“A battery will do for the electricity supply chain what refrigeration did to our food supply chain.” That is the claim of Donald Sadoway from the Massachusetts Institute of Technology in an interview with Grist in 2017. This still seems to be the received wisdom today. The use of battery systems is certainly growing at all scales and uses, including electric vehicles, with a massive 55% growth per annum expected for lithium-ion batteries until 2022.
A report by Bloomberg in 2018 predicted that the overall global market for battery storage in the power sector would be worth $548bn by 2050. And in its latest report, Bloomberg New Energy Finance says that there could be 1 TW of energy storage in use by 2040 — up from under 10 GW now.
Batteries are fine for a few hours or maybe days, but not for weeks or months
Battery storage is one way to deal with variable renewables, so as lithium-ion battery costs fall – by almost 85% since 2010 — they are seen as the way ahead. Especially at domestic level where they are an ideal match with photovoltaic (PV) solar. However, there is still a way to go to get prices down below $100 per kWh, and although some are hopeful that this can be done, not everyone thinks that batteries can or should be the main way ahead.
Storage has limits
Batteries have low storage capacities and can only provide energy for relatively short periods — unless you have a lot of them. They are fine for a few hours or maybe days, but not for weeks or months. Indeed, not many of the storage systems we have at present can do that. Even large pumped hydro plants can only provide power for a day or so at most, depending on the size of their reservoirs.
A study by the European Academies Science Advisory Council claims that storage “will not substantially reduce EU needs for back-up generating capacity in the short to medium term”, while adding that storage has traditionally been used to smooth out peaks in demand. “[Storage] can similarly be used to smooth out peaks in supply,” the report notes. “However, where over-capacity exists, it is difficult to justify significant additional investments in storage”.
That has certainly been the experience — for good or ill — with the UK capacity market, which was set up to stimulate investment in balancing technologies. Storage has hardly featured in it with most of the contracts heading to gas plants.
Not everyone is convinced that storage, and batteries especially, will necessarily be the main way ahead
Some power companies are now using large arrays of batteries, although mainly for short-term frequency support. Some domestic “prosumers” are using batteries to allow them the use PV power captured during the daytime to provide power at night — although few can rely just on PV and batteries to do this thought the year. There will be times when power companies must import power from the grid. Even so, from the power system point of view, the availability of a distributed network of storage batteries may help to reduce short-term demand on the grid, particularly at peak periods.
As renewables take over a majority role in power supply, we will also need longer-term grid balancing to deal with, for example, occasional long lulls in wind and solar availability. Storage is obviously part of this, but some worry that the current battery rush may be distracting us from possibly better options for storage and balancing. There is a risk of what is called “lock in” — a premature focus on one solution.
Moreover, it is not just a question of lock-in to lithium-ion batteries, or even to batteries and storage in general. There are other options for balancing at various scale and for various durations. As the International Renewable Energy Agency put it: “Energy storage is only one of many options to increase system flexibility”. Indeed, it is not yet clear what the optimal mix of systems will be for optimized grid balancing or the role that storage can and should play in this and in frequency support. For example, supergrid imports from other countries may be easier for overall balancing and smart-grid demand-side load management measures can reduce or delay peaks, and also, it is claimed, provide frequency support.
Beyond batteries?
Not everyone is convinced that storage, and batteries especially, will necessarily be the main way ahead. Indeed, the co-ordinator of the review by the European Academies of Science Advisory Council (EASAC) notes that “there is nothing that storage can do that something else can’t do”. However, that is not to say that some new storage options might not be suited to for longer-term balancing. Compressed-air storage is one option with great potential. Liquid-air storage also has its attractions – it was claimed it might get down to £110 per MWh. Another option, with a range of flexible applications, is large-scale Power to Gas (P2G) production of green hydrogen and its storage in salt caverns underground. With costs falling, P2G is being pushed quite strongly at present.
The EASAC was, however, a bit sniffy about the P2G route to green hydrogen production. It says that the costs of this route are “far too high and their round-trip efficiencies too low” to be deployed commercially for seasonal grid electricity storage applications “within the foreseeable future”. It adds that they could “perhaps be deployed within the 2050 timeframe”.
That may be too pessimistic — there are some very efficient P2G electrolysis cells emerging. Some are less flexible than proton-exchange membrane fuel cells as used by ITM power (who are pushing ahead with a 1 GW per annum manufacturing plant in Sheffield). And while solid-oxide cells usually require high temperatures, a new enhanced system claims to have 96% efficiency. That makes hydrogen look like a good option. A 2030 UK energy plan
Yet there may be better batteries. Indeed, the cost of “flow” batteries is falling. They mix separate chemical electrolytes to create a charge, in a reversible process. In an impressive scheme being developed by German gas company EWE Gasspeicher, two salt caverns, each of around 100 000 cubic meters in volume, will be used to store the brine based electrolyte fluids to create a redox flow battery with capacity of up to 120 MW and 700 MWh. Small above-ground prototypes are to be tested first.
Conventional batteries are fine for doing what they are good at – short-term storage. Especially for mobile applications, although ultra capacitors may yet challenge them in some of those roles, or even small hydrogen-powered fuel cells. Batteries will get even better, backing-up domestic scale PV fully overnight and, in terms of grid power, helping to provide supply to meet demand peaks, which typically only last for an hour or two. Some see electric-vehicle batteries as helping out with short-term grid balancing — the “vehicle to grid” idea, which I will discuss next week.
Certainly, the power system is changing, as it should, with batteries being part of the challenge as we move to a new more efficient smart-grid system based on renewables. But batteries are not the answer to all or even most energy storage needs or to balancing variable renewables over long periods.
