Post By
Samarth Gara

Lead-acid vs Lithium-ion battery for Solar

February 1, 2021

In this article, we will discuss one of the most important aspects of creating a solar panel system, which is the battery. Regardless of whether you are planning to move off the grid or add some extra energy storage capacity to your existing grid-connected system you have two main options to choose from, in terms of battery types. These are Lead-acid and Lithium variants and both have their own set of pros and cons. We will discuss some of these in detail and give you the most comprehensive picture regarding which battery type is suitable in different situations and setups.

For starters, we can say that Lead Acid batteries offer a tried and tested technology that costs much less but require a lot of rigorous consistent maintenance. 

On the other hand, lithium is one of the best current battery technologies present and they are known for having longer shelf lives and a higher degree of efficiency. It does however cost more than lead-acid battery types. In the following section, we will discuss some of the specifics regarding the two types of batteries. 

 

Flooded Lead Acid (FLA)

This type of a lead acid battery is distinguished from others by the submergence of their plates in water. Not only do they require regular and thorough checking, these batteries also require refilling every one to three months, so as  to function at optimum efficiency levels. If sufficient care and testing is not carried out, the warranty on these products may become void, which is to be ensured.. Also, FLA batteries need to be kept in a very well ventilated enclosure as they emit gases. These gases need to be expelled through a good ventilation system. 

 

Sealed Lead Acid (SLA)

This is the second variant of lead-acid batteries which are very popular in the market, when it comes to people setting up solar panels. SLA batteries can also be divided into two different types. These are called Absorbent Glass Mat(AGM)  and Gel which are slightly different from one another and at the same time shares quite a few properties. Not only are these batteries spill-proof, they also require the most minimum levels of maintenance on a daily basis. 

 

The main point of difference that sets apart AGM batteries from Gel types is that the latter tend to have relatively lower charge rates as well as a lower and more limited output capacity. Gel batteries are also not ideal for handling higher amounts of charge current. This also means that they require frequent charging and are also not capable of consistent high output levels. 

 

Lithium

Lithium batteries are the last option at your disposal and are often considered to be state of the art batteries, in terms of technology used and the efficiency they offer. Even among the lithium battery models, there are some which are better than others in case of usage with solar panels. 

The most recommended lithium battery chemistry to use with solar applications is Lithium Iron phosphate which is  also commonly known as LFP batteries in many local markets around the world. Not only have lithium batteries proven to last t longer, they can also be put under great pressure with deeper cycles and higher loads. Another important thing to consider is that they do not require a good ventilation system like the lead-acid battery variants. 

Since they represent the best in battery technology at present , lithium batteries are costlier compared to the rest mentioned here. However, they are more efficient and this can potentially save some money over time.. This is because you might end up paying significantly less per kilowatt-hour of capacity in the case of lithium variants. 

 

Key Differences between Lead Acid and Lithium Battery 

Life Cycle 

One charge cycle is referred to as the total time taken to discharge a battery by connecting it to appliances and then recharging with the help of panels. In the case of solar panel batteries, their efficiency is measured not in terms of the number of years the battery can run for, but the number of cycles they are capable of, before they wear out and expire. 

An analogy that might help you to understand this concept better is the things you consider before buying a used car. Obviously, the mileage is a lot more important than the year of production in order to give you an idea whether it's worth buying or not. 

It's more or less the same in the case of batteries. It all depends upon usage frequency. For instance, in the case of a vacation home, a sealed-acid battery may go through 100 cycles in 4 years. The same battery will go through more than 300 cycles in the case of a full-residence in roughly the same amount of time. Obviously in this case, the one that has gone through lesser cycles will be in better shape. 

An important factor that has a bearing on the cycle life, is the depth of discharge. It is used to denote the capacity of usage before recharging the battery. Deeper discharges tend to put more pressure on the battery and this results in the shortening of life cycles. 

 

Depth of Discharge 

As mentioned before, the discharge depth basically denotes the overall usage capacity of a battery before it gets recharged. So for instance, if you use 3/4th of your battery’s capacity, the discharge depth will be  75 percent. It's important to note that batteries actually do not discharge fully when in use. They also have a recommendation telling the user the ideal depth of discharge rating before it requires a recharge. 

In the case of lead-acid batteries, it is recommended to use up to 50 percent of its discharge capacity before recharging the battery again. Beyond that, there is a chance of a negative impact on the lifespan of the battery. 

On the other hand, lithium-powered batteries are equipped to handle deep discharge levels of upto 80 percent. This automatically translates to a higher usage capacity. 

 

Efficiency 

It is common knowledge that lithium batteries are generally more efficient across all devices. They are capable of storing and using more solar power. 

Lead-acid batteries have around 80-85 percent efficiency, depending on the particular model in question. So for instance, if you have 1000 watts of solar energy absorbed by the batteries, you will have around 800-850 watts available for usage after the charging and discharging process. 

Lithium batteries on the other hand are more efficient and generally have an efficiency rating in the high 90’s, depending upon the model and other specifications. 

Higher efficiency levels entail that batteries charge faster. Also, depending upon the specifics of your setup, it could also mean that you don't need as many solar panels or you can easily work with a smaller backup generator and lesser battery capacity. 

 

Charge Rate 

As lithium batteries are more efficient, they can also charge much faster and thus saves time. As they are able to handle a higher degree of amperage from the charger, they are equipped to refill much faster as opposed to the sealed lead-acid batteries. 

The rate of charge is expressed as a fraction such as C/5, where C = the capacity of the battery is amp-hours(Ah). So this means that a battery with a 430 Ah rating would receive 86 charging amps. 

In the case of Lead-acid batteries, they are a lot more limited in terms of charging capacity. This means that the battery is at risk of overheating if you charge it continuously for too long. Apart from this, another issue with these types of batteries is that the charge delivered gets weaker and slower as you approach maximum capacity. 

Lead acid batteries are capable of charging at around C/5 during the bulk phase at around 85 percent capacity. After the bulk period, the charger slows down automatically in order to top off the batteries. So, the conclusion that is drawn from this discussion is that lead-acid batteries usually take a longer time to charge and in some cases it might take up to twice the amount of  time compared to a lithium-powered battery. 

Energy Density 

In terms of mass and weight, it is a general rule of thumb that lead-acid batteries are heavier in terms of weight compared to lithium variants. For fixing solar panels, most of the installers can handle the extra weight without any issues, so no need to worry. However, if you are planning to do DIY style, then you should know that lithium batteries may prove a bit more tricky to install without any kind of professional help. We recommend you to get some help in lifting and fitting the panels. 

However, like everything in life, here also you have a trade-off to keep in mind. Lithium batteries have a higher energy density as compared to lead-acid variants. This means that lithium batteries are able to fit a higher amount of storage capacity in less space. 

 

Lithium vs Lead Acid: Which battery is ideally suited for you? 

In this section, we will look at different applications and try and give you the benefits of using each different battery variant. 

 

Full-Time Off-Grid Assistance 

In this case, we would urge you to go for either Flooded Lead Acid or Lithium battery variants. In case you plan to live off the grid full time, we would highly recommend FLA battery types. This requires regular maintenance. However, if you plan to undertake heavy usage, Lithium battery types are the best bet. 

 

Off-Grid Cabin/Vacation Home

If a solar panel system is set up for your vacation home or cabin, it is likely to be in use for a few days in a year on particular occasions. For this, a Sealed Lead Acid battery variant is recommended  as against FLA batteries, which requires regular maintenance.. In these situations, we always recommend SLA types as they are a lot more resilient and are capable of functioning over longer periods without having to undergo regular maintenance checks. 

 

Battery Backup System 

In this case, we would once again recommend SLA battery types. If you are setting up a solar panel for emergency power requirements during power cuts, then you will not be using the system all the time, but only on certain occasions. The requirement, in this case, is to have a battery that you use occasionally  and that doesn't demand too much maintenance. This rules out  FLA variants.  Additionally, you should not spend on lithium batteries for a backup solar power setup. Thus, the only other viable option left is to choose  SLA types. 

 

Remote Industrial Use 

You can go with either an SLA battery or a lithium battery for this type of setup. Industrial sites or areas with high power requirements should always go for lithium batteries as they would offer you the best price to performance ratio. 

Conclusion 

In this article, we tried to give you some pointers on various types of batteries best suited for different solar panel setups. We started off with a small intro on the various options available and what they offer. Then,  in the subsequent sections, we tried to offer more details in terms of FLA, SLA, and Lithium battery variants and where they should be ideally used. Hopefully, this article finds some good use for you and you can get the right kind of batteries for your solar setup as early as possible. 

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