There are 4 key features to consider when looking to buy a solar battery: the power and capacity ratings, the depth of discharge, the efficiency rating, and the warranty.
Let’s take a closer look at each of these terms and what they mean.
1. Power and capacity ratings
The first two things you need to look at when purchasing solar battery storage is its capacity rating and the power rating.
The capacity rating tells you how many kilowatt-hours (kWh) of electricity a solar battery can hold. This represents the actual supply of (or how much) electricity you have stored in your battery.
The capacity rating isn’t very useful on its own. You also have to consider the power rating of a battery. The power rating tells you how much electricity a battery can deliver to your home at one time, measured in kilowatts. This will give you an idea of how many appliances you can power in your home with a solar battery.
Batteries with a high capacity and a low power rating are useful as emergency backup generators, as they can power a few important appliances, like a refrigerator or a washing machine, for a prolonged period of time.
A battery with a low capacity and a high power rating will be able to power the whole house, but only for a few hours because there is less electricity stored in the battery.
2. Depth of discharge (DoD)
The depth of discharge (DoD) of a solar battery is the percentage that a battery has been discharged relative to the total capacity of the battery. Most solar batteries will have a specific DoD listed to maintain the health of the battery.
Higher DoD ratings allow you to use more of the energy stored in your solar battery before you have to recharge it.
For example, let’s say you have a solar battery with a 10 kWh capacity and a recommended DoD of 60%. This means you shouldn’t use more than 6 kWh of electricity before you recharge it. Using any more than 6 kWh could damage the battery.
3. Round-trip efficiency
The round trip efficiency of a solar battery represents the amount of energy you can use from your solar battery compared to the amount of energy it took to store that energy.
So, let’s say your solar panels sent 10 kWh of electricity into your battery, but only 8 kWh of that electricity was actually stored and can be used. This means 2 kWh of electricity were used by the battery’s operating system to actually store and release the electricity, making the battery’s round-trip efficiency rating 80%.
High efficiency batteries will end up saving you more money, because more of the electricity that you produce will be usable than if you had a lower efficiency battery.
A solar battery’s warranty will give you an idea of how long the battery should last. Most solar home batteries are believed to have a battery life of at least 10 years with regular use.
Solar battery manufacturers usually measure warranties in terms of ‘cycles’. A cycle occurs when your battery fully charges and then drains to the recommended DoD. Each time a battery cycle is completed, the battery’s ability to hold a charge decreases.
How you use your solar battery influences how many cycles it will go through. Because of this, a solar battery warranty will guarantee the battery will operate at a certain capacity not only after a specified number of cycles, or cycle life, but also after a specified number of years.