Solar Battery Storage

How Does Battery Storage Work?

Solar battery storage works by storing excess solar production during the day for use at night. This is more cost effective than selling it back to your retailer during the day at a cheaper rate. On a time of use tariff, you can also purchase gridpower during cheaper periods, reducing how much you purchase during peak periods. Battery systems can also be configured to provide power in an outage. There are a few different types of storage systems like Hybrid inverter, AC Coupled and DC Coupled solutions.

What’s the ‘useable’ capacity?

Capacity is the amount of energy in kWh (units) that a battery can store. Batteries should never be drained completely. However, some are misleadingly sold quoting ‘total’ capacity. Check what’s being stated. ‘Useable capacity’ is the figure you need to know. Though Sofar Solar is 2.4kWh to 19.2Kw, it can only use 80% of the batteries, 20% is useable. It will never fully discharge to prevent damage.

What are ‘cycles’?

A cycle is one complete discharge and one complete charge. In reality it doesn’t happen like that. A battery may only discharge 25%, then recharge 25%. This would be 1/4 of a cycle. So you need to know how many cycles a battery is warrantied for. Only then can you work out how many kWhs (units of electric) your battery will deliver over its warrantied lifetime.

What’s the battery chemistry?

There are two main types available:

Lead Acid


Lead Acid is very cheap to install but it’s inefficient and won’t last for long. Though the price of Lithium (ion or iron phosphate) is higher, it’s much better value. It’ll last far longer and deliver more kWhs (units) during its lifetime.

What’s the power output?

Some battery storage systems only deliver 800w (watts) of power. No good if you want a cup of tea (your kettle needs 2000 watts).

So it’s essential that you check the power output before you buy, otherwise you may find yourself drawing a lot of energy from the grid even though you have energy in your battery.

What’s the price per kWh?

Some storage offers a price per kWh lower than current grid prices, meaning you can ‘bulk buy’ future electric fixing costs for the life of the system. Some systems p/kWh is much higher than current grid prices, meaning you’re throwing your money away on expensive electric. Worth remembering too, is that quality battery storage systems are likely to work past their warranty.

What about power cuts?

Most systems are designed just for storage. However, some offer back-up capability. Two things to consider. First: to prevent damage to your battery or appliances you may need to rewire some of the house. Second: you’ll need a larger storage capacity to keep some power in reserve. If backup is essential.