An important aspect to consider while going solar is the type of solar battery technology you will use to store the excess energy generated by your solar panels. Connecting a solar battery to your system can help you make the most of your solar investment by allowing you to store and use the excess energy rather than send it back to the grid.
But which technology is the best for solar and why?
There are several types of solar batteries available, each with its own unique features and benefits. In this article, we will explore the various options and help you understand each type’s pros and cons, so you can make an informed decision about which one is right for your needs.
Whether you’re looking for a battery that can store a lot of energy for later use, or one that is more compact and easy to install, we’ve got you covered.
Types of solar batteries
Here is a detailed overview of the different types of solar batteries available and how they can help you to make the most of your solar photovoltaic system.
Lead acid solar batteries
Lead acid batteries, as the name suggests, utilize lead and sulfuric acid to function. The lead is submerged in the acid, allowing for a controlled chemical reaction to generate a charge—the sulfate in sulfuric acid separated from the acid and bonded to lead. To recharge the battery, this chemical reaction is reversed.
Lead acid batteries are the tried-and-tested and most commonly used batteries worldwide. In fact, until around the early 2010s, this was the only option for solar homeowners and businesses who wanted to store their solar energy. They are also one of the oldest types of rechargeable batteries. Since its invention in 1859 by the French physicist Gaston Plante, the technology has been improved, having much better performance (around 85% efficiency) and lifespan today.
These batteries come in two varieties: flooded lead acid (FLA) batteries and sealed lead acid (SLA) batteries. Compared to sealed lead-acid batteries, FLA batteries with lead-acid chemistry are the most common, especially in the car industry. What distinguishes FLA batteries from sealed-acid batteries is their maintenance requirements. FLA batteries require regular maintenance, such as periodically adding water to maintain the balance, while SLA batteries are maintenance-free. The latter also goes with other names, such as a valve-regulated battery, an Absorbed Glass Mat (AGM) battery, or a gel battery.
Pros and cons of lead-acid batteries
| Advantages of lead-acid batteries | Drawbacks of lead-acid batteries |
| Cost-effective—costs less than other types of solar batteries. | Lower lifespan—depending upon your usage, they may last only 2-7 years. |
| Tried-and-tested—they have a sound and well-understood technological base. | 60% depth of discharge—you can only use 60% of their capacity. Use more, and you will shorten their lifespan. |
| Low self-discharge—self-discharge exists but is among the lowest in rechargeable batteries. | Temperature requirements—work best at 20 degrees Celsius. At higher temperatures, their performance and lifespan will keep on degrading. |
| Takes up lots of space. |
You may also like to read: 5 Different Types of Solar Panels: Which One Is Best for Me?
Lithium-ion solar batteries
Lithium-ion batteries are a recent addition to the family of secondary (rechargeable) batteries that uses lithium ions as the main charge carrier. They are widely used in portable electronic devices and electric vehicles. But they are perfect for stationary energy storage systems, such as solar, because they have a high energy density, low self-discharge rate, and low maintenance cost.
They are also relatively lightweight, compact, and have a low risk of overheating, making them a safe and efficient choice for many applications. Given their longer lifespans of 10-15 years, 85% depth of discharge*, and 95% energy efficiency, they are considered an excellent option for solar PV systems.
*Depth of discharge refers to the extent to which the battery can be safely discharged.
Pros and cons of lithium-ion solar batteries
| Advantages of lithium-ion batteries | Drawbacks of lithium-ion batteries |
| Zero maintenance—Li-ion batteries require zero to no maintenance, unlike lead-acid batteries. | Expensive—cost 3x more than their lead-acid counterparts. |
| Compact—occupy less space. | End of life—lead acid batteries are recycled 95% of the time, while only 5% of Li-ion batteries are recycled. |
| Faster charge—quickly recharge than other solar batteries. | Require inspection—while zero maintenance, they still require periodic inspections. |
| Longer lifespans—often come with a 10-year warranty and can work properly for up to 15 years. | |
| Efficient—with an efficiency of 95%, they require less energy to charge. |
Flow batteries
A rather new addition, flow batteries are a type of rechargeable battery that stores energy in a water-based liquid electrolyte (Zinc Bromide) solution. This liquid flows between two tanks to produce electricity, hence the name. They are well-suited to applications that require long-duration energy storage, such as solar and wind.
An added benefit of flow batteries is their scalability. Their energy capacity can be increased by simply increasing the size of the tanks holding the electrolyte solutions, whereas other batteries have a fixed energy capacity. This makes flow batteries particularly useful for large-scale energy storage systems.
They also have a relatively long lifespan, with some estimates suggesting they can last for up to 30. They are also relatively safe, as they do not produce flammable gases like some other types of batteries. On top of that, they have a 100% depth of discharge, which is excellent for off-grid solar systems.
In terms of their suitability for use with solar power systems, flow batteries can be a good choice for storing excess solar energy that can be used when the sun is not shining. While they are ideal for solar systems, they can be relatively expensive compared to other types of batteries. Also, the technology is still in its infancy and may not be as well-proven as more established technologies.
Did you know?
Irrespective of the type of solar battery you choose, you will get back 30% flat income tax credit when you buy solar batteries for your system.
Pros and cons of flow batteries
| Advantages of flow batteries | Drawbacks of flow batteries |
| 100% depth of discharge—you can discharge the battery completely without affecting its performance and longevity. | 100% discharge is needed to clean the electrodes. |
| No chance of thermal runaway, as different components of the battery are physically separated. Also, Zinc Bromide is a natural fire-retardant. | Expensive—cost much more than lead-acid and Li-ion batteries. |
| Can work efficiently in hot temperatures, up to 50 degrees Celsius. | Emerging technology—may not be as durable as other batteries. |
| Low maintenance—they do not require regular maintenance like lead-acid batteries. | Occupies more space—to store a large amount of energy, your battery needs to be large. |
| Unlike other batteries, which need a minimum level of charge to avoid degradation over time, flow batteries do not need charge if not in use. |
Nickle Cadmium solar batteries
Nickel-cadmium (NiCd) batteries use nickel oxide hydroxide and cadmium as electrodes. Nickle-based batteries are old, having been in use since the late 1800s, but they became popular only in the 1980s with the introduction of NiCd batteries.
NiCd batteries have a relatively low self-discharge rate, meaning that they can retain a charge for a long time even when not in use. They also have a relatively long lifespan, with up to 2000 charge-discharge cycles before their performance begins to degrade. Thanks to their high energy density and ability to quickly deliver a large amount of power, they are generally used in the aircraft industry and large power projects.
Are they good for solar? Not exactly! They are relatively expensive compared to other types of batteries. Cadmium is also a highly toxic metal that can be harmful to the environment if disposed of improperly—some countries have banned it. In addition, NiCd batteries can be sensitive to high temperatures, which can reduce their performance and lifespan.
They may have some potential uses in large-scale solar power, such as utility solar storage, but they are generally not considered to be the best choice for residential solar. Other types of batteries on the list are more suitable for use with solar power systems due to their lower cost and better performance in high-temperature environments.
Pros and cons of Ni-Cd batteries
| Advantages of flow batteries | Drawbacks of flow batteries |
| Durable—can last for more than 20 years. | Toxicity—Cadmium is toxic and can cause potential damage to the environment. |
| Maintenance-free—doesn’t require regular maintenance. | Called the memory effect, they don’t hold the charge for long. |
| Low temperature-friendly—can work at -40 degrees Fahrenheit | Expensive—cost more than Lithium-ion batteries. |
Which solar battery is best for you?
We have discussed all the major types of solar batteries available in the market. NiCd batteries are a straight no for small-scale solar, like residential PV systems. Flow batteries are comparatively better, but they are expensive. Also, it is an emerging technology, and nothing can be said about its technical base with certainty.
That brings us to lead-acid vs. lithium-ion batteries. Here, it depends on your budget and how much space you can afford for batteries. If your budget is not an issue, we recommend Li-ion batteries, as they work excellently with solar systems. But the same is the case with their lead-acid counterparts, though their lifespans are lower and require regular maintenance.