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There is an increasing interest in the use of hydrogen (H2) for power generation, the use of which can reduce carbon emissions from fossil fuels in existing gas generation plant and provide an energy storage solution for power-to-gas-to-power schemes, which would complement the increasing share of non-dispatchable renewable energy resources.
Hydrogen is seen as a means of storing “surplus electricity” from renewable energy sources. Current thinking is that, as an alternative to other forms of energy storage, H2 could be produced when surplus wind or solar power is available, and then used to generate electricity when needed.
The use of H2 as a fuel has held a fascination for many years, mainly because the resultant gas from hydrogen combustion is water,
a “clean” substance. H2 is also storable in bulk, can be transported in liquid or compressed gas form, or piped to consumers. The aim of using H2 as a fuel for gas turbines is to reduce CO2 emissions in the electricity generation industry.
Power-to-gas-to-power (PGP)
Perhaps the best place to start would be to put the “green hydrogen” cycle using gas turbines in context. Table 1 shows the requirements and output of three different sizes of open cycle gas turbine operating on 100% green hydrogen fuel for a period of 8000 hr/year, using current electrolyser efficiency figures.
The PGP storage process using green hydrogen and open cycle gas turbines has a round-trip efficiency of approximately 20%.
Hydrogen fuelled turbines: Industry experience
Turbines designed to run on industry off-gases which contain hydrogen have been used successfully for years. The question that arises with PGP is whether existing turbines can be modified to accept a high percentage of H2 in the fuel. In addition to pure hydrogen, the industry is investigating H2 carrier fuels, such as ammonia, as an alternative fuel.
All of the major gas turbine manufacturers, including Siemens, Hitachi, GE, and Ansaldo Energia have set goals of producing new turbines, or upgrades of existing turbines, which could accommodate up to 100% hydrogen fuel. Current commercial versions can handle H2 up to 50%.
Let us now consider the properties of H2 and how these differ from those of conventional gas turbine fuels. Table 1 compares significant properties of H2 and other common gaseous fuels.
