With utility rates soaring and net metering policies eroding, home battery storage systems have become essential for homeowners to control their essential electricity costs. But picking a solar battery isn’t as easy as picking a AAA to power your TV remote.

One of the key decisions homeowners confront is whether to invest in AC- or DC-coupled solar batteries — which can impact the cost, efficiency, and overall complexity of their system.

In this article, we’ll explore the key differences between AC- and DC-coupled batteries and how to choose a battery type that best serves your energy goals.

What’s The Difference Between AC-Coupled vs. DC-Coupled Solar Batteries?

The main difference between AC- and DC-coupled batteries is the type of electrical current that flows into the battery. All solar batteries store DC electricity, but AC-coupled batteries are designed to receive alternating current (AC) while DC-coupled batteries are designed to receive direct current (DC).

On a practical level, DC-coupled batteries are more efficient because they can receive the DC electricity produced by solar panels. On the flip side, AC-coupled battery systems are less efficient because the direct current from the solar panels must be inverted twice — from DC to AC, then back to DC — before actually going into the battery for storage, and a little bit of energy is lost each time the current is inverted.

In both instances, the stored DC electricity must be inverted to AC as it exits the battery so it can be distributed throughout the home or local power grid.

So why even have AC-coupled battery systems if they are more complicated and less efficient? To better understand that, we need to take a look at your home energy ecosystem.

AC vs DC electricity in your home

As mentioned above, there are two types of electrical currents — AC and DC — that are used in different ways. AC is better suited for transporting electricity over distances and is therefore used by the electrical grid, the wiring inside your home, and certain household appliances like toasters, garage door motors, and washing machines. DC is better suited for energy storage and powering certain household devices like laptops, TVs, and microwaves.

So, in a typical solar system without battery storage:

1. The solar panels produce a direct current
2. A solar inverter changes it to an alternating current to distribute throughout the home or export onto the grid
3. Certain appliances use AC current while others have dedicated inverters (like the black box on your laptop chord) to invert the current once again to DC

Many modern solar-only systems have microinverters attached to each solar panel, so the first inversion takes place before the electricity ever leaves the solar panel. In order to add batteries to these systems, the battery needs to be able to receive AC electricity and invert it back into storable DC electricity — hence AC-coupled batteries.

As you might have guessed, there are unique advantages and disadvantages to AC- and DC-coupled batteries.

Advantages and Disadvantages of AC-Coupled Solar Batteries

AC-coupled solar batteries seamlessly integrate with existing solar inverters, making them a popular choice for retrofitting solar systems. This compatibility with the grid and solar inverters simplifies installation and reduces initial costs.

On the flip side, these systems suffer from double conversion losses — once when DC from solar panels is converted to AC for home use, and again when storing excess AC as DC in the batteries. Due to energy losses during these inversions, the maximum round-trip efficiency for today’s AC-coupled batteries is 90%. So, if your solar system sends 10 kWh of electricity to your battery during the day, you’ll only draw 9 kWh from your battery at night.

So, while upfront costs are lower, the long-term value may be impacted by these efficiency losses and potentially higher maintenance costs.

Advantages and Disadvantages of DC-Coupled Solar Batteries

DC-coupled solar batteries shine in efficiency, with only a single inversion as the current exits the battery, boasting round-trip efficiency of up to 97.5%.

With fewer components, DC-coupled batteries can be easier and less expensive to configure into new solar systems. However, their integration can be complex in existing solar setups, potentially limiting their appeal to new installations or homeowners willing to overhaul their current system.

Examples of AC and DC Solar Batteries

Of our top 8 best solar batteries of 2023, five are AC-coupled and three are DC-coupled (including the Panasonic Evervolt which can be configured either way).

Our top AC-coupled batteries include:

Our top DC-coupled batteries include:

Based on round-trip efficiency alone, DC-coupled batteries are the easy choice. However, there are more factors to consider when deciding which type of battery is best for your solar system.

Factors to Consider When Choosing Between AC and DC Solar Batteries

Selecting the appropriate solar battery coupling hinges on multiple factors, including the current solar setup, efficiency concerns, installation specifics, and compliance with legal standards.

Let’s start with the most obvious factor: Whether the battery is being configured into a new or existing solar system.

Existing Solar Infrastructure

As a rule of thumb, AC-coupled batteries are better suited for adding into existing solar systems while DC-coupled are better suited for installing at the same time as the solar panels. However, with enough time, money, and installation expertise, it is possible to configure a DC-coupled battery into an existing solar system.

As we covered above, many modern solar systems have microinverters attached to each panel that flip the current from DC to AC before it even leaves the panel. In order to configure a DC-coupled battery into such a system, you’d need to remove the microinverters from each panel — which requires additional labor and essentially wastes the microinverters.

The process can be a bit simpler in systems with a single “string inverter” that inverts electricity for all the panels. However, there is still a significant amount of labor and waste in such a re-configuration.

Efficiency and Battery Usage

Another key factor to consider when deciding between AC- and DC-coupled batteries is the system’s round-trip efficiency and how you are going to use your battery storage.

Let’s say you are deciding between an AC-coupled battery with 90% round-trip efficiency and a DC-coupled battery with 97.5% round-trip efficiency. If you only plan on using your battery for essential backup power when the grid goes down, that extra 7.5% efficiency may not be worth paying for — especially if you need to configure the DC-coupled battery into an existing solar system. However, if you plan on charging and discharging the battery every day in self-consumption mode to reduce your electricity bills, then that 7.5% difference in efficiency will certainly add up over time.

Efficiency becomes an even greater factor if you plan on powering large loads like air conditioning and home EV charging. If you have a three-battery system with 40 kWh of usable capacity, then a 90% efficient system would allow you to access 36 kWh while a 97.5% efficient system would give you access to 39 kWh.

Over time, 3 kWh per cycle adds up to significant energy and cost savings.

Installation Complexity and Costs

One of the most influential factors in large purchases like a home battery is the upfront cost. Battery prices vary based on a number of factors, but perhaps the most influential is the scope of work.

In general, it’s more cost-effective to install batteries at the same time as solar panels, because many of the soft costs (labor, permitting, inspection, etc) overlap. In that case, it’s also more cost-effective to buy a DC-coupled battery because it requires fewer inverters and simplifies the system configuration.

On the other hand, if you are adding a battery to an existing solar system, installing an AC-battery is typically more cost-effective because you are avoiding the addition labor of removing the solar inverters and re-configuring the system.

Regulatory Restrictions and Grid Connection

Navigating the complex landscape of energy regulation is crucial when selecting a solar battery system. Local and national electrical codes often dictate whether an AC- or DC-coupled system is permissible, with some jurisdictions having specific requirements for grid-connected solar installations. These regulations can influence the type of inverter you can use, the manner in which your solar battery integrates with the grid, and even the overall efficiency and cost-effectiveness of your setup.

For instance, certain areas may mandate anti-islanding protection, which is more straightforward to implement with AC-coupled systems. Conversely, regions with policies that favor self-consumption might align better with the efficiency of DC-coupled systems during daylight hours. It’s essential to consult with a knowledgeable local solar installer who is well-versed in the latest regulations to ensure compliance and optimize your system’s performance.

Is AC- or DC-Coupled Battery Better?

The best battery is that one that empowers you to achieve your energy goals. While DC-coupled batteries offer greater efficiency, AC-coupled batteries are easier to configure into existing solar systems. The best type of battery for your system also depends on how you plan on using your battery.

Connect with an Energy Advisor to design a custom system and compare battery prices from local installers.

Solar and battery systems offer homeowners an unprecedented opportunity to own and control the production, storage, and consumption of their essential electricity needs.

While installing solar panels is relatively straightforward, pairing them with battery storage is a little more nuanced given the various types of batteries available and what they’re able to do. 

So, in this article, we’ll explore which batteries pair best with solar panels to accomplish the three most common energy goals: Cost savings, essential backup, and whole-home backup.

Click to jump to a section:

• Best batteries for cost-savings
• Best batteries for essential backup
• Best batteries for whole-home backup

Let’s start with a quick recap of the different types of batteries on the market.

What types of solar batteries are there?

There are three distinguishing features that determine a battery’s “type.”

1. Chemistry (what it’s made of)
2. Current type (AC vs DC)
3. Capabilities (Backup vs Consumption-only)

Battery chemistry: Lithium-ion versus Lithium Iron Phosphate (LFP)

There are no fewer than five types of battery chemistries that could be used (theoretically or practically) for residential energy storage. However, Lithium-ion (Li-ion) and Lithium Iron Phosphate (LFP) have emerged as the dominant chemistries today, as they provide an ideal balance of energy density and efficiency.

Side note: The “F” in LFP is for “ferro,” which is a synonym for iron.

Compared to Lithium-ion, LFP batteries generally last longer, allow greater depth of discharge, handle a wider range of temperatures, and have a virtually non-existent risk of thermal runaway. 

On the other hand, Lithium-ion batteries tend to cost less and are less affected by maintaining a high state of charge, which is common for essential backup systems.

AC vs DC batteries

Another distinguishing feature to consider is whether a battery is AC- or DC-coupled. Certain batteries can charge on Direct Current (DC) electricity while others charge on Alternating Current (AC) electricity. 

In general, DC batteries are more efficient while AC batteries are much easier to configure into existing solar systems.

Whether or not you already have a home solar system – and how that system is configured – will determine whether an AC- or DC-coupled battery is best.

Consumption-only vs backup 

The third distinction to consider is whether the battery is backup-enabled or configured for self-consumption only. While backup power is typically thought of as the primary benefit of battery storage, there is a growing demand for battery storage without the additional costs attributed to the equipment, labor, and programming required to enable backup power when the grid goes down. Given this smaller scope of work, consumption-only battery projects typically costs around two-thirds of comparable backup-enabled battery projects.

With that in mind, consumption-only batteries (aka “non-backup” batteries) are typically used by homeowners who:

1. Have the primary goal of energy cost savings
2. Are largely unaffected by power outages

For example, under California’s NEM 3.0 solar billing policy, it’s much more cost-effective to store and use your own solar production in a consumption-only battery than to trade electricity back and forth with the utility grid. 

Best batteries for cost savings

If your primary goal is energy cost savings and you have no need for backup power, then the best battery to pair with solar panels is a Lithium Iron Phosphate (LFP) consumption-only battery. Whether an AC- or DC-coupled battery is best depends on whether or not you already have solar panels.

Some of the best LFP batteries currently on the market include:

• Enphase IQ (AC-coupled)
• Panasonic EverVolt (AC or DC-coupled)
• SunPower SunVault (AC-coupled)

Many of these batteries are offered as consumption-only packages.

Why is LFP battery chemistry best for cost savings?

Batteries used primarily for cost savings typically operate in solar self-consumption mode. This means that the battery will only charge on solar power and discharge as soon as the solar panels can’t meet household electricity demand.

In self-consumption mode, the battery is charged and discharged (aka “cycled”) on a daily basis and carries a very low charge overnight (known as a low “state of charge”).

Based on a 2020 study by the National Renewable Energy Laboratory (NREL), LFP batteries are more resilient to daily cycling and actually prefer a low state of charge, which makes them particularly suited for self-consumption mode.

Why consumption-only battery for cost savings?

By leaving out the equipment, labor, and programming required to enable backup power, consumption-only batteries typically come at around two-thirds of the cost of a traditional backup battery. And if your primary goal is to save money, then a battery with a lower upfront cost provides a quicker return on investment.

While consumption-only batteries can provide greater energy cost savings, it’s worth emphasizing that they do not provide backup power during grid outages.

Connect with an Energy Advisor to design a custom solar & battery system for your goals.

Is AC or DC battery better for cost savings?

While DC batteries are more efficient – and thus provide more energy bill offset per kWh of solar production – they typically come with a greater upfront cost, especially if when adding a DC battery to an existing solar system.

If your primary goal is cost savings, it’s worth crunching the numbers for your specific situation to see whether an AC or DC battery provides the greatest return on investment.

Best batteries for essential backup power

If the primary goal is powering essential systems (lights, Wi-Fi, refrigeration, etc) during grid outages, the best battery to pair with solar panels is a backup-enabled Lithium-ion battery. Again, whether an AC- or DC-coupled battery is best depends on whether or not you already have solar panels.

Some popular batteries that fit this criteria include:

• Tesla Powerwall (AC-coupled)
• Generac PWRcell (DC-coupled)
• LG RESU 10H Prime (DC-coupled)
• LG ESS Home 8 (AC-coupled)

Obviously, if you want to provide backup power, then a backup-enabled battery is required and consumption-only configurations are not an option.

Why is Lithium-ion (NMC) chemistry better for backup mode?

Unlike LFP batteries, which prefer a low average state of charge, Lithium-ion batteries (particularly the NMC chemistry used by Tesla, LG, and Generac) tend to prefer maintaining a high state of charge – which aligns well with backup batteries.

In backup mode, batteries go through fewer charge/discharge cycles and maintain a high state of charge until the grid goes down. According to the NREL, Lithium-ion (NMC) batteries maintain their original capacity longer under these conditions than LFP batteries, as shown in the figure below.

Is an AC or DC battery better for essential backup?

The choice between AC and DC batteries is typically dictated by whether you already have solar panels installed. 

If you have an existing system, then AC-coupled batteries will be easier (and less expensive) to add to the mix. If you don’t have solar panels, then DC-coupled batteries becoming a much more attractive option. 

In an essential backup scenario, having a more efficient DC battery allows you to squeeze more power out of every kWh of solar production during the outage. That means more time with the lights on and, possibly, more systems to power with your backup battery!

Best Batteries for whole-home backup

If the primary goal is to power every system in your home – during outages or when the grid is online – then the best batteries to pair with solar panels are the ones that can be stacked together to provide enough peak and continuous power output for large loads like air conditioning and EV charger.

Based on that criteria, here are a few of the best batteries for whole-home backup:

You’ll also want to consider battery chemistry. For example, if your goal is simply to store enough energy to power your entire home during a grid outage, the NMC chemistry is more suitable. However, if you plan on using charging and discharging on a daily basis, LFP chemistry is more suitable.

Additionally, round-trip efficiency plays an important role in battery systems of this scale. With a 10 kWh battery, 90% efficiency means losing 1 kWh per cycle. But with a 40 kWh system, 90% efficiency means losing 4 kWh per cycle.

So, if you don’t already have solar panels, it’s worth exploring more efficient DC-battery – as long as they’re stackable. If you already have solar panels, then keep an eye on the most efficient AC-coupled batteries.

Find the best battery for your solar system

With power outages increasing and net metering policies eroding, home batteries are becoming more mainstream and beneficial by the day. And while every battery company claims to have the best product, the best battery for your solar system is the one that empowers you to achieve your energy goals.

Connect with an Energy Advisor to set goals and find the best battery for your new or existing solar system.