Spare capacity: The gas network has plenty of readymade storage space
Could the gas grid be used as a ‘battery’ for storing unpredictable supplies of renewable energy? That is the intriguing question being asked in some quarters as engineers try to make progress with an encouraging technology that is gaining interest on a worldwide stage.
Power-to-gas is the means of converting electricity from renewable sources into hydrogen, which can then be injected into the gas grid. The benefits are clear: the technology could provide a means of managing better periods of excessive supply on the power network. Surplus wind energy, for instance, could be converted into hydrogen, rather than being ‘curtailed’ as it is at present when transmission and operational constraints dictate. This hydrogen could then be stored or sold to the gas network when importers are paying a premium or when demand suddenly rises. That would improve fuel security and level out demand for electricity networks.
Such attributes mean that power-to-gas is starting to take centre stage. Earlier this year a pilot plant was opened in Frankfurt, in Germany, as part of a project to take the technology towards commercialisation. And the UK government has funded the GridGas scheme to assess the range of potential applications.
It is a British firm that has emerged as a key player in power-
to-gas systems. Sheffield-based ITM Power has developed an advanced rapid-response electrolyser that is positioned at the heart of the conversion process. One of the main selling points of ITM’s proton exchange membrane electrolyser is the speed at which it responds to changes in electrical load – less than one second. It also uses water as an operating medium, as opposed to the potassium hydroxide solution commonly used by alkaline electrolysers, and so is more environmentally friendly.
Graham Cooley, ITM’s chief executive, says the performance of the electrolyser means that power-to-gas is a technology whose time has come. “We are seeing real market pull,” he says. “We have power utilities from all over the world contacting us about power-
to-gas storage.”
Cooley has been interested in energy storage for many years. Back in the 1990s he worked for a company called National Power, which developed a regenerative flow cell system called Regenesys that had been proven at pilot level with a 100MWh plant built at Little Barford in Bedfordshire. Interest in that solution waned, he says, because there wasn’t a clear business need for it. Today, there is a killer application for effective energy storage – renewable power.
At present, the UK runs at around 40% baseload, provided mainly by nuclear, coal and gas-fired power stations. These baseload providers are kept running for long periods, as it takes a while to re-energise a power station once it has been switched off. Typically, that process can take anywhere between six hours and two days.
So when there is excess supply from renewables, network operators are unwilling to turn off baseload sources, as the unpredictable nature of wind energy means it cannot be factored-in for a guaranteed period. Instead, that surplus wind energy is effectively refused, even though the owners of the turbines still get paid for what they have produced.
“National Grid spent £700 million in 2010-11 on grid balancing services,” says Cooley. “Last year it spent £1.1 billion, and estimates suggest that it could spend anywhere between £2 billion and
£6 billion in the future.”
One solution to this would be the introduction to the network of more demand-side load management capability. And that’s where ITM’s electrolyser comes in. It can be quickly switched on when balancing against excess renewable power, producing a product that can be easily stored and distributed, being pumped into the gas grid.
“Our technology is ideal for grid balancing and connecting directly to renewable power,” says Cooley. “Conventional alkaline electrolysers have to be turned on and run up very slowly. Ours offers a truly rapid response.
“The other advantage is the high-pressure nature of the ITM electrolyser. It can make hydrogen at up to 80bar, which is slightly higher than the high-pressure gas grid all over Europe. So we inject hydrogen directly into the gas grid without the need for a buffer store or any compression. It’s a direct transducer between balancing renewable power and making renewable gas for the gas network.”
Because of these attributes ITM was chosen by German utility Thuga to supply a 360kW power-to-gas energy storage plant for Europe’s largest pilot project for the technology. That plant, in Frankfurt, is now up and running, with Thuga and its industry partners converting electricity to hydrogen and pumping it into the gas distribution network at levels below the 5-10% compliance limit. The trial will last for three years, giving the companies valuable operational experience and supplying them with crucial data as to how the plant works under practical conditions.
The site was chosen because the electrolysis plant could be easily connected to existing network infrastructure. ITM’s components take up a relatively small footprint, being housed in a standard 20ft ISO container. The equipment is fully CE marked and has Atex regulatory approval. The plant will produce 60m3 of hydrogen an hour. That will enable it to feed 3,000m3 of natural gas enriched with hydrogen into the grid every 60 minutes. An expansion of the pilot plant is planned from 2016, when the hydrogen will be converted to methane and fed into gas network.
Cooley says that Germany has been quick to recognise the potential of power-to-gas energy storage. And he adds that there are plenty of persuasive factors that support its development in the UK: “The electricity network in the UK has 350TWh of energy flowing through it. The gas network has 1,000TWh flowing through it – so it is roughly three times the size in terms of energy. The difference is that the gas grid has lots of storage – we effectively already own huge assets for storing energy. It is a fantastic place to put excess renewable electricity in the form of renewable gas.”
He says that power-to-gas has obvious advantages over other storage techniques. “If you look at storage availability, it is segmented by discharge time and energy storage size,” he says. “If you want extremely small bursts of energy, then you use a flywheel. If you want, say, two hours of storage you use a battery. But the problem with batteries is that, if you want four hours of energy storage, you have to go out and buy another battery.
“With hydrogen the energy rating and the power rating are separated. You buy an electrolyser and you can run it as long as you want. That makes the gas grid a huge hydrogen tank that we already own.”
The numbers are big, he says. “If you look at achieving 2020 targets for wind output, and you curtail 4% of that, that’s 2.8TWh of energy. That’s a lot of electrolysis.”
At present, hydrogen can be blended with natural gas at a maximum of 0.1%. The GridGas project partners have made a recommendation to the Health and Safety Executive that that should be increased to 3%.
Most gas used in the UK goes towards providing heat – domestically and industrially. So what electrolysis offers, says Cooley, is the opportunity to provide renewable heat on a very large scale. “The government says we need 12% of all our heat from renewables by 2020. That’s very ambitious. And I think one of the best ways of getting there is power-to-gas energy storage.
“It reduces renewable curtailment. It decarbonises gas. And we are making gas domestically from an excess product, which is good for energy security. It’s a valuable solution,” he says.
Open the box: the electrolysis plant fits inside a standard shipping container