When the sun is shining on your PV Modules they are producing energy. You will need storage for that energy for night time use or cloudy days. Battery Storage is the heart of your off-grid system. This is where your power is stored. By running power from your solar panels through a charge controller and into your battery bank, power is available 24 hours a day, regardless of weather.
Your solar powered system needs little or no maintenance. The battery bank is the exception. Maintenance is not difficult or very time consuming, but if the batteries are neglected, degradation can occur at a very rapid pace. The right choice of the size, type and number of batteries is important to insure your power system performs properly and to maximize the life of the batteries.
Choosing the right battery
Use a sizing calculator
Battery sizing is essential but often overlooked by users and installers. Batteries in PV systems are routinely undersized due to cost or because the system loads were underestimated. It’s important to know your power needs and correctly plan. Many online calculators provided by battery manufacturers and other software simplifies determining battery capacity for load requirements.
Consider cost of ownership
There are several factors that should be taken into account when determining the total cost of ownership over the life of the battery:
- Price. A battery with a low price is always attractive, but if low price comes at the expense of quality and battery life, the need for frequent battery replacements could boost the cost over time. That’s why it’s important to consider issues other than price when making the decision.
- Capacity. Battery capacity is important because it’s a measure of the amount of energy stored in the battery.
- Voltage. The battery bank voltage must be considered to ensure it matches the system requirements. The battery bank voltage is often determined by the inverter specifications if installing a DC-to-AC system or by the voltage of the loads in a DC system.
- Cycle Life. The most critical consideration is cycle life, which provides the number of discharge/charge cycles the battery can provide before capacity drops to a specified percentage of rated capacity. Batteries from different manufacturers may have the same capacity and energy content and be similar in weight. But design, materials, process and quality influence how long the battery will cycle.
Sizing your battery bank
The number of batteries in your battery bank depends on many factors such as:
- How many appliances you use and the amount of power they take
- Days of autonomy: The number of days the batteries go without charging, due to bad weather or other factors
- Depth of discharge: The level of discharge you wish to go to before re-cycling
- Temperature of the area where the batteries are stored
- Size of your charging system
- The size of your budget
Generally speaking, the more batteries in your bank the better, because you will have more reserve power available and the level of discharge will be lower. For the best overall performance in the long run, choose the largest, best quality battery bank that you can afford.