Utility Energy Storage
The growing share of RE sources, such as solar and wind, calls for a more flexible energy system to ensure that the RE sources are integrated in an efficient and reliable manner. Battery storage systems are emerging as one of the potential solutions to increase system flexibility, due to their unique capability to quickly absorb, hold and then reinject electricity.
Utility-scale battery storage systems have a typical storage capacity ranging from around a few megawatt-hours (MWh) to hundreds of MWh. Different battery storage technologies, such aslithium-ion (Li-ion), sodium sulphur and lead acid batteries, can be used for grid applications.
Lithium-Ion batteries are currently the dominant battery of choice for deployed energy storage systems worldwide. Lithium is a lightweight metal that an electric current can easily pass through. Lithium ions make a battery rechargeable because their chemical reactions are reversible, allowing them to absorb power and discharge it later. Lithium-ion batteries can store a lot of energy, and they hold a charge for longer than other kinds of batteries. The cost of lithium-ion batteries is dropping because more people are buying electric vehicles that depend on them.
A megawatt-hour (MWh) is the unit used to describe the amount of energy a battery can store. Take, for instance, a 120 MWh lithium-ion battery with a maximum capacity of 60 MW. Now imagine the battery is a lake storing water that can be released to create electricity. A 60 MW system with 2 hours of storage could work in a number of ways:
You can get a lot of power in a short time or less power over a longer time. A 120 MWh battery could power 30 MW over 4 hours, but depending on its MW capacity, it may not be able to get 60 MW of power instantly. That is why a storage system is referred to by both the capacity and the storage time (e.g., a 60 MW battery with 2 hours of storage) or—less ideal—by the MWh size (e.g., 120 MWh).