Todays renewables, wind and solar power, have a fluctuating nature, making the grid less stable. However, with the increasing share of intermittent sources of renewable power, novel options have to be created to stabilize the power grid. One of these options is energy storage via the conversion of excess power to hydrogen during periods of high generation from wind and/or solar. In periods of power shortages hydrogen is converted back to power. In this work, a number of high efficiency thermodynamic cycles, based upon the Graz cycle and the Toshiba Reheat Rankine cycle, both a coupled closed Brayton cycle with a Rankine cycle, are investigated and improvements are proposed leading to LHV efficiencies of 75%. Also the addition of fuel cells to the cycles is studied leading to potential LHV efficiencies of 85%. Application of pressurized H2/O2 usage leads to several improvements over conventional thermodynamic cycles and conventional fuel cells.@en