Grid stability |


mode, the generator isn’t heated by supplying active power, and so, just like a synchronous condenser, it can provide a significant amount of reactive power. In the event of a short circuit in the grid, it can temporarily supply up to seven times its rated current, also similar to a synchronous condenser.


This capability ensures that fuses operate correctly. In contrast, power electronics like those used in battery systems can only deliver their maximum rated current. When the gas turbine is kept spinning, it’s also ready to instantly provide active load. It’s already hot and synchronised to the grid, so the fuel supply is only ramped up to increase power at the rate requested, up to the allowable ramp rate limits of the machine. Certain machines have the capability to accept a limited amount of reversed power, which means frequency stabilisation in both directions of power flow, even under zero load conditions. The disadvantages of maintaining an idle operating mode typically include continuous fuel consumption and potentially high emissions from the machine. Therefore, under normal fossil-fuel operation, idling is considered to be a temporary measure when other grid resources are under significant stress.


How does hydrogen operation enhance idle mode?


When operating in idle mode during periods of high renewable power availability and using hydrogen as fuel, the operational cost of hydrogen should be low. Producing hydrogen from cost-effective renewable energy sources and supplying it to the gas turbine effectively means utilising inexpensive renewable grid power to maintain grid operations, with hydrogen only serving as an internal intermediate energy carrier. In the future, the operating cost should be compensated by revenues generated from supplying these grid services, strongly needed for the management of the grid. And because hydrogen is burned at the same time as it’s produced, no gas storage is needed except for minute scale damping. In addition, a hydrogen gas pipeline wouldn’t be needed.


formation may be lower during idle conditions when burning hydrogen, as opposed to operating in the same mode with natural gas. NOx


Operating the gas turbine on hydrogen doesn’t produce carbon monoxide, because there’s no carbon present. The usual problems with poor combustion performance, high carbon monoxide, and unburned hydrocarbon emissions at low load are magically eliminated. Thanks to the high reactivity of hydrogen, the proportion of gas supplied to pilot burners can be reduced compared to natural gas operation. As a result, NOx


emissions at idle may thus be


kept at a level that can be sufficiently reduced by a downstream catalyst. By operating


continuously, just alternating between green idle mode and active power dispatch, the downstream catalyst remains hot and prepared and experiences minimal thermal cycling stress because it rarely cools down.


Additional grid services through flexible operation of the electrolyser


The required storage volume for hydrogen between the electrolyser and the gas turbine is relatively small when fuel is consumed at the same rate and time as it’s produced. A small amount of storage (minute scale) for the purpose of system control may be needed, because the GT control needs to be stable and able to respond to frequency disturbancies. When specifying the storage, the designer should consider adding a little extra volume to allow for operating the electrolyser for short-term demand response: in other words, an even greater provision of grid support. But the total storage volume required is still very small compared to when storage needs to be scaled to bridge hours of full load operation.


How should the fuel supply for power dispatch be provided? When the gas turbine needs to supply residual power, it may ramp up instantly by adding another more easily stored fuel. Even if the machine can operate entirely on hydrogen in the future, it may be more practical to use a combination of fuels if there isn’t a nearby hydrogen pipeline. This approach would allow each fuel to serve its specific purpose, even at full load. This means that the fuel supply can


Visualisation of Siemens Energy Silyzer facility for production of green hydrogen via electrolysis (image: Siemens Energy)


18 | June 2025| www.modernpowersystems.com


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