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.
- Energy density refers to the energy contained in a unit of
- Volumetric energy density (VE) refers to the amount of energy per unit of volume and is expressed in MJ/m3.
- Gravimetric energy density or specific energy (SE) refers to the amount of energy per unit mass and is expressed in MJ/kg.