Solar storage: Coupling solar with storage makes economic sense. Adding batteries to your photovoltaic system increases self-consumption and thereby reduces reliance on the grid. There are specifications one needs to consider when evaluating battery options ie power ratings, depth of discharge, round trip efficiency and warranty.

Capacity and power: The total amount of electricity that a battery can store is measured in kilowatt hours (kwh). Deep cycled batteries are designed to be stackable’, meaning that you can add more to get extra capacity. Capacity tells you how big your battery is, but not how much electricity it can supply at any given moment. You also need to consider the battery power rating. In the context of solar batteries, the power rating is the amount of electricity a battery stack can deliver at due time, which is measured in kilowatts (kw). A battery with a high capacity and a low power rating delivers a low amount of electricity for a longer period. A battery with a low capacity and a high power rating can run your entire home, but only for a few hours.

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Depth of discharge (D.O.D): Refers to the amount of battery capacity that has been used eg a 10kwh battery that had a D.O.D of 80 percent means that you should not use more than 8kwh of capacity before recharging it. A higher D.O.D means that you can utilise more battery capacity.

Round trip efficiency: Is the amount of energy that can be used as a percentage of the amount of energy that it took to store it eg: if you feed 5kwh of electricity into your battery and get 4kwh of useful electricity back, the battery has an 80 percent round trip efficiency 4/5kwh=80 percent. The higher the round trip efficiency means that you will get more economic value out of your battery. However, there are internal resistance losses due to its construction.

Battery life and warranty: “Charge and discharge is called a ‘cycle’. The ability to hold a charge will gradually decrease the more you use it. Batteries come with a warranty that guarantees a certain number of years/cycles of useful life. Performance degrades over time. How long a battery stack will last will depend on the quality of the brand and how much capacity it will lose over time. A warranty of 5 000 cycles or 10 years at 70 percent of its original capacity means that at the end of the warranty, it would have lost more than 30 percent of its original ability to store energy.

Home energy storage and electric vehicles (EV) are based on the same technology using advanced batteries to create more efficient, sustainable products that can reduce green house gas emissions. A fully charged battery system can run your home overnight when your panels are not producing. You will need to establish a few variables such as how much energy you consume per day, capacity and power ratings an whether you are off the grid or grid tied. One needs to be ultra conservative, reduce heavy loads and consumption to maintain storage power.

Best batteries for solar systems: Lithium ion battery technology is the best option for storing power to use when required in a photovoltaic system. They are built compact, lighter and has a higher depth of discharge with a much longer lifespan. Designed maintenance free, scaleable and stacked with falling prices and improving efficiencies.

Affordable deep cycled lead acid, absorbed, glass matt and gel batteries require maintenance, low depth of discharge, requires a cool, dry and ventilated area and a short lifespan.

Mahomed Iqbal Peerbhay

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