As we increase our use of renewable energy, it’s important to ensure that electricity supply meets demand. This is especially important when it comes to energy generation through the likes of solar. After all, solar generates electricity when there is sun, but our demand for electricity is strongest early in the morning and in the evening, when there is little to no sunshine.
To ensure power generation matches consumption, both in terms of power and time of day, having the right battery installed alongside your solar system is essential. This guide will give a rundown of the two main types of batteries for solar so that one can be sure to make the right purchasing decision!
Table of Contents
What is a battery? Why is it necessary for solar systems?
What is a lead-acid battery?
What is a lithium battery?
Lead-acid vs. lithium batteries: The key differences in solar
Which battery should you buy for your solar system?
Conclusion
What is a battery? Why is it necessary for solar systems?
A battery is a device that can store energy and discharge it when required. This makes it an essential component of those energy systems that only produce energy at certain times, or under certain conditions — such as solar or wind.
There are different types of battery, each with different functionalities and requirements. The two main types of battery used in solar photovoltaic systems are lead-acid batteries and lithium batteries.
What is a lead-acid battery?
Lead-acid batteries are one of the oldest battery systems available, with over 150 years of history and development. It stands to reason, therefore, that there are newer and more efficient batteries on the market. However, the reliability and price tag of lead-acid batteries have kept them at the forefront of renewable developments.
There are two main types of lead-acid battery: flooded lead-acid battery (FLA) and sealed lead-acid battery (SLA).
What are FLA batteries?
FLA batteries are characterized by having plates that are submerged in water. This protects them but means that they must be checked regularly, with the batteries needing refilling every 1 to 3 months. Despite this inconvenience, FLA batteries are the cheapest option. They are also slightly lighter than SLA batteries and have a longer life cycle.
What are SLA batteries?
SLA batteries are sealed and spill-proof, meaning there is no need for maintenance. There are two types of SLA batteries, absorbent glass mat (AGM) and gel. Of these, AGM batteries can cope with a higher charge current, meaning they recharge faster and output more charge than gel batteries. AGM batteries are also cheaper and work in a wider range of environments. Gel batteries have the added safety measure of being gel, as opposed to liquid, meaning a very low chance of leakage.
What is a lithium battery?
Lithium batteries are a newer premium battery technology than lead-acid batteries, requiring no maintenance or venting and able to go through much deeper cycles, meaning more power available during times of no charging electric current.
The main lithium battery type used in solar photovoltaic systems is lithium iron phosphate, shortened to LiFePO4 or LFP batteries. These batteries are particularly well-suited to solar applications due to their long life, higher efficiency, deep discharge capacity, light weight, and compact size. However, although prices level out over a long period, the initial investment cost is much higher with LFP batteries than with lead-acid batteries.
Lead-acid vs. lithium batteries: The key differences in solar
Cycle life
The cycle of a battery refers to the cycle of one discharge and subsequent recharge. As with a car, batteries become worn by usage more than age, meaning the available cycle life dictates how long the battery will efficiently hold the solar system’s charge — the cycle life is understood as the life of the battery. Lead-acid batteries tend to have a cycle life of between 1000 and 1500 cycles, with FLA batteries having a higher cycle life than SLA batteries. Lithium batteries have a cycle life of between 3000 and 5000 cycles, with some reaching much higher. A battery’s cycle life can be extended with proper care and lower discharge percentages.
Efficiency
The efficiency of a battery affects the charging time and power availability during charging, with faster charging meaning more available power. Lithium batteries are the most efficient, with an efficiency rating of 95%. This means that after the charge and discharge process, a user can access 950 watts of every 1000 watts of energy coming in through the solar panels. With lead-acid batteries that efficiency goes down to 80%-85%, meaning that 800 to 850 watts of every 1000 watts would be available during charge.
Depth of discharge (DOD)
Lithium batteries have a depth of discharge (DOD) of up to 80%-95%, meaning they can be discharged up to this percentage without having to be recharged and without damaging the battery. Comparatively, lead-acid batteries only have a DOD of up to 50%, and discharging more than this will damage the battery. This means that with a lithium battery, users have much more available charge at times of no energy production — at night when using solar panels, for example.
Recycling
Recycling is a constant problem with batteries, however, thanks to the long history of lead-acid batteries, the infrastructure is already in place to make these 100% recyclable, with all components able to be turned into new batteries. Lithium batteries, as a newer technology, are not as efficient in this space. Currently, 25% to 96% of a lithium battery cell can be recycled, depending on the separation technology. However, in recent years, research has been underway to develop a method to recover some of the key raw materials, including cobalt, nickel, copper, aluminum, lithium, graphite, and manganese from lithium battery cells.
Price
Lithium batteries have a much higher up-front cost than lead-acid batteries. However, lithium batteries have a life cycle of around 10 years against only 3 to 5 years for lead-acid batteries. This means that over time, the sum of the cost of batteries evens out. Moreover, due to lithium’s higher DOD, lithium battery holders will get more charge for their money at any one time.
Which battery should you buy for your solar system?
The best battery for your solar system will depend on your needs: frequency of usage, power needed, budget, and more.
For full-time usage, such as homes that are completely off-grid, the best option would be to opt for lithium batteries. These have a long battery life, very high discharge rates at times of not much charge current (when there is no sun for solar), and are more efficient than lead-acid batteries. If a lower price option is needed, FLA batteries can also work well, since they have a longer cycle life than SLA batteries and maintenance is not a problem if the owner is there full-time.
For part time usage, such as a leisure battery for an RV or a holiday home that runs on solar, SLA batteries will work fine. They have a lower cycle life than lithium batteries but since they will only be used on occasion, they should still last a long time. Additionally, since they do not require the maintenance that FLA batteries need, they can be left idle and will not become damaged. SLA batteries are a good back-up battery option for the same reasons.
For industrial-scale energy needs, lithium is a great choice thanks to its DOD, high efficiency, and cycle life. However, if the energy needs are not too high at times of no sun, a cheaper and efficient option would be to use SLA batteries.
Conclusion
Both lead-acid batteries and lithium batteries are great options for solar, with each offering its own pros and cons. On the whole, the most efficient option is to use lithium batteries if the price is acceptable. However, recycling remains an issue.
For price and efficiency reasons, buyers in developed countries usually opt for lithium, while those in developing countries opt for lead-acid. Another reason for this is that those users in developing countries will often recycle and reuse the parts themselves, making lead-acid batteries a better option for them.
