German utility EnBW is planning to switch one of its combined heat and power (CHP) plants in Stuttgart from coal to green hydrogen, but says it will burn fossil gas until sufficient quantities of H2 become available at affordable prices, project partner Siemens Energy said yesterday.

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Two 62MW Siemens SGT-800 turbines capable of burning 75% hydrogen will be installed at the Stuttgart-Münster CHP plant by 2025, replacing three coal boilers and paving the way for the region to go coal-free by 2026.

The CHP plant provides heat to the local area via a district heating system, as well as power.

But the utility does not expect to burn any hydrogen in the plant for ten to 15 years, due to difficulty sourcing affordable quantities. Until then, the 124MW plant will burn fossil gas.

“We can’t yet reliably predict when green hydrogen will be available in sufficient quantity and at affordable prices,” said EnBW’s chief operating officer of generation, Georg Stamatelopoulos. “But the technology should be in place by that time. We’re not going to put the cart before the horse.”

Siemens says that it will enable Stuttgart-Münster to go 100% hydrogen as part of the overall package deal it has agreed with EnBW. This will likely involve upgrading or replacing the turbines as technology advances.

Currently, there are no turbines on the market that can burn 100% hydrogen, although researchers the University of Stavenger in Norway recently achieved the 100% milestone in their micro gas plant — but with lower efficiency than burning fossil gas.

Overall, hydrogen is expensive and inefficient to burn in a turbine for power compared to natural gas, as it has a lower energy density by volume. However, Siemens and EnBW both emphasised the role they believe hydrogen has to play in providing dispatchable renewable power.

“Hydrogen makes it possible to store energy generated by wind and solar farms, to transport this energy, to convert it back into electricity, and to use it where it’s needed,” said Siemens Energy managing board member Tim Holt. He added that the flexible “H2-ready” approach to fuel-switching protects Siemens’ customers’ investments, presumably meaning that utilities can continue to opt for fossil gas if it remains cheaper and more available than hydrogen.

“This is the only way we can support the expansion of renewable energy,” said Stamatelopoulos.

However, the International Energy Agency (IEA) has suggested that renewables could be effectively deployed in district heating and CHP, either through solar thermal or bioenergy such as biomass.

“District heating and cooling networks are potentially one of the most effective means to harness renewable energy to meet heating and cooling demand because they offer economies of scale and high efficiency potential through aggregation of demand, renewable energy storage possibilities (thanks to thermal inertia), and the opportunity to integrate thermal storage technologies and benefit from heat and power coupling,” the IEA said in a 2019 report How can district heating help decarbonise the heat sector by 2024?.

The H2-ready fuel switch is also the plan for EnBW’s nearby Altbach/Deizisau CHP plant, which is expected to be upgraded from coal to fossil gas with “hydrogen-ready” turbines by 2026. That facility will produce 750MW of power and 170MW of heat for the local area, reducing carbon emissions from the plant by 63% even when burning only fossil gas, EnBW said.

Once the Altbach/Deizisau fuel-switch is complete, the Stuttgart region will be coal-free, it added.