What Use Is Hydrogen?
Here's an informative interview with Professor David Cebon of Cambridge University Engineering Dept on the Fully Charged Youtube channel: How Clean is Hydrogen, Actually? I've summarised the most useful bits below.
10:00: If you build a new wind turbine for the purpose of making hydrogen, it's not being used for de-carbonising the electricity grid.
11:30: 2% of world CO₂ emissions come from making hydrogen from methane and steam - that hydrogen is mainly used to make fertliser; the CO₂ is released into the atmosphere.
13:30: If you're going to deliver the same amount of energy from hydrogen made from methane as you would get from raw methane, you require 40% more methane.
15:00: Green hydrogen (made from electricity) is a smokescreen for blue hydrogen (made from methane with carbon-capture) - because green hydrogen requires so much energy.
16:00: Converting from electricity (work) to hydrogen (heat) is 75% efficient; the 2nd law of thermodynamics means that to convert back from hydrogen (heat) to electricity (eg in a hydrogen fuel-cell car) can be at most 50% efficient. Inefficiencies of transportation and compression mean the overall efficiency of using green hydrogen as a fuel is about 30%.
21:00: Therefore, if we use green hydrogen as a fuel, we will require 3 times as many wind turbines as if we used their electricity directly.
23:00: Steel gets hydrogen-embrittlement as a result of hydrogen getting into the cracks; most cast-iron and steel pipes will need to be replaced.
24:00: Because the flame temperature is much higher, burning hydrogen produces much higher NOx emissions than burning methane, leading to problems with air quality in the home.
26:30: Compare a heat pump with hydrogen: if you heat a home using a heat pump powered by renewable electricity, you end up with 3 times as much heat as the electrical energy you started with; if you heat a home using a condensing boiler burning hydrogen made using renewable electricity, you end up with half as much heat as the electrical energy you started with.
28:00: If you want to heat the country's homes using green hydrogen, that would require 6 times as many wind turbines than if you use the electricity in a heat pump.
28:15: To heat all our homes with green hydrogen would require a 10-times increase in electricity generated, and all provided by renewables.
31:45: If you drive a truck on grey hydrogen (made from methane with no carbon-capture) it's far worse in carbon-emissions terms than driving it on diesel.
37:20: The blue-hydrogen route (made from methane with carbon-capture) is not at all clean/green, due to fugitive emissions of methane from upstream processes.
39:35: The carbon capture and storage has got problems: getting high-percentage capture rates is not straightforward.
Here the argument against blue hydrogen wasn't 100% persuasive: based on the lack of any incentive to capture carbon and the practical difficulties of doing so. Just maybe, if incentives were imposed, technology might be invented that captures enough CO₂ cost-effectively to make blue hydrogen a more viable option.
40:30: Plants built to the government's current clean-hydrogen standards will not be clean enough to operate when standards need to be tightened in future.
41:15: We should only use green hydrogen to de-carbonise sectors where it's used as a chemical: for ammonia and where fossil carbon is used today (eg steel-making).
41:30: We shouldn't under any circumstances delay deployment of electrification by talking about hydrogen for heating or for transport.
43:00: 6% is the maximum fraction of hydrogen you can blend into the gas system; this leads to a less powerful fuel and therefore only a 6% reduction in carbon emissions.
44:00: Shipping hydrogen is terrible: it's hard to compress and hard to contain - that's why all hydrogen today is made at the point of use.
46:45: There are about 20,000 hydrogen-fuel-cell vehicles in the world; there are about 20 million battery-electric cars in the world.
51:45: A green-hydrogen-powered truck requires 3 times as much renewable electricity as one powered by batteries.
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