Storing pressurised hydrogen in underground salt caverns could help to back up variable renewables in the UK’s future energy landscape. Stuart Nathan reports.
Over the next few decades, the way that electricity is generated in the UK is predicted to change considerably. Nuclear power stations will make a larger contribution to the total generating capacity, and fossil fuel stations will increasingly be built or retrofitted with equipment to capture their carbon dioxide emissions so that they can be compressed and stored, most likely in offshore repositories below the sea bed.
Meanwhile, more renewable generating capacity, based around wind farms and tidal generation and possibly wave power, will be coming on stream from sites around the UK’s coast.
This represents a problem. Nuclear power is inflexible — reactors work best when producing a stable amount of thermal energy throughout the day, which has to be fed to the boilers to raise steam. Similarly, although conventional fossil-fuelled turbines can be operated flexibly, the addition of CCS technology again means that they are best run at as near a constant rate as possible.
But renewables are, by their nature, variable; the tides predictably so, the wind notoriously not. This means that some kind of variable capacity is going to be needed to top up the Grid when renewables are falling short, whether that variation is regional or national.
One answer currently being studied by the Energy Technologies Institute (ETI) might be a national network of turbines configured to run on hydrogen, which would be generated by gasification of gas and coal and stored underground in salt caverns, mainly offshore. This, the ETI’s CCS programme manager Andrew Green told The Engineer, has would have several advantages, providing a flexible generating capacity while still making the best use of capital plant which prefers to be operated at full capacity.

The ETI operates as a public-private partnership bringing together energy industry majors to accelerate the development of low-carbon energy technologies, often by doing the groundwork to remove some of the uncertainty around them and give financiers more confidence to invest in their development. This, so the strategy goes, is key to helping innovative green technologies bridge the gap from conceptual research to a deployable commercial offering.
‘We’re developing most of the ETI’s strategy on something called the Energy Systems Modelling Environment or ESME, which is a national tool that looks at the whole energy system — generation, distribution, storage and consumption — and looks at finding the lowest-cost solution,’ Green explained. ‘What it indicates is that systems which adopt flexible generation but make the most effective use of capital equipment are extremely highly valued, because they’re the best way to complement baseload nuclear and intermittent renewables.’
‘These sorts of systems would be of a similar scale to a commercial power station, and this is part of the general roll-out of CCS
Andrew Green, ETI
The advantage of configuring turbines to burn hydrogen, rather than to operate directly on fossil fuels, is that it strips the carbon away from the fuel and captures it at source, rather than having to capture it post-combustion. Gasification — converting fossil fuels (which might already be gases) into CO2 and hydrogen — is a well-established process, and Green explained that gasifiers, like most chemical plant, are best operated at a constant baseload, whereas gas turbines, if freed from the integration that’s necessary in a CCS-equipped power station, can be operated flexibly with no efficiency penalty, allowing them to be run to fill in for low production periods for renewables.
This strategy is being formulated assuming that a CCS infrastructure is in place, Green stressed. ‘You would be looking to store the CO2 in a depleted oil or gas well, or saline aquifer, offshore,’ he said. ‘These sorts of systems would be of a similar scale to a commercial power station, and this is part of the general roll-out of CCS.’
Sites suitable for storing CO2 are no good for hydrogen, however, and this is where salt caverns come in. Large salt deposits occur in many locations in and around the UK — reserves in the Northwest have supplied a large chemicals sector for many years — and salt caverns, which can be made by dissolving away a void within the salt stratum, using techniques originally developed for salt-mining by ICI, have the right sort of volume and strength to store a significant amount of pressurised hydrogen safely, Green said.
‘One of the issues is whether you can store the hydrogen at a suitable pressure,’ he explained. ‘It will come out of the gasifier plant under pressure and you don’t want to lose energy, either in letting it down or in compressing it further.’
Of course, whenever hydrogen is mentioned, safety concerns are close behind: the gas is, after all, flammable, explosive and difficult to contaon because of the very small dimensions of hydrogen molecules. ‘We’re looking carefully at security,’ Green said, explaining that the caverns would be formed so that they are still surrounded by thick, strong deposits of crystalline salt, which can contain hydrogen safely. ‘If these facilities were onshore, they’d be in highly industrialised areas, away from anywhere residential, but they’d be more likely to be offshore.’

The ETI is working with the British Geological Survey (BGS) for this part of the project, surveying possible sites for salt caverns and establishing the potential for hydrogen storage. Another part of the project, which engineering contractor Foster Wheeler, aims to investigate the scale, configuration and cost of the gasifiers and turbines needed to provide the generation capacity which would be needed for such a system — tens of gigawatts, Green estimates, with each installation providing about a gigawatt
‘We launched this five-year project to get a better idea of how these systems might look in detail,’ Green said. ‘The costs are very important — putting in storage increases the cost, for example, so you have to balance that against the potential benefit. When we have an idea of the cost and technical issues, it’ll give us some idea of the key development issues that might be faced if you were going to use such systems, and at the very least it’ll provide us with more robust costings that we can use in our energy system modelling.’
One such development issue might be the turbines that would drive the generators, but Green pointed out technology is available. ‘There are potentially two sorts of turbine that might work,’ he said. ‘There is they type that’s currently used in gasifier-fed power stations, and there’s aero-derived turbines which are similar to jet engines.’
Another possibility for such systems is to use power generated by renewable capacity to electrolyse seawater during times of low demand but high production — such as night-time high tides and especially windy days — and use the caverns directly as energy storage. ‘That could be a minor use for the systems,’ Green said, ‘but we’re anticipating that gasifier-linked operation would be the majority application.’
Green is keen to point out that this project, projected to cost £5million, is just a first step in a long process. ‘If successful, the benefits could potentially be huge,’ he said.
The sooner that Engineers see off these CO2-phobic lunatics, the better.
What level of CO2 emissions should we worry about, Keith?
Or do you believe that no amount of CO2 emitted by man could hurt?
Currently we are emitting 43 times the planets ability to absorb; we are asymptoting toward 1.2% CO2.
Far to complicated and hazardous for me.
Why not encourage greater fully electric vehicle ownership and use the electrical power storage capacity of the vehicle batteries by means of smart grid and smart metering systems?
I have a small electric vehicle with a 16KWhr capacity battery which can easily cover 75 miles on a single 6 to 8 hrs charge at home or to 80% full in half an hour at a high rate charging point. Charging from my roof mounted PV panles is free in the day time when the sun is out or 6p/KWhr at night equivalent to over 500 mpg at current UK petrol prices.
There are 30 million petrol/diesel vehicles in this country and some 850 million in the world. Conversion of just one million existing roadworthy cars to electric power with batteries of the same capacity as mine would provide some 10GW of electrical power storage capacity.
If we wait for the trickledown of affordable second hand electric cars from the small new EV market we will wait forever so lets get started on converting our existing cars to electric power.
Stuart Saunders you say-
“What level of CO2 emissions should we worry about,”
Perhaps we shouldn’t worry about CO2 emissions at all !!
(altough levels of 5,000 ppm can cause dizziness or lack of co-ordination in some humans)
Consider these facts: (My thanks to Ashley Mote)
The largest gas in the earth’s atmosphere is Nitrogen
The largest ‘Greenhouse Gas’ in the earth’s atmosphere by far is water vapour.
CO2 is a minor component of the earth’s atmosphere, at barely one-third of one percent – 0.0375 percent to be precise.
Levels of CO2 today are amongst the lowest they have been in the known history of this planet. CO2 is absorbed naturally by water, the oceans, soil and all plant life. It is odourless, tasteless and non-toxic.
The largest and most significant source of CO2 is underwater volcanic eruptions. Just one of the larger submarine volcanoes can, when active, emit more CO2 in a few days than all human activity might generate in a year. There are numerous eruptions on the seabed every year, almost none of which are ever noticed or reported outside the scientific community.
Any impact of a higher level of CO2, such as it might be, is logarithmic, not arithmetic. In other words, the higher the figure the less the effect. Double today’s CO2 level, and no-one would notice any difference.
Ice-core research has demonstrated that any increase in average temperature levels lag any increase in
CO2 levels by some 500 to 600 years. So, even if there were a slow, long-term connection, there is no practical purpose in attempting to change CO2 levels with a view to controlling average global temperatures. The proposition is scientifically absurd.
This is the effect of 3 x CO2 increase on plants
http://www.youtube.com/watch?v=P2qVNK6zFgE&feature=player_embedded
that’s why we spray CO2 into greenhouses –
http://www.omafra.gov.on.ca/english/crops/facts/00-077.htm
– to produce better plants.
Back to the original article that started this discussion thread, the following item just goes to show that hydrogen storage in salt domes is not a totally risk free solution.
http://theadvocate.com/home/5510933-125/tremors-at-bayou-corne-salt
Regarding motorised transport, it is not just the potential for CO2 from fossil fuels impacting climate change but also the respiratory health problems arising from breathing PAHs, NOx, SOx and ultra fine particulates emitted from vehicle exhaust pipes in city centres and along transport corridors around the world. Hence my support my fully electric EVs.
I’ve often seen EV batteries offered in this way. I’ve not seen an estimate of how many charge/discharge cycles a typical EV battery will last for, but surely this could seriously reduce their life.
One item to consider is the impact of gasification and carbon capture on overall combined cycle plant efficiency. In order to be economically competitive an H2 fueled gas turbine powerplant requires considerably higher efficiency than current designs. This has been the subject of funded research in the United States, led by the Department of Energy in cooperation with Siemens and General Electric.
I’ll avoid making CO2 statements and just point out that hydrogen(methane gas) storage is already a success in the mid-US in the salt mines there. They’ve been using them as natural gas storage vessels for years, and has only had one incident where leakage led to minor disasters. This one time incident was even less a problem than some of the huge oil and gas disasters you see in ordinary pipeline transmission – so I say it is also a success inland, and not just off shore. This in the US anyway.
Not to put too fine a point on it, but what you get when you combust hydrogen in an atmosphere which is 70% nitrogen is lots of invisible clouds of airborne anhydrous nitric acid looking for metal and human flesh to dissolve.
Try touching off a bit of hydrogen with a match in a test tube using electrolysis to dissociate hydrogen and oxygen from salt water some time.
How come these sites do not get more input from refinery tekkies and chemists, I wonder?
It’s time to talk to the Germans about their plans to create carbon neutral natural gas. Sequestration of carbon dioxide is a good thing but it is WAY cheaper to utilise the existing natural gas system! CNG and LNG is much easier to work with and store for vehicles, and natural gas turbines are great for peaking the high demand times. Why go to all the lengths that hydrogen demands when the above-mentioned technology exists?
A useful counterpoint to the above technology-based discussions would be consideration of Freeman Dyson and Allan Savory’s work on natural rates of CO2 capture and storage. Professor Dyson calculates that building just one inch of soil per Century on currently available land enables absorption rates that match the CO2 emissions attributed to human activity. Much of this soil-building capability can be achieved using Mr Savory’s long-proven methods on livestock management. There are virtuous circles availae to solve these problems in an elegant fashion… In a world where energy returns on energy invesed are falling, it is doubtful that increasing the complexity of our designs is a successful strategy for future generations.