Renewables are expanding rapidly, but since some of them have variable power outputs, there is a need for balancing systems, including energy storage. That may have to cope with occasional long lulls in renewable power availability. The need for long duration electricity storage (LDES) has certainly been recognised by policy makers, but at present, according to a new study by Aurora Energy Research, ‘high upfront costs and long lead times, combined with a lack of revenue certainty and missing market signals, leads to under investment, resulting in higher power sector costs and emissions’. So it is not happening yet.
However, Aurora says the UK will need 24 GW of LDES by 2035 to effectively manage the intermittency of renewable generation, and as part of 46 GW of overall storage. And it claims that this will be very worth-while, since ‘introducing LDES in large quantities in GB by 2035 can reduce carbon emissions by 10 MtCO2 p.a., reduce system costs by £1.13 bn p.a. (2.5%) & reduce reliance on gas by 50 TWh p.a.’
First, to set the scene, to achieve net zero by 2035 in the power sector, Oxford-based Aurora says significant increases to annual deployment rates will be needed for all renewables, on top of new innovative capacity such as hydrogen, CCUS and BECCS. The Aurora Net Zero UK scenario requires the buildout of 40 GW of wind, 23 GW of solar PV, 11 GW of storage, 6 GW of conventional gas ‘peaker’ plants (to meet peak power demands), plus 11 GW of gas-fired CCS-linked plants and hydrogen-fired CCGTs, all between 2021 and 2035.
In order to meet demand, but also reach net zero emissions, it says total GB generating capacity must increase by at least 85 GW from today’s levels by 2035, due in part to the lower load factors of intermittent renewables. As indicated above, this increase also includes significant peaking/standby capacity. It notes that ‘gas-fired technologies currently remain the only source of reliable capacity to keep the lights on during extended periods of low wind after shorter duration storage technologies become depleted.’ However, that may change, given the emergence of long duration electricity storage, which is ‘a viable alternative to gas-fired plants to provide reliable capacity during periods of low RES generation’.
The merits of storage in general are clear enough. As Aurora says, it can provide ‘firm, flexible capacity to help shift residual demand on a daily and weekly basis’, and avoids using peaking (gas fired) technologies, which have higher carbon emissions. Typically it says, peak demand periods are under 4 hours in duration, meaning existing storage technologies, including batteries, can contribute to grid balancing. However it says ‘shifting demand to mitigate the effects of longer term weather fluctuations, which can last from days to weeks, can only be addressed by long duration storage’. It has to be fast as well as long since, by 2050, Aurora says renewable output, between two consecutive hours, is likely to fluctuate by up to 26 GW. And it has to be large since, as the electrification of heating spreads, peak power demand in cold periods is expected to be amplified - although this effect may be offset by smart EV charging, Demand Side Response, and hydrogen production.
The later actually could do a lot- and could be one of the main very long term storage large scale options. Aurora says that ‘residual demand could be met by inter-seasonal storage such as hydrogen to power’. i.e. P2G/G2P conversion/storage. In addition to that, and flow batteries, it looks to pumped hydro and other gravity based systems (which will not necessarily be able to provide very long duration storage), as well as cavern-stored compressed air and heat storage (which might do). Some of these will become particularly important if stress on the long distance transmission grid is to be avoided. Indeed, Aurora says ‘long duration storage presents an alternative to transmission infrastructure reinforcement as curtailed energy could be stored and dispatched in low wind periods, reducing constraint-induced system costs and emissions’.
In addition, it notes that ‘a shift away from un-abated thermal generation towards non-synchronous renewables lowers system inertia which must be replaced. As renewables erode the load factors of thermal capacities, new sources of voltage control are needed, which could be provided by storage assets’. Aurora says ‘long duration electricity storage will be able to contribute to these system requirements, reducing costs of procuring these services from elsewhere’, with synchronous conversion of storage power providing virtual inertia to help maintain voltage and frequency stability.
In all, Aurora estimate that, by 2035, 31TWh would be available to be shifted from periods of excess renewable generation for storage and reuse rather than being curtailed. But that means there would be a need the equivalent of 38 GW off suitable storage. Maybe not all of it might have to be LDES, but it would still be costly. However, overall, Aurora says the introduction of LDES could result in up to 2.5% lower total system costs by 2035, with the use of LDES resulting in a 50 TWh(th) cut in gas used in the power sector in 2035, cutting GB’s reliance on imports.
Policy support to make this happen ‘could be provided through direct support mechanisms, or via other market reforms to strengthen market signals’. A Cap & Floor mechanism is seen as the best positioned to support the deployment of LDES, but ‘may not incentivise effective dispatch, and additional reforms could be required to incentivise investment.’
An interesting study, even if some say it down-plays smaller scale local battery storage and decentral supply options. Well yes, they can and should also play a role, but I’m not sure how even lots of small batteries could help with responding to week-long lulls in wind and PV inputs. The Aurora study looks to systems able to supply power for ‘4 hours or more’, whereas an earlier US study went for 10 hours or more. That was if anything even more up-beat, in terms of its assessment of overall benefits, than the Aurora study. It noted that long duration storage (LDS) was very valuable in system terms, especially inter-seasonal and multi-year storage.
The US study concluded that ‘the introduction of LDS lowers total system costs relative to wind-solar-battery systems, and that system costs are twice as sensitive to reductions in LDS costs as to reductions in battery costs’. i.e. long-duration storage cost reductions lower system costs 2 times more than batteries. Perhaps that is not surprising: there can be economies of physical scale, and also it seems of temporal scale. So, while some small systems may have role, some ‘big and long’ is probably also vital- basically, for storage, we are going to need a bigger boat!
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