Energy storage |
Looking to longer time horizons in the UK
Short-duration storage in the form of batteries has been an investment focus in GB in the last few years. Now attention is turning to storage on other timescales and the role of hydrogen
Janet Wood
The UK has built several GW of battery storage over the last few years, which is largely providing short term reserve and frequency support, with batteries responding over a few seconds or minutes. Batteries with an hour’s storage have been the norm, with a shift towards slightly longer timescales – two hours – over the last year. System operator NGESO has set up a number of new markets around reserve and response, where short-duration storage is making its mark. But now NGESO is looking towards longer duration storage to address a looming set of issues as the UK moves towards a renewables- led system. Alex Hart, EV and storage manager at NGESO, explained the system operator’s view of progress at a recent meeting on medium- duration energy storage hosted by the UK’s Institution of Mechanical Engineers. He said the system operator had identified seven services that would be required and it had already made progress with five – managing frequency, stability (inertia), voltage, thermal constraints and restoration (sometimes known as ‘black start’). Storage was playing a major role in markets for several of these services already, and is being trialled at the moment for the others, such as black start, where Hart said “Storage is probably going to be a critical part.” The two issues next on NGESO’s agenda are flexibility and adequacy, which both need to be in place by 2030. For NGESO, flexibility means specifically “moving supply and demand within time,” Hart said, and especially between different times of the day (ie ‘within day’). “Some of that will be [load shifting using] electric vehicles, heat pumps or appliances. If that is not enough, storage is well-placed to supply it,” he said. So-called ‘medium duration storage’ developers
Frequency Stability Voltage Thermal Restoration Flexibility Adequacy
• Batteries well suited to very fast (<1 second) frequency response • Other technologies can support for minutes till other generation is dispatched
• Storage with a rotating snchronous generator can provide stability • Storage connected to wind farms to provide ‘virtual synchronous machines’
• Storage with a rotting synchronous genertor can provide voltage support • Voltage support from inverter connected storage via power electronics
• Can help by charging while behind an active export constraint (if they can later discharge when constraint is not active)
• Storage with grid forming inverters can provide power or demand as part of a restoration plan (a distributed ‘Black Start’)
• Moving energy through time, within settlement periods to manage forecast errors and within day to flatten peaks and follow renewable generation
• Moving energy between seasons to ensure firm generation capacity is always sufficient to satisfy inflexible demand
Above: Services required by the UK system operator (source: NGESO)
were keen to respond and the meeting heard details about several options. They included familiar options such as pumped hydro storage, as well as options at various stages of development such as compressed air or liquid air storage, thermal storage and carbon dioxide storage. All were keen to stake a claim for a place in what Hart described as the need to “move a vast amount of energy around” in the future. The most testing issue was adequacy, which for NGESO has two aspects. First is having substantial storage ready for events that happen fast, such as losing a large power station or interconnector. The other is preparing to manage variation over the longest time scales, which may be seasons, years or decades. This aspect of adequacy has to cover options available for low renewables availability over seasons or weeks - and even longer timescales and durations. But in Northern Europe and the UK, that
means occasional late winters when there can be two or more weeks of cold, still days with no wind power available to meet winter-level needs. Hydrogen has been seen as a potential answer to this need, both because it can be stored and because it is an energy vector. But funding any form of storage for these ‘one in 20-year’ events is problematic because of its low utilisation rate. “You need a lot of storage and it spends a lot of time doing nothing. Can you make that economic? How do you set up market arrangements to get the investment you need?”, asked Hart. Recently storage developers have been in discussion with the government over adapting a ‘cap and floor’ regime similar to that used for many GB interconnectors. This would mean consumers underwrite the development, but profits are capped. Continuing revenue arises from tolling fees when power is transmitted across the interconnector (or in the case of storage, charged or discharged).
Above: Battery storage (50 MW/75 MWh) at Thurcroft, UK (photo: Gresham Energy Storage Fund)
28 | May 2022|
www.modernpowersystems.com
Do we already have the capacity? If hydrogen is the solution to long-duration energy storage, as well as being a useful vector at other times, a key question to be addressed is where the hydrogen will be stored, ready for use. Hart raised that question in his discussion of the issue, asking what financial model could prompt companies to build and charge a hydrogen store and keep it in that situation of readiness for a decade or more, so it can be available for that ‘one in 20 year event’. But of course the industry is not starting from zero. There is a hydrogen economy in existence in the industrial sector. And there are huge gas
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