While the concept of energy storage has been around for decades, new solar power generation systems have received a lot of press lately. The number of homes and businesses venturing off the grid has increased drastically over the last few years and their upwards trajectory is showing no signs of slowing down. In fact, here in Canada, there were around 2.5 gigawatts worth of installed solar energy systems, which represented a million homes, in 2016.
With the global interest in solar energy skyrocketing, the advancements in solar battery technology have been significant as well. Modern solar power storage systems are more innovative and efficient than ever, with exciting improvements in every aspect.
A couple of decades ago, home and business owners that relied on solar power typically turned to nickel-based batteries for their solar energy storage needs. However, now there are better and more efficient options available, with lithium-ion and lead acid batteries being the two main battery types used today.
Over the course of this article, we’ll discuss how lithium-ion and lead acid batteries compare with each other when used for power storage in a solar energy generation system.
Lithium-ion Vs Lead-Acid Solar Batteries: The Basics
When you build a solar energy generation system, there are three main battery options you have:
Flooded Lead-Acid (FLA)
Starting with FLA batteries, their distinguishing feature is that their electrodes, or “plates” as they’re commonly referred to, are submerged in water. In order to be kept performing optimally, an FLA battery needs to be checked regularly and refilled every one-to-three months.
Failure to maintain them properly can void the warranty and shorten the life of batteries significantly. Furthermore, FLA batteries have to be installed in a ventilated enclosure so the battery gases can escape.
Sealed Lead-Acid (SLA)
There are two types of SLA batteries available, Gel and Absorbent Glass Mat (AGL). Both of them have similar properties, are spill-proof and require little to no maintenance. The main difference between gel and AGM batteries is that gel batteries generally have lower outputs and charge rates. They typically can’t handle as much charge current, which is why they take longer to recharge and put out less power.
Lithium
When it comes to solar applications, the best lithium battery chemistry is Lithium Iron Phosphate (LFP/LiFePO4) batteries. Since it lasts longer, this new technology can be put through deeper cycles. Moreover, unlike lead acid batteries, lithium-ion batteries don’t require any venting or maintenance.
While lithium batteries have higher up-front costs, their superior efficiency means potentially lower costs per kilowatt/hour of capacity over the lifespan of the battery.
Lithium-ion Vs Lead-Acid Solar Batteries: Costs
When it comes to upfront costs, lead acid batteries cost significantly less than lithium-ion ones. A lead acid solar battery system may cost hundreds or thousands of dollars less than a lithium-ion setup of similar size.
However, while lead-acid batteries have lower purchase and installation costs, the superior lifetime value of lithium ion batteries means that the scales are fairly even.
Key Differences Between Lithium-ion and Lead-Acid Batteries
Now that we’ve given a basic overview of how these two types of batteries work, it’s time to delve into how they compare with each other. The following are some of the major differences between the two.
Cycle Life
When a battery is discharged (used to power appliances), then charged back up with solar panels, the process is referred to as a single charge cycle. The lifespan of batteries is measured not in months or years, but in terms of how many charge cycles they can handle before they die. The concept can be compared to putting miles on a car. When you’re assessing the condition of a pre-used car, its mileage is a much more important consideration than the year it was produced, right?
The same applies to batteries and the number of charge cycles they’ve undergone. An SLA battery at your vacation home may have gone through 100 cycles in five years, whereas the same setup may have gone through 400+ cycles in a year at your permanent residence. There are no points for guessing which setup would be in the better shape.
Cycle life is also a function of depth discharge (how much of the battery’s capacity is used before its recharged). The deeper you discharge a battery, the more the stress you put upon it, and the shorter its cycle life.
Depth of Discharge
Like we’ve just discussed, the depth of discharge refers to how much of the battery’s capacity is used before it’s recharged. For instance, if half of a battery’s capacity is used, the depth of discharge would be 50%.
With lead-acid batteries, it’s generally recommended that they should not be run to a depth of discharge any higher than 50%. Discharging the battery beyond that can negatively affect its lifespan.
Lithium-ion batteries, on the other hand, can easily handle deep discharges of 80% or more, which means that they have a higher usable capacity.
Higher efficiency translates into faster charging times. Depending on your system’s configurations, it could also mean you purchasing fewer solar panels and a smaller backup generator.
Efficiency
When it comes to efficiency, lithium-ion batteries are much superior to lead-acid ones. This means more of your solar power is stored and used.
Lead acid batteries only have an 80 to 85% efficiency based on the condition and the model. This means that if you have 1,000 watts of solar energy coming into the batteries, there will only be 800 to 850 watts available after the charging and discharging process.
Lithium-ion batteries, on the other hand, are more than 95% efficient. So, you’d have over 95 watts of power available.
Charge Rate
Lithium-ion batteries can also handle higher amperage from the charger. This means that, compared to lead-acid batteries, they can be refilled much faster.
Lead acid batteries are limited in terms of the charging current they can handle. This is mainly because they overheat if charged too quickly. Furthermore, the charge rate slows down significantly as you reach full capacity.
Energy Density
A lithium-ion battery will be noticeably heavier than a lead-acid battery of the same capacity. While this isn’t a problem for most installers, it may be quite challenging if you’re installing the batteries in your solar energy generation system yourself.
However, this comes with a trade off. Lithium-ion batteries have a much higher battery density when compared with lead acid. This means you can fit more storage capacity into less space. For instance, it typically takes eight lead acid batteries to power a 5.13-kilowatt system. On the other hand, you would only require two lithium-ion batteries to do the same job. So, if you take the size and weight of the entire battery bank into consideration, you’ll find that lead-acid batteries weigh more than twice as much as lithium ones. This can be very useful if you’re operating with limited space.
Environmental Impact
As far as the environmental effects are concerned, lead acid batteries really don’t impress. Compared to lithium-ion batteries, lead acid batteries require a significantly higher amount of raw materials to provide a similar level of solar energy storage capacity. And as we all know, more raw materials mean a bigger carbon footprint.
Furthermore, the lead acid industry is also extremely energy intensive. Even producing the battery itself requires a lot of energy. This results in large quantities of pollution being dumped into the environment.
While the lithium in lithium-ion batteries is sourced from mining, the material required by each battery is lesser, which minimizes the impact on the environment. Lithium-ion solar battery manufacturers are also looking into renewable energy sources for power, which can potentially result in a impressively small carbon footprint.
Imagine creating batteries for storing renewable energy in a manufacturing plant that runs on renewable energy itself. It’s a win-win situation, right?
Recycling
Currently, the recycling rate of lead acid batteries is much higher than lithium-ion batteries, which boosts their credentials for environmental friendliness. However, with that being said, lithium-ion solar batteries have a very high ability for recovery and recyclability, even though they’re recycled much less frequently than lead acid batteries.
The main reason why lithium-ion batteries aren’t recycled as frequently as lead acid ones is simply because the former is still a relatively new technology, and the equipment needed to recycle them is still being developed—which makes it costly. However, as the demand and industry of lithium-ion batteries continues to grow, their recycling is expected to quickly catch up with that of lead acid batteries. In fact, the recycling of lithium-ion batteries may even surpass lead acid when you consider that using recycled lithium is much more cost-effective than mining for more. It’s safe to say to say that the lithium-ion solar battery recycling industry is set to experience dramatic growth over the coming years.
Lead-Acid vs. Lithium-ion: Which Should You Choose?
While the long-term costs of both types of batteries are quite similar, lithium-ion batteries are a much steeper upfront investment. Therefore, we wouldn’t recommend them to those who’re not going to use their solar energy generation system every day.
The type of batteries that are best for you also depends upon other factors, such as the type of the solar energy generation system and its application. Below are the battery types we’d recommend for different applications:
Full-Time Off-Grid Establishment
For solar power generation systems that are going to be used full-time in an off-grid establishment, we’d recommend FLA batteries (if you don’t mind regular maintenance), or premium Lithium-ion batteries for heavy use.
Off-Grid Vacation Home/Cabin
If you own an off-grid vacation home or hunting cabin, chances are, you only visit it a few times a year. This means that you won’t be able to keep up with the regular maintenance required by FLA batteries. Therefore, SLA batteries are your best bet. They don’t require any maintenance at all and won’t go flat if they’re left sitting idle for a few months.
Battery backup System
Let’s say you’re building an energy generation system with battery storage to provide backup during power outages. This means that you’ll be using the system only once or twice a year, or a few times if the power grid in the area is extremely unreliable. Now, the system won’t see enough use for you to consider investing in lithium-ion batteries.
FLA batteries, on the other hand, can be a good option. But again, they require regular maintenance, which can be a headache considering the system will only be used sparingly. This leaves SLA batteries as the best option.
Remote Industrial Use
The decision-making process here is more or less the same. For off-grid industrial sites that see heavy use, lithium-ion solar batteries can be a worthy investment. However, when it comes to powering rudimentary monitoring equipment at an off-grid outpost, SLA batteries can be a more cost-effective way of getting the job done, and you still won’t have to worry about scheduling regular maintenance visits.
The Final Word
As fossil fuel prices continue to rise and emission standards continue to get stricter around the world, the demand for solar power generation and energy storage solutions will continue to grow. Both the battery technologies we have discussed in this article have their own pros and cons and deciding which solar battery technology is better ultimately depends upon your requirements and budget.
If you’re looking into energy storage solutions for a solar power generation system, and want to learn more about the properties of lead acid and lithium batteries, get in touch with the experts at CANBAT. They’re one of the leading general purpose battery manufacturers and suppliers in Canada.
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