Grid stability |
SGT-800 gas turbine (photo: Siemens Energy)
power supply could help in obtaining permits to increase electricity use for electrifying the rest of the steam production, because it can help eliminate grid congestion issues.
When will the technology be ready?
Constructing this type of plant is already technically possible, and H2
-capable burners
are in development. Siemens Energy’s DLE burner gas turbines are commercially available for a 30 to 75% hydrogen-to-natural-gas ratio, depending on the turbine frame. However, that range applies to high load operation; low load hydrogen combustion is easier to manage, and therefore full hydrogen capability for low-load operation is expected soon. Some of the fuels mentioned above require the creation of dual-fuel hydrogen burners and modifications to fuel supply systems. These developments are underway and are relatively straightforward. Once there’s market demand for a new fuel capability, as OEMs we’ll develop and engineer the appropriate systems to meet that need.
Steam turbine green idling and use of high-temperature storage Steam can be produced using an electric boiler to run a steam turbine, not at zero
load, but at least at a very low load. The benefit of providing grid services in this mode is similar to that for GT green idling, except that the frequency stabilisation capability is rather limited because providing active power depends on starting up another boiler. If the steam turbine is situated in a CHP plant and the outlet steam downstream of the steam turbine is used, then the energy losses are negligible.
One of the benefits of steam turbine green idling operation occurs in a combined cycle that is intended for cycling operation. At start of the gas turbine, the steam cycle is already up and running, and bottoming cycle startup time and related stress are significantly reduced.
An interesting concept is the option of integrating a high-temperature thermal storage system with the bottoming steam cycle of a combined cycle, especially in CHP applications. The storage system doesn’t require a separate re-electrification system, because the steam cycle is shared. And again: when the storage is emptied and it’s time for the GT to start, the steam turbine is already hot and running. When this kind of storage system is combined with GT green idling, electricity produced internally from the storage system in certain periods may be cheaper than
20 | June 2025|
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external grid power for keeping the green idle GT operation running. These periods may occur when other storage systems dispatch power, but the grid price is still too low for GT dispatch.
Heat from storage or an electric boiler may also be used in periods of GT standstill for pre-warming or maintaining the HRSG temperature.
Green idling: an option to consider In summary, keeping generators spinning ensures grid stability, and the concept of green idling makes this possible without the drawbacks of emissions and fuel costs associated with low- load fossil fuel operation.
Of course, its feasibility depends on the availability, and thus the economic viability, of green hydrogen. If dedicated electrolysers are installed it’s not enough that the price of electricity to feed them is low and compensation for grid services is high, but it must also occur for a sufficient number of hours per year to pay for the electrolyser investment.
Nevertheless, it makes sense to consider this approach as a possible option when designing new power generation, or as an upgrade to an existing plant, to improve revenues, reduce cycle stress and become hydrogen ready at the same time.
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