7 Questions to Ask Before Buying Solar Battery Storage

Thinking about adding a battery to your solar system to store the excess power your panels produce? As severe weather events and power safety shutoffs prevail, now is a great time to make that smart investment. But you'll want to ask yourself a few questions first to make sure that you get the right home battery backup system to meet your needs.

1. Do I Really Need to Add a Battery to My Solar System?

The short answer is: If you want to take advantage of the benefits of solar power even when the sun isn’t shining or the power grid is down, you’ll need battery storage for your solar electric (or photovoltaic) panels. If you live in an area that implements time-of-use (TOU) rates, the amount you pay for electricity will vary depending on the time of day you use it. By installing a home battery backup system, you can use your battery during peak demand hours to send any power you’re not using back to the grid, and receive more credits on your electricity bill for doing so.

 

2. What Do I Need to Power During an Outage? 

The amount of backup energy you’ll have varies depending on several factors, including:

• How much power your solar system is producing
• How much solar energy your household consumes
• How much energy is stored in the solar battery
• What you are powering during the outage

The more power you’re consuming, the less time your backup power supply will last. So, we recommend avoiding high consumption appliances, such as multiple air conditioning units or other large appliances, for long periods of time.

If you want to be able to power certain things during an extended outage, such as your Wi-Fi modem, fridge, and electric furnace, use Sunnova’s battery duration tool to get an idea of how much home battery storage you might need to power your essential and large appliances.

You’ll also want to speak with a professional about your needs. You can start by requesting a no-obligation quote here.

 

3. Will I Use a Solar Battery to Charge My Electric Vehicle (now or down the road)? 

The step from a solar system with battery backup to an electric vehicle (EV) is not a huge one. If you care about affordable energy and sustainability, these are all for you. But electric vehicles use a lot of power — whether you’re using solar power you generate yourself or pulling electricity from the grid. In fact, an EV could deplete your entire solar battery if you’ve only planned for enough storage to power your home in between charges.

If you have an electric vehicle — or want to get one — you should have a plan for charging it. And if you want to use solar power to charge your EV at night, make sure you have enough backup energy to do so. With home battery storage, you can also charge your EV during a power outage.

 

4. Have I Installed an Energy Intensive Feature Like a Pool (or do I plan to)?

Failing to account for a major energy user, like a pool, a refrigerator, or one of another many things that has an outsized effect on your overall energy usage, can lead to a battery that’s too small. Before sizing a solar system with battery backup, use Sunnova’s battery duration tool to get an idea of what some major energy drains could be and how to account for them when planning your battery storage solution.

 

5. Am I Affected by “Time of Use” Rates? 

Aside from electricity prices varying based on time of use, in some cases, the price may vary from season to season. Basically, customers pay less for electricity at times of the day when there is less demand on the electric grid, and they pay more for electricity during times of day when there is more demand. These are often referred to as off-peak and on-peak periods.

When you add a battery to your solar system, you can program that solar battery to power your home during on-peak hours, when the utility rate is higher. That means you can factor in those reduced costs when you’re thinking about the return on investing in home battery storage. Also, if you live in a place that has TOU rates and you need to charge an electric vehicle, it makes the most sense to charge your EV with your battery during times when rates spike.

 

6. What Factors Go into Correctly Sizing My Battery Backup System?

To correctly size your system, you need to know how much energy from the grid you use now. You can find that amount on your electric bill. This will give you an idea of how much energy your home is using during times when solar panels are not currently powering your home. That is the power that your home storage system should aim to replace.

You’ll also want to speak with your installer to see if it would be a good idea to add any additional solar panels to up the amount of energy you capture once you can store extra power.

 

7. Is My Home Battery Storage System Eligible for State or Federal Incentives? 

Incentives for home battery storage do exist, and vary depending on where you live. To take advantage of tax incentives, you need to own your system outright by paying upfront or through a loan, not a lease or power purchase agreement (PPA). There is one federal tax incentive — the investment tax credit (ITC) — that was extended by the Inflation Reduction Act in 2022 to include energy storage. Customers who own their storage systems may be eligible for 30% tax credit on the cost of their installed system from 2023 through 2034. 

There are other state-specific and utility-specific solar battery incentives that you can apply for, ranging from property tax exemptions and tiered rebates to post-installation bill credits.

Whether you’re interested in solar plus battery storage, or adding a battery to your current solar system, Sunnova is here to help. By requesting a quote, we can connect you with an expert in your area who can help you find the right home battery storage system and reduce your solar battery cost through rebates and storage incentives.

 

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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 on 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. 

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. 

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.

Further reading:
What are the best practices for EV charging stations?
How do you compare solar systems?
Whole Home Battery Backup: What Every Homeowner Needs to Know
How much does it cost to run air cond?
What is the difference between base load and peak load?
How many solar panels would be needed to run a home ...
Electric Power Sector Basics | US EPA

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. 

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 backup 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 independence

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. 

FAQs

Why do I need a battery with solar panels?

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.

Can I install my own solar battery?

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.

Do solar batteries qualify for the federal tax credit?

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.

How many solar batteries do I need to power my house?

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