The Energy Management System (EMS) in Carmanah EverGEN systems controls and monitors the batteries. Carmanah uses Trojan batteries because they have very long cycle life, compared to other batteries.

Battery lifespan is defined as the time taken for the battery capacity to degrade to a certain level, usually 80%. This lifespan depends partly on the way the battery is made, but the lifespan of all batteries depends on the way it is charged, the depth of discharge and temperature.

Battery Capacity

When given a choice between two batteries, most people would choose the one with the largest capacity. While initial capacity is important, how that capacity lasts over time is much more important. For solar LED lighting the most important criteria for a battery is the number of charge-discharge cycles it can deliver. This determines how often batteries will have to be replaced.

Initial battery capacity in Amp Hours (Ah) is often used when specifying batteries; however (as seen in the graph below), batteries with high initial Ah capacity can actually have a shorter cycle life. A better method of specifying batteries is by the cycle-life rating, which is the number of cycles the battery is rated for at a given level of discharge.

Battery Cycle Life

As batteries charge and discharge, a small amount of damage is done to them. The amount of damage depends on the type of battery and how deep the discharge is (i.e. how far the batteries are depleted). Batteries are lab-tested to determine how many cycles the battery can experience before it dies. These cycle test results are an excellent way of comparing batteries. However, there are other factors that affect battery life, such as grid corrosion and dry-out. As a result, cycle test results alone can’t be used to determine expected battery life.

The depth of discharge a battery experiences is determined by the way the solar LED lighting system is configured. Factors include the lumen output of the system, the location of the system, and the operating profile the system is running. It is critical that system modelling take battery depth of discharge into account to preserve battery health and lifespan and to ensure system performance over the long term.

Ambient Temperature

High temperature accelerates battery aging, making thermal management of the batteries an important consideration in solar LED lighting design.

Battery charge acceptance varies with temperature, making them prone to over and under-charging when temperatures reach high or low extremes. Over and undercharging affects the life span of the battery. The negative impact of temperature extremes can be mitigated by controlling the ambient temperature of the batteries.

Heat

As temperature increases, batteries accept charge more rapidly at a given voltage and the voltage at which they indicate full charge will decrease. If the battery charger does not account for temperature variations, it may believe that the battery never reaches full charge. This can create thermal runaway with batteries becoming hot, accepting more charge, creating more heat, which allows them to continue accepting charge. In this way, a hot battery can become overcharged if accepting charge at a voltage intended for room-temperature charging. This situation significantly reduces battery life span.

Temperature must be taken into consideration in the design of the system, including battery placement and battery charging technology.

Learn more about temperature compensation and battery charging in the energy management system section.

Cold

Cold conditions result in reduced battery capacity. Batteries in lower states of charge are more likely to freeze in lower temperatures. System modelling tools must account for temperature extremes to avoid deep discharging batteries in cold conditions. This preserves system health and ensures reliable system operation in cold temperature extremes.