What are the different types of solar batteries?
There are many factors to take into consideration when shopping for solar batteries for your home solar power system. Two things to keep in mind are the type of battery you’re looking for and what exactly you want to get out of your battery.
There are four types of solar batteries: lead-acid, lithium-ion, nickel cadmium, and flow batteries. The most popular home solar batteries are lithium-ion. Lithium-ion batteries can come as AC or DC coupled. AC-coupled batteries can be connected to existing solar panel systems, while DC-coupled batteries are most suited for being installed at the same time as solar panels.
We’ve broken down the most popular energy storage technologies to help you find the right battery backup for your solar panel system.
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Types of solar batteries
There are four main types of battery technologies that pair with residential solar systems:
- Lead acid batteries
- Lithium ion batteries
- Nickel based batteries
- Flow batteries
Each of these battery backup power technologies has its own set of unique characteristics. Let’s take a closer look at what each type of solar battery has to offer.
Lead acid batteries
Lead acid batteries are the tried and true technology of the solar battery world.
These deep-cycle batteries have been used to store energy for a long time - since the 1800's, in fact. And they’ve been able to stick around because of their reliability.
There are two main types of lead acid batteries: flooded lead acid batteries and sealed lead acid batteries.
Some popular lead acid batteries available to homeowners include:
- Trojan J185E-AC Deep Cycle Flooded Lead Acid Battery
- Crown Battery’s Crown1 absorbent glass mat (AGM) Sealed Lead Acid Battery
- Deka Solar’s 8g30H Gel sealed lead acid battery
Lead acid batteries are the cheapest energy storage option, making them the most cost effective. They are also reliable. Plus, because the technology has been around for years, they can be easily disposed of and recycled.
Flooded lead acid batteries require ventilation and regular maintenance to operate correctly, which increases the chances of the battery leaking.
This also limits how flooded lead acid batteries can be installed, because they can’t be placed on their side. They also have a low depth of discharge (DoD), so they need to be charged more often.
Having a low depth of discharge also means they have a shorter lifespan - between 5 and 10 years.
The reliability of lead-acid batteries is great for off-grid solar systems, or for emergency backup storage in case of a power outage.
Lithium ion batteries
Lithium ion batteries are the new kids on the energy storage block.
As the popularity of electric vehicles began to rise, EV manufacturers realized lithium ion’s potential as an energy storage solution. They quickly became one of the most widely used solar battery banks.
The most popular lithium ion solar batteries for residential installations include:
Lithium ion batteries require almost no regular maintenance.
They also have a higher battery energy density, meaning they can hold more energy in a smaller space than a lead acid battery.
Lithium ion batteries have a longer life cycle, or lifespan, as well - most have a guaranteed warranty of at least 10 years. This longer lifespan has to do with lithium ion batteries having a higher depth of discharge, so you can use more of the energy stored within the battery before it has to be recharged.
One of the biggest disadvantages of lithium ion batteries is that they are more expensive than other energy storage technologies.
Also, because of their chemistry, lithium ion storage systems have a higher chance of catching fire due to something called thermal runaway. However, if installed properly, the chance of your battery catching fire is close to zero.
Lithium ion batteries are best for residential solar installations because they can hold more power in a limited space, and allow you to use more of the energy stored within the battery, which is great for powering a home.
Nickel cadmium batteries
Nickel cadmium (Ni-Cd) batteries aren’t as widely used as lead acid or lithium ion batteries.
Ni-Cd batteries first sprung on the scene in the late 1800's, but they got a makeover in the 1980s that greatly increased how much energy they could store. They are a favorite amongst the aircraft industry.
The main benefit of Ni-Cd batteries is that they are durable. They also have the ability to operate at extreme temperatures. Additionally, they don’t require complex battery management systems and are basically maintenance-free.
The biggest downfall of Ni-Cd batteries is that cadmium is extremely toxic.
In fact, the use of cadmium is banned in some countries. This makes them hard to dispose of. They also are prone to the memory effect, which limits their ability to hold a charge.
Ni-Cd batteries are popular for large scale applications, like utility solar energy storage, because of their durability.
Flow batteries are an emerging technology in the energy storage sector.
They contain a water-based electrolyte liquid that flows between two separate chambers, or tanks, within the battery. When charged, chemical reactions occur which allow the energy to be stored and subsequently discharged. These batteries are now beginning to rise in popularity.
Their larger size makes them more expensive than the other battery types. The high price, combined with the large size, makes it hard to adapt them to residential use. However, redflow manufacturers a residential flow battery, which they call ZCell.
One of the best things about flow batteries is that they have a 100% depth of discharge. This means you can use all of the energy stored in the battery without damaging the battery’s health.
The liquid within the battery is also fire retardant, so you don’t have the risk of thermal runaway. Flow batteries have the longest lifespan on this list - 30 years! And as an added bonus, they’re low-maintenance.
Flow batteries are unfortunately much more expensive than other types of solar batteries. They also have a relatively low storage capacity compared to other battery systems, so in order to hold a substantial amount of energy they need to be large.
They have very low charge and discharge rates, which also means that in order to be effective, they must be large in size.
Flow batteries are best for large-scale installations.
Because of how they work, they need to be very large to hold any substantial amount of energy, which increases their price. This has prevented flow batteries from becoming a popular residential option.
DC-coupled vs AC-coupled solar batteries
The type of electricity used in homes and buildings is alternating current, or AC power, but batteries must be charged with direct current, or DC power. Solar panels also produce DC power.
In order for the energy stored in batteries to be used in your home, the DC power must first be converted into AC power by an inverter. Each time the power is converted from DC to AC (or vice versa), a little bit of energy is lost.
The difference between DC-coupled batteries and AC-coupled batteries has to do with where the inverter is in the setup. A DC-coupled battery connects directly to a hybrid string inverter, allowing the DC solar output to flow directly to the batteries, while an AC-coupled battery has its own inverter.
Pros and cons of DC-coupled batteries
Because they can be charged directly from solar panels, the energy stored in a DC-coupled battery only gets converted to AC one time, which means a DC-coupled battery is more efficient. This setup also means a DC-coupled battery can be cheaper to install alongside a new solar system, because there is no need for a battery-specific inverter.
Unfortunately, this also means a DC-coupled battery is not ideal for a home that already has solar panels, unless those solar panels are already connected to a hybrid string inverter that is battery-ready.
Pros and cons of AC-coupled batteries
AC-coupled batteries are simple to add to any home, because they come with their own inverter and can be charged using the home’s regular AC circuits and also from already-converted solar power from any kind of existing inverter or microinverter.
Unfortunately, this also means an AC-coupled battery is less efficient, because the power must undergo two or three conversions from DC to AC and back. The drop in efficiency is around 1%-2% for each conversion.
How to find the right solar battery type for you
In most cases, the best solar battery for a home solar installation is a lithium battery.
They are able to hold more energy in a small amount of space, discharge most of their stored energy, and they have high efficiencies. Also, because these are the most common, many solar companies will be able to install a lithium ion solar battery both accurately and safely.
If you are on a budget, lead acid batteries could be the best option for you. They have been used for decades, plus they come at a low cost.
Although you could get a Ni-Cd battery or a flow battery to pair with your solar system, lithium ion and lead acid are the go-to solar batteries for a reason. To find out which type of solar battery will best meet your needs, you should call local solar installers.
- The four main types of solar batteries are lead acid, lithium ion, nickel cadmium, and flow batteries.
- Lead acid batteries have been around for the longest and are known for their low prices and reliability, but they require regular maintenance.
- Despite being expensive, lithium ion batteries are becoming the most popular choice for residential solar batteries because they have a long lifespan and require no maintenance.
- Nickel cadmium batteries are more popular for commercial-scale projects because they can operate at extreme temperatures and don’t require complex battery management systems.
- Flow batteries are large in size and very expensive, which is why this emerging battery technology is mostly used for large-scale battery storage.