With battery technology becoming an increasingly important sector of the solar panel installation market, it is now more important that the consumer understands the terminology and definitions which are widely used by representatives, surveyors and installers.
The following are some of the most commonly used terms that relate to batteries connected to a solar panel installation.

Useable Capacity

Capacity is the amount of energy in kWh (units) that a battery can store. Batteries should never be drained completely but some are misleadingly sold quoting ‘total’ capacity. Check what is being stated. ‘Useable capacity’ is the figure you need to know.
Most home solar batteries are designed to be ‘stackable’, meaning that you can include multiple batteries with your solar-plus-storage system to get extra capacity.

Capacity gives you the size of the battery but it does not tell you how much electricity a battery can provide at a given moment. To get the full picture, you also need to consider the battery’s power rating. In solar batteries, a power rating is the amount of electricity that a battery can deliver at one time. It is measured in kilowatts (kW).
A battery with a high capacity and a low power rating would deliver a low amount of electricity (sufficient to operate a few important appliances) for a reasonable amount of time. A battery with low capacity and a high power rating could run the whole house, but only for a few hours.

Cycles & Depth of discharge (DoD)
A cycle is one complete discharge and one complete charge. Usually though, it does not work that way in real life. A battery may only discharge 25%, then recharge 25%. This would be 1/4 of a cycle. So you need to know the number of cycles covered in the battery warranty. Only then can you work out how many kWhs (units of electric) your battery will deliver over its warrantied lifetime.

Generally, solar batteries always need to retain some charge owing to their chemical composition. If you use 100 percent of a battery’s charge, its useful life will be significantly shortened (just like a mobile phone battery).
The depth of discharge (DoD) of a battery refers to the amount of a battery’s capacity that has been used.

Most manufacturers will specify a maximum DoD for optimal performance. For example, if a 10 kWh battery has a DoD of 90 percent, you shouldn’t use more than 9 kWh of the battery before recharging it. A higher DoD means you will be able to utilize more of your battery’s capacity.

Round-trip efficiency
A battery’s round-trip efficiency represents the amount of energy that can be used as a percentage of the amount of energy that it took to store it. So, if you feed 5 kWh of electricity into your battery and can only get four kWh of useful electricity back, the battery has 80 percent round-trip efficiency (4 kWh / 5 kWh = 80%). A higher round-trip efficiency means you will get more economic value out of your battery.

Some battery storage systems only deliver 800w of power; but bear in mind that a kettle needs 2,000 watts. Also, if you are generating 4kW but the battery can only take on 3kW then 1kW of your free electricity will be wasted by being sent to the grid.
It is important therefore 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.

Batteries will ‘cycle’ (charge and drain) daily and just like in a mobile phone, its ability to hold a charge will gradually decrease the more it is used.
A solar battery will have a warranty that guarantees a certain number of cycles and/or years of useful life. Because battery performance naturally degrades over time, most manufacturers will also guarantee that the battery keeps a certain amount of its capacity over the course of the warranty. So when the question regarding the lifespan of a battery is raised, then the answer will depend on the manufacturer of the battery and how much capacity it will lose over time.
If a battery is warrantied for 5,000 cycles or 10 years at 70 percent of its original capacity it means that at the end of the warranty, the battery will have lost no more than 30 percent of its original ability to store electricity.

Most systems are designed just for storage. However, some offer backup capability to provide power when there is a power cut. To prevent damage to your battery or appliances some of your circuits may need to be rewired. In addition, you will need a larger storage capacity to keep some power in reserve.

The type of battery that is installed will determine whether it requires regular maintenance and if so, how much is needed. 

NMC batteries, like LFP batteries, require zero maintenance.

With certain exceptions, nearly all types of solar-driven batteries are sealed, so there is no need to refill them. One such exception is a solar lead acid battery where at the appropriate times you lift the cap off it and replace the solution. However despite the lower initial price, this type of lead-acid solar battery is highly inefficient when compared with lithium-driven solar batteries.


Solar batteries do not last as long as solar panels. Currently, a high-quality solar battery will last for approximately10-15 years, which is dependent on the quality of the equipment, the skill used in the installation and how much use is made of the battery over a period of time.

Click here to get a free quotation on a battery installation

⇐ Previous Page      Next Page ⇒