Batteries

Battery Storage Technologies

Energy storage technologies are used to provide power when there is insufficient power being generated, and to store excess production when there is more power being generated than can be used. Wind and sunshine are not always available when there is a demand for energy, so backup storage is generally required when using renewable inputs especially in Stand-alone Power Supply (SPS) systems. There are many types of battery technologies available. These include: lead-acid, alkaline, carbon-zinc, nickel metal hydride, nickel-cadmium, lithium-ion, vanadium-redox, zinc bromine, sodium sulphur, zinc-air, zinc chloride, silver-oxide, lithium manganese, mercury, thermal, molten salt etc. However the most common type of battery for renewable energy SPS systems are deep cycle lead-acid batteries. Deep-cycle lead-acid batteries are similar to car batteries, but are better suited to the heavy charging and discharging that is typical of SPS systems. When several batteries are connected, they are called a battery bank (see Figure 6). There are Australian Standards for battery installations and safety regulations that need to be followed in a SPS system installation.

Battery storage can provide all the storage in renewable SPS systems that do not have a backup system. However, if a backup generator is available, less battery storage is required. Battery ratings are expressed using the voltage and the storage capacity of the battery. The storage capacity of a battery is the quantity of electricity that a fully charged battery can deliver under specified conditions. This capacity is expressed in Ampere-hours (Ah) and is usually specified at an operating temperature of 25°C. The capacity is determined by the time taken to discharge the battery at a constant current until a specified cut-off or final voltage is reached, which is dependent on the battery type and manufacturer. The capacity is stated as an Ampere-hour value at a discharge rate, which is noted by a "C" followed by a number indicating the rated hours. An example of a typical rating is 2-volt battery with a capacity of 100 Ah @ C100 rate.

Battery banks consist of many batteries connected in series to provide the correct voltage for a system. Typical system voltages are 12, 24, 48, & 120 Volts DC. These can consist of many individual batteries, either 12, 6 or 2 volts connected in series. Occasionally batteries will be connected with 2 (or 3) parallel strings to increase the overall capacity of a battery bank.