Hydrogen is often proposed as a low or zero carbon alternative energy source to fossil fuels. However, there are certain situations where hydrogen may be a better alternative, and others where electricity from renewable energy makes the most sense both in terms of lowering carbon emissions and ease of use. Hydrogen is not the way forward for all energy sectors. Where hydrogen is a viable option, its carbon footprint depends on how it is made, if made with fossil fuels, it losses all value environmentally, so the type of hydrogen has to be considered.
The production of hydrogen defines its environmental impact. Hydrogen is produced using various methods and these are indicated by a colour.
- Grey hydrogen is produced using fossil fuels and so is completely unsustainable, you may as well use the fossil fuels directly.
- Green hydrogen is produced using zero carbon electricity (such as wind or solar) to split water into hydrogen.
- Blue hydrogen is produced in the same way as grey hydrogen, but some of the CO2 produced is then captured and stored.
Blue hydrogen is an expensive alternative and rarely all carbon emitted is stored. If one were to be cynical, it may be noted that oil companies would push for this method as their existing oil fields could be used and they would see financial gain from this, another use for their potentially stranded assets.
The proposed benefit of blue versus green is that it is lower cost. However, there is debate to whether it is actually zero carbon. Research done at Cornell and Stanford found that the emissions from blue hydrogen are high, with total carbon dioxide equivalent emissions only 9-12% less than grey hydrogen (Howarth & Jacobson, 2021). If hydrogen is produced in unsustainable ways, it renders all its uses unsustainable, so hydrogen will only ever be green if it is in fact green hydrogen.
Hydrogen may be beneficial as a domestic fuel. Currently, heating houses is responsible for up to a third of greenhouse gas emissions in the UK. Much of this is powered by natural gas and the main question is, could this be replaced by hydrogen gas to lower these emissions. Supposedly, the customer would not see much of a change in the infrastructure needed in their house; boilers could be used in the same way as they are with natural gas. The greater challenge lies in creating a hydrogen network like that of the existing natural gas grid. This could take years or decades and would cost vast sums. At the moment, there is no clear proposal or plan of how this would be paid for, presumably it would involve the government subsidising the conversions. For residential and office buildings, new equipment and installations will be needed as hydrogen has a different energy density and flame characteristics, which will require money and have an environmental impact in itself.
Using hydrogen as vehicle fuel again would not see the consumer having to change lifestyle much at all, cars could be fuelled in the same way as with petrol or diesel, just with this different fuel. But again, infrastructure would be needed to accommodate having hydrogen gas stations. With electric cars, all that was needed was to link charging stations with the current electrical grid, possibly part of the reason electric cars are greatly outselling hydrogen cars. There is the advantage of hydrogen being much more abundant that petrol or diesel. It also has the potential to be 2.7 times more efficient than a gasoline internal combustion engine in terms of energy content of fuel (Ahluwalia, et al., 2004). It also takes less time to fuel up a hydrogen vehicle than some electric vehicles, which can take a few hours. However, it is more expensive to fuel a hydrogen car than an electric car. There are currently only three hydrogen fuel cell cars on the market in the UK and a limited number of places they can be filled up. There is also a much greater range of electric cars for consumers to choose from, from convertible sports cars to SUVs. Hydrogen fuel cells are only 50% efficient, yet BEVs are 100%. So, it is clear to see why currently, EVs are the alternative to petrol or diesel cars of choice currently.
For larger vehicles, such as lorries, it may make sense to use hydrogen fuel cells over electrification. Hydrogen offers more flexibility due to its shorter refuelling times and a hydrogen powered lorry would have a similar range to a diesel lorry. This means the systems logistics for lorries would not have to change much, operating patterns would remain similar. There would still need to be a substantial hydrogen grid to enable this to occur, however. Hydrogen also remains more expensive than electricity. Electrification would need some changes to logistics but has the advantage of this lower cost, and possible lower environmental impact depending on the type of hydrogen it is compared to. Both would require new infrastructure but electrification less so than hydrogen.
One of the main problems associated with hydrogen is how to store it. Its density at ambient temperatures sees a lower rate of energy per volume, so more advanced storage methods are needed to obtain higher energy yields. It can be stored as either a gas or a liquid but storage as a gas requires higher pressure tanks and storage as a liquid requires cryogenics. At the moment, it requires large volume storage systems, which poses challenges for transportation (Felderhoff, et al., 2007). Again, this hampers the spread of hydrogen usage as transportation can be tricky and requires a more complex grid system than that of the electric grid. If there was serious investment and time put into this, hydrogen may be a viable alternative to natural gas as well, although it remains much more expensive, and this may put many off.
In conclusion, hydrogen has potential to be a more sustainable solution to fossil fuels. However, it needs to be green hydrogen. Blue hydrogen currently has little benefit for greenhouse gas emissions. It is also too expensive, so it is closer to greenwashing than showing real emissions reduction. A huge amount of investment and infrastructure would also need to be seen, and it is unclear whether this could come from government or private companies or a mixture of the two. If this, together with better storage solutions, is achieved then hydrogen could quite easily become a main energy source, with a much lower carbon footprint than fossil fuels. However, other options are likely to be more beneficial for most applications.
Ahluwalia, R. K., Wang, X., Rousseau, A. & Kumar, R., 2004. Fuel economy of hydrogen fuel cell vehicles. Journal of Power Sources, 130(1-2), pp. 192-201.
Felderhoff, M., Weidenthaler, C., Helmolt, R. v. & Eberle, U., 2007. Hydrogen storage: the remaining scientific and technological challenges. The Royal Society of Chemistry, Volume 9, pp. 2643-2653.
Gielen, D., Taibi, E. & Miranda, R., 2019. Hydrogen: A Renewable Energy Perspective, s.l.: IRENA.
Howarth, R. W. & Jacobson, M. Z., 2021. How green is blue hydrogen?. Energy Science & Engineering, 9(10), pp. 1676-1687.