If you’re new to solar power storage, the sheer number of technical terms used to discuss a battery’s overall functionality can be overwhelming. What does “capacity” mean, and how does it differ from “power rating”? What about “depth of discharge” and “round-trip efficiency”? Learn what these terms mean in this basic glossary for solar battery terms.
For solar batteries, “capacity” refers to the total amount of electricity a solar battery can store. This measurement is expressed in kilowatt-hours, or kWh. For most residential solar systems, batteries are designed to be “stackable” so that you can add many batteries to increase the overall capacity of your system. Increasing your capacity means getting more hours of energy from your battery bank—that’s the “hours” in “kilowatt-hours.” However, this measurement doesn’t tell you just how much energy a battery can give you at once. For that, you’ll need to look at the next term.
A battery’s power rating tells you how much electricity that battery can provide to you at any given time. This is measured in kilowatts or kW. (Note the absence of “hours” or “h” in this measurement.) So, a battery with a low power rating but a high capacity could provide you with a small amount of energy over a long period of time; a battery with a high power-rating but a low capacity would be able to power your entire home, but only for a few hours. This is why it’s essential to look at both of these measurements on a battery and understand how they relate to one another.
Depth of Discharge
This is another important term that relates to a battery’s capacity. Most batteries must maintain a minimum level of charge at all times, which means that the capacity listed on the battery doesn’t accurately reflect the amount of usable power it can store. Depth of discharge (DoD) tells you just how much of the stored energy you can expend before damaging the battery. For example, if you have a 10 kWh battery with 80% DoD, you really only have 8 kWh available to you; a battery with the same capacity and a 90% DoD would offer you 9 kWh of usable energy. Be sure to look at the DoD in conjunction with the capacity when sizing your batteries.
This term refers to how much energy the battery can provide to you in relation to the amount of energy it takes to store that power. All batteries use up some energy as they store it; the higher the round-trip efficiency, the less power they lose. As an example, if your battery has a round-trip efficiency of 80%, it would be able to supply you with 4 kWh of useful energy for every 5 kWh of electricity you feed it. Be sure to look for high-efficiency batteries like Full River batteries to get more out of the power your panels create.