Battery banks give a constant level of electrical power and stores energy produced from the large rooftop solar system (>500kW approximately) during the day and power appliances at night. For large scale rooftop solar systems, we need batteries with long, reliable life and low cost of ownership. Today’s batteries are better than ever before and they definitely have improved performance characteristics.

Types of batteries available for solar power generation

A high-capacity solar battery with deep-cycle storage capability is ideal for solar systems. Deep cycle, lead acid batteries are the most commonly used batteries for solar applications. A deep cycle battery is designed to be capable of discharging up to 80% of its total battery capacity and thus ensures that it delivers a large volume of electricity when needed.

Apart from the deep cycle lead acid batteries; there are other types of batteries such as the Lithium-Ion, Nickel-Cadmium and Nickel-Iron batteries. These are not as common as the deep cycle lead acid batteries, though use of types such as Lithium-ion battery is on the increase, thanks to efforts by companies such as Tesla.

Some of the disadvantages for these batteries when compared with deep cycle batteries are:

  • High cost
  • Lower efficiencies
  • Higher rate of self-discharge
  • More susceptible to temperature changes than lead acid batteries

Pros and cons of installing batteries in large scale rooftop solar

Pros Cons
Maximize your self-consumption of solar power Increased  initial and O&M costs
Reduce your grid costs Charge/discharge efficiency
Immediately cut-in during power failures Careful maintenance required
Smoothen power delivery during the day Shorter lifetime than the PV systems
Optimise time-of-use billing Added size to the system

Conclusion

As pointed above, the need for battery in the large scale rooftop solar comes down to the criticality of the operations that require solar power. If the operation involved is very critical, selective use of battery is recommended, which does not relatively add up to the overall costs.

We do not recommend coupling solar PV plants with battery backup unless absolutely necessary. If batteries are required, we urge you to perform a lifetime cost-benefit analysis to understand the effect on cost of solar power from your rooftop. With emerging storage solutions that use lithium-ion batteries and have autonomous capabilities, battery backup may become a more attractive option by reducing the costs and complexity.

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