If you’re exploring the possibility of adding battery storage to your current solar PV system or purchasing a combined solar PV and battery system all in one go, you’ll want to understand the terms Depth Of Discharge (DoD) and Cycle Life when it comes to choosing a battery. These two specifications are important factors when considering battery and could impact your savings, the lifespan of the battery and the way you use your stored energy.
Depth of Discharge
In simple terms the depth a battery is discharged is the percentage a battery has been emptied to its total capacity. The DoD is usually referred to in a percent, so a battery that has had a DoD of 100% means it has discharged to its full capacity. For example, if a 15-kWh battery was fully charged and had a DoD of 100% it has discharged 15kW. If it had a DoD of 80% it would have only discharged 12kW.
Most solar batteries require to preserve some charge at all times, as discharging at 100% or too deeply can considerably shorten the batteries lifespan.
Generally speaking, batteries these days have a lifespan between 10-15 years however this can be heavily affected by the number of discharge cycles it has been through and the depth of those discharges. For example, a discharge of 10% will make less of an impact or degradation to a battery’s lifespan, than a discharge of 40%.
When researching into different batteries the manufacturers will usually specify a maximum DoD for best performance. For example, if it’s specified that a 10-kWh battery recommends a maximum DoD of 70%, you shouldn’t use more than 7-kWh from the battery without allowing it to recharge.
A battery’s cycle life is based on the number of times a battery can be charged and discharged before the battery reaches the end of its functional life. The depth of each discharge will be a major impact on the cycle life of a battery. For example, a manufacturer may state that a battery has 1,200 cycles at a 80% DoD which would mean the same battery would have 4,800 cycles if your typical DoD was at 20%.
Is Adding Battery For You?
For a battery to be beneficial, a solar system needs to be generating excess energy during the day for the battery to store. This excess energy is there to run appliances at night or when the sun is not out. If you have a solar system without battery your home will run off the grid during these times and any excess energy will be fed to the grid in return for a feed-in tariff.
Adding a battery to your solar system is the next step for energy independence, however the benefits of batteries are still secondary to the benefits of installing a solar system. For some households adding a battery system can be of great benefit and minimise a home’s reliance to the grid or allow you to become 100% independent from the grid as part of a standalone (off-grid) system. For others the cost of a battery can outweigh the benefits, especially if you have a solar system under 5kW or your system is not generating enough excess energy.
Learn more about batteries and whether they’ll benefit your household!