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Hydrogen storage to maximise renewable energy recovery


In advance of the RenewableUK Green Hydrogen Conference on 3 May, Sarah Kimpton, Vice President, Energy Transition & Innovation Development, DNV, discusses the role of hydrogen in our energy mix, and the need for long-term geological storage. You can read DNV's Hydrogen Forecast to 2050 here.


Renewable energy is very precious, and we need to recover as much of it as possible as we strive to meet our 2050 net zero ambitions. However, there is often a mismatch between when renewable electricity is generated and consumer demand. There are times when there is too much wind or solar energy and there are also times when there is too little. For example, one of the most challenging scenarios occurs during the winter when high-pressure settles over the UK and there is little solar energy and almost no wind – the ambient temperature drops below zero and the demand for heat increases substantially. It does not matter whether domestic heat is provided by heat pumps or hydrogen, we need more renewable power during these periods of low generation.


So, what are we supposed to do? We could go back to generating electricity from fossil fuels, but for that to be considered low carbon, we would need carbon capture and storage which is not a very flexible technology to cope with repeated stops and starts. Alternatively, we could use stored renewable energy and then use batteries to cover the gap if the period of low energy generation is short. But if the period is much longer, for example a couple of weeks or more (which does happen), then we need to look for another low-carbon solution. Many people suggest we should then resort to importing energy but if the area of high-pressure is sitting over the UK, it is highly likely to be sitting over Northern Europe too which makes imports unlikely, even if we had the infrastructure.


Although battery technologies have, without doubt, advanced considerably, long-term energy storage options involve molecules rather than electrons. If we also want the molecules to be low carbon, then hydrogen is the answer. Hydrogen can be stored above ground in high-pressure tanks or converted to liquid hydrogen, ammonia, or liquid organic hydrogen carriers – all these options are viable and can cover slightly longer periods of low power generation than batteries, but we still need storage at a much bigger scale. Additionally, ammonia or liquid organic hydrogen carriers will need energy input to release the hydrogen back into the system. The only solution is geological storage of low-carbon hydrogen and this really needs to be in the UK. This gives us the scale that we need, is cost effective and enables us to maintain a low-carbon energy system as well.


There are several geological storage options of varying technical readiness. Salt caverns have been used to store hydrogen by the oil and gas industry for many years, so we know that this works. There are also salt caverns that currently store natural gas, so these could be converted to hydrogen. There are other options being investigated too, such as repurposing spent hydrocarbon fields, but these will need to be checked out on a case-by-case basis to ensure that the hydrogen does not disappear and can be retrieved. As with everything, even geological storage has a downside. The problem is that it takes a long time to create. A new salt cavern can take between five and ten years to develop, a salt cavern can take between three and five years to repurpose and it can take a similar period to convert a spent hydrocarbon field. It is now 2023 and there are only 27 years left before the world needs to reach net zero in 2050. If it takes up to ten years to set up the geological storage that we need to achieve our net zero targets, then we really need to get going right now. But we need policy decisions and business models for large scale storage to kick-start investors and developers into action. Large scale and long-term hydrogen storage is the way to maximize the recovery of renewable energy and it is needed whether we electrify domestic heating or take the hydrogen route or a combination of the two which is most likely. According to the recent Long Duration Energy Storage report for the Department for Energy Security and Net Zero (formerly BEIS), longer duration storage solutions reduce net zero system costs by £13-24 billion a year, and that the largest savings arise from a combination of hydrogen storage and hydrogen combined-cycle gas-turbines (CCGT).


Instead of making curtailment payments to renewable generators when we do not have the electricity infrastructure or consumer demand to use that power, we need to convert the power to hydrogen by electrolysis of water and then pipe the hydrogen to geological storage sites until required. This hydrogen can then be used directly or converted back to electricity using hydrogen CCGTs. There are those who look at this from a purely academic point of view and claim that this is thermodynamically inefficient. It is but they are forgetting that real people, real industry, and the energy market is much more complex than a thermodynamic cycle, so we must be pragmatic.


Long-term geological storage of hydrogen is the only way to keep security of supply, costs, and decarbonization in balance for the future – the energy trilemma is as important as ever and we need to think about the whole system and not just one part of it. As I said at the beginning, renewable energy is precious and we need hydrogen storage to maximise its recovery – there is no time to waste if we are to keep the energy trilemma in balance.


Learn more about the role of hydrogen in the energy mix towards 2050 by downloading our complimentary research report, Hydrogen Forecast to 2050.

 

Sarah is the Vice President, Energy Transition & Innovation Development for DNV’s Energy Systems business in the UK & Ireland. Sarah has over 30 years’ experience working as a consultant to the natural gas industry, focusing on the impacts of gas quality on network operation, customers, and measurement systems. Together with colleagues at DNV, Sarah works closely with the gas networks to demonstrate whether it is safe and possible to replace natural gas with low-carbon hydrogen. Sarah is a Chemist and holds a BSc and PhD from University College London.

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