10 Things to Consider When Buying Solar Battery Storage System

As electricity costs continue to rise, solar panels are a smart way to tap into efficient and clean energy from the sun. A recent CNET survey found that 78% of US adults are worried about rising home energy bills, and 70% are actively taking steps toward energy efficiency. If you’re thinking along the same lines, now might be the right time to explore solar power. Installing solar panels and connecting them to the grid can help reduce your monthly bills and cushion costs when the sun isn’t shining. But if you want real energy independence, you’ll need to get a solar battery. Without one, even a roof full of solar panels won’t help during a grid outage -- you’ll still be left in the dark.

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"Something that people don't consider is that if they're on natural gas, and the power goes out in the winter, they think their heater is going to work, but most have an electric fan, so if the power goes out you still need something," said Mike Murphy, owner of Utah-based PrepSOS, which sells solar batteries, generators and other emergency-preparedness equipment.

Plenty of folks, including those in a recent Reddit thread, often wonder if solar batteries are worth the investment. The short answer is absolutely. A battery completes your solar setup, giving you access to stored solar energy day or night and can keep your lights on and essential devices powered during emergencies. Plus, if your area supports net metering, you could knock extra money off of your electric bill by selling surplus energy back to the grid when it’s most valuable.

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Solar batteries come with a price tag, and choosing the right one can feel overwhelming. That’s where we come in. This guide breaks down everything you need to know to shop smart and find the right solar battery for your home.

How solar batteries work

The simplest way to think of batteries is to imagine that the electricity in your house flows through wires in much the same way as water through plumbing. Batteries fill the role of a storage tank, making electricity readily available when it's needed, just as indoor pressure tanks and water heaters do with water. When batteries are tapped for energy, their reserve of stored electricity is depleted, but in a properly wired system, they can be automatically replenished by "catching" any excess electricity flowing through the system from sources like solar panels or the grid.

Depending on your goals for installing batteries, your system might look a bit different.

1. Connect just to solar panels: Batteries connected only to solar panels will fill when the sun shines and will discharge when you use electricity and the sun is down or behind clouds. It's one option if you are off-grid and away from electrical utilities.

2. Connect to solar panels and to the grid: If you have a solar inverter that can temporarily disconnect you from the grid, you have what's known as a hybrid solar system. In such a system, you can charge your battery with your solar panels or the grid and use the energy stored there in your home or send it back to the grid and save some money via rate arbitrage (if you have time-of-use rates). A hybrid system can also keep your house powered during a power outage.

3. Connect just to the grid: While we wouldn't call them solar batteries, you can install batteries without solar panels at all. They would charge from the grid and would be useful for backup power or for enrolling in a virtual power plant.

Pros and cons of solar batteries

The pros and cons of buying a battery largely boil down to savings (and backup power) versus cost.

The extra solar electricity you store in your solar batteries can be used in place of electricity you'd normally have to buy from your utility, or sold back to the grid when it's most valuable. This can save you some money and relieve some pressure on the grid when there's peak demand. (Whether this is a viable money-saving option for you depends on your utility's net metering rules.)

Some companies are starting to allow people to enroll their batteries in virtual power plants, a fleet of batteries, smart thermostats and other household appliances that work together to decrease demand on the grid. Where available, virtual power plants might come with additional perks for the battery owner.

In addition, you'll be able to use your battery bank in the event that the grid goes down due to a failure, natural disaster or even a solar flare.  A backup generator can also help keep the power on in an emergency (and charge your batteries), but it requires burning fossil fuels, usually either gas or propane.

Batteries do add considerable expense to your home energy system, but federal tax credits and other incentive programs usually can be applied to the cost of storage.

Different types of solar batteries 

There are several kinds of batteries used in battery backup systems, including lithium-ion and lead-acid batteries. Here's a quick overview.

Lithium-ion batteries

There are multiple lithium chemistries on the market, including nickel-manganese-cobalt, lithium polymer and lithium iron phosphate. The latest lithium technology comes with less danger of fire than older headlines might lead you to believe. They're capable of a deeper discharge than lead acid batteries (you can use up to 90% of a charge per cycle without inflicting much damage) and are much easier to maintain with a longer lifespan. They're also significantly more expensive and sensitive to temperature. Increasingly, they are becoming standard in residential solar applications.

Lead-acid batteries 

The basics of this technology are essentially unchanged for over a century. They remain inexpensive and widely available. For solar systems, it's popular to use somewhat more expensive sealed batteries that require less maintenance and eliminate the risk of dealing with a potential acid spill and hydrogen off-gassing. For a while, sealed lead acid seemed to be the future of solar batteries.

However, all lead acid batteries require more careful monitoring of charge levels compared with lithium-ion and can't compete in terms of efficiency, energy and lifespan but are a good and plentiful budget alternative. 

Flow batteries

Flow batteries (or redox flow batteries) are less common in home systems since they're mainly designed for commercial use. The technology appears promising, and it could become more widely used in residential battery backup systems in the near future.

Nickel-cadmium batteries

Nickel-cadmium batteries have a high energy density with double the energy of a lead-acid battery. Nickel-cadmium batteries are very durable, expensive and work well in extreme temperatures making them a good choice for large-scale commercial and industrial projects. Cadmium is toxic and generally not appropriate for residential use.

Buying a backup battery system

In general, a solar battery bank can cost between $10,000 to $25,000 for 10 to 25 kilowatt hours of power. (The US Department of Energy says solar batteries can cost anywhere from $12,000 to $22,000.)

That said, it ultimately comes down to your budget and energy needs. A small off-grid solar system with enough battery capacity for the basics (no air conditioning or electric heaters allowed) using a pair of high-capacity flooded lead acid batteries can be had for $500 total. Upgrading to lithium-ion costs $1,300 for a system with comparable capacity. 

Adding batteries is a significant expense for any system, but the good news is that nearly a third will come back to you in the form of the 30% federal renewable energy tax credit. Other incentives may also be available from state and local governments, utilities, and even credit unions.

How to set up a battery backup system

It's best to use a certified solar installer or electrician to install your solar batteries and connect them to your solar array, your home, the grid and an EV charger if you desire. You should expect to spend a few thousand dollars for the labor involved, and there may be additional components like inverters, charge controllers and EV charge stations that can also add hundreds or thousands of dollars in expense.

If you have confidence in your DIY skills and experience with electricity, it is possible to install batteries yourself. Just be sure to check with local regulations, building codes and equipment warranties.

If you go the DIY route, make sure all batteries are the same age (ideally new). Don't mix new batteries with older ones to help make sure they charge evenly.

Maintaining a battery backup system

For all batteries, follow any manufacturers' instructions regarding monitoring the depth of discharge. Generally, for lead acid batteries, this means trying to keep them over half charged as much as possible. Many lithium-ion batteries can safely be taken down to only 10% charge. Flooded lead-acid batteries also need to be topped off with distilled water a few times a year.

Lifespan and warranties

A few years after installation, you may notice that your battery backup system doesn't hold a charge as well as it used to. That's because, like other types of batteries, battery backups lose storage capacity over time. 

To account for this, battery backups include a warranty that expresses how efficient the battery should be by the end of the warranty period. Many of the top solar batteries offer 10 years and 70%, meaning that by the end of the 10-year warranty, the battery should still operate at 70% of its original performance. Lead acid battery warranties typically last for two to five years.

Inverters and batteries 

Inverters play an important role in how the battery stores and converts solar energy. While solar panels generate electricity in direct current, the electric grid and homes generally use alternating current. An inverter can convert AC to DC or vice versa, and most solar batteries include an inverter to store the energy in DC form, as well as an inverter to convert it back into AC to be used in the grid or the home.

Because inversion of current isn't perfectly efficient, battery producers are always experimenting with how to invert less often and increase the efficiency of the battery. As a result, some batteries will not have inverters for both input and output included in the system. Talk to your solar installer about the battery system you're considering so that you can make sure you have all the external inverters you need.

Beware cheap inverters, which are everywhere. To power modern household appliances, a pure sine wave inverter is essential; otherwise, you may end up frying some of the more delicate electronic circuits in your home.

In the last year, nearly two-thirds of solar.com customers paired their solar panels with a home battery energy storage system (aka BESS). Why? Because home battery storage has something to offer everyone—from backup power to bill savings to self-reliance.

With this in mind, there is no single “best” battery. There are different solutions to meet the varying requirements and needs of homeowners across the country. 

In this article, we’ll explore some of the best home battery storage products on the market today and what to look for in a battery storage system. To find a solution that best meets your needs, consult a solar.com Energy Advisor to review custom designs, proposals, and savings estimates.

Jump to a topic:

• What can home battery storage do for me?
• Best solar batteries of
• Solar battery features
• How to choose the best battery for your needs
• Frequently asked questions

What Can Home Battery Storage Do For Me?

June update: Congress is proposing to end the 30% tax credit for solar and battery storage effective December 31, . If you want battery storage for any of the reasons below, connect with a solar.com Energy Advisor to get your system designed and installed before the tax credit expires.

To find the best battery for your home, start with a goal. What problem are you trying to solve? There are three main use cases for adding a battery storage system to your home.

Time-of-Use Shifting

Sometimes called solar arbitrage or load shifting, Time-of-Use shifting allows you to capture the excess power your solar array generates relative to what your home is consuming. It then banks this power and discharges it in the late afternoon or early evening when utility rates are typically higher and your solar array isn’t producing as much.

This cost-saving strategy also works well in areas where the net metering or buy-back rate is less than your purchase rate, and is especially true in California under NEM 3.0.

Self-Consumption

Some areas and utilities don’t actually allow solar generators to send power back to the grid. Or, if they do, they provide no value for it. In this instance, battery storage acts like a giant sponge to soak up your excess generation and discharge it in your home later to avoid buying power from your utility provider.

Resilience

With power outages from natural disasters such as hurricanes, earthquakes, fires, and ice storms occurring with greater frequency, almost every area of the US experiences periodic grid outages. And, unless you have a specifically configured system called “sunlight backup,” your solar array will shut down if there’s a grid outage (this is to code for the safety of line workers, working to re-establish power). Because of this, many homeowners choose to add a battery to provide an element of resiliency to their project so they can keep food at safe temperatures, have some lights at night, and be able to keep their phones charged.

Need to dial in your home energy goals? Connect with a solar.com Energy Advisor to explore your home’s potential for savings and self-reliance.

Best Solar Batteries of

Evaluating the best home battery storage system goes beyond published specifications. The solar.com team also considers pricing, the bankability of the manufacturer, and the controlling software, as the best battery hardware is useless without operating controlling software to tell it what to do. And, as discussed above, different battery use cases will dictate what capacity (size) and capabilities you’ll want to look for when selecting a home battery storage system.

It’s also important to note that some utility providers offer generous rebates for homeowners to install a home battery system that’s on their approved list, and not every battery qualifies for every program. 

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Because there’s no perfect battery for every solution, here are the battery storage systems that solar.com Energy Advisors find work well with homeowners who invest in solar and battery. 

Quick tip: If you’re unfamiliar with some of the technical terms, we left a handy guide below!

Tesla Powerwall 3

From a hardware and software perspective, the Tesla Powerwall 3 is an outstanding product. Building on the successful prior generations of Powerwalls, Tesla continues to pack a lot of value in a high-feature set, high-capacity product. Because the Powerwall 3 has an integrated inverter built in, if you install a Powerwall 3 with your solar array, you can eliminate the need for a standalone solar inverter. 

Tesla Powerwall 3 tech specs

Feature Measurement Usable capacity 13.5 kWh Peak power 185 LRA (75% higher than Powerwall 2) Continuous power 11.5 kW Warranty Up to 10 years Round-trip efficiency 90% Depth of discharge 100%

Things to consider about the Powerwall 3

As of early , demand for the Powerwall 3 is far outpacing supply, which is creating significant lead times and delaying installations. It’s for this reason that solar.com energy advisors are not currently recommending the Powerwall 3 to homeowners, although we can still quote and arrange installation if requested.

Enphase IQ 5P

The leading inverter company, not surprisingly, offers a fantastic home battery storage solution in the Enphase IQ Battery 5P. This smaller capacity battery comes in at a lower price point than larger capacity competitors, and can often get the job done in Time-of-Use shifting applications for bill savings. And, the Enphase app provides powerful insights in a user-friendly format.

Enphase IQ 5P tech specs

Feature Measurement Usable capacity 5 kWh Peak power (3 seconds) 7.68 kW Continuous power (with solar) 3.84 kW Warranty Up to 15 years Round-trip efficiency 90% Depth of discharge 98%

Things to consider about the Enphase 5P

The downside is, of course, lower capacity means less availability for power if the grid goes down. But, if you live in an area with a relatively stable grid that isn’t prone to long-duration outages, the 5P might just get the job done. And, if you like the Enphase ecosystem but the 5P is too small? Enphase offers a 10C battery, which offers higher capacity.

Franklin aPower2

Franklin is a relatively new entrant to the home battery storage space but has quickly cemented its position as offering a sleek all-in-one package that’s simple to install and provides “whole home” backup. What makes Franklin’s aPower2 a great option for resiliency applications is that it can be integrated with almost every solar inverter (great if you already have solar and want to add battery storage), AC power generator, or the grid itself. 

The aPower2 is a 15kWh capacity battery that offers 10kW of continuous output, which means you can power just about anything as long as you have enough charge in the battery. The aPower2 is controlled by the aGate, which runs your charge and discharge algorithms, and feeds information to Franklin’s well-designed app.

Franklin aPower2 tech specs

Feature Measurement Usable capacity 15 kWh Peak power 15 kW (10 seconds) Continuous power 10 kW Warranty Up to 15 years Round-trip efficiency 89% Depth of discharge 100%

Things to consider about the Franklin aPower2

Quoted prices are typically at the high end of the spectrum, which makes the solution from Franklin a premium choice. And while it does offer a premium user experience and feature set, the extra cost might not be warranted in all applications. Franklin is also a relatively new company, and so we have to flag whether they can survive long-term to continue to operate the app and provide warranty support. While there’s no known financial issues today (they’re privately held), the home battery storage space is notoriously challenging.

Solar Battery Features

Frankly, there is a lot to consider when choosing a solar battery. The industry jargon doesn’t help, and neither does the fact that most battery features are things we don’t think about on a daily basis.

So, in this section, we’ll give a brief summary of some common battery terms and what they mean.

AC vs DC-coupled

It’s important to understand the difference between Alternating Current (AC) and Direct Current (DC) batteries because DC batteries, while more efficient, can be challenging to add to an existing solar system.

This is due to differences in which type of power is generated, stored, and used in each system, shown in the table below.

System Type of current Solar panels Produce DC power Batteries Store DC power Home (lights, AC, fridge) Use AC power Utility grid Distributes AC power

Existing solar systems typically have solar inverters, which change the DC power produced by panels to AC power that can be consumed in your home or exported onto the grid. But if you want to store that AC power in a battery, it needs to be inverted again to DC power.

Each time the power is inverted, a little bit is lost during the inversion process (hence the lower efficiency of AC-coupled systems).

In a DC-coupled system, the DC power produced by the panels can be directly stored in the battery and inverted only once to be used in your home or exported to the grid.

Round-Trip Efficiency

Related to AC vs DC coupling, round-trip efficiency is a measure of how much of the original power put into the power can be retrieved later on.

As we mentioned above, a small amount of power is lost each time it is inverted from AC to DC, or likewise. So, for AC-coupled systems with multiple inversions, efficiency is typically around 85-90%, while DC-coupled systems with fewer inversions can boast up to 97.5%.

If you plan to use your battery on a daily basis to charge an EV or avoid peak time-of-use rates, small differences in efficiency can really add up.

Types of Solar Batteries

The next thing to consider is the composition of the battery. Every battery on our list is either lithium-ion or lithium iron phosphate (LFP). While similar, the differences are noteworthy. LFP batteries typically have longer lifespans and increased thermal stability (aka less heat and fire risk). They also do not use nickel or cobalt, which can be toxic and dangerous to mine.

Learn more about the different types of home battery storage here.

Batteries can also be categorized as backup versus consumption-only.

Traditionally, the main feature of solar batteries was to provide backup power for grid outages. However, as net metering policies are weakened and removed, there is a growing demand for batteries that allow homeowners to save money by storing and using their own solar production without providing backup power – known as consumption-only or non-backup batteries.

Why would anyone want this? Well, the components, programming, and labor that go into providing backup capabilities are expensive, and removing these things can reduce the cost of a battery by 20-30%.

So, consumption-only batteries enable all of the bill savings of a traditional backup battery at around 75% of the upfront cost – which can be well worth it for homeowners who aren’t concerned with grid outages.

Peak and continuous power

Most batteries feature two numbers that represent their capacity to provide power.

Peak power is the measure of the battery’s ability to handle surges of power, like when an air conditioner turns on. This is a short burst of energy that can typically only be sustained for 10 seconds or so.

Continuous power is a measure of how much output the battery can sustain over long periods of time. This figure is especially important if you plan on using a battery for backup power during grid outages.

Usable Capacity

Usable capacity is a figure that represents how much power you can draw from your battery at one time. This is different from the nameplate capacity, which represents the total amount of power a battery can store.

The key difference is that draining a battery all the way down to 0% can damage the system and reduce its lifespan. It’s typically recommended to leave at least 10% of the nameplate capacity in the battery at all times to prevent damage, hence the term “usable capacity.”

Depth of Discharge (DoD)

Depth of Discharge is the manufacturer’s recommendation for how much power you can pull from the battery at one time relative to its total capacity. This figure ranges from 84% to 100%. Some manufacturers say “go ahead and empty the tank,” while others say it is best to keep a minimum charge of 16%.

Battery Warranties

Like solar panels – and everything else – batteries naturally degrade over time. Battery warranties guarantee a certain level of performance over a stated time frame.

For example, every battery on our list has a warranty guaranteeing that it will have 70% of its original usable capacity available after 10-15 years or a certain level of usage (measured in throughput capacity or cycles), whichever comes first.

How to Choose the Right Solar Battery for You

As we’ve shown above, not all solar batteries are created equal, and the best battery is the one that serves your needs. So, it’s important to begin your search with some goals, beginning with your energy needs.

Assessing Your Energy Needs

In , there are several reasons to want battery storage for your solar system. These include:

1. Backing up essential systems for outages (lights, refrigeration, Wi-Fi, medical devices)
2. Backing up your entire home (air conditioning, EV charging, heat)
3. Load shifting to reduce your energy bill
4. Reducing your carbon footprint as much as possible
5. Adopting new and pioneering technologies

Your energy goal(s) will play a big part in dictating the best solar battery for you. For example, if your primary goal is bill savings, then you will likely be shopping for smaller batteries than if your goal is to back up your entire home.

Comparing Battery Specifications

Once you’ve used your energy goals to narrow down a few brands and models, take a deeper dive into the specifications. If you’re comparing backup batteries, pay attention to usable capacity and continuous power. If you’re comparing self-consumption batteries that will charge and discharge every day, focus on efficiency.

Evaluating Battery Warranties

Finally, if you’re having trouble deciding between two battery models that check all your boxes, use the warranty offerings as a decision-maker.

While the goal is to never have to use your warranty, it can be worth the peace of mind to have a more robust guarantee on your side.

Conclusion

Let’s face it: Choosing a solar battery can be daunting. However, by starting with your energy goals and focusing on two or three batteries that check your boxes, it can be much easier to identify a storage system that meets your needs.

Solar.com’s best solar batteries of are a great place to start. If you’re ready to compare prices, connect with an Energy Advisor to see exactly how much solar batteries cost through installers in your area.

Solar Battery FAQs

Which batteries are best for solar panels?

Solar.com’s top choices for best solar batteries in include the Tesla Powerwall3, Enphase IQ 5P, and the Frankling aPower2. However, it’s worth noting that the best battery for you depends on your energy goals, price range, and whether you already have solar panels or not.

Which is the best solar battery company?

Some of the best solar battery companies in include Tesla, Enphase, and Franklin. These companies all have a track record of producing quality products and offer some of the most robust warranties on the market.

Which solar batteries last the longest?

Since solar batteries are a relatively new technology, we are still waiting to see which batteries last the longest. In , you’ll see battery makers offer up to 15-year warranties, but it’s worth paying attention to how many cycles or power output are tied to those warranty lengths.

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