Battery storage power station
A battery storage power plant is a form of storage power plant, which uses batteries on an electrochemical basis for energy storage. Unlike common storage power plants, such as the pumped storage power plants with capacities up to 1000 MW, the benefits of battery storage power plants move in the range of a few kW up to the MW range - as of 2017, the largest installed system has a storage capacity of 300 MWh. Battery storage power plants, like all storage power plants, primarily serve to cover peak load and in networks with insufficient control power and the grid stabilization. Small banks of rechargeable batteries with a few kWh of storage capacity, are mostly in the private sector operated in conjunction with wind turbines or similarly sized photovoltaic systems to daytime bring revenue surpluses in yield poorer or unproductive hours in the evening or at night, and to strengthen their own consumption. Sometimes battery storage power stations are built with flywheel storage power systems in order to conserve battery power. Flywheels can handle rapid fluctuations better.
Structurally battery storage power plants and uninterruptible power supplies (UPS) are comparable, although the former are larger. The batteries are housed for security in their own warehouses or in containers. As with a UPS, the problem is that electrochemical energy is stored or emitted in the form of direct current DC, while electric power networks are usually operated with Alternating current AC voltage. For this reason, additional inverters are needed to connect the battery storage power plants to the high voltage network. This kind of power electronics include GTO thyristors, 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 time and, of course, the costs. In the 1980s, 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 fast decrease in the cost of this technology, driven by the electric automotive industry. This is the case of the battery Park Schwerin, the battery storage in Dresden or the storage of BYD in Hong Kong. Lithium-ion batteries are mainly used, some redox flow system have emerged and lead-acid batteries are still used in small budget applications. There are numerous suppliers of large battery storage.
Since they do not require any mechanical movement, battery storage power plants allow extremely short control times and start times, in the range of few 10s of ms at full load. Thanks to that reactivity, they can shave power peaks in the range of minutes, but they can also dampen the fast oscillations (second) that appear when electric power networks are operated close to their maximum capacity. These instabilities consist in voltage fluctuations with periods of up to several 10 seconds and can soar in worst cases to high amplitudes, which can lead to regional blackouts. A battery storage power plants properly dimensioned can efficiently counteract these oscillations. Therefore, applications are found primarily in those regions where electrical power systems are operated at full capacity, causing a risk in the grid stability. Large storage plants (Na-S)can also be used in combination with (Na-S)intermittent renewable energy source in standalone hybrid micro-grids.
Some systems, operating at high temperature (Na-S) or using corrosive components are subject to failure even if they are not used (calendar ageing). Other technologies suffer from deterioration caused by charge-discharge cycles (cycle ageing), especially at high charging rates. These two types of ageing cause a loss of performance (capacity or voltage decrease), overheating and may eventually lead to critical failure (electrolyte leaks, fire, explosion). In order to prevent the loss of performance due to ageing, some batteries can undergo maintenance operation. For example, non-sealed Lead-acid batteries produce hydrogen and oxygen from the aqueous electrolyte when overcharged. The water has to be refilled regularly to avoid damage to the battery and the inflammable gases have to be vented out to avoid explosion risks. However, this maintenance has a cost and recent batteries, such as Li-Ion, are designed to have a long lifespan without maintenance. Therefore, most of the current systems are composed of securely sealed battery packs which are electronically monitored and replaced once their performance falls below a given threshold.