Solar batteries are the clear and obvious answer to the question “How does solar work when the sun goes down?”
But while most homeowners love the idea of having energy independence and backup power for grid outages, solar batteries are a major purchase that can be difficult to understand — let alone shop for.
So, in this article, we’ll discuss the different types of solar batteries, including their strengths, weaknesses, and best use cases. Our hope is to help you narrow down which type of solar battery best suits your needs so you can focus your search on one or two specific brands or models.
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Let’s start with a quick recap of why and how homeowners use batteries to store solar power.
Why use solar batteries?
While typically thought of as a backup power source, there are a handful of additional reasons to add battery storage to your solar system. These include:
And let’s not forget that some people just like to adopt new technologies and be on the cutting edge.
We welcome all homeowners interested in battery storage, but it is important to establish goals before diving into the world of solar batteries because your goals will help determine which type of solar battery best suits your needs. For example, a new tech enthusiast will likely choose an entirely different type of solar battery than a homeowner looking to maximize their cost savings.
With some goals in place, let’s start by exploring the different types of solar batteries by their chemical compositions.
What are the different types of rechargeable solar batteries?
Solar batteries can be divided into six categories based on their chemical composition: Lithium-ion, lithium iron phosphate (LFP), lead-acid, flow, saltwater, and nickel-cadmium.
Frankly, the first three categories (lithium-ion, LFP, and lead-acid) make up a vast majority of the solar batteries available to homeowners. However, battery technology is evolving at lightning speed, so it’s worth keeping an eye on them all.
Let’s start with the one we’ve all heard of: Lithium-ion.
Lithium Ion Batteries
Lithium-ion (Li-ion) batteries have become the predominant choice for home energy storage (among many other things) due largely to their high energy density. Basically, you can pack a ton of power in a small space – which is ideal for storing thousands of Watts of solar production in your garage.
Another reason lithium-ion is so ubiquitous is that it is an entire category of batteries that includes six different chemistries:
- Lithium Iron Phosphate (LFP)
- Lithium Cobalt Oxide (LCO)
- Lithium Manganese Oxide (LMO)
- Lithium Nickel Manganese Cobalt Oxide (NMC)
- Lithium Nickel Cobalt Aluminium Oxide (NCA)
- Lithium Titanate (LTO)
There are a few major downsides to lithium-ion solar batteries. First, as a new technology made up of high-demand elements, they are relatively expensive. Second, if certain lithium-ion batteries are not properly installed, they pose a risk of catching fire through a process called thermal runaway. Finally, some Li-ion batteries contain nickel and cobalt, which in some cases, are mined through questionable practices.
Popular lithium-ion solar batteries include the LG RESU Prime, LG ESS Home 8, Generac PWRcell, and Tesla Powerwall.
Lithium-ion solar battery pros and cons
| Pros |
Cons
|
| High density |
Higher cost |
| No maintenance |
Risk of thermal runaway (fire) if not properly installed |
| Long lifespan (10+ years) |
Questionable nickel and cobalt mining practices |
| >80% depth of discharge |
|
| Widest range of make/model options |
|
Lithium iron phosphate (LFP) batteries
Wait, lithium again? Yes, lithium iron phosphate (LFP) batteries technically fall into the category of lithium-ion batteries, but this specific battery chemistry has emerged as an ideal choice for home solar storage and therefore deserves to be viewed separately from lithium-ion.
Compared to other lithium-ion batteries, LFP batteries:
- Last longer
- Have a deeper depth of discharge
- Are more eco-friendly since they do not use nickel or cobalt
- Can handle a wider range of temperatures
- Have a near-non-existent risk of thermal runaway
The drawback to LFP batteries is that, at this point, they are typically more expensive than standard Li-ion batteries because it’s an even newer technology with fewer suppliers.
Regardless, LFP batteries make up four of our eight best solar batteries of 2024. Our highest-rated models include Franklin Home Power, Panasonic EverVolt, SunPower SunVault, and Enphase IQ.
Lithium iron phosphate (LFP ) vs Lithium-ion (Li-ion)
| Feature |
LFP |
Li-ion
|
| Lifecycles before degradation |
1,000 to 10,000 |
500 to 1,000 |
| Energy density |
40-55 Wh per lb |
45-120 Wh per lb |
| Depth of discharge |
Up to 100% |
80-95% |
| Operating temperature |
-4 F to 140 F |
32 F to 113 F |
| Risk of thermal runaway? |
Near non-existent |
Noteworthy if not properly installed |
| Ideal usage |
Self-consumption & TOU modes |
Backup mode |
| Cost |
$$$ |
$$ |
Lead Acid Batteries
Lead acid batteries were once the go-to choice for solar storage (and still are for many other applications) simply because the technology has been around since before the American Civil War. However, this battery type falls short of lithium-ion and LFP in almost every way, and few (if any) residential solar batteries are made with this chemistry.
Compared to the lithium-ion batteries described above, lead acid batteries are much bigger, heavier, and often require regular maintenance. In general, this battery type is best at providing short bursts of energy – which is great for starting gas cars but not ideal for prolonged home backup needs.
Pros and cons of lead acid batteries
| Pros |
Cons
|
| Low upfront cost |
Low depth of discharge (~50%) |
| Proven technology |
Shorter lifespan (around 5 years) |
| Around 95% recyclable |
Low energy density (take up more space) |
| Wide operating temperature range |
Higher long-term costs after maintenance and replacements |
Flow Batteries
Flow batteries are an exciting technology that has yet to really enter the residential solar storage market.
Instead of a single tank of battery soup (like lead acid and lithium-ion) flow batteries feature two tanks of positively and negatively charged solutions that are separated by a thin membrane. When the battery is charging, the solution flows from one tank to another to store energy. And when it’s discharging, the solution releases electrons as it flows back to its original tank.
Image source.
Flow batteries can be discharged 100% without affecting battery health, have no risk of thermal runaway, and last around 30 years. However, they require a lot of space due to their low energy density.
As such, residential flow batteries are currently few, far between, and expensive.
Pros and cons of flow batteries
| Pros |
Cons
|
| 100% depth of discharge |
Relatively expensive (even for batteries) |
| Long lifespan (~30 years) |
Bulky due to low energy density |
| No risk of thermal runaway |
Not yet available for residential use |
| No maintenance |
|
| Fully recyclable |
|
Saltwater batteries
Akin to flow batteries, saltwater batteries are a newer technology with the potential for longer-lasting, more environmentally friendly home energy storage. As the name suggests, this type of solar battery uses saltwater as its electrolyte instead of the lithium-based solutions used in lithium-ion batteries. Saltwater is easier to procure and less hazardous throughout manufacturing and performance.
However, just like flow batteries, there are currently considerable limitations standing in the way of residential use. Saltwater batteries are currently too bulky and expensive for home solar applications and will likely need widespread utility-scale adoption before trickling into the residential market.
Saltwater batteries pros and cons
| Pros |
Cons |
| Long lifespan |
Expensive |
| Eco-friendly (no heavy/toxic metals and easily recyclable) |
Lower energy density (require a lot of space) |
| 100% depth of discharge |
Few (if any) residential products available |
| No risk of thermal runaway |
|
Nickel Cadmium Batteries (Ni-Cd)
Nickel-cadmium batteries are a mature technology that’s used to power everything from toys to aircraft. However, due to the high toxicity of cadmium and the “memory effect” (which can cause this battery type to suddenly die), nickel-cadmium batteries are rarely used for residential solar storage.
It’s very unlikely that you will find a nickel-cadmium battery through a full-service solar installer.
Saltwater batteries pros and cons
| Pros |
Cons |
| Long lifespan |
Cadmium is extremely toxic |
| Performs in extreme temperatures |
Prone to the memory effect |
| Low maintenance |
|
Backup vs. consumption-only batteries
If you’re buying a battery within the next few years, your first decision will be between lithium-ion or lithium-iron phosphate (LFP). Your second decision – especially if you live in California – will be whether you want your battery to provide backup power or not.
Thanks to California’s NEM 3.0 Solar Billing policy, which drastically reduced the compensation homeowners receive for pushing excess solar electricity onto the gird, a new type of “consumption-only” battery emerged in 2023 that is specifically designed to provide all the cost-saving benefits of storing and using your own electricity without the added cost of backup capabilities.
To better understand this new option, let’s first review the traditional backup battery.
Backup batteries
Backup batteries are typically the first thing that comes to mind when someone says “solar battery.” These battery systems typically consist of a:
- Battery cabinet (where power is stored)
- Control box that controls when/how the battery charges and discharges
- Sub-panel that dictates which electrical systems are backed up
For many years, backup power was essentially the only reason to invest in home battery storage. However, under NEM 3.0 solar billing, batteries are now crucial for maximum bill savings from a home solar system – even if you don’t necessarily need or want backup power.
So, the industry has responded with a new type of solar battery that we’re calling consumption-only battery.
Consumption-only batteries
As the name suggests, consumption-only batteries allow homeowners to store and consume their own solar electricity instead of importing and exporting it from the grid. Also known as non-backup, rate-saver, and many other things, consumption-only batteries are essentially a stripped-down and less expensive version of traditional backup batteries.
By removing the additional equipment (control box and sub-panel), programming, and labor that enables backup capabilities, consumption-only batteries provide all the cost-saving functions of a traditional backup battery at around two-thirds of the upfront cost.
These batteries allow customers of California’s investor-owned utilities (PG&E, SCE, SDG&E) to avoid exporting their solar production to the grid for little-to-no value and avoid buying grid electricity during peak time-of-use rates. However, when the grid goes down their system is shut off just like a solar-only system.
This solar battery type is great for homeowners who are just looking for maximum cost savings and are not bothered (or affected) by grid outages, and will likely become more widespread as more utilities adopt weaker net metering policies.
AC vs DC-coupled batteries
A third way to categorize solar battery types is by AC-coupled versus DC-coupled batteries. AC-coupled batteries make up a majority of the residential solar battery market, however, DC-coupled batteries are gaining popularity – and for good reason.
The practical difference between AC- and DC-coupled batteries is their round-trip efficiency (i.e., how much of the power that goes into the battery is actually used to power your home). In AC-coupled systems, the solar energy needs to be inverted (changed from AC to DC, or vice versa) multiple times before it’s discharged from your battery into your home. Each time electricity is inverted, a little bit is lost in the process, making for a less efficient system. As such, AC-coupled systems typically have round-trip efficiency of around 85-90%, which means 10-15% of the energy is lost during the inversion processes.
In DC-coupled systems, only one inversion is required, which allows for round-trip efficiency up to 97.5%.
Are AC or DC solar batteries better?
While DC-coupled batteries are the clear choice in terms of round-trip efficiency, they are notoriously difficult to configure into existing solar systems. That’s because existing solar systems already have inverters that change the DC electricity produced by the panels to AC electricity that’s usable in the home.
So, AC-coupled batteries are typically the primary choice for homeowners adding battery storage to an existing system, while DC-coupled batteries are becoming increasingly desired by homeowners who are installing solar panels and battery storage at the same time.
What’s the best type of solar battery?
Lithium-ion – particularly lithium iron phosphate (LFP) – batteries are considered the best type of batteries for residential solar energy storage currently on the market. However, if flow and saltwater batteries became compact and cost-effective enough for home use, they may likely replace lithium-ion as the best solar batteries.
Regardless of the chemistry, the best solar battery is the one that empowers you to achieve your energy goals. If your goal is to reduce your energy costs as much as possible, consider a smaller, consumption-only lithium-ion battery. If your goal is to install a solar and battery system that can back up your entire home, consider a larger, DC-coupled LFP battery.
Connect with an Energy Advisor to set energy goals and get binding quotes for solar batteries.
Frequently Asked Questions about Solar Batteries
What are the different types of rechargeable solar batteries?
The six types of rechargeable solar batteries include lithium-ion, lithium iron phosphate (LFP), lead acid, flow, saltwater, and nickel-cadmium. Currently, lithium-ion and LFP (which is technically a type of lithium-ion) batteries are the primary options for residential purposes, although there are ongoing efforts to make flow and saltwater batteries small and affordable enough for home applications.
What type of battery is best for solar?
Lithium-ion – particularly lithium iron phosphate (LFP) – batteries are considered the best type of batteries for residential solar energy storage currently on the market. However, if flow and saltwater batteries became compact and cost-effective enough for home use, they may likely replace lithium-ion as the best solar batteries.
Regardless of the chemistry, the best solar battery is the one that empowers you to achieve your energy goals.
What is the most common solar battery?
Lithium-ion batteries are the most common type of battery used in residential solar systems, followed by lithium iron phosphate (LFP) and lead acid. Lithium-ion and LFP batteries last longer, require no maintenance, and boast a deeper depth of discharge (80-100%). As such, they’ve largely replaced lead-acid in the residential solar battery market.
