Batteries
BATTERY TYPES
- Lead-acid batteries are used most often in renewable energy systems. Less common are nickel-cadmium batteries which last longer but are much more expensive.
- Most batteries are composed of a number of cells. For example a car battery is 12 volt, but is supplied as one unit (monoblock), that comprises 5 x 2 volt cells. In stand-alone power systems the battery banks are supplied as either 12V, 24V, 48V or 120V. These batteries could be supplied as monoblock (12V or 6V) batteries but are generally supplied as individual 2V cells. A 12V battery bank will consist of 6 x 2V cells, and so on.
- Battery banks can be designed to provide many days energy requirement with no input from the charging source.
- Lead-acid batteries can be supplied as either wet batteries, as used in cars, or valve regulated batteries commonly called "sealed" or "gel" batteries. Wet batteries are most commonly used in renewable electricity systems.
- The life of a battery bank is affected by the average daily depth of discharge, (D.O.D.). If the battery bank capacity is large enough to keep the D.O.D. low, the battery life should be at least ten years. Battery manufacturers will provide information on the cycle life of the battery compared to D.O.D.
- A good quality 12V battery bank will cost from $1000 to $3000 depending on the capacity. A 24V bank will cost from $2000 to $6000.
BATTERY INSTALLATION
- Batteries emit a corrosive and explosive mixture of hydrogen and oxygen gas during the final stages of charging. This can ignite if exposed to a flame or spark.
- Batteries must be installed in a well- ventilated environment, preferably in an appropriately designed structure away from the house.
- Because the gases rise, ventilation design must permit air to enter below the batteries and exit the room at the highest point.
- Ventilation can be achieved naturally or by installing fans and electrical vents. The amount of ventilation required depends on the number of battery cells and the charging current. A large battery bank using large charging currents needs more ventilation.
- Do not install electronic components above a battery bank because of the risk of explosion and the possibility of component corrosion.
- Install batteries in a drip tray to trap any spilled acid. Alternatively, wash any spillage to a sump and then neutralise it with bi-carbonate of soda (baking soda).
- Batteries should be mounted on stands to keep them clear of the ground. If the batteries are ground mounted they should be thermally insulated from the ground temperature. They should not be installed directly onto concrete, as concrete will cool to ground temperature, causing the electrolyte to stratify. This is detrimental to a battery's long-term life and performance. Low electrolyte temperatures also reduce the capacity of a battery.
- Batteries must not be installed where they will be exposed to direct sunlight, as high temperatures may cause electrodes to buckle.
- The typical area required for the installation of a battery bank is:
12V 1.4m x 0.3m or 0.7m x 0.6m
24V 1.4m x 0.6m
48V 2.8m x 0.6m
- The batteries can be as high as 700mm, and if installed in a box it must have a removable lid or at least 500mm clearance above them to allow access for a hygrometer to check the charge level.
- Access to the battery room or container should be limited to responsible people trained in system maintenance and shut down procedures.
- Safety signs are required in accordance with Australian Standards.
- The installation must include a switch/fuse near the batteries to enable the bank to be electrically isolated from the rest of the system.