Finding ways to implement the cost-effective storage of electrical energy has been an objective of power system planners and operators since the beginning of public electricity supply more than 100 years ago. Indeed, some of the very early direct current municipal supply systems used large flooded batteries to feed lighting systems through the night. More recently, a small number of large pumped hydro schemes have provided specialist services such as frequency response. There have also been demonstration projects of other storage technologies such as compressed air energy storage and flywheels, but these have not led to widespread deployment. The low-carbon power systems now being developed in response to climate change offer greatly increased opportunities for electrical energy storage systems to assist in balancing supply and demand as well as supplying a whole range of ancillary services.
However, the commercial case for energy storage in large power systems has yet to be demonstrated clearly and its use is presently restricted to niche markets. The convenience and low price of fossil fuel, which is really energy stored in chemical form, have been too great to allow energy storage systems to be developed and used widely. This is now changing and the number and type of energy storage systems is rising rapidly. The increasing importance of energy storage and how it can be implemented led to this themed issue and it was encouraging to receive such a strong set of papers.
Our briefing note is by Price (2015), addressing the all-important regulatory issues. Without regulation that rewards its value to the power system fairly, a sustainable business case for energy storage cannot be made. The briefing addresses the particular issues for energy storage within the UK and makes comparison with other countries. The present regulatory structure in the UK does not allow easy access to all the various multiple revenue streams that are likely to be required for a commercial case to be constructed for energy storage and so stimulate its use.
Three research papers discuss the role of storage in our changing power system. Alexander and James (2015) report a study on the use of distributed energy storage in a UK power system supplied mainly by renewables, while Tomlinson (2015) addresses the topical subject of local energy markets and how storage can assist in their operation. Teng et al. (2015) report continuing work by Imperial College on establishing the value of distributed energy storage on the Great Britain power system.
A paper by Dennehy et al. (2015) provides a fascinating insight into the feasibility of a 1200 MW pumped hydro scheme in Lesotho. The scheme outlined uses four 300 MW Francis pump/turbine units and the paper contains a wealth of engineering detail. Morgan et al. (2015) describe an analysis of liquid air as an energy storage medium and their paper pays particular attention to the engineering design and cost of a plant. Liquid air energy storage is one of a number of potentially exciting technologies being developed for large-scale storage. A final paper, by Ooi et al. (2015), describes a study of the connection and balancing of very large numbers of lithium-ion batteries. A key problem of a number of battery technologies is that the capacity of each individual cell is small and so means must be found of combining them in such a way that failure or degradation of one cell does not result in poor performance of the entire system.
Energy storage is a subject area to which many disciplines contribute and so papers must be accessible to non-specialists. Our authors have succeeded in making their papers eminently readable and of practical relevance while retaining technical rigour. For many years energy storage struggled to find its role in large electricity systems. This is now changing and we can look forward to increasing numbers of installations of a wide range of energy storage technologies.
