Batteries old

A battery’s capacity is the total amount of energy it can store, measured in kilowatt-hours (kWh). The power rating is the amount of electricity that a battery can deliver at one time, measured in kilowatts (kW). A battery with high capacity and low power rating will deliver a low amount of electricity for a long time. A battery with low capacity and high power rating can run an entire home or larger operation, but only for a few hours.

Most solar batteries need to retain some charge at all times due to their chemical composition and to prolong their lifespan. The DoD refers to the maximum amount of a battery’s capacity that should be used. For example, sealed lead-acid solar batteries are usually operated at ≤50% DoD to achieve a reasonable cycle life, while lithium-ion batteries can operate at 80% DOD, 8kWh from a 10kWh battery, and still provide 5 years or more cycle life.

Round-trip efficiency represents the amount of energy that can be used as a percentage of the amount of energy required to fully charge a battery. For example, if a 5kWh capacity battery, which delivers 4 kWh electricity, would typically require 110% to 120% times the 4kWh to be fully recharged. The battery has 80% to 90% in round-trip efficiency. One should, however, remember that the battery is part of the total system, and the system also has inefficiencies and energy losses.

A battery’s ability to hold a charge gradually decreases the more it is used. For example, a battery might be warrantied for 5 000 cycles or 10 years at 70% of its original capacity. This means that at the end of the warranty, the battery will have lost no more than 30% of its original ability to store energy.

Solar batteries come with warranties that guarantee a certain number of cycles and/or years of useful life.