Battery and Other Energy Storage Technologies
A battery storage power plant uses electro-chemical reaction batteries as its input source to convert into a more useful power format (AC power) for use by customer connected loads. Unlike more common storage power technologies, such as the pumped hydro storage power plants with capacities beyond 1000 MW, the benefits of battery storage power is that plants can be easily scaled in the range of less than 1 kW up to the MW range - with the largest installed systems (2017) reaching capacities beyond 300 MWh. Battery storage power plants generally are designed to manage peak load demand events and also assist networks with stabilizing the grid performance as required.
Chinese company BYD operates battery banks with 40 MWh capacity and 20 MW maximum power in Hong Kong. The large scale storage is used to cushion load peaks in high energy demand scenarios. Likewise, the storage capacity can be used in dynamic frequency stabilization in the network. The Hong Kong battery storage plant is made up of almost 60,000 individual lithium iron phosphate cells, each with 230 amp hour capacity. The project was started in October 2013 and went into service in June 2014. The actual installation period for this facility was three months. The use of electricity price differential tariffs between loading and unloading by day and night mitigated the need for grid expansion to service peak loads and saved expenditure on expensive grid services such as frequency stabilization, enabling continued economic operations without subsidies. Currently there are three locations for a 1,000 MW peak power capacity storage power plant being investigated.
Small scale solar battery storage of less than 50 kWh capacity, are mostly used in the private sector in conjunction with similarly sized photo-voltaic systems to store excess daytime solar power production for use at other times (night time for example) to assist with supplying the customers load demands.
Sometimes battery storage power plants include flywheel power storage systems that work in tandem with traditional battery storage banks, in order to conserve battery power. Flywheels have similar fast response performance attributes to batteries in that they both handle rapid load shift fluctuations near instantaneously.
Structurally battery storage power plants and uninterruptible power supplies (UPS) are comparable, although the former are larger, with the batteries being housed for security in their own warehouses or in containers. As with a UPS, the problem is that electro-chemical energy is stored and supplied in the form of direct current DC, while electric power networks are operated by alternating current AC. For this reason, additional inverters are needed to connect the battery storage power plants to the high voltage network. Power electronics include GTO thyristors, which commonly used in the high-voltage direct current transmission (HVDC). Various accumulator systems may be used depending on the power-to-energy ratio, the expected life of system and, of course the costs.
In the 1980's lead-acid batteries were used for the first battery-storage power plants. During the next few decades, nickel-cadmium and sodium-sulfur battery were increasingly used. Since 2010, more and more utility-scale battery storage plants rely on lithium-ion batteries thanks to the rapid decrease in the cost of this technology driven by the electric automotive industry. This is the case of the large scale battery Park Schwerin Germany, or the BYD storage facility in Hong Kong. Lithium-ion batteries are the main technology used at the moment with some Redox flow systems also. Lead acid batteries are still popular in small budget focused applications.
There are numerous global manufacturers and suppliers of large battery storage.