“Escapey, explodey expanded polystyrene”. This is how technology advisor Michael Liebreich recently described hydrogen.

In some renewable energy circles, green hydrogen is all the rage. It can be made from ordinary water and electricity. It can be burnt like fossil gas but without the greenhouse gas emissions. And, it can be used in fuel cells to make electricity again. What is there not to like? Quite a lot, it turns out.

The usual argument against using green hydrogen for energy is the abysmally poor efficiency of turning electricity into hydrogen and then turning it back into useful energy. Presently, a hydrogen fuel cell vehicle gets back only about 30% of the electrical energy used to make the green hydrogen in powering the vehicle. A typical battery electric vehicle gets back around 80% of the electrical energy used to charge its batteries.

The Parliamentary Commissioner for the Environment, in a December letter to Megan Woods, criticised proposals to use wind power to make green hydrogen at Taranaki, store it underground until needed then burn it to make electricity again, due to the lifecycle efficiency of only 20%. By comparison, pumped hydro storage has a lifecycle efficiency of about 75%. There are better ways to store energy than converting electricity to green hydrogen.

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