Hydrogen is an energy vector. Like electricity it is a man-made form of energy that can be transported and converted into other forms of energy. However, unlike electricity, hydrogen’s energy can be stored on a large scale at relatively low cost. On the Orkney island of Eday, a 0.5MW electrolysis plant exports surplus wind power as hydrogen to Kirkwall on Orkney’s mainland where it powers ferries berthed overnight.
However, this is an inefficient process. Typical efficiencies for electrolysis and fuel cells are respectively 68% and 52%. Compressing hydrogen for storage, typically at 350bar, requires 6% of its chemical energy. So the overall cycle efficiency is 33%. Hence hydrogen traction requires 3kW of electricity to deliver 1kW of power to the wheel. An electric train has no on-board energy conversion so only needs 1.2kW.
This low overall cycle efficiency potentially undermines the green credentials of hydrogen trains as they require 2½ times the electrical energy of a comparable electric train, especially if hydrogen is delivered by the much cheaper CO2-producing reforming process. However, if otherwise surplus overnight wind-turbine generating capacity is used to produce and store hydrogen, this low efficiency is not an issue. Used in this way, hydrogen production also addresses intermittency issues associated with electrical generation from renewables.
Isn’t it cleaner and more efficient just to use the methane as a fuel, rather than heat it to produce hydrogen, leaving CO2 and CO as waste products?
Nameless: Possibly. But if hydrogen is produced, the CO2 produced at the hydrogen factory could (in theory) be captured, if any of the schemes for doing so ever turn out to work properly. I know this is unlikely, but a lot of current climate-change-avoiding plans already rely on this aspiration.
As for the CO, and other potentially harmful products, there is much more chance of preventing them from poisoning people (by dispersion, dilution etc) if they are produced at a central site rather than in thousands or millions of vehicles (which have to be near where people are breathing).
This is just another version of “Bionic Duckweed” being used to kick the can down the road & “avoid” electrification …..
All…an option for producing hydrogen is to use energy from renewables that would otherwise got to waste. In these circumstances, the electricity is effectively free. I’m not commenting on whether manufacturing hydrogen is the most efficient way of storing renewable energy, but it is a comparatively cheap method.
Efficient storage of electricity from renewable electricity generation is one of the big issues still to be resolved if we are to have a carbon free future. I’m aware of pumped storage, hydrogen, and running trains up hills to store potential energy. There are probably more.