“System-level energy efficiency is the greatest barrier to development of the hydrogen economy”, Shannon Page, et al, Energy Policy, 37 (2009), pp 3325-3335
“In the wonderful future, all our cars will run on hydrogen” – as said by approximately every futurist for about thirty years. So where is this hydrogen economy then?
Hydrogen is an energy carrier, like electricity. You have to put energy in to make it, and then you get energy out at the other end, from fuel cells that make electricity to turn motors. Fuel cells are clean, therefore hydrogen is clean, right?
Wrong, says more of the Canterbury researchers. This all depends upon the overall system efficiency, on the whole chain from where the energy comes from and how many steps there are along the way from the original source to the final, useful energy.
For a car right now, we dig up some oil, pump that to a refinery, convert it to petrol, ship and truck it to the petrol station, burn it in combustion engine. The useful energy coming out of this chain, motion in your car, is about 25% of the energy in the original oil. That’s not great, but hey, it worked for the entire Twentieth Century, so don’t knock it.
For a different energy chain, say battery powered cars with the eleccy coming from wind turbines, the energy chain goes: wind turbine -> grid transmission-> car battery -> electric motor. Overall efficiency? 70% Hell yeah.
For a hydrogen version, the chain goes: wind turbine -> central electrolysis -> hydrogen pipeline -> compression -> fuel cell -> electric motor. There’s losses at each stage, so overall efficiency? 25%
So if you want to use hydrogen, then you’ll need three times as many wind turbines to power your car, at three times the price. That’s a non-starter.
Ref to Energy Policy‘s September 2009 NZ special edition.