Like solar panels, batteries need an inverter to convert their stored DC electricity into usable AC electricity. Different types of inverters exist, depending on whether your battery system is AC- or DC-coupled. DC-coupled batteries often come with an integrated hybrid inverter for both solar and storage. AC-coupled batteries sometimes come with an integrated storage inverter, which only works with storage, meaning you'll need a separate solar inverter. Some batteries don't come with an inverter, so you must pair it with a separate, third-party inverter.
You may be able to save on equipment costs with a hybrid inverter, but you could have higher installation costs if retrofitting to an existing solar system, and you could miss out on some incentives, as we previously described.
There are two ways to measure the output you'll get from your battery: usable capacity and power rating. Usable capacity is measured in kWh and describes the maximum amount of electricity your battery can store on a full charge. The higher the usable capacity, the longer your battery's runtime. When comparing the usable capacity of different batteries, you'll also want to consider how many batteries you can stack in parallel; even if the usable capacity of one battery is low, if you can connect multiple batteries to one inverter, it may allow you to customize your system to meet your energy needs better.
Your battery will come with two power ratings, both measured in kW. Its peak power rating measures the amount of power your battery can output in a short period. It's important to have a battery with a high peak power rating if you need it to run appliances that require a lot of energy to start, like an air conditioner or a sump pump. Your battery's continuous power rating measures the amount of power your battery can output consistently. The higher its continuous power rating, the more appliances you can run at once.
Ultimately, the amount of capacity and battery backup power you need depends on how much of your house you plan to power with your battery—and for how long.
Two primary metrics differentiate batteries in terms of performance. Depth of discharge (DoD) indicates the percentage of the battery that can be discharged relative to its overall capacity. In other words, it's the amount of your battery's capacity you can use in one cycle for optimal battery performance: The higher the DoD, the more you'll get out of your battery.
Roundtrip efficiency measures the electrical losses involved with charging and discharging a battery. Batteries with higher roundtrip efficiencies better convert incoming electricity into stored electricity and back to usable electricity; they're considered higher-performance batteries.
Every time you charge and discharge your battery, it slightly reduces its ability to hold a full charge. A battery system is a big investment, so you'll want to ensure it lasts. The best way to feel confident that your battery will continue working efficiently is to choose one with a strong warranty. Battery warranties include many different components and clauses, which all impact the assurance you can feel when choosing a long-lasting battery.
Your battery's warranty period is measured in years and covers the integrity and output of your system–typically, battery companies offer 10-year warranties. Most battery warranties also include an end-of-warranty capacity guarantee, which states that by the end of the warranty period, the battery will still maintain a certain percentage of its original usable capacity. Batteries also often come with a cycles clause (a specified number of times you can drain and charge your battery under warranty) and/or a throughput clause (the total amount of energy the manufacturer expects the battery to deliver throughout its lifetime). Similar to how many car warranties come with a time and/or mileage component (i.e., ten years, 100,000 miles), if you hit your warranted cycle life or throughput before your battery reaches the end of its warranty period, it could end your warranty term.
You'll also want to look at other warranty information, like if labor and shipping costs are covered for repairs and replacements; batteries are considered hazardous waste, which means that these costs can be extremely high in some cases if you need to send the battery back to the manufacturer for diagnostics.
Energy or load management systems enable you to both monitor and control your energy consumption, typically at the circuit level. In most cases, if you're installing a battery, you'll need to install a critical load panel, which protects your appliances and battery from unintended electrical failures and enables you to power only your most essential devices during power outages.
Energy management systems replace the need for a critical load panel by providing real-time flexibility, allowing you to turn circuits on and off remotely. They can replace your main electrical panel, serve as a sub-electrical panel (similar to a critical loan panel), or be installed along individual circuit lines for a more modular approach. Most importantly, these systems allow you to get more out of your battery during power outages by only powering the most important loads at a given time. One of the most prominent energy management system brands, Span, claims that their smart home panel provides 40% longer backup than battery-only systems.
Some battery companies are now manufacturing their own energy management systems, while others are compatible with third-party systems like Span and Lumin. Not all batteries are compatible with all energy management systems, so make sure to pick a battery compatible with the energy management system you prefer.
You'll want to get the most bang for your buck when purchasing a home battery. Battery cost comes down to two key factors: the equipment and installation time. Some batteries are more expensive due to factors like their chemistry or supply chain strength, while others may be bulky and large and, therefore, more difficult (and expensive) to install.
Thousands of homeowners request battery quotes through our Marketplace every year, providing us with unparalleled insight into the cost of different battery brands. Based on our latest Solar & Storage Marketplace Report, there's an extensive range in battery prices: HomeGrid offers the lowest cost batteries at $480/kWh, likely in large part due to their flexible configuration, which makes them easy to transport and quickly install, while Sonnen offers the highest cost batteries at $1,570/kWh, likely due to their extremely strong warranty. The most quoted battery company on the EnergySage Marketplace is Enphase, which surprisingly is the second most expensive battery brand at $1,490/kWh.
While there are many great battery companies, a few stand out above the rest. Depending on what you're looking for in a battery system, HomeGrid, Villara Energy Systems, Sonnen, and SolarEdge offer some of the best solar batteries today:
Solar panels are a great way to capture free, clean energy from the sun for yourself or to feed it into the grid for more savings on your utility bill, but it's attaching a battery bank that gives you real energy independence.
Without solar batteries, even a house covered in photovoltaic panels will leave homeowners literally powerless when the grid goes down.
"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.
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Batteries are the key component that ensures your home can always stay lit and warm and that vital pieces of electronics such as medical equipment continue functioning. Depending where you live, they might be able to save you some extra money by returning energy to the grid at times when it's more valuable.
However, all of these benefits come at a cost, and wading through specifications to find the right match for your needs can be a bewildering task. Here's a concise primer on what you need to know before you go shopping for independence in a box.
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.
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.
Battery Pros Battery ConsCan reduce energy bills Savings vary depending on local utility and net metering rulesGetting cheaper, and eligible for tax credits and incentives ExpensiveStored power for when the grid goes down Large battery banks require significant storage spaceStoring and releasing energy during peak usage hours can reduce stress on the grid Not all utilities encourage or reward this practiceCleaner source of back-up power than a generator A generator may be more useful in a major emergencyLatest battery chemistries (like Li-PO4) are exceedingly safe and simple to maintain Some batteries pose health and fire risks and require management and maintenanceIncreased energy independenceThere are several kinds of batteries used in battery backup systems, including lithium-ion and lead-acid batteries. Here's a quick overview.
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, though, they are becoming standard in residential solar applications.
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 (or redox flow batteries) are less common in home systems since they're mainly designed for commercial use. However, the technology appears promising, and it could become more widely used in residential battery backup systems in the near future.
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, however, and generally not appropriate for residential use.
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 cost $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.
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 take a charge evenly.
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.
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 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.
Solar power is available for only part of the day. Adding a solar power storage battery system ensures you always have power when the sun isn't out or during a power outage.
A professional solar electricity system installer can help you select a battery that works well with your goals, whether you want to be entirely off-grid, have an emergency store for outages or minimize your costs from the electric company during peak hours.
DIY battery installation instructions abound online, but beware. Working with electrical equipment is dangerous and doing so without the proper training may also void your warranties and put you out of compliance with codes and other regulations.
Yes. The 30% federal solar tax credit can be applied to the total cost of your solar battery system if your battery can hold at least three kilowatt-hours of energy and is installed in 2023 or later.
It depends on how you intend to use them. Likely, fewer batteries are required if you simply hope to maximize net metering savings. To keep your home powered during an extended blackout, you will need to calculate your total power needs
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