Battery Energy Storage Systems (BESS)
A battery energy storage system is a system that stores energy via the use of a battery technology for it to be used at a later time. There are a large range of battery technologies that form the generic term Battery Energy Storage System. This includes:
- VRLA or valve regulated lead acid batteries. These are the traditional batteries used in Uninterruptible Power Supplies and in existence since 1934, their cost is relatively low in comparison to other battery technologies. Deep cycle VRLA batteries are the type most suited to energy storage to ensure that they have a long enough life span for this use.
- Lithium Ion batteries. This is the type of battery that is commonly found in modern consumer electronics such as your smartphone. They have a high energy density with the potential for even higher capacities (lithium ion technology is constantly changing and improving). The main benefit with lithium ion batteries are that they can be charged and discharged more often that VRLA batteries with less deterioration in terms of storage capacity of longevity of product. The main downside is cost although this is coming down progressively.
- Vanadium Flow batteries. This battery uses vanadium ions to store chemical potential energy. They are currently quite bulky in size but offer the ability to completely discharge without any adverse effects and a long life time (20+ years).
- Sodium Nickel batteries. These batteries use molten salt as the electrolyte. This allows the batteries to withstand greater temperature extremes as the cells themselves operate at 270+ degrees Celsius and are insulated so that the external chassis is just above ambient temperature.
- Liquid metal batteries. This battery technology uses liquid metals as both the electrodes and the electrolyte. As there is a constant regeneration between cycles, the electrodes do not degrade with time. The cost of liquid metal is currently the main stumbling block.
As well as Battery Energy Storage Systems, there are a number of other energy storage systems both currently available and under development. This includes:
- Compressed air storage – this involves storing air under pressure which can later be used to spin turbines and produce electricity
- Molten salt storage – this involves storing energy as heat rather than a chemical storage (e.g. battery) or gravitational potential energy (e.g. hydro-electric). Heat is stored within the salt, which becomes molten due to the high temperature. When power is required, this molten salt can then be used to heat water, which in turn spins steam turbines and generates electricity.
- Hydro-electric pumped storage – water is stored behind dams in reservoirs and released when required to generate electricity. Once the water has passed through the turbines, it is normally kept in a lower reservoir and later re-pumped to the top reservoir to be used again
- Flywheel storage – rotating flywheels store energy as kinetic energy which can then be released. This is typically for relatively short periods of time (e.g. 30 seconds) although some flywheel systems allow up to 4 hours.