Solar battery bank sizing: set battery bank at 12, 24 or 48VDC?

A solar battery bank is used to store excess power to power loads later whenever required. This articles explains different voltages for solar battery banks.

What is a solar battery bank?

There may be periods when there is no sunlight: evenings, nights and cloudy days are examples of such situations beyond our control. In order to provide electricity during these periods, excess energy, which is produced during the day, is stored in battery banks and is used to power loads later whenever required. INSERT scheme: diagram of Off-Grid system with battery bank Battery Banks are installed downstream of the solar panel and upstream of the solar inverter. They store the charge in form of DC current and depending upon the system configuration, could be rated at 12VDC, 24VDC, 48VDC or even higher. [caption id="attachment_4936" align="aligncenter" width="309"] Solar wind hybrid system with solar battery bank[/caption]

How to size your battery bank

The rating of the battery bank depends upon the overall system configuration as well as the profile of the loads. Originally, when solar panels were manufactured, they were targeted at providing electricity to small recreational loads such as sign boards and outdoor lighting. These loads were rated to use DC power at 12 Volts. In those days, there was no need for an inverter and only DC rated loads could be used from solar panels. Nowadays solar panels have come a long way and have shown remarkable flexibility and modifications. As a result solar panels can now provide electricity to the whole house including both AC as well as DC loads. Advancements in the Power Electronics equipments such as inverters have also played their part in making this happen. As a result of which, the rating of your battery bank does not really matter.

Lower cable costs at higher voltage levels

As most of the household loads require AC power, you could use either a 12 VDC, 24 VDC or a 48 VDC Battery bank and connect to an inverter. This will transform your DC current to AC at a required voltage level (usually 120VAC or 240VAC) and provide power to your household loads. The higher the voltage level, the further away you could place your solar panels and still use the same gauge wire without experiencing significant voltage drop. For the same electrical output, higher voltage level systems will need a smaller, less expensive wire, thereby reducing the cost significantly. Having said that, if you have a lot of 12 VDC loads, it is more feasible to use a 12 VDC battery bank as you would eliminate the need to change your loads. Most grid tied systems are required by the utility to operate at a voltage level of 48 VDC or even higher.