Examining the history and fate of many technologies, and reading the analyses of others, I have come to understand some general rules, one of which is that some technologies look great on paper, but are terrible in reality. The reason they look so promising at first is because they have some key advantage that just seems to make sense. Using hydrogen as an energy storage medium, I think, is one of those technologies (at least for some applications). The idea of hydrogen is very appealing – it can be stored as a gas, transported in pipelines, and burned for energy, combining with oxygen to make water as the only combustion product. No CO2 or other greenhouse gas is produced. That sounds really good. But the more you crunch the numbers, the less good hydrogen looks (at least with current technology). Researchers recently did just that, looking at the utility of hydrogen for heating homes. Their assessment was soundly negative.

The idea is that hydrogen would be produced by electrolyzing water, using excess energy from intermittent sources like solar and wind. That hydrogen can be stored, and then supplied to homes when needed for heating. This would replace fossil fuels for heating, which would have multiple advantages (especially if you happen to live in Europe during a conflict that reduces your fossil fuel supply). But when you take a closer look, the shine fades. Jan Rosenow, the report’s author and Europe Director at the energy think-tank the Regulatory Assistance Project, had this to say:

“However, all of the independent research on this topic comes to the same conclusion: heating with hydrogen is a lot less efficient and more expensive than alternatives such as heat pumps, district heating and solar thermal,”

The simple reason for this is that hydrogen is just expensive. Using hydrogen for heating would cost six times using a heat pump, which is an existing proven technology. Any money spent doing further research and development into a hydrogen heating infrastructure would be better spent simply subsidizing heat pumps. These systems can be a bit expensive to install, but they are cheap to run, very energy efficient, and do not directly burn fossil fuels.

Further still, the “advantage” of hydrogen assumes the use of green hydrogen. But 95% of the hydrogen produced in the world is gray hydrogen – it is made from methane, producing more CO2 than just burning the methane directly. In other words, it’s a con, or a bait and switch. Even so-called “blue” hydrogen just captures some of the CO2 produced in the process, but is still worse than just burning methane. We have not been able to scale up to industrial level significant green hydrogen, made from hydrolyzing water. That could be a disruptive technology, if someone figures out how to make large quantities of energy-efficient green hydrogen. Until then, hydrogen as a “green” fuel is a deception.

To the extent that we can make green hydrogen, that resource would be wasted burning it for heat in homes. There are industries that will be difficult to decarbonize, like steel making and commercial jets. Hydrogen could be very useful for those industries, while we use proven technology simply to heat our homes.

Hydrogen is also simply not the best energy storage medium. It’s not that energy dense, we still haven’t figured out a way to safely store it in a medium that can rapidly release it (for use in a hydrogen fuel cell car, for example) and so we are left storing it is pressurized tanks which have obvious safety issues. Also, the “round trip” energy efficiency of hydrogen is less than that of current battery technology. “Round trip” efficiency refers to how much energy you get back out of the storage medium. So if 100 units of energy are converted into hydrogen, how many units do you get back out when you burn it for energy? The laws of thermodynamics indicate that it has to be less than 100, but how much? Estimates are that the round trip energy efficiency of hydrogen is 18-46%. Meanwhile the round trip efficiency of storing energy in a lithium ion battery is 70-80%. That’s 2-4 times as energy efficient – which I think is why hydrogen fuel cell cars will never beat out battery electric vehicles. For grid storage we have several options better than hydrogen. Pumped hydro is likely the best, with efficiencies of 70-85%.

One of my main principles when it comes to skeptically analyzing the potential of technology is this – never bet against the known laws of physics. Thermodynamics is just not on the side of hydrogen.

Having said that, I also think that hydrogen is an extremely useful high-energy molecule. It has a lot of industrial uses. Our focus should be on trying to replace all that gray hydrogen with truly green hydrogen. But we should not use hydrogen in industries for which there are far better options. We need to use it where it can do the most good, displacing technology that will otherwise be difficult to convert to all electric or to decarbonize. It’s also great fuel for getting rockets into orbit, and will likely be a mainstay of the space industry indefinitely into the future. Hydrogen is the lightest element in the universe, and when it comes to the rocket equation, the weight of the fuel and propellant is key.

But if you want to heat your home in a green way, get a heat pump.