ENERGY STORAGE EDUCATION
As we consider Solar-plus-Storage options, there are a lot of detailed product specifications to be accounted for. The most important ones are the Energy Storage’s capacity & power ratings, depth of discharge (DoD), round-trip efficiency, and battery life.
Capacity & Power
Capacity is the total amount of electricity that a Solar Battery Energy Storage System (ESS) can store, measured in kilowatt-hours (kWh). Most Energy Storage Systems are designed to be “stackable,” which means that you can include multiple batteries with a Solar-plus-Storage system to get extra capacity as needed.
While capacity tells you how big your Energy Storage is, it doesn’t tell you how much electricity an Energy Storage System can provide at a given moment. To get the full picture, GXG technical experts consider the Energy Storage’s power rating. In the context of Energy Storage, a power rating is the amount of electricity that an ESS can deliver at one time. It is measured in kilowatts (kW).
Depth of Discharge (DoD)
Most Energy Storage Systems need to retain some charge at all times due to their chemical composition. The depth of discharge (DoD) of an Energy Storage refers to the amount of an Energy Storage’s capacity that has been used. Most our partner manufacturers specify a maximum DoD for optimal performance. For example, if a 10 kWh Energy Storage has a DoD of 90 percent, users shouldn’t use more than 9 kWh of the Energy Storage before recharging it. Generally speaking, a higher DoD means you will be able to utilize more of your Energy Storage’s capacity.
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. For example, if you feed 5 kWh of electricity into your battery and can only get 4 kWh of useful electricity back, the battery has 80 percent round-trip efficiency (4 kWh / 5 kWh = 80%). Generally speaking, a higher round-trip efficiency means you will get more economic value out of your battery.
For most uses of Energy Storage, the system will “cycle” (charge and discharge) daily, especially in the case of centralized Energy Storage. The battery’s ability to hold a charge will gradually decrease the more you use it. In this way, Energy Storage Systems are like the battery in your cell phone – you charge your phone each night to use it during the day, and as your phone gets older you’ll start to notice that the battery isn’t holding as much of a charge as it did when it was new.
Lithium Ion Battery Chemistry
The majority of new home Energy Storage technologies use some form of lithium Ion chemical composition. Lithium Ion batteries are lighter and more compact than lead acid batteries. They also have a higher DoD and longer lifespan when compared to lead acid batteries. Specifically, the Lithium Iron Phosphate chemistry has excelled in the field of renewable power ESS units.