Decentralised storage and renewable energies have been described as ‘the perfect match’. Storage can smooth out the peaks and troughs of intermittent electricity supplies from renewable energies, essentially by storing energy when it is plentiful (e.g. during daylight hours for solar energy) and making it available for consumption when generation output is low. But relatively small storage facilities near to the point of production – in contrast to large, remote storage facilities such as hydropower – may also have more far-reaching implications for the design and operation of the electricity distribution grids of the future, not least smart grids.
A joint report published in April this year by the European Association for the Storage of Energy (EASE) and the European Energy Research Alliance (EERA), points out that storage solutions can have benefits at all levels of the electricity system. “At the central generation level,” says the report, “they help in arbitrage, capacity firming or reducing curtailment. When it comes to transmission, they can play a role in frequency and voltage control and black starting [after a shut-down]. Distribution solutions support voltage control, and the reduction of curtailment. Finally at the customer level they are needed for peak shaving [shifting demand from peak to off-peak times], islanding [keeping a local network operational during a black-out] and general demand response.” However, at an EASE policy briefing in March, Jean-Marie Bemtgen, Policy Officer at the EC’s Energy Directorate (see also the interview in this issue), warned that storage is “the weakest link in our energy chain today,” adding that, in the future, every new EC energy policy initiative will be considering potential opportunities for storage developments.
The stakes could indeed be high: a study by researchers at Imperial College, London, commissioned by the Carbon Trust,1 found that “…in a 2050 high renewables scenario, the application of energy storage technologies could potentially generate total systems savings [for the U.K.] of GBP 10 billion per year, by avoiding distribution network reinforcements driven by electrification of the heat and transport sectors”. Today, the grid is designed to cope with peak loads that usually occur for only a few hours on a few days a year. It has capacity far beyond its requirements most of the time. But, as a report by Eurelectric (the association representing the European electricity industry)2 points out, in the future, decentralised smart and small-scale storage will make grid expansion less imperative, by enabling active grid management as part of a two-way process involving ‘prosumers’ – consumers who also feed electricity into the grid from their own solar panels, wind turbines or electric vehicles.
So long as renewable energy sources make up less than 25 % of the energy mix, conventional, centralised storage can balance out fluctuations in the grid, ensuring that supply matches demand on a second-by-second basis. This can be reinforced if necessary by back-up supply, e.g. from open cycle gas turbines, depending on how quickly and for how long the shortfall lasts, as well as by demand-side management, such as demand response, where consumers themselves modulate their electricity use to match supply – often driven by price incentives. But as the proportion of renewable energy sources in the electricity generation mix increases – with a target of 55 % under the EC’s 2050 Energy Roadmap scenario and over 90 % expected in Germany – the corresponding increase in fluctuations, because of the intermittent nature of the supply, will challenge these existing stabilising capabilities.
A number of technological solutions are already available to provide electricity storage, depending on how quickly and for how long the stored power is required. The choice of storage – from existing massive remote hydropower down to transportable batteries in smart cars – also depends on how much space is required and where in the distribution and transmission chain, from high voltage to medium and low voltage networks, it is required.3 Apart from space, the main obstacle is cost, as the technology is still young and incentives are still required to attract investors to back research and development. But, as the Eurelectric report points out, “where a storage solution proves to be competitive against the cost of expanding network capacity, it should be preferred, as it reduces the overall cost for ratepayers (consumers), improves the utilization of distribution assets and, in the end offers DSOs (distribution systems operators) a better use of capital for other projects.”
A number of demonstration projects are already underway or being planned in Europe to test the contribution of alternative forms of large-scale storage on the running of the electricity grid. One of the most recent, and largest, is a 6 MW capacity lithium manganese battery installation in Leighton Buzzard (U.K.), costing €22.4 million, mostly funded by the U.K. government, and being built by a consortium of S&C Electric Europe, Samsung SDI and Younicos. The project is expected to come on-stream in 2016.
Distributed generation technologies, combined with local storage, can also have much higher efficiencies than large centralised facilities and also have greatly reduced, even negligible transmission infrastructure costs. Indeed, in the future, with a high proportion of small-scale renewable energy sources connected to local storage, most of the grid could consist of local, low voltage lines, with high voltage transmission lines only used to link large wind farms, solar arrays and conventional power stations with urban areas.
But much of the potential for decentralised storage in the future could be via the smart grid. Unlike the conventional grid, the smart grid is two-way, with consumers also supplying electricity. As the Eurelectric report puts it, “a future smart grid without decentralised electricity storage could be like a computer without a hard drive: seriously limited.” Decentralised storage can help to balance out unacceptable voltages or currents from intermittent sources, allow renewable sources to continue producing electricity, rather than be curtailed, when they would otherwise lead to grid congestion. It can also overcome short-duration voltage sags and interruptions, help DSOs postpone grid expansion by making more efficient use of existing capacity and improve the reliability of local supply.
Decentralised storage may also have a longer-term role to play in energy management, by decoupling electricity production from its instantaneous consumption (i.e. arbitrage). As small-scale storage technology close to the point of production becomes more affordable, it will help renewable energy to move away from a subsidised system of feed-in tariffs towards a market-driven approach, by increasing the availability and reliability of the energy supply from intermittent sources and creating a more solid business case.