- Sep 22, 2021 8:23 am GMT
It’s well known that a common concern for producing green hydrogen is cost. But the outlook is not as dire as some may suggest. Here an example of a combined cycle hydrogen power plant paired up with proton exchange membrane (PEM) electrolyzers that not only improves the plant’s environmental performance but also makes a lot of sense economically.
Despite the every-increasing share of renewables in our energy mix, gas-fired power plants are still crucial to the security of energy supply. They produce electricity when the sun doesn’t shine, the wind doesn’t blow, they top up the grid during periods of peak demand – and they emit CO2, albeit a lot less than coal-fired power plants. But their carbon footprint can be reduced by burning a mixture natural gas and hydrogen. And not just any hydrogen, but green one that can be produced with the help of a coupled electrolyzer that produces hydrogen when there is renewable power to spare.
The beauty of this scenario is that it ensures that the power plant is flexible and future proof, as the share of green hydrogen can be increased until it reaches 100 percent. At Siemens Energy, we have a vision of a combined cycle hydrogen power plant that would utilize renewable energy or spare capacity to generate green hydrogen using Siemens Energy’s proton exchange membrane (PEM) electrolyzers – the latest model being the Silyzer 300. Now, it’s well known, though, that a common concern for producing green hydrogen is cost. But the outlook is not as dire as the hearsay may suggest.
Let’s take a Siemens Energy SGT5-9000HL gas turbine that can burn up to a 50 percent hydrogen mix. For our example, we’ll pair it with nine Silyzer 300 electrolyzers and six tonnes of H2 storage. Currently a typical day with optimum weather for this dual firing power plant in the Netherlands, the electricity price can be sold for varies dramatically. Starting the day in the early hours of the morning at €70/MWh, it climbs to a peak of around €100/MWh in the morning and evening peak periods but drops as low as €50/MWh at other times. In the future with the volumes of available solar power increasing the variation would be even more dramatic. With optimum weather conditions and the sun shining brightly, the variation is even more dramatic. Between the hours of 9 am and 5 pm, the price does not climb above €10/MWh and even dips into negative figures for five hours during the day, reaching a nadir of -€40 mid-afternoon. During these 9 hours, the average electricity price was -6.8 euro/MWh. Not an ideal scenario for a power plant operator.
However, if that power plant was coupled with electrolyzers to produce hydrogen, the picture is far more advantageous. During the nine hours of low prices, the power could be diverted to the electrolyzers to produce green hydrogen. This hydrogen can be stored and used for co-firing in the turbines saving on fuel, increasing grid earnings, and reducing emissions. In fact, the revenue outlook changes dramatically. Making assumptions that the natural gas costs €8/MMBTU and the current rate of CO2 tax was €55 then over the day, there is a total savings of €45,401. This comprises €23,431 saving on fuel, an extra €11,425 in grid earnings and a reduction of CO2 tax of €10,545. Aside from the financial benefit, there is also improved environmental performance with a reduction in CO2 emissions of over 190 tons a day.
This solution is not only relevant for large-scale power plants like the one we have been speaking about with the SGT5-9000 turbine. The optimized standard integration of hydrogen production, storage, re-electrification, and heat recovery can be adapted to power plants of all sizes. A system using the SGT-400 gas turbine can cater for outputs as low as 10 MW. Particularly in Europe, which has smaller district heating systems, this size can still be effective. It also complements the growing trend toward smaller, decentralized power generation.
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