Why are gravity and hydrogen now at the forefront of the UK energy storage strategy?

In the aftermath of the UK government's first round of funding awarded under the Longer Duration Energy Storage Demonstration Programme, inspiratia explores the technology behind two of the most successful bids. We speak to David Surplus of B9 Energy and Peter Fraenkel of Gravitricity

As the UK becomes ever more reliant on intermittent renewable energy sources for its electrical power, the role of grid scale energy storage solutions is being brought into sharper relief. The UK has so far relied on pumped hydro plants in the mountains of Wales and Scotland to provide a total of 2.8 GW of additional generation capacity to the grid, quickly dispatchable at the times of greatest need. Successful though this technology has been, the future will need new and innovative solutions. Pumped hydro sites require very particular existing geological features and does not easily scale up to meet the needs of the whole grid.

The rapid advances in lithium-ion technology in the past few years have massively increased the dispatchable energy storage capacity available to the UK grid. An analysis by Solar Media Market Research found that 1.3GW of battery storage projects were already active on the grid, with a pipeline of over 16GW. However, due to the limitations of both pumped hydro and lithium-ion batteries, the UK government's Department for Business Energy and Industrial Strategy (BEIS) has awarded funding to other nascent technologies, hoping for these to be the next breakthrough in energy storage. This is the Longer Duration Energy Storage Demonstration Programme.

inspiratia has previously explored the technologies and business models behind some of the programme's other winning bids, such as compressed air storage with Highview Power and vanadium flow batteries with Invinity Energy.  

Using hydrogen to balance renewable generation

As inspiratia has documented, there has been a rise in green hydrogen projects in the past two years. Its use as a renewable energy vector has opened the door to decarbonisation in a growing number of sectors, including grid scale energy storage.

One of the companies that has received funding under the government's programme was B9 Energy Storage, for its 20MW green hydrogen project at Ballylumford power station in Northern Ireland. inspiratia spoke to David Surplus, Managing Director of B9 Energy Ltd, on the recent successful bid,

"Phase one of the Power-to-X project will see the delivery of a front-end engineering design (FEED) to demonstrate the concept of innovative, first-of-a-kind, longer duration energy storage technologies which can be deployed at scale," Surplus comments on the scope of funding that has so far been awarded to B9 from BEIS.

Phase one of the project is being conducted by a consortium of B9 Energy, Mutual Energy, Islandmagee Energy Ltd and the Net Zero Technology Centre.

Surplus goes on to describe the full delivery of the project as including a "20MW membrane free electrolyser inside a repurposed building at Ballylumford, Larne in Northern Ireland, to provide long duration electrical balance for wind energy that would otherwise go unused."

B9 plan to bring hydrogen blend to gas turbines

The membrane free electrolyser that B9 is planning to use on this project comes with several advantages over more conventional designs. Most prominently, the lack of a membrane means that there are fewer potential failure modes, and less of the associated drop off in performance over time. The operation of a flow electrolyser is less reliant on a constant base load than other models, meaning that they are more suitable to the fluctuating energy supply of renewable energy production. A study published in Nature in July 2021 highlighted the advantages of the membrane free flow electrolyser as a means of achieving higher current densities through the cell with relatively common catalysts.

Surplus concludes by explaining some of the longer-term ambitions for the energy storage facility in Ballylumford.  "The latter application will involve firing trials of a relocated 20MW Open Cycle Gas Turbine, typically used for electricity generation on oil and gas platforms. We expect to see successful fuel switching reach more than 70% hydrogen by volume in natural gas.

"Results from the project will help inform future electrolyser deployment at GW scale, allow curtailment-free connection of offshore wind farms at Ballylumford and help define effective security of supply solutions for the net zero era."

Gravitricity is going back to the basics of energy storage

Whilst new forms of energy storage like hydrogen are taking off, there are some developers that are taking a hard look at the oldest and simplest methods of storing energy with renewed vigour. inspiratia spoke with Peter Fraenkel, Director of Gravitricity and the engineer behind the company's core projects, about the viability of storing energy in weights.

Gravitricity have also been awarded funds by the UK government for a FEED study to be followed by a full-scale demonstration project if successful.

"The idea is to use surplus power – at a time when it's not needed – to lift a heavy weight and then to recover that power when needed," explains Fraenkel. "It's based on the concept of potential energy, one of the most basic physical principals people learn in school."

In addition to the project that BEIS is funding in the North of England, Gravitricity also has a number of different projects that are currently in various stages of completion. This includes a 250kW demonstration project that has been constructed above ground in Edinburgh, standing at just 15m high. However, there are also plans in place for much more ambitious projects. The Staríc Mine in Czechia has been scoped as a potential site for a full-scale gravity storage project, with an existing mine shaft of over a kilometre down.

Gravitricity plan to use existing mine shafts where available, with the long-term ambition of using their own mining equipment to excavate shafts in ideal locations.

Why pump water when you can winch steel?

The total amount of energy stored in the weight will depend on its mass and the total usable height of the shaft (approximately 12,000 tonnes and 1km respectively), though the output power is variable and depends on the speed of descent. A completed unit storing 25MWh of energy would be capable of producing between 1MW and 20MW and would have a power output duration between 15 minutes and eight hours. The round-trip efficiency of a single cycle has been predicted at between 80% and 90%.

"That is why Gravitricity exists," says Fraenkel on the need for gravitational storage in comparison to lithium-ion batteries. "We have come up with something which is much more in line with what is expected of a grid asset. A lifetime of half a century or more, no limited number of cycles, no internal discharge, and high efficiency."

On the topic of the limitations of pumped hydro systems and the evolution of those principles, Fraenkel explains that "There are a very small number of sites that are naturally suited to pumped hydro, with one body of water at surface level and another up a mountain. So, instead of pumping water up and down a mountain, you could build a huge cavern underground and create a pumped hydro system between that and the surface. But then you might ask, why do you use something with a density of 1g/cm³ when we could easily use something much denser? We originally intended to use scrap steel with a density of 7.81g/cm³, much better than water." Fraenkel went on to explain that black iron powder was chosen as the material to pack the weights.

There has grown a certain degree of confidence in recent years around the future of renewable energy generation. However, the energy storage scene is far more turbulent by comparison. The winning technologies in the next decade will be crucial to the long-term stability of the whole energy market on the road to net-zero.