It has often been argued that hydrogen makes a poor electricity storage medium because of the round trip inefficiencies associated with the kinetics of electrolysis and fuel cells. Allow me to offer a different perspective.
An energy source contains a reservoir of energy. An energy currency taps that source to deliver energy to a load or service.
Examples of energy sources include:
1)nuclear fusion (solar radiation)
2)nuclear fission
3)natural gas reservoir
Examples of energy currencies include:
1)electricity
2)hydrogen
3)natural gas in pipeline
To address the climate problem, Electricity and Hydrogen are the two energy currencies that we need to build our systems around. Electricity is distributed to its loads/services on a JIT (Just in Time) grid. Hydrogen is distributed to its loads/services on a grid with intrinsic storage. Electrolysers are an electricity load which creates the H2 currency. Fuel cells are a H2 load which creates the electricity currency.
As currencies, both electricity and H2 need to be created from an energy source. From a climate perspective both currency grids have a carbon footprint. When deciding how best to deploy a low carbon source the carbon footprint of both grids should be counted together. Eg. Renewable electricity should first be used to offset fossil electricity. Surplus (curtailed) electricity should be used to create H2 to offset the H2 carbon footprint.
Fossil fuels can be viewed as both an energy source and a currency because the time between their creation and their extraction, distribution and use is measured in eons. BEVs and heat pumps are examples of electricity services/loads which offset carbon footprint from a fossil currency. FCEVs, green steel and syn fuels are H2 loads which do the same.
When making investment decisions about low carbon services we should not be arguing about round trip efficiencies of individual tech, but rather optimizing carbon footprint of the whole electricity + H2 ecosystem.