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solaxpowerBattery storage is one of the most exciting technologies at the forefront of our transition to a smarter, low-carbon energy system.

Now you can reduce the amount of money you put in your energy supplier’s pocket. Adding battery storage to Solar PV systems increases your self consumption and reduces your reliance on the grid. So what should you look out for when choosing a battery storage system? Here’s 5 key points to get you started.

What is the ‘Useable’ capacity

Capacity refers to the amount of energy in kWh (units) that the battery can store. No battery should ever be drained completely, however some batteries are sold quoting their ‘total’ capacity while others will state their ‘useable’ capacity, check what’s being stated. e.g. Tesla Powerwall 2 is actually a 14kWh battery, it’s sold as 13.5kWh, it’s useable capacity. 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% and then recharge 25%, this would be 1/4 of a cycle. You need to check how many cycles a battery is warrantied for and then you can calculate how many kWhs (units of electric) your battery will deliver over it’s warrantied lifetime.

What difference does battery chemistry make?

The main two chemistries available are Lead Acid or Lithium. Lead Acid is very cheap to install but is inefficient and won’t last very long. Lithium (ion or iron phosphate) will last longer and deliver more kWhs (units) during it’s lifetime.

Power output

Some battery storage systems only deliver 800w (watts) of power, not much good for a kettle that needs 2000 watts! Check the power output before you buy, otherwise you may find yourself drawing a lot of energy from the grid even when you have energy in your battery.

p/kWh. If a 5kWh battery is warrantied for 3000 cylces it will deliver 5 x 3000 = 15000kWh (units) of electricity over it’s warrantied life. If you divide the installation price by 15000 you will have a p/kwh price. Some battery storage systems will offer a p/kWh price lower than current grid prices, meaning you can ‘bulk buy’ your future electric at lower than today’s grid prices, fixing your costs for the life of the system. Some systems p/kWh price is much higher than current grid prices, meaning you’re throwing your money away on expensive electric that would be cheaper to draw from the grid. You can also consider that most battery storage systems are going to last longer than their warranty.