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Solar panels are good for the environment, help you save money, and free you from dependence on the power company.

However, they can’t provide power at night.

And weather conditions may interfere with the amount of energy generated during the day.

Yet, there’s a solution.

A solar battery bank ensures you always have power by making it possible to store solar energy for use during these times.

Let’s look at how to select the perfect bank for you!

How to Choose the Right Solar Battery Bank

All solar batteries sold in the United States must meet reliability and safety standards.

However, beyond those two factors, there isn’t a lot of standardization in the industry.

This can make choosing the battery bank you need a challenge.

This guide will walk you through the process to have peace of mind that your battery backup works when you need it.

What Is a Solar Battery Bank?

A solar battery bank is a piece of equipment that allows you to store some of the energy captured by your solar panels and use it when your solar system cannot generate enough power for your home.

Your battery backup makes it possible to gain independence from the power company, provide power for yourself and your neighbors during a blackout or emergency, and maximize the environmental benefits of going solar by reducing the power you need to draw from the grid.

What Specifications Does My Solar Battery Bank Need?

There are several factors to consider when choosing your bank:

1. How Much of Your Home Do You Want to Power?

If you want to be able to power your entire home from the backup, you need a battery with a high power rating.

2. Do You Need to Run Energy-Intensive Appliances?

Appliances that require a lot of power to start up, such as a sump pump, require a battery backup with a high rating for instantaneous power.

3. How Long Do You Want to Run on Battery Power?

If your goal is always to have power available, choose a battery with a high capacity.

4. How Important Is Efficiency?

A higher roundtrip efficiency rating helps you get the most out of every kilowatt of solar energy your system generates.

5. Is Space a Concern?

A battery with a small footprint is essential for recreational vehicles and other small spaces.

6. Is Battery Life Important to You?

Choose models with a long lifespan if you want a battery that can cycle more times without needing replacement.

7. Do You Need to Have the Safest Solar Batteries?

All solar batteries must meet specific safety standards.

To purchase a solar battery bank with the highest possible safety rating, choose batteries that have been tested and certified to standards beyond the minimum.

What Do All These Terms Mean?

Evaluating solar storage options involves a lot of technical jargon.

These are some of the terms you are likely to encounter.

Power Rating

The power rating of a solar battery is the kilowatts of power that the battery can produce at one time.

This rating is helpful to determine which appliances you can run and how many you can run simultaneously time when using the battery.

The power requirements of various appliances are presented as either watts or Amps.

Solar batteries are usually rated in kilowatts, which is thousands of watts.

To convert watts to kilowatts, take the number of watts on the label and divide by 1,000.

For appliances that express their capacity in Amps, you can convert the number of Amps to kilowatts by multiplying the Amps by the volts and dividing by 1,000.

For example, a 12W LED lightbulb requires 12/1,000 = 0.012 kW. A 55″ LED television requires about 0.077 kW.

It takes about 0.3 kW to run an energy-efficient washing machine and 3.5 kW to run a 3.5-ton air conditioning unit.

Most solar batteries have a power rating of 5 kW.

Additionally, you should check the battery’s continuous and instantaneous power rating.

Some batteries can provide brief periods of higher power to support appliances, such as sump pumps that require a large amount of energy to start up but then run on lower amounts of power.

Battery Size 

Battery size refers to the usable storage capacity of the battery.

This is the total amount of electricity that the battery in your solar battery bank can store and then supply to your home.

Battery size is expressed in kilowatt-hours (kWh).

The number of kWh a battery can store tells you how long your battery can power the various electrical systems in your home.

A kWh is the energy it takes to run a 1,000-watt appliance for an hour.

To calculate a kWh, check your appliance’s capacity label for wattage and divide that number by 1,000.

This gives you the number of kilowatts your appliance needs to run for one hour.

Roundtrip Efficiency

Roundtrip efficiency measures how much energy your solar battery bank loses when you put energy into or take energy out of your battery.

Your battery’s roundtrip efficiency indicates how much of every unit of electricity you store in your battery is usable.

Battery Lifetime

The lifetime of your battery is measured in expected years of operation, anticipated cycles, and expected throughput.

Throughput measures the amount of electricity you can expect to be able to pass through your battery over its lifetime.

Cycles measure how many times you can charge and empty your battery.

To calculate your battery’s expected lifespan, divide the throughput by the usable capacity.

This gives you how many cycles you can achieve before replacing the battery.

Divide the number of cycles by 365 days to get the number of years your battery should last if you run one cycle per day.

Safety

All solar battery bank batteries are tested to meet the minimum safety requirements.

However, some are tested to ensure they go beyond the minimum standards.

You can check the spec sheet of the batteries you are considering to determine which safety and rating certifications they have.

Chemistry

The primary compound your battery uses to store electricity is called its chemistry.

The chemistry of your battery is what drives many of the factors discussed above.

Different chemistries have different advantages and price points.

How Many Batteries Do I Need?

The answer depends on how much power the appliances you want to use and what you want to use your solar battery bank for.

The Appliances and Circuits You Want to Run

Most homes in the United States have a 200 amp electrical panel.

You aren’t likely to have enough battery power for the entire panel.

Fortunately, you won’t need to.

To figure out your power needs, you or your installer need to calculate the power usage of the various appliances and circuits you want to be able to run off battery power.

If you don’t know the energy requirements of your appliances, you can estimate it online.

The Length of Time You Plan to Run Your Appliances

Once you have the power requirements of the appliances you want to run, you need to know how long you want to be able to run them.

For example, you might need your TV and your computer for just a few hours each but want to keep your air conditioner on all day and your refrigerator on 24-7.

Calculating the Size of the Solar Battery Bank You Need

To calculate what size bank you need, first make a list of everything you hope to run off the battery and how many kW each appliance or circuit uses.

This gives you the minimum power rating you need for your battery. Next, write down how many hours you need to run each item.

Multiply the number of kWh each item uses by the number of hours you want to run that item and add all the results to get the battery size you need.

What Kinds of Batteries Are There?

The two primary differences to consider with solar batteries are whether they are direct current or alternating current-coupled and the battery chemistry.

Flooded Lead-Acid Batteries

This type of battery has been the industry standard for many years because it is the most cost-effective and longest-lasting of lead acid batteries.

These batteries contain an electrolyte that can freely move within the battery encasement.

When the battery is charged, the acid and lead plates react to store electricity.

To avoid leakage, these batteries must be mounted upright in your solar battery bank.

You must check them monthly and top them off with distilled water to ensure they last as long as possible.

They must also be enclosed and vented to prevent toxic hydrogen gas from becoming a hazard.

Sealed Lead-Acid Batteries

These batteries resemble the flooded version, but you cannot access the internal compartment and do not need to add distilled water.

Instead, the electrolyte is sealed to last the battery’s lifetime.

These come in absorbent glass mat and gel types.

AGM Batteries

AGM batteries contain an electrolyte suspended in a thin fiberglass mat located between the lead plates.

This makes the battery resistant to vibration.

They can be mounted in any orientation.

However, they cost more than flooded lead-acid batteries and don’t last as long.

They may be good choices for mobile applications, such as RVs, remote locations, areas where leaked acid could be a problem, and regions in extreme cold.

Gel Batteries

Gel batteries are like AGM but use a thick paste instead of a fiberglass mat.

AGM batteries can handle higher charge and discharge rates, while gel batteries work better for slow, deep discharge applications.

They also work better in heat.

Because they are more expensive than other types, they are recommended for a solar battery bank in a location with high temperatures.

Lithium-Ion Batteries

Lithium iron phosphate batteries are the best lithium batteries for solar applications.

The main advantage of this type is that they last longer and can handle deeper cycles.

Additionally, they don’t require maintenance or venting.

The upfront costs are higher, but because they are more efficient, the overall cost over the battery’s life is about the same as lead-acid batteries.

AC Versus DC-Coupled Solar Batteries

Grid-tied inverters require the power grid to function.

With an AC-coupled solar battery bank, your grid-tied inverter is matched by a battery bank controlled by an off-grid inverter.

The inverter is a second power source that keeps the grid-tied inverter online during power outages.

This makes it possible to run your essential appliances and charge your batteries during a power outage.

AC-coupled systems are the easiest install for retrofitting an existing system.

However, they can be challenging to properly size, and if they aren’t sized correctly, the system will perform poorly or not at all.

The battery bank is connected directly to the solar array with a DC-coupled system.

DC coupling is compatible with a wider range of off-grid inverters and battery bank sizes.

However, it requires you to operate a manual transfer switch to charge the batteries from the solar array.

Which Solar Battery Bank Is Best for Me?

There’s no simple answer to which solar battery bank is best for you.

You must consider all the various factors and choose based on your budget, needs, and preferences.

Fortunately, you don’t have to do it by yourself.

We at Unbound Solar are ready to help you customize your solar system.

Download our free solar battery guide, or contact us to find out more!

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