Turn-Around Efficiency of Hydrogen (H2) Powered Electric Power Plant
The turn-around efficiency of a hydrogen (H2) powered electric power plant is the overall efficiency of extracting hydrogen (h2) molecules from water, store it, and use that hydrogen to generate electricity. The energy conversion process is similar to a pumped storage hydro-electric power plant where its turn-around efficiency is around 70% to 80% - the process has lost 20% - 30% (electric) energy. The turn around efficiency of pumped storage hydro, however, is still high, making it a financially viable project in some countries around the world.
The turn around efficiency of hydrogen powered plant can be computed by combining the efficiency of the whole energy conversion process;
Extracting Hydrogen from Water
The efficiency of some best methods of extracting hydrogen (H2) from Water (H20) is as follow;
• Thermo chemical production: 35% - 49% LHV (ref: en.wikipedia.org/wiki/Hydrogen_economy)
• Electrolysis: (ref: The Bellona Foundation report)
- Norsk Hydro Electrolysers (high): 80% HHV
- PEM Electrolyser (Theoritical): 94% HHV
Compression Efficiency
Once the hydrogen has been extracted from water, it is necessary to store in an efficient manner - Hydrogen has to be compressed and pressurized in a tank. This process takes around 10% more energy (or 90% efficiency).
(ref: Efficiency of Hydrogen Fuel Cell, Diesel-SOFC-Hybrid and Battery Electric Vehicles, Ulf Bossel, European Fuel Cell Forum, October 20, 2003)
Efficiency of converting hydrogen to electricity
Hydrogen (from the tank) can be converted to electricity either through a fuel cell or a through a conventional power plant. The theoretical efficiency of a fuel cell is around 50% while the approximate efficiency of a conventional power plant, assuming that the technology used is a combined cycle power plant, is 60%.
Refs: en.wikipedia.org/wiki/Combined_cycle
Efficiency of Hydrogen Fuel Cell, Diesel-SOFC-Hybrid and Battery Electric Vehicles, Ulf Bossel, European Fuel Cell Forum, October 20, 2003
Summary
Considering the efficiency of each of the stage of the process, the best case turn-around efficiency of hydrogen powered electric plant is only around 43.2% (0.8*0.9*0.6). This means that 56.8% of energy is lost in the process making it less financially viable (excluding the cost factor of constructing such power plants). Note that we don’t use the efficiency of the PEM Electrolyser in the computation since the 94% efficiency is still theoretical and the said technology have yet achieved an efficiency higher than the best alkaline electrolysers (Ref: The Bellona Foundation report)
Filed in: Power Plant Technologies - 
