It is a commonplace that the uncontrollable variability of the most prominent modern renewables, solar and wind power, requires electricity storage to make them viable as free-standing and independent technologies. Consequently, batteries and other storage systems are sometimes presented as the key to the problem of intermittency, storing green energy at times of surplus for those times of dearth when the wind isn’t blowing or the sun shining, and so unlocking the wholly renewable future. Batteries are now on the verge of broad deployment in the UK, but they do not appear to be taking up the function expected of them, and instead seem to be gravitating towards close working with conventional generation.
The UK government, amongst others, has taken a close interest in the encouragement of energy storage research and deployment, sponsoring a competition to reduce the cost of energy storage technologies and more recently proposing a revision to the planning regulations to make it easier for developers to obtain consent for smaller proposals where storage is combined with a generation asset. (BEIS, Consultation on Proposals Regarding the Planning System for Electricity Storage (January 2019)
This reform, which aims to reduce the burden on the Nationally Significant Infrastructure Project (NSIP) system by directing projects towards local authorities, has clearly been prompted by the strength of interest in developing electricity storage projects in general and combined generation+storage projects in particular. The rapid growth in that interest can be gauged by examination of planning system data now being released by the Department of Business, Energy and Industrial Strategy, as part of its Renewable Energy Planning Database, a choice of venue that clearly indicates the sector in which government expects storage to have most relevance. The following charts, generated by REF from this data, provide an overview.
Figure 1: Electricity energy storage sites by technology type and status in the planning system. Chart (a) shows the installed peak discharge capacity in MW in each category and (b) the number of sites.
The operational fleet is dominated by long-established conventional pumped storage (Cruachan, Dinorwig, Ffestioniog and Foyers), with a major contribution from the 800 tonne flywheels used to provide surge power for the Joint European Torus (JET) fusion project in Culham. As yet, there is relatively little operational battery storage, with only twenty-nine projects totalling a total peak output capacity of somewhat over 300 MW.
However, there are already 182 battery proposals either consented and awaiting construction or in the planning system and seeking permission. The majority of those projects are below 50 MW in peak output, but the aggregate total is about 3 GW, slightly exceeding proposals for new pumped storage.
Things are obviously beginning to move fast for batteries, and two operational projects are already visible in the Balancing Mechanism (BM), Arenko’s Bloxwich scheme a battery with a peak output of 41 MW, and Centrica’s Roosecote, a 49 MW project at the former gas-fired power station site in Barrow-in-Furness. (In passing it should be noted that in the charts and commentary above we have corrected the omission of the Bloxwich scheme from the government’s planning data on energy storage, as well as errors in the entry relating to the Coire Glas pumped hydro scheme, but this raises the possibility that there may well be other significant errors and omissions in the government’s data; this is clearly work in progress.)
Many of the battery schemes currently in development are built alongside generation, and some 63 are, to use the jargon, “co-located” in this way. What will, perhaps, be surprising to many is that 20 of these schemes, with a peak capacity of 563 MW, are in fact co-located with fossil fuel generation, not renewables. The following figure charts the relevant data, showing batteries described as standalone, co-located with fossil fuel generation and with renewable energy:
Figure 2. Breakdown of large scale battery storage in the planning system showing difference between stand-alone installations compared with those co-located with conventional fossil fuel plant or renewable energy – typically onshore wind or solar PV.
A prominent example of this tendency can be found at Tilbury Power Station (now rebranded as the Tilbury Energy Centre), where RWE has planning consent to build a battery with a peak output of 100 MW. Other elements in the Tilbury proposal include a 2.5 GW Combined Cycle Gas Turbine, and a 299 MW Open Cycle Gas Turbine (OCGT). While standalone battery projects dwarf co-located schemes, batteries co-located with fossil fuels currently dwarf co-location with renewables.
There are several reasons making co-location at fossil fuel sites highly attractive. With an existing grid connection, and a skilled workforce, the addition of another revenue earning asset on the site may well be a straightforwardly sensible move. Furthermore, the presence of a large renewable generating fleet has meant that electricity demand on the Transmission System is becoming increasingly stochastic (random), with low inertia making system frequency excursions more likely, and the System Operator is consequently finding it much harder to balance demand and supply and to maintain power quality. As a result, favourable contracts are available to generators able to offer very rapid response to requests for grid balancing services, extra generation at very short notice amongst them. Fossil fuel generators can respond quickly, within an hour, and some much more quickly than that, but even reciprocating diesel engines and OCGTs need minutes or at best several seconds to react, and the System Operator would ideally like a response that is almost instantaneous. Batteries can provide such super-rapid services, in a fraction of a second, but are not ideally suited, largely because of cost, to sustaining the service over a longer period if required. Consequently, it makes sense to combine a battery and a conventional generator, with the battery providing the first phase of that response for seconds and minutes until the co-located fossil generator can ramp up and take over. Since the fossil fuel generator can operate at will, the battery can easily and inexpensively be kept fully charged.
This close combination is most readily achieved by physical co-location, as described in the government’s data, but virtual combination between battery and fossil fuel generation is also entirely feasible, leading us to suspect that some, at least, and perhaps many of the stand-alone battery projects are also operating in tandem with conventional generators.
None of this should provoke either surprise or outrage. Given the need to address the emergent balancing and power quality problems on the UK system, mostly caused by renewables, the real or virtual co-location of electricity storage and conventional generators is perfectly rational engineering, and probably makes the best of a bad job for the consumer. But it is not at all the role for batteries that many, perhaps even government, will have expected. Rather than storing green energy to smooth wind and solar output over longer periods, leading to a future where renewables become independent of conventional generation support, many of the UK’s batteries will actually be storing fossil electricity to enhance the ability of conventional fossil-fuelled generation to react to the difficulties arising from wind and solar. That independent future for renewables may be a little closer, but it is still very distant.