How Many Batteries Do You Need for Solar Energy Storage?

Installing solar batteries means you can store and use solar power around the clock - not just when the sun is out. This dramatically increases the effectiveness of your solar panel system and allows you to save more money, reduce your carbon footprint, and become less reliant on grid power. 

In this guide, we look at how many batteries you need to run your house on solar depending on the three most common solar energy goals: cost savings, resilience, and independence from the grid. We also discuss other factors that can affect the number of solar batteries you purchase. 

How many batteries do I need for solar?

The truth is, there’s no one-size-fits-all answer when it comes to how many batteries you need to power a house on solar. This is because everyone’s energy usage and solar power goals are different. 

The best way to find out how many solar batteries you need is to consider your energy goals. The three most common energy goals are:

• Cost savings: Saving money on energy bills.

• Resiliancy: Having backup power to use during power outages. 
• Self-sufficiency: Being less reliant on the grid. 

Let’s take a look at how many batteries would be needed to achieve each of these goals. 

Goal 1: Saving money on energy bills

If your goal is to save money on electricity bills, you’ll want to store and use as much solar energy as possible to further reduce the amount of electricity you will need to purchase from the utility. The amount of stored solar energy needed to achieve your savings goals will depend, in larger part, on your electricity rate plan: 

• Fixed rate: If you have a flat-rate structure, having enough battery storage lets you use solar power when you need it most so you can save money in the long run. 
• Time of Use: If you’re on a variable-rate plan, also referred to as a Time of Use rate plan, your solar batteries will need  enough storage capacity to offset the most expensive hours. Utilities typically refer to these times as “on-peak” because that is when people are using the most grid electricity. Grid electricity is priced much higher during on-peak times. 

Essentially, if cost savings is your goal, then you want enough storage capacity from your solar batteries to keep you self-sufficient during on-peak electricity pricing hours. These hours might be different depending on your utility, chosen electricity plan and season. In most cases, 1 to 2 batteries should be enough to keep you from using grid power during on-peak hours and possibly even enough capacity to also power your home into the evening hours when your solar panels stop producing electricity. 

This doesn’t mean you won’t be using the grid at all, it just means you’ll be getting the most out of your solar panel installation while still having backup power available in the event of a grid outage. 

Goal 2: Backup power during outages

The most common reason why people opt for solar battery storage is to have backup power during grid outages. Solar systems are usually turned off during power outages to prevent the backflow of electricity from harming utility lineworkers as they execute repairs. Because of that, you can’t rely on solar panels alone during grid outages. This requirement is known as “rapid shutdown.”

Solar batteries allow you to continue using solar power even when the grid goes down, often referred to as resiliency. The number of solar batteries you’ll need for resiliency will depend on how many appliances you want to continue running during a power outage and how resilient you want to be. Most solar batteries are configured to power particular systems, like lights, refrigeration, Wi-Fi, medical devices, AC and other essentials. 

According to a study by the Lawrence Berkeley National Laboratory, a single 13 kWh battery is enough to power essential household systems for three days in almost all US counties at any time of year. Keep in mind that heating and cooling systems require much more power than most household appliances, especially in Arizona during the summer. As such, if you wish to connect your AC to your solar battery you’re likely to need more battery capacity to ensure a cool home for the desired timeframe.

Goal 3: Independence from the grid

If your goal is complete self-sufficiency, you’ll need a larger battery bank than for any other use case. Also known as going ‘off the grid’, this means you’ll no longer be receiving electricity from your power company. You’ll need to plan carefully to ensure you have enough stored energy to get through extended periods of low solar production as you won’t be able to fall back on grid power on cloudy days or during an extended period of bad weather. 

For that reason, planning a solar system to go off grid can be extremely complicated and expensive. How many solar panels or batteries you’ll need will depend on your location, your energy usage patterns, the efficiency of your home and appliances, local weather patterns, and other factors. In short, you have to design the system for the worst case scenario so that you’re sure to have enough power to cover the unexpected. It’s best to consult with a professional solar company that can make your transition off the grid much smoother and more reliable. 

To give you a rough idea of how many solar batteries it takes to go off grid, you might need anywhere between 8 to 12 standard lithium-ion batteries. This should store enough solar energy to get you through periods of low or no sunlight. It’s also wise to consider a generator, which is a good fallback in the event that weather prevents your solar panels from fully charging your batteries. Again, the exact configuration will really depend on your location, energy goals, the number of appliances you run, and so on. Get in touch with our team to discuss moving off grid and how we can help you plan a customized solar power system to keep you self-sufficient. 

Other factors to consider

Beyond understanding your energy goals, there are a few other factors that can determine how many batteries you need. We look at some of these below. 

Size of your home

There are two reasons why the size of your home can impact the number of solar batteries you need. Firstly, larger homes tend to consume more electricity and therefore have more storage needs. Secondly, a larger home means potentially being able to install more solar panels. With more solar panels you’ll be generating more power, which means you may require more battery capacity to store all the excess energy. 

Battery capacity

Different types of batteries offer varying energy storage potentials. For example, the Tesla Powerwall has a fixed capacity of 13.5 kWh while Generac PWRCell ranges from 9 to 18 kWh depending on the design. In 2024, we’ll likely see batteries with even higher capacities and modular expansion capabilities. Essentially, the type of battery you opt to purchase will affect how many you need, depending on their storage capacity. 

Amount of storage you need

The number of batteries you’ll need will also depend on how much storage you’re looking for. If you want to achieve full self-sufficiency and minimize your reliance on the grid, you’ll need larger battery storage capacity. On the other hand, if you’re mainly looking for backup power during outages or to offset peak electricity rates, then you’ll need less storage. Most homeowners install solar panels to save money and reduce their carbon footprint. With this in mind, one battery may be enough for households that don’t use a lot of electricity, and 3 or 4 for homes that generate more electricity. 

Your household’s energy usage

Every household uses electricity differently. Some families use more major appliances, drive an electric vehicle, or have a swimming pool, all of which increase energy uses. The amount of batteries you’ll need will really depend on your power consumption as a household. To find out how much energy your household uses, you can review your utility bills over the last year. Add up the number of kilowatt-hours consumed and divide it by 12 to find out your average monthly usage. With this in mind, you can accurately estimate how many solar batteries you need to run your house on solar. 

Net metering / Net billing

Depending on where you live, net metering may affect how many solar batteries you choose to purchase. When your solar panels generate more electricity than your home needs, excess electricity is sent back to the grid. With net metering, or net billing, this excess electricity is tracked by your utility meter and credited to your account. 

The difference between net metering and net billing is pretty simple. With net metering you get credited at the same rate for excess solar electricity you send back to the grid as you pay for electricity from the grid. With net billing you are credited for excess solar electricity at a lower rate than what you pay for grid electricity. In Arizona, most utilities practice Net Billing, with the buyback rate dropping annually since 2017

During periods when your solar panels aren't generating enough power to meet your needs, like evenings or cloudy days, you can draw from the grid as usual. The electricity you consume is then offset by the credits you've accumulated through net metering or net billing. At the end of a billing cycle, your utility company reconciles the difference between electricity you consumed from the grid and electricity you supplied. If you supply more than you consume, you'll receive a credit on your bill or compensation (depending on where you live). 

In this way the grid acts like a battery, storing your excess solar electricity as credits that can help to further offset your utility bill. But, since Arizona’s net billing model only credits you at the wholesale value, rather than the retail value, a battery actually offers a better ROI because you can store energy generated during cheaper off-peak hours for use during the expensive on-peak hours. In this way, you’ve gained the upper hand with the utility by keeping and using your energy, rather than selling it back at a cheaper rate. 

The policies around net metering vary from state to state. To see whether your state has solar net metering or net billing, you can view the table on this page.

How to calculate the number of solar batteries you need

Now that you understand the three main goals of solar batteries, and other factors to take into account, let’s look at how to calculate the number of solar batteries you need to run your house on solar. 

The best way to find this out is to partner with a reliable solar battery installation company that can provide you with customized advice based on your home, location, and goals. Contact our friendly team anytime for a free consultation and estimate. If you’d rather do some quick math yourself, here’s how to estimate the amount of batteries you’ll need.

Step 1: Determine your energy usage & storage needs

Start by identifying how much storage you need from your batteries. In other words, how much electricity do you need to achieve your goals?

Cost savings: If your goal is to save money on energy bills, then you’ll want enough storage to cover your electricity usage during more expensive on-peak hours. In this model, solar panels are not required since you can charge your battery from the grid during cheaper off-peak horus, and then discharge during the most expensive on-peak hours. Think of it like an energy time shift. 

With that said, adding solar panels allows for even more savings by powering your home during the day, while charging your batteries at the same time. In other words, a battery alone allows for some saving, a battery and solar together allows for more. Here are the on-peak times for Arizona’s two largest utilities.

APS On-Peak Hours:

• Summer (May 1 - October 31): On-peak hours are typically from 3 PM to 8 PM, Monday through Friday.
• Winter (November 1 - April 30): On-peak hours are usually from 6 AM to 9 AM and 5 PM to 9 PM, Monday through Friday.

SRP On-Peak Hours:

• Summer (June 1 - September 30): On-peak hours are generally from 3 PM to 7 PM, Monday through Friday.
• Winter (October 1 - May 31): On-peak hours are usually from 6 AM to 9 AM and 5 PM to 9 PM, Monday through Friday.

Backup during outages: If your goal is to provide battery backup during outages, then you’ll need to think about what exactly you’ll want to power during an outage, and for how long. For example, you might want to power your lights, TV, Wi-Fi, kitchen appliances, refrigeration, and water heating for 24 hours. If you want to also power your HVAC system, that will require more capacity. 

Your energy usage is measured  in kilowatt hours (kWh) consumed during a specified time period. The easiest way to find your usage is to look over past utility bills or multiply the wattage of appliances you use by the number of hours you use them in the day. To simplify the process, the U.S. Energy Information Administration estimates the average U.S. household consumes around 30 kWh per day.

Step 2: Choose a battery size

Next, you can look at batteries and choose an appropriate size for your needs. Most lithium-ion batteries provide around 9 to 15 kWh usable capacity. Some types of batteries, such as the Enphase IQ series, come in smaller sizes that can be stacked together to create more customized battery systems. 

Step 3: Configure your system to meet your needs

Now that you know how much storage capacity you need to cover your goals, and the type of battery size you’re looking at, you can configure your system to meet your storage needs. The number of batteries you need will depend on the brand and model you choose. 

The below table shows the most popular solar batteries, their storage capacity, and how many batteries you’d need to power 15 kWh per day - or half the energy usage of the average U.S. household.

Summary: How many batteries do you need to run a house on solar?

Ultimately, the number of solar batteries you need to run a house on solar depends on various factors, such as your energy goals, storage needs, and the type of batteries you purchase. To sum it up, here’s how many solar batteries you’d typically need to achieve the three most common solar energy goals:

• Cost savings: 1 to 2 solar batteries should provide enough storage for you to use during expensive on-peak periods when energy is the most expensive. 

• Resiliency: If you only need backup power to use during power grid lapses, the number of batteries will be dictated by which appliances you wish to have functional during the outage. If you only need to run a few lights, internet, hot water heater and a refrigerator, one battery should get you through the night. If you wish to connect your AC or heating system, you’ll surely need 2-3, depending on the size of your home and energy usage patterns. 
• Independence: If your goal is to be self-sufficient, then you’ll want anywhere between 8 to 12 solar batteries to keep your entire home off the grid. 

If you’d like a more accurate estimate, the team at Sun Valley Solar Solutions would love to help. Our expert team is trained and fully authorized by the most respected solar battery manufacturers, allowing us to design a customized solar energy system that meets your goals. Reach out to our team now for a free consultation and solar battery quote.