By Dave Elliott
Energy storage is usually seen as a very good idea – it would help cope with variable renewables. Indeed some enthusiasts now even say that cheap battery storage will make PV solar so viable at the domestic level we may not need grid power! Or even grids! That seems unlikely – they help to balance variable demand with supply from a range of sources near and far. But one thing is clear – energy storage, large and small scale, is becoming a big issue, with many new ideas emerging.
At the small scale, the ‘grid defection’ idea certainly has its supporters: http://www.rmi.org/electricity_grid_defection and http://thinkprogress.org/climate/2014/10/03/3575371/hsbc-solar-battery-germany/ Others, however, are not so sure; at whatever scale, storage is, and will likely remain, expensive and there are other, arguably better, ways to balance variable renewables, including using the grid. It’s a complex debate, as I try to explore in two parts in this and my next post.
It is certainly true that most forms of storage are at present expensive. Indeed some say this will always be the case since, by definition, storage systems only deliver energy for part of the time – so their capital cost/kWh output is bound to be high. The only time that storage makes economic sense is when there is no alternative energy source available; that is why we pay a huge amount (in £/kWh terms) for small portable batteries – e.g. for torches and radios. But in terms of bulk energy supply, it’s only viable if the cost of the input energy is very low and/or the price that can be charged for the energy output is high – as is the case when variable renewables supplies are low, but energy demand high, and no other sources are available. However in most cases, other sources are available, and are often low cost, such as natural gas. So the argument goes, storage will never compete with cheap gas turbines – which we already have on the grid. Especially if you need to store energy over any length of time – hours or days or even weeks. You can store gas more or less for ever, at low cost.
This issue has come to a head in Germany, where a leading think tank has claimed that energy storage may not be cost effective in helping the transition in Germany to a higher grid penetration of renewable energy until that penetration level reaches as high as 90%. Agora Energiewende’s report, ‘Electricity Storage in the German Energy Transition’, says that in the next 10 to 20 years, the use of energy storage is not likely to be more effective for allowing renewable energy to be integrated into the grid than a mixture of other options aimed at giving energy systems more added flexibility.
Part of the ostensible attraction of storage is that it can use surplus energy from wind or solar PV, produced when demand is low, for sale at a higher price when demand is high, but renewable power is perhaps not available. That seems sensible – a flexible approach to surpluses and shortfalls. But Daniel Fuerstenwerth, project manager at Agora Energiewende, said in terms of surpluses ‘there are cheaper ways of adding flexibility than storage, for example you can just turn off coal, or gas fired power plants, you can use electricity for power-to-heat, you can exchange with neighbouring countries. There are other opportunities that are cheaper than storage, from the overall system perspective.’ He could have also mentioned ‘power to gas’, but that is really a storage system – surplus power being converted to (storable) hydrogen and perhaps methane, for later use to make power. Either way some say it will be much too expensive, even if the input energy is in effect free – excess power that would otherwise be dumped.
However, the Agora study did see circumstances where storage could help, for example with fast, short-term grid balancing for use when the grid suddenly lost power due to a large plant failure or sudden demand rise. Fuerstenwerth said ‘So far this can only be provided by fossil fuel power plants and what we saw in the study was that batteries can add value there and are really well technically suited for that’. So he was not dismissive of domestic-scale batteries used with PV. Customer-sited storage could have a ‘relieving effect on the distribution network when used in a grid-supporting manner’. EV batteries might also do that: the vehicle-to-grid idea. But large-scale bulk storage was not on – yet. www.pv-tech.org/news/energy_storage_not_needed_in_germany_until_nation_hits_90_renewables_penetr
Agora’s view flies in the face of much conventional thinking, and drew criticism from amongst others DENA, a leading German Energy Agency : http://www.dena.de/en/press-releases/pressemitteilungen/dena-fordert-stromspeicher-muessen-zuegig-ausgebaut-werden.html. Certainly large-scale pumped hydro storage is often seen as a key way forward for balancing variable renewables, along with newly emerging ideas like Compressed Air Energy storage www.gaelectric.ie/index.php/energy-storage/ and Liquid Air Energy storage www.highview-power.com/. Some flow batteries also look promising: http://pubs.rsc.org/en/Content/ArticleLanding/2014/EE/C4EE02158D
Some of this may get underway soon. For a very ambitious $8bn project proposed in the US, involving a 2.1GW wind farm in Wyoming sending power by HVDC grid 525 miles to an underground salt cavern compressed air storage facility in Utah and then 490 miles on to Los Angeles, see: www.pennenergy.com/articles/pennenergy/2014/09/8b-renewable-energy-initiative-proposed-for-los-angeles.html and http://bigstory.ap.org/article/3084cb4c459f4ffd9b666f5d5d2e44e3/wind-energy-proposal-would-light-los-angeles-homes However, that’s a one-off so far, and even the more established pumped storage option is facing challenges: http://www.consultkirby.com/files/NREL-CP-5500-58655_Role_of_Pumped_Storage.pdf and http://www.utilityweek.co.uk/news/mountain-ahead-for-battery-of-europe/824882#.VEIxoZRdVWI
The debate on storage is surprisingly charged. ‘Electricity storage facilities are essential for the energy turnaround,’ said Stephan Kohler, Chief Executive of Dena. ‘Anyone who alleges otherwise is damaging the energy turnaround and, in the end, is risking the supply security in Germany’. But anti-renewables lobbyists sometimes argue that variable renewables need storage, and since that is expensive, they are not viable. That may be why some pro-renewables lobbyists argue that storage isn’t necessary. And as can be seen, that may be true in general terms – at least not yet, while there are still other plants on the grid, and maybe not for some time, if grid balancing can be achieved by smart grid demand management and supergrid power exchanges.
However, in this debate, we need to be clearer about the scale and purpose of storage. Not all storage systems are the same – some can store large amounts of energy for long periods (hours, days or even weeks), others are good at fast discharge for short periods. If you want very long-term inter-seasonal storage, heat stores are probably best (e.g. for solar thermal), but if you want fast electric grid balancing, then conventional batteries or advanced chemical flow batteries are better. Horses for courses. Some can be used for local voltage support, others for bulk storage. And there are other factors – some options are geographically determined (e.g. pumped hydro), others can be sited anywhere, nearer end users, but still possibly at large scale. For example, Lithium Batteries: www.renewableenergyworld.com/rea/blog/post/2014/10/will-lithium-ion-work-for-grid-scale-storage
There is no question that the energy storage industry is facing unprecedented innovation: some new ideas are being tested out and niches may exist for many of them, including big batteries: a 5MW/5MWh project has opened in Germany and some still see that as a way ahead. http://cleantechnica.com/2014/09/16/first-100-green-grid-online-figuratively-speaking and http://digital.renewableenergyworld.com/renewableenergyworld/20140910 The UK is also looking at large (2MW) battery stores: https://www.sheffield.ac.uk/faculty/engineering/enews/giant-battery-1.426169
In my next post, at the other end of the scale, I will focus more on the domestic scale energy storage options.