine power plants come in. With any number of individual gas engines hooked up together, power can be ramped up and down with enormous flexibility. The key advantage being that they don't have to be operated inefficiently in the partial load range, as is often the case with gas turbines. On the contrary, the precise number of gas engines required at any one time are simply ramped up and then run at full load. For example, if a power plant has an output of, say, 50 megawatts, but just 30 megawatts are needed, then only 12 engines start up and then run at full load. All of this under the control of our mtu automation system which can regulate deployment so only those gas gensets that are genuinely needed are put to work. This is the more efficient and cost-effective solution in the long-term.  

Can you be more specific?

Chatterjee: Yes, we've crunched the numbers based on a real use case: There's one gas turbine power plant which used to run at full load for more than 4,700 hours a year. Since we started integrating more renewables into the German grid, it's only been running at full load for around 2,000 hours, and is ramped up around 100 times a year. If you compare the costs of a gas turbine power plant with those of a gas engine power plant, the gas turbine power plant is cheaper when operated conventionally as in the past – i.e. several thousand hours at full load. However, when dealing with the variable load profiles mentioned before, the gas engine power plant is actually less expensive.  

Stipa: It's safe to assume that the share of renewables in our electricity mix will continue to increase. As a result, gas-fired power plants will be running less and, above all, operating more dynamically. Gas engine power plants will therefore always be the better proposition for the future. In a nutshell, you could put it like this: Gas turbines are an efficient solution – for yesterday's requirements. But for today and tomorrow, when flexibility is key, gas engines are the more cost-efficient and environmentally-friendly concept.  

Do you have any experience of mtu gas power plants serving as backup?  

Stipa: Yes, the UK has been transitioning from coal to renewables and gas power plants for several years now, and introduced a capacity market in 2014. Since then, Rolls-Royce has been facilitating the energy transformation in the UK with highly efficient gas gensets. Around 500 mtu gas gensets are already being deployed for decentralized power generation and to secure the British power grid.

A key part of the power plant strategy envisages running the power plants on hydrogen in the long-term. Will mtu be offering hydrogen solutions anytime soon?  

Stipa: Yes, Rolls-Royce is gradually introducing more sophisticated mtu gas engines to the market, running on a hydrogen admixture of 25% by volume depending on demand. A conversion kit is under development for existing mtu natural gas gensets to convert them for 100% hydrogen operation. In a few months' time, we'll be shipping the first upgraded mtu gas engines to the new, climate-neutral Duisport terminal. These will be running 100% on hydrogen.  

Will gas engines continue to play a role, and how should the power plant strategy unfold?

Chatterjee: They certainly will. The UK clearly demonstrates the significance of gas engines as used there. In this case, the electricity supplied is not remunerated as in the present, active power market. The operators are paid for providing a certain amount of electricity – regardless of whether it is actually used or not.   However, the German government has yet to put a capacity market out to tender. And such an invitation to tender is urgently needed to create an incentive to invest in gas-fired power plants and battery energy storage systems.