Energy storage technologies can harness the potential from renewables and underpin the shift to lower carbon emissions, in line with international targets.
New storage technologies will play an increasingly central role in smarter energy systems that enable more efficient management of how energy is supplied and used by people, organisations, distribution network operators and national grid.
The means being explored by companies to store energy are diverse. A number of projects highlight current innovations in the market and the potential of other technologies in development.
Pumped hydro power
According to the US-based Energy Storage Association, pumped hydroelectric power is the most common type of energy storage technology in use and is an example of a storage technology which has been around for a number of decades.
Pumped hydro power is generated by pumping water to an elevated height at non-peak times when electricity is cheaper and storing it behind a dam. When energy is required the water is released through the dam and is channelled down through turbines so as to generate electricity to be fed into the grid at times of peak demand when prices are higher.
One location in the UK where pumped hydro power is in operation is at the Scottish Power Cruachan plant near Oban on the west coast of Scotland. The Cruachan plant has been operational since 1965.
Recently Scottish Power announced the results of a two-year long feasibility study into the expansion of the Cruachan plant. It said that an expanded plant at Cruachan, which would involve excavating a new cavern and installing new dams, could generate between an additional 400 and 600 MW of electricity for the national grid.
According to a report by the National Infrastructure Commission (NIC) published earlier this year, the current total capacity of the pumped hydro plants in the UK is about 3,000 MW.
Scottish Power is due to discuss its findings with the government and regulators. It said it would discuss "potential support mechanisms" for the expansion project which it estimates would take 10 years to complete and £300-400 million of investment.
Compressed air energy storage (CAES)
Like pumped hydro power, CAES is a mechanical type of energy storage technology. Siemens-owned business Dresser-Rand was integral in the development of the technology having been involved with CAES for more than 20 years.
The National Infrastructure Commission described CAES as being where "air is compressed and stored under pressure either in underground caverns or in above ground vessels" before being "released to drive a turbine and generate electricity".
The Renewable Energy Association (REA) in the UK (35-page / 820KB PDF) said that although CAES systems consume energy whilst being operated they can generate approximately three times the amount of energy that "a similar sized conventional gas turbine would produce".
In an analysis of the cost of energy storage technologies (30-page / 610KB PDF), financial consultancy firm Lazard said that CAES compares favourably to other types of storage technologies. Lazard said, though, that exposure to natural gas price changes and finding suitable geological locations for underground storage and compression of air are two of the main disadvantages of CAES.
Flywheels are devices that spin at high speeds to generate electricity which is then released as the flywheel's rotor is slowed.
Although pumped hydro power and CAES can offer a large amount of power it can take a while for that power to be generated and fed into the national grid. In contrast, flywheels offer access to power within a very short period of time, although the overall storage capacity is less in comparison. The devices offer the potential to help meet sudden demand for power.
Engineering business AECOM said in a report for Australia's Renewable Energy Agency that one of the other main benefits of flywheels is that they "require minimal maintenance".
According to Business Green, an environmental news publication, the flywheel is a relatively recent innovation in energy storage that derives from technology used in Formula One motor racing. Scottish Renewables said that flywheels are being installed on the Isle of Eigg and Fair Isle in Scotland (16-page / 877KB PDF).
Battery technologies – Lithium-Ion
Lithium-Ion (Li-Ion) batteries have been in commercial use for the past 25 years and have been common in a range of consumer products, from laptop computers to mobile phones.
Li-Ion batteries work by harnessing chemical reactions involved in the transfer of lithium ions between the cathode and anode components of the battery to first charge the battery then discharge that power.
According to a good practice guide on electrical energy storage published by the Energy Storage Operators Forum (ESOF), Li-Ion batteries can be charged and discharged many thousands of times before running out of life and also require little maintenance.
The reduction in the cost of Li-Ion batteries, from more than $3,000/kWh in 1990 to less than $200/kWh today, as the NIC in the UK noted in its report, means that Li-Ion is becoming an increasing attractive energy storage technology. The proven technology of Li-Ion batteries and the modular nature of the systems means they are an attractive proposition for funders as projects can be deployed relatively quickly and can offer the flexibility for both storage and frequency response applications.
Approximately 50,000 Li-Ion batteries help UK Power Networks manage demand for electricity from its substation in Leighton Buzzard.
"By charging during the day, the Big Battery stores electricity that can then be dispatched in the evening when residential customers in Leighton Buzzard need it," the NIC report said. "During low or average electricity demand times, the storage capacity of the Big Battery is enough to power about 1,100 UK homes for a whole day or over 27,000 homes for one hour."
Battery technologies – Flow batteries
The flow battery is another type of rechargeable battery that offers energy storage potential.
These batteries differ from traditional battery technologies as the energy is stored within the electrolytes that are transferred as part of the charge and discharge process.
According to the ESOF guide, flow batteries offer greater storage capacity compared to other batteries and can also store that energy longer. In addition, the storage capacity can be adjusted to meet specific energy requirements and scaled up at costs that are competitive.
A flow battery has been installed to help meet the energy needs of Washington State University in the US.
Together with flow batteries and pumped hydro power, thermal-to-electric storage is identified as one of the most promising energy storage technologies capable of delivering "the greatest benefit for the UK", according to Low Carbon Innovation Co-ordination Group ((LCICG), an umbrella body for government departments and public sector organisations backing low carbon innovation.
One thermodynamic energy storage method that has already undergone extensive testing is the Liquid Air Energy Storage (LAES) system, developed by Highview Power Storage. It was installed and tested over a period of three years at SSE's power plant in Slough and has been resituated at the University of Birmingham "for recommissioning and further testing and research", according to the Modern Power Systems publication.
According to lobby group the Liquid Air Energy Network, the LAES system works by first turning air into liquid and then turning that liquid into gas. Intense cooling systems can turn air into liquid air which can be stored in a tank. The liquid air can then be heated to make it boil and the boiling process turns the liquid air back into gas form. The volume of the gas produced in this process is approximately 700 times that of the liquid air and this change in condition can be used to spin turbines and generate power.
The LAES system offers the potential to generate energy from waste, can be scaled up to increase capacity and "has the potential to offer multi-MW storage for multiple hours", the ESOF good practice guide on electrical energy storage said. Burning from exposure to extremely hot or cold pipes, as well as of explosions caused by pressure system failings are among the risks that have to be managed when operating LAES systems.
Energy storage good for the environment and business
New energy storage technologies are good for both the environment and business.
From an environmental perspective, the UK, together with other countries around the world, earlier this year agreed plans to keep global temperatures from increasing by more than 2°C. It also previously set out it a target of delivering 15% of the UK's energy demand from renewable sources by 2020.
By supporting the development and commercialisation of energy storage technologies, the UK government can work towards these targets.
Energy storage technologies if "deployed at every level from the large scale through to households" could deliver 15,000 MW, or 15GW, of capacity to the national grid by 2030, according to the National Infrastructure Commission's report.
In relation to electrical storage alone, the LCICG has estimated that the UK could have between 7.2GW and 59.2GW of grid-connected storage in the UK by 2050.
A truly smart grid that uses stored energy to meet demands for power could address the intermittent nature of some renewable power sources and deliver great efficiency savings too. The cost of the UK's energy system could be reduced by £10.1 billion by 2050 through "successful innovation", the LCICG has claimed.
In addition, by becoming a global hub for energy storage innovation, UK businesses could benefit financially. The LCICG has quantified the potential growth to the UK economy from energy innovation as being up to £25.7bn up to 2050.
James Mashhadi is an expert in energy storage technologies at Pinsent Masons, the law firm behind Out-Law.com.