Energy storage is a key technology to facilitate a move to widespread renewable and distributed energy generation. The technology exists today on numerous scales for many different applications. However, the current technologies are not suitable for high-volume energy storage required on grid-scale.
Current examples of energy storage range from a 1.2V DC battery to a pumped-hydroelectric dam. In fact pumped-hydro is the only viable energy storage technology that currently exists on suitable scale, although there are few suitable remaining sites for hydro in the UK. This technology works through intelligent monitoring of the grid demand profile: when demand is low extra water is pumped up-hill to a reservoir, ready to be released when demand is high. This produces large amounts of power for a period of roughly two hours so is suitable for moderating peak energy demand profiles.
There are two feasible options for energy storage in a future energy network, these are: large-scale grid-tied storage; and small-scale domestic storage.
Large-scale storage must be able to meet instantaneous demand fluctuations and be able to cope with large variability. For instance wind farms have the potential to power much of the UK’s needs. However, often the wind does not blow strongly enough and occasionally the wind blows too strongly, with the turbine suddenly shutting down for self-preservation. Storage technologies must be able to react to this situation if an entire wind farm suddenly goes offline. Aside from hydroelectric a few other options have been suggested. These include: batteries; giant flywheels; hydrogen; and ultra-capacitors. A flywheel is a very old technology for storing energy and with modern improvements can achieve very high efficiencies, but must be massive and extremely heavy for the scale intended. Hydrogen would be suitable if a ‘hydrogen economy’ was in place, or alternatively if the stored hydrogen could be used in thermal power generation or in a fuel cell. Ultra-capacitors have been in development for many years but are currently prohibitively expensive.
Small-scale storage is currently employed in many off-grid locations, particularly in rural communities in Developing Countries. Typically these will consist of a 12V car battery that can run lighting, heating and cooking equipment. However, these systems are not ideal since car batteries are designed for a single rapid discharge followed by a gradual re-charge. Alternative battery technologies are being developed specifically for domestic settings. Lithium-ion batteries are much better suited to this setting although suffer from cost and reliability issues. It is unlikely that domestic customers in urban settings would require energy storage if they deployed distributed generation since a feed in tariff would offer a more economically viable alternative of sharing electricity with the grid.
Combining small-scale storage to the grid in such a way that it becomes large-scale storage is one of the core ideas of developing a ‘smart grid’. This could be achieved through ‘plug-in hybrid electric vehicles’ (PHEV) or fully electric vehicles allowing access to the car’s batteries when not in use. With a large penetration of these vehicles a high-quality and high-capacity storage infrastructure could be built.
Energy storage is currently much more of a ‘technology-push’ than a ‘market-pull’, with investors anticipating huge demand in the coming decades. Demand will be from utilities ensuring security of supply and individuals/communities who wish to store excess energy produced by their own distributed energy infrastructure.
Much of the research into batteries and capacitors has been driven by the technology companies for applications in consumer goods such as mobile telephones and laptop computers. This research has tended to be ‘ported’ over to other areas such as electric vehicle construction rather than specific directed research. Over the last few years though, this trend has been reversed with large investments in R&D for specific storage situations. Battery makers are increasingly aligning themselves with the automotive sector in anticipation of large uptake of electric vehicles.