The future of hydrogen fuel

Heaters and cookers may one day burn climate-friendly hydrogen instead of natural gas.

A fuel cell
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When I was very young, our gas stove ran on town gas. I didn’t know it at the time but it was a mixture of hydrogen and carbon monoxide produced from coal.

One day a serviceman came round to change the nozzles on our stove and gas heater, and very quickly our house, and eventually the city, were converted to natural gas (methane). It was a leap into modernity.

Not only did it eliminate pollutants emitted during gasification, it promised a seemingly unlimited supply of clean burning methane from offshore gas fields. But that was in an era where “clean” meant “free of the toxic chemicals and particulates released by coal gasification”. Today, clean also means free of carbon dioxide.

As the global community works to decarbonise its electricity supply, one of the biggest remaining sources of carbon dioxide emissions will be from burning methane for heating and cooking. In a back-to-the-future step, many futurists are contemplating a variation of town gas – pure hydrogen.

Today, most hydrogen is produced from fossils fuels, emitting large quantities of carbon dioxide as a by-product, so that’s no help. But there’s increasing interest in producing it from pure water. In a well-known process called electrolysis, excess electricity from wind or solar farms is passed through water to crack it into its atomic constituents – hydrogen and oxygen.

When the hydrogen is used for stoves, or space heating, the only combustion product is water vapour! So what’s standing in the way of this utopian fuel? Problem one is that producing hydrogen from electricity is only 70% efficient, so you need a very cheap electricity supply. It could be coming.

As our electricity is increasingly sourced from wind and solar, the amount available will often exceed the electrical load. Owners of the generators will seek an economically worthwhile purpose for this excess, such as charging batteries, desalinating water, or making hydrogen.

Instead of burning the hydrogen, an alternative use would be to use it to store energy, like in a battery, then regenerate electricity in a turbine generator or a fuel cell.

Problem two is that the current large-scale electrolysis units are so expensive that the cost of producing hydrogen is several times more than natural gas. But one thing we know for sure is that as manufacturing volumes increase, costs come down. We’ve seen it already in related industries. Wind turbine prices have halved in the past five years and solar prices have dropped even faster. Similar cost reductions are likely for electrolysis units.

Problem three is that steel pipes – a major part of the current gas delivery infrastructure – aren’t suited to transporting hydrogen. They become brittle because the hydrogen molecules work their way into the spaces between the iron atoms and eventually cause cracks to form.

Fortunately, modern piping used for gas distribution is mostly made from polypropylene and does not suffer from this problem. Hydrogen can be mixed at up to 10% with the methane in the existing gas distribution network without any risk of corrosion nor need to change the nozzles on stoves or space heaters. Above 10% hydrogen concentration it’s easier to commit and convert all gas appliances to run on pure hydrogen. The city of Leeds in the UK has a plan to do this in the late 2020s.

Instead of burning the hydrogen, an alternative use would be to use it to store energy, like in a battery, then regenerate electricity in a turbine generator or a fuel cell. But it makes for a very inefficient battery.

The round-trip efficiency – electricity to storage medium and back to electricity – is about 35%, much worse than the 90% efficiency of a lithium ion battery. So this is a less attractive use for the hydrogen than using it to replace natural gas in our cities for space heating and cooking.

If we can successfully make the transition to hydrogen for heating and cooking we will have a winning fuel that we can keep using literally forever.

The main impediment today is cost. I used to be sceptical that hydrogen use would become widespread, but given the rapid rate of reduction in the price of renewable electricity, and a reasonable expectation that the price of electrolysis will continue to fall, the economics might indeed work out.

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