David Cebon: "A green hydrogen bus consumes three times as much electricity as an electric bus"

BarcelonaGreen hydrogen is often presented as the key to energy transformation, but producing it still requires a lot of energy. This is the warning scientists such as David Cebon, professor of mechanical engineering at the University of Cambridge and member of the Hydrogen Science Coalition, created by academics and researchers to nurture the debate on the future of hydrogen. Cebon was in Barcelona to participate in the Global Assembly on Green Hydrogen, inaugurated by the Minister of Ecological Transition, Teresa Ribera, and there he wanted to make it clear that some of the uses we are now giving to green hydrogen are highly inefficient.

Is green hydrogen the solution to the climate crisis?

— I don't think it is the solution. As a fuel, for example, it is not efficient at all, and for heating buildings it is also a bad solution. It takes six times more energy to heat a building with green hydrogen than with an electric pump. This means that if it takes one wind turbine to heat a building, it would take six turbines to heat the same building with green hydrogen. Overall, green hydrogen generation requires so much electricity that you are choosing a solution that will never be achieved, and while doing so you are slowing down the overall decarbonisation process. Green hydrogen is a solution to replace grey hydrogen.

What is grey hydrogen?

— Right now the hydrogen which is produced, which is mainly for chemical plants and fertiliser production, generates the equivalent emissions of the entire aviation sector (2% of global emissions) because it is made with electricity from polluting sources. Replacing it with green hydrogen, i.e., generated with clean energy, is not easy, but it is important to do so. This is the first thing that should be done with green hydrogen.

What about green hydrogen buses that cities like Barcelona have bought?

— Green hydrogen buses consume three times more electricity than an electric bus would. Electrifying vehicles directly is much more effective. For example, if all the trucks and buses in the UK were hydrogen-powered, it would double the total amount of electricity we need overall on average. And to do this would be delaying other decarbonisation projects. It's much better to use electricity directly to run vehicles and make sure it's renewable.

And what about aviation and shipping?

— These are the two most difficult sectors to decarbonise and each account for 2% of global CO2 emissions. This means that they have very low priority in the decarbonisation process: if you transform all the rest and do nothing with aviation, you will already be reducing 98% of emissions. The first thing to transform is heating and land transport. Still, if you want to use green hydrogen, maybe it is a solution for aircraft, but not as a direct fuel because it needs too much space inside the aircraft. For aviation, there are two options: biofuels, even though there are not enough of them at the moment, and e-fuel or synthetic fuels derived from hydrogen. This would be very expensive, but, if you need a much more expensive form of transport than the rest, what would you choose? It would not be cars and buses, but rather aeroplanes.

Are boats easier to convert?

— Ships for coastal routes can be electrified, the problem is long distance routes. In my opinion, the solution for these is biofuel. Because another problem with hydrogen for shipping is that most shipping companies want to use it to generate ammonia as fuel. And this has two problems: the first one is that you need much more energy and therefore it is very inefficient, but the second problem is that ammonia is poisonous. Now we see ships sinking, spilling oil and destroying the environment, but just imagine if they spilt ammonia. It can poison very large areas of the oceans and would be an ecological catastrophe.

In short, what could green hydrogen be used for?

— For the uses that are now given to grey hydrogen, such as chemical and fertiliser production, and perhaps for heavy industry, such as metallurgy, which requires very high temperatures which could be generated with green hydrogen.

What is the recipe for the energy transition?

— It boils down to two things: the first is energy efficiency, i.e., using as little energy as possible for all uses. And the second is to make all this energy from renewable sources.