BATTERIES FOR YOUR PV SOLAR SYSTEM
If you are planning to implement an off-grid solar photovoltaic system, the choice of batteries is a key element in the success of your project. You must choose the right capacity, the most efficient battery, and balance quality and price to control costs. Of all the elements that make up the average construction of an off-grid solar system, the choice of battery is the one that requires the most research.
If you are planning your own off-grid solar photovoltaic system project, this article will introduce you to the main considerations to take into account when purchasing off-grid batteries.
TYPES OF OFF-GRID BATTERIES
There are currently two main types of off-grid lead or lithium batteries. Lead batteries are flooded, sealed, AGM, or GEL.
Sealed lead-acid AGM batteries are ideal for high currents, they recharge quickly, offer high efficiency, and require no maintenance. Lead-acid batteries do not operate efficiently at low temperatures and are slower to charge through a generator than lithium batteries under all conditions.
Lithium batteries are highly efficient, are lighter than lead batteries, have a good life span, and have a depth of discharge greater than 80%. They do not work as well at low temperatures (<14C) and are more expensive than lead-acid.
Lead-acid AGM batteries work best where maintenance is difficult and you work with higher currents. Lithium works best in permanent structures with insulation and where space and weight are critical or where a generator is regularly required.
Flooded batteries are submerged in water to operate and will need to be recharged every 30 to 90 days. Sealed batteries are more expensive but require no maintenance.
CAPACITY AND POWER
The capacity and power of off-grid batteries take into account the amount they can store in kWh/AH. The battery rating will tell you how much a battery can deliver in kW.
An off-grid battery should slightly exceed the daily generation potential of your solar panels while providing enough power to power the property for 24 hours.
DEPTH OF DISCHARGE
The depth of discharge refers to the amount of energy supplied by the battery in a given cycle. The maximum recommended depth of discharge for lead-acid batteries is 50%, while lithium can withstand up to and sometimes more than 80%. Therefore, to avoid damage to lead batteries, the size of the battery bank should be increased.
Lithium batteries have an integrated management system that prevents deep discharge and therefore damage to the batteries.
The loading time is exactly that. It’s the time it takes to recharge off-grid batteries to 100%. Lithium batteries charge faster and have a lower self-discharge rate than lead batteries.
Lead-acid batteries take longer to charge and lose about 5% of their charge each month when not in use.
Round-trip efficiency measures the amount of energy lost between production and use.
For example, if you produce 10 kWh of energy from your panels and get 8 kWh of energy from your battery, you have a round trip efficiency of 80%.
BATTERY LIFE AND WARRANTY
The life of off-grid batteries is measured in cycles. A complete cycle is a charge of the panel and a discharge of the building. A cycle is usually performed daily when the system is in service.
As long as you do not deep discharge your batteries, a battery will generally reach its guaranteed life. Some manufacturers measure this life in years and offer a 5- or 10-year warranty, while others measure it in actual cycles.
Cost is always a factor in solar projects. You will need to balance the features and requirements of your system with the most practical battery.
Lithium batteries are more efficient but more expensive. Lead batteries are cheaper but less efficient. Some types of lead-acid can withstand higher currents, while lithium has a greater depth of discharge and longer life.
As you can see, there is a lot to consider when choosing solar batteries. There is no “best overall solar battery” off-grid, but only the type that best suits your application, your needs, and your budget.