What is the best solar battery overall?
The Tesla Powerwall 2 is CNET’s pick for the best solar battery overall. The Powerwall earned an average score in nearly every category, making it the most well-rounded solar battery we’ve scored; this makes it more likely to be a solid option for more homes. It’s also one of only two batteries we’ve seen that includes an unlimited-cycle warranty. It’s important to remember that batteries aren’t a one-size-fits-all product. Even though the Tesla Powerwall 2 doesn’t have many glaring weaknesses (aside from Tesla’s poor customer service reputation), every battery is different. Another battery might suit your home and individual energy needs much better.
The Tesla Powerwall is the most average home battery on the market, which works in its favor. But its unlimited cycle warranty is a standout. The Powerwall falls short in modularity and customer service. And it’s only available in one size. If you need a capacity upgrade, you’ll need to buy another 13.5kWh battery.
The LGES 16H Prime has solid performance specs at a reasonable price. If you’re looking for a larger battery on a budget, the 16H Prime is worth considering. And you won’t need solar panels to use it. But the 16H Prime doesn’t offer much else beyond large capacity. The warranty is pretty standard, and capacity upgrades are difficult and expensive.
Bluetti’s whole-home battery, the EP900 Home Battery Backup, is a solid option if you’re looking for power and modularity. The system’s EP900 inverter has an impressive power output at any capacity. And Bluetti’s end-of-warranty capacity guarantee is higher than other options. But it isn’t the most efficient.
How do solar batteries work?
A solar battery’s main function is to store excess electricity generated by your solar panels. If you have a solar battery installed, extra electricity from your solar panels doesn’t go to waste. Instead, it goes into storage so you can use that energy during periods of inefficient electricity generation, such as nighttime or cloudy weather.
Solar batteries make it possible to have power during outages. With the right battery setup, you can even go completely off-grid. An off-grid system means energy independence and eliminating your electricity bill altogether. You can still opt for a grid-tied solar system with a solar battery, as well. An on-grid solar system with a battery — a hybrid solar system — can help you save some money on your electricity bill by using your stored electricity generated by solar panels.
Pros and cons of solar batteries
Just like solar panels, solar batteries come with their own pros and cons. A solar battery can help you lower your electricity costs, provide protection against power outages and lower your reliance on the power grid. Solar batteries are also very expensive, too, sometimes costing as much as solar panels themselves.
Depending on your solar system size, you’ll likely need more than one battery. If you plan to go off-grid, be prepared to spend even more money on solar storage.
Advantages:
- Backup power during outages
- Less dependence on the power grid
- Less affected by increases in electricity rates
- Easier energy monitoring
Disadvantages:
- Solar batteries are very expensive
- You might need multiple batteries
- Maintenance costs
How to choose the best solar battery
There’s much more to consider beyond price. You’ll want a battery that matches your household’s energy usage and can output enough power to support your home’s electricity needs. The more large appliances you have, like HVAC equipment, refrigerators or even electric vehicles, the more power output you’ll want.
You should also consider battery modularity (being able to add more energy capacity if you need it) and compatibility with your solar panels. Since solar batteries are expensive, it’s a good idea to compare battery warranties as well. A solar battery’s lifespan is five to 15 years. Most manufacturers will warranty their batteries for 10 years.
Choosing a solar battery isn’t easy, and it’s not a decision that should be made on impulse. Take your time evaluating all your options and get quotes from different installers to find the best battery for your household’s specific energy needs.
The difference between AC and DC coupling
Your solar battery system will be either AC-coupled or DC-coupled. The big difference between the two is the path the electricity takes from your solar panels into your battery. DC means direct current, in which electricity flows only one way, while AC is alternating current, in which the current changes directions in intervals.
If you have an AC-coupled system, the electricity stored in your battery needs to be inverted — switched between AC and DC — multiple times before it can be used to power your home. In AC-coupled systems, DC electricity flows from your solar panels to an inverter. The inverter transforms the DC electricity into AC electricity that powers your home. The AC electricity is then transformed back into DC electricity to store in the battery.
If you have a DC-coupled system, the DC electricity generated from your solar panels only needs to be inverted once (to AC electricity) so it can power your home, or it can remain as DC electricity and head straight for battery storage.
Each system type comes with its ups and downs. AC-coupled systems tend to be easier and cheaper to install if you already have solar installed, but these systems are less efficient than DC-coupled systems. DC-coupled systems are the way to go if you don’t already have solar installed. These systems are more efficient and require less wiring and components.
Compatibility
Not every solar battery is compatible with every solar panel system. Some batteries are only compatible with a few solar panel manufacturers, while other batteries are more third-party friendly. Before deciding on a solar battery, make sure you know which batteries are compatible with your solar panels.
If you already have solar panels installed, but not a battery, be aware that some batteries are not compatible with existing solar systems and can only be installed with a brand-new system. An installer should be able to tell you which solar batteries are compatible with whatever your current solar situation may be.
Battery capacity
A battery’s capacity is the amount of energy it can store expressed as a unit of power over time, referred to as kilowatt-hours. The larger the kWh capacity, the more energy your battery can store and use. The more energy you use, the larger your battery capacity will need to be. That said, a smaller battery isn’t necessarily a bad battery. Its power output ratings are likely going to be much lower, but if you can live with that, then it’s fine.
Long story short: Size doesn’t always matter. Install a battery that can keep up with your home’s energy consumption, and that is modular enough that you can upgrade if you need to in the future. To find the right size battery for your home, consider getting a home energy audit done or ask your installer if they can perform one for you.
Battery modularity
A battery’s modularity (or stackability) is how flexible the battery’s overall capacity can be. Another way to look at modularity is how easy it is to customize your battery to best meet changes in the energy requirements of your home. Your home’s energy needs could grow over time, meaning you’re going to need a bigger battery.
When it comes to a battery’s modularity, here are a few questions to ask: Can I upgrade the same battery? If not, do I have to buy an entirely new battery? How many batteries can I have hooked up at once? Do they have to be the same size?
For example, let’s say you bought a battery with a capacity of 12kWh, which is enough for the time being. But if a year later you decided to install an EV charger or build an addition to your home, your energy needs might exceed your 12kWh battery. If your battery is modular, you’ll be able to expand your capacity by hooking up another battery of the same size, installing another battery of a different size to the existing system, or upgrading your existing battery’s capacity in smaller increments (usually of 2 or 3kWh). How modular your battery is will depend on the manufacturer. Some batteries are built for easy capacity upgrades, while others are not.
Round-trip efficiency
A battery’s round-trip efficiency is exactly what it sounds like; how efficient the battery is at storing energy. Round-trip efficiency is what percentage of the energy supplied to the battery actually makes it into storage for later retrieval. The higher a battery’s round-trip efficiency, the less energy is lost through the storage process, making your battery more efficient. If your battery’s round-trip efficiency is 80%, this means 20% of electricity is lost on its way to storage. On the other hand, if you have a battery with a round-trip efficiency of 100%, no electricity is lost or wasted on its way into storage. Most solar batteries have a round-trip efficiency of around 90%.
Depth of discharge
Depth of discharge is the amount of energy you can use (discharge) from the battery relative to its maximum capacity. Most manufacturers will disclose a battery’s maximum depth of discharge. This number represents the amount of energy (in percentage form) you can safely use from your battery without damaging the battery, according to the manufacturer. The closer the battery gets to 100%, the better.
It’s not recommended that you completely drain 100% of your battery’s usable capacity. This can shorten its lifespan and make it harder for your battery to hold a charge over time. You’ll get more cycle life out of your battery by using as little energy from your battery as you can at a time.
Most solar batteries will have a specified maximum (overall) capacity and a usable capacity.
- Maximum capacity: The total amount of energy the battery allows you to store.
- Usable capacity: The total amount of energy the battery allows you to use.
These capacity numbers can be used to calculate the depth of discharge by dividing the usable capacity by the maximum capacity and then multiplying the answer by 100. For example, if a battery has a maximum capacity of 10kWh and a usable capacity of 9kWh, then its depth of discharge is 90%.
Power output
All solar batteries will have peak and continuous power output ratings. Your battery’s peak power output is essentially how much power the battery can put out all at once without risking damage. A battery can only “peak” for so long though, so each battery should also disclose how long (in seconds or minutes) it can output its maximum power. Continuous power output is the amount of power the battery can output at all times. If you live in a large home or have a lot of large high-power appliances, you’re going to want higher power output ratings. A reputable installer will be able to provide power output recommendations for your home based on your energy usage and power needs.
Note that these power output ratings will also be different depending on if your system is grid-tied or off-grid, and some manufacturers are more transparent about providing these ratings on their product datasheets than others. If you plan on going off-grid, you’ll likely need multiple batteries.
Warranty
Since solar batteries are an expensive investment, it’s reasonable to expect a good warranty. Most solar battery warranties will cover up to a certain number of years, cycles, end-of-warranty capacity and throughput. You can expect most solar battery warranty periods to last at least 10 years.
Cycles: Any time you drain your battery, it needs to recharge. This process is called a cycle. Like most batteries, your solar battery will slowly lose its ability to hold a full charge over time. Many manufacturers will typically cover a certain number of cycles in the warranty agreement. The average warranty usually guarantees somewhere between 4,000 and 6,000 cycles.
End-of-warranty capacity: Your battery’s overall capacity will decrease over time. A solar battery’s end-of-warranty capacity is the manufacturer’s guarantee that your battery will be able to store up to a certain percentage of energy capacity by the time your warranty is up. Most manufacturers will guarantee that your battery will still be able to hold at least 60% of its original capacity by the time your warranty ends. This means if you buy a battery with a usable capacity of 15kWh, your battery should be able to store at least 9kWh of energy before your warranty expires.
Throughput: Some battery warranties include a throughput number. A throughput number is the overall amount of energy (typically measured in megawatt-hours) that the battery is expected to deliver during its entire lifetime. This means your warranty is valid until your battery hits its throughput number. In some cases, if you manage to hit your throughput number before your warranty period ends, your warranty will expire.
The typical solar battery warranty covers about 10 years, 4,000 to 6,000 cycles and up to 60% or 70% of your batteries’ end-of-warranty capacity. As you shop around for solar batteries, be sure to compare warranties and carefully read the fine print in the agreement.
Types of solar batteries
There are four main types of solar batteries: lithium-ion, lead-acid, flow and nickel-cadmium batteries. Most solar batteries you’ll encounter are lithium-ion batteries, while flow and nickel-cadmium batteries are more industrial-focused and not suitable for residential use. On the other hand, lead-acid batteries are lower quality, but cheaper. Here’s a breakdown of the different types of solar batteries.
Lithium-ion batteries
If you’re installing a solar battery for your home, it will likely be lithium-ion. These batteries are one of the most common types of residential solar batteries and have a high energy density, allowing them to hold more energy capacity in a smaller space. Lithium-ion batteries usually have a higher depth of discharge too, allowing you to drain more energy from your battery with a lower risk of damage. Plus, they require little to no maintenance, which makes them popular for computers, cell phones and vehicles. The downside is that lithium-ion batteries are expensive, and they tend to overheat and become damaged at higher voltages. If not properly installed, this could result in a fire.
Lead-acid batteries
Lead-acid batteries have been around for a long time, making them another popular choice for home battery needs. These batteries have a lower energy density and efficiency rating than other battery types, but they do have a long lifespan (with proper maintenance) and a more mature technology base. Lead-acid batteries are generally cheaper as well.
Flow batteries
While flow batteries are indeed a type of solar battery, you won’t be seeing them in many homes. Flow batteries are larger batteries (around 2.2 MWh in capacity) and are normally used for grid-scale energy storage. Since these batteries are so large, they are incredibly expensive. They are best suited for industrial use and are not intended for household energy storage.
Nickel-cadmium batteries
Because nickel-cadmium batteries are very durable and work well in extreme temperatures, they are a popular battery choice for large-scale commercial and industrial projects. Nickel-cadmium batteries have a high energy density, yielding twice the energy of a lead-acid battery. Unfortunately, cadmium is toxic and is banned in certain parts of the world. Nickel-cadmium batteries are very expensive, too. These batteries are generally not appropriate for residential use.
How much does a solar battery cost?
A solar battery could run your solar estimate up quite a bit. In most cases, the battery will cost almost as much as your solar panels. Solar batteries can cost anywhere from $12,000 to $22,000, according to the US Department of Energy. You can usually find smaller batteries (8kWh or less) for less than $10,000 before installation. The larger your home, the more money you’ll spend on solar. As a general rule of thumb, you can usually expect to pay between $1,000 and $2,000 per kWh of energy storage. And solar battery installation fees are typically around $3,000 or more.
Want something smaller than a whole-home solar system? See our picks for the best portable solar panels and solar generators.
Other batteries we reviewed
Panasonic Evervolt Home Battery: The Panasonic Evervolt Home Battery offers homeowners a modular battery without sacrificing power. It’s available in 9, 13.5 and 18kWh capacity sizes, and is expandable in 4.5kWh increments. The Evervolt Home Battery comes with a strong 12-year warranty and a solid continuous power output (7.6kW). In our scoring, the battery falls slightly short in its AC round-trip efficiency and depth of discharge.
SunPower SunVault: The SunPower SunVault is a solid battery, with a great warranty. It’s also backed by a solar company with a proven track record and the most efficient solar panels on the market. If you’re considering SunPower as an installer, the SunVault is a solid choice for a battery. The biggest standouts with the SunVault are its large capacity options and unlimited cycle warranty. The SunVault is sold as either a single unit (13 or 19.5kWh) or a double unit (26 or 39kWh). The SunVault falls short in efficiency and modularity. It also tends to be more expensive than some peer batteries.
Franklin Home Power: The Franklin Home Power battery received average scores in nearly every category. The standouts for this battery are its 12-year warranty and the fact that you can install up to 15 batteries on one system. It’s a good battery if you’re looking for a well-rounded battery for adding large capacity expansions. Franklin Home Power is more expensive than similar batteries on the market, and it’s a fairly new system, so availability and reliable customer reviews are harder to come by.
Enphase IQ 10T: Enphase batteries are a popular budget pick for home battery systems, but you’ll be sacrificing power output and efficiency (on AC-coupled systems) for price.
LG ESS Home 8: While the Home 8 isn’t necessarily a bad battery choice, it was beaten out by the LG Resu 16H Prime, which had higher efficiency, performance and capacity scores at a lower price. In comparison, the LG ESS Home 8 system is more modular, allowing you to stack up to four Home 8 systems versus only being able to stack two 16H Primes.
SonnenCore Plus: The SonnenCore Plus falls a bit short in just about every category except for its warranty and price. The warranty is good for 10 years or 10,000 cycles, which is pretty substantial in comparison to other battery warranties, particularly the cycles.
Emporia Alpha-ESS DC Coupled: The Emporia Alpha is a good option if you’re looking for a smaller battery with good customer service. This battery is decently modular, too. Unfortunately, the Emporia Alpha falls behind its competition due to lower performance numbers.
Delta BX 12.6: Delta’s BX 12.6 battery has decent round-trip efficiency (96%) and depth of discharge (98%), but that’s about all it has going for it. Lack of modularity, a subpar warranty and poor power output ratings are what held this battery back.
How we evaluated the best solar batteries
First and foremost, it’s important to point out that not every solar battery is right for every home. Solar is a very site-specific and personalized decision process, so it’s a little tricky to pinpoint exactly which solar battery is the “best” battery for your home’s energy needs without doing an on-site consultation. It should also be said that we didn’t have any form of hands-on testing with any of the batteries we scored. We used a few ways to evaluate and compare these batteries to find the stand-outs. Here’s how we developed our list of top solar batteries.
First, we determined which categories would be used to evaluate each battery’s efficiency, performance, capacity and value. We also weighted each category. The weight of each category reflects the importance we felt was relevant to the average consumer.
After a thorough research process, these were the categories we chose to evaluate each battery on.
- Battery modularity (stackability): 20%
- Warranty: 20%
- Round-trip efficiency: 15%
- Depth of discharge: 10%
- Power output: 10%
- Price: 10%
- Customer reviews: 10%
- Battery capacity: 5%
We looked at 15 of the most widely available batteries on the market and collected the data for each category to compare the numbers. Each category (for every battery) was given a tier-style rating (from 1 to 5) to evaluate which aspects of each battery were above average (among our list), just average or below average.
Solar battery FAQs
What is the Tesla Powerwall 3?
The federal solar tax credit covers 30% of the total cost of your solar system in tax credits. Solar batteries qualify for the federal solar tax credit as long as your battery can hold at least 3kWh of energy and is installed in 2024 or later.
How long do solar batteries last?
Because solar is so site-dependent, there is no definitive answer for the number of batteries it takes to go off-grid. It’s going to be different for everybody. Most homeowners are going to need multiple batteries to go completely off-grid. Your home’s energy usage and the size of your solar system are two of the biggest factors determining how many batteries you’ll need to go off-grid.
Will a solar battery power my house during an outage?
Deep-cycle lithium-ion batteries are the most popular type of solar battery for residential solar applications. These batteries are durable and require little to no maintenance. They also come with a higher energy density and depth of discharge.
