How Does Solar Battery Storage Work?

Solar batteries – also know as energy storage systems (ESS) – are quickly becoming a staple in solar installations, and to understand why, we only have to look as far as California.

The Sunshine State’s government has made the gains from delivering power generated by solar panels far less favorable. Why sell power to the grid for peanuts when you can keep it and use it yourself?

As a result, the use of solar batteries has exploded, with over 90% of California’s solar installations now including batteries. 

Although Colorado remains one of the best states for selling power to the grid, you never know when that may change. Furthermore, gaining independence from the grid puts you in charge of your own energy supply and gives you the opportunity to go off-grid altogether.

But how do solar batteries actually work? And what affects their performance? Read on to discover more about this exciting technology.

In a Nutshell

  • Solar batteries give you an independent energy supply instead of relying on the grid.
  • There are four main types of solar batteries: lead-acid, lithium-ion, nickel-cadmium, and flow.
  • Depth of discharge, battery life, and efficiency all affect how well the batteries work.
  • Lithium-ion and flow batteries are best suited for solar energy storage but are the most expensive option.

How Do Solar Batteries Work: A Quick Overview

Solar panels in a field

Before we get into the nitty gritty of solar batteries, here’s a quick overview of what they do, broken down into a simple five-step process:

  1. During the day, your solar panels harvest the sun’s energy and convert it into electricity.
  2. The direct current (DC) generated by the panels flows into an inverter which converts it into alternating current (AC) electricity (the type you can use in your home and for your business).
  3. You consume the generated electricity throughout the day.
  4. Any excess electricity that you don’t consume flows into the solar battery and charges it.
  5. During times when you would normally have to draw power from the grid (at night when the solar panels aren’t generating electricity, for example), instead, you draw power from your battery.

How Does Battery Storage Work With Solar Panels?

Batteries standing end up

The energy that your solar panels harvest during daylight hours has to go somewhere. 

In the first instance, it will be utilized by whatever appliance, machinery, or device you are using at the time the energy is produced. For example, if you are operating a mill, the power is used for that purpose.

During periods of low electricity consumption or days with an abundance of sunshine, your solar panels often produce more electricity than you can actually use. When this happens, the excess power will flow into the grid. 

However, if you have a solar battery installed, instead of sending excess power to the grid, it’ll flow into your battery and charge it up, so it’s ready for you to use when you need it.

On average, it takes about 4.5 hours of sunlight on your solar array to provide sufficient power to charge your batteries. 

As we know, solar panels don’t work during the dark hours and they are less effective when there is shade or heavy cloud cover. During these times, it is necessary to draw additional power from the grid but if you have a solar battery installed, you will draw from this instead.

In essence, having a solar battery removes your reliance on the grid and provides you with an independent energy supply. It also opens up new possibilities of having an entirely “off-grid” electricity supply. For example, cabins and irrigation systems can be situated far from your electricity supply. In these cases, an off-grid system is ideal because it doesn’t need to be close to the meter.

How Does a Solar Panel Work Without Battery Storage?

If you don’t have a solar battery storage system installed, the excess energy generated by your solar system will simply flow into the grid.

The grid will then exchange that power for credit (usually one kWh worth of credit per kWh of power produced) in a process called “net metering.” 

This has the same effect in reducing your energy bills but it does not allow you to be energy independent.

What Are the Different Solar Battery Types?

While all batteries essentially work the same in that they store your excess power for later use, there are several different types of batteries on the market each offering their own set of characteristics.

The most common solar battery types are:

  • Lead acid batteries
  • Lithium-ion batteries
  • Nickel cadmium batteries
  • Flow batteries

Lead Acid Batteries

The lead acid battery is the most common type of battery around and it has been used to store energy since the 1800s. You will find this battery used frequently in the automotive industry, uninterruptible power supplies (UPS systems), and large-scale power stations.

The lead acid battery presents two options:

Flooded lead acid battery: This battery features a removable cap on the top of each cell, which allows you to top it up with distilled water. 

  • The battery consists of flat lead plates that are submerged in a pool of electrolytes (consisting of water and sulfuric acid).
  • When in charging mode, the electricity flows through the water which converts it into gas and oxygen.
  • The water-to-gas conversion process causes the battery to lose water, which is why it needs topping up.
  • Ensuring the water levels are just right keeps the battery safe and operating at optimal levels of efficiency.

Sealed lead acid battery: This battery type is sealed and, therefore, doesn’t require additional water. 

  • When the water splits into hydrogen and oxygen, it then goes through a recombination process from within the battery to transform it back into water.
  • Through this process, no water is lost.
  • The battery features a low-pressure safety valve that “vents off” gas if the battery starts over-charging or malfunctions.

Lithium-Ion Batteries

Lithium-ion is a much newer technology compared with lead acid that’s proving to be the best and most efficient option for solar energy storage. While it’s more expensive than a lead-acid battery, it provides superior storage capacity, longevity, and reliability.

  • The lithium-ion battery consists of an anode, cathode, separator, electrolyte, and one positive and one negative current collector.
  • When charging, the cathode releases lithium ions into the anode.
  • The cathode and anode store the lithium while the electrolyte carries the charged ions between the two via the separator.
  • This movement creates free electrons within the anode, which then creates a charge in the positive current collector.
  • This creates the electrical current necessary to power your home and business.

Nickel Cadmium Batteries

A less common option that has also been around since the 1800s, the nickel-cadmium or “ni-cd” battery went through a renaissance in the 1980s that greatly increased its energy storage capacity.

The batteries are ultra-durable and can withstand very high temperatures, which makes them more suitable for industrial applications, most notably the aircraft industry.

  • This battery uses nickel oxide in its cathode and cadmium in its anode.
  • Potassium hydroxide makes up its electrolyte solution.
  • When charging, the nickel undergoes a chemical reaction and oxygen atoms become nickel hydroxide. This process is what allows the energy to be stored.
  • When the battery is in use, the chemical reaction is reversed and the cadmium hydroxide releases the stored energy.

Flow Batteries

Finally, flow batteries are the newcomer in the energy storage sphere. What makes them appealing for solar energy storage is their 100% depth of discharge, meaning you can fully charge the battery without damaging it. Additionally, they have an excellent lifespan of around 30 years.

The downside is that they are large in size. While this makes them unsuitable for residential solar systems, they are a viable option for solar farms and large-scale agriculture.

  • Flow batteries contain two separate negative and positive electrolyte solutions.
  • When charging, the two electrolyte solutions pass through a stack of electrochemical cells.
  • The electrical energy from the charging process is converted into chemical energy and stored in the electrolyte solutions.
  • When discharging the battery, the electrolyte solutions are circulated through the battery the opposite way.

What Affects a Solar Battery’s Performance?

In principle, all solar batteries outlined above work the same but their unique compositions alter their effectiveness. Here’s a quick look at what affects a solar battery’s performance and how it works:

  • Depth of discharge (DoD): This refers to how much of the battery’s energy can be used before recharging it is necessary. Most types of batteries cannot be drained 100% without damaging them.
    • A flow battery is the only type of battery that can be drained 100%.
    • Lithium-ion and nickel-cadmium batteries have a DoD of about 80 – 90%.
    • Lead acid is the least efficient here with a DoD of about 50%.
  • Efficiency: An amount of energy is always lost in the process of storing and transferring it. Some batteries perform better than others.
    • Lithium-ion batteries have the best efficiency rate for solar.
    • Flow batteries also have great efficiency but slightly less than lithium-ion.
    • Lead acid batteries are about 80 – 85% efficient.
    • Nickel Cadmium has the lowest efficiency.
  • Battery Life: All batteries need to be replaced eventually, so it’s important to consider their lifespan:
    • Flow batteries have a lifespan of up to 30 years.
    • Lithium-ion and nickel-cadmium batteries have a lifespan of between 5 – 15 years.
    • Lead acid batteries have a lifespan of between 3 – 5 years.
  • Surrounding Temperature: Most batteries should be kept at a consistent temperature. If they get too hot or cold, their performance will deteriorate:
    • Lithium-ion’s optimal charging temperature is 32°F to 113°F and discharge is -4°F to 122°F.
    • Lead-acid’s charge and discharge range is -4°F to 122°F.
    • Flow batteries operate best in temperatures that are between 14°F – 104°F
    • Nickel-cadmium has the greatest range of  -40°F to 158°F

Note: Where temperature is concerned, if a battery gets too cold, its performance will continue to lessen until it shuts down. This won’t necessarily void the warranty of your battery but you won’t be able to use it until the surrounding temperature rises sufficiently.

Additionally, “best” operating temperatures range between battery types and brands, so be sure to check yours to understand what it is.

How to Choose the Right Solar Battery: Things to Consider

US power outlet and cable

Now that you understand how solar battery storage works, you should be able to decide which type of battery is best for your requirements. 

If you’re still unsure about which solar battery to pick, consult with your solar developer to see what they recommend.

In general, here’s what you need to consider before making a purchase:

Battery placement

The area in which the battery is to be placed can affect which one you choose. For example, flooded lead acid batteries have to be placed upright in an area where they can’t be tipped over. Due to their size, Flow batteries require a large amount of space.

Additionally, some batteries are designed to be wall-mounted and mounted vertically, which limits where you can place them. Some vertical batteries can also be placed in a special storage unit, but this depends on the manufacturer.

Other batteries have to be mounted horizontally – flooded lead-acid, for example – and are designed to be placed next to one another. Bear in mind that this type of mount will take up more floor space.

Battery Location

As a farmer in Colorado, you can install a solar battery outside or within a garage. However, there are certain regulations that you must follow. 

According to the National Fire Protection Association (NFPA), a solar battery can pose a potential fire risk and should, therefore, only be installed: 

  • In attached garages
  • In detached garages
  • On exterior walls at least 3 ft away from doors or windows
  • Outdoors at least 3 ft away from doors or windows, utility closets, and storage or utility spaces

These installation locations also comply with the National Electrical Code (NEC), which the state of Colorado follows.

Use Cases

How and when you intend to use your battery also matters. Lithium-ion batteries are best suited to shorter bursts of power, like during dark hours, while lead-acid batteries are better for emergency backup power.


Farms are vulnerable places, therefore, the safety of your solar battery is paramount. Lithium-ion batteries are more prone to catching fire, Nickel-cadmium batteries are extremely toxic if not handled properly, and lead-acid batteries require good ventilation and ongoing maintenance.

Solar Battery Advice and More

Solar batteries are just one piece of the large puzzle that makes up an entire solar installation. And as energy bills rise, batteries are becoming a necessity in gaining independence from the grid.

Whether you want a battery for an existing solar system or would like one included with your new installation, 8760 Solar can help. We run complete analyses on farms and agricultural businesses to determine the best solar setup and accompanying battery for their requirements.

We’re also on hand to offer advice and answer any questions you may have about going solar. Text “READY” to 719 470-0254 or get in touch via email: sales@8760solar.com and we’ll contact you right away. 8760 Solar is looking forward to hearing from you.

Frequently Asked Questions

Are Solar Batteries Worth It?

Solar batteries are worth it because they remove your dependence on the grid for additional power and provide you with an ongoing power source when the solar panels aren’t harvesting energy.

However, it is important to weigh up the different battery options and choose the right one for your solar system and budget.

How Do Solar Lights Work With Batteries?

Solar lights work with batteries by harvesting the sun’s energy via the light’s solar panel during daylight hours. The energy is then stored inside the battery which is contained within the light. When the sun goes down, a sensor triggers the battery to start powering the light.

How Do Rechargeable Batteries Work in Solar Lights?

Rechargeable batteries work in solar lights by storing the energy generated by the light’s solar panel. During the night, the battery’s power is drained by powering the light so that it can then be charged up again during the next set of daylight hours.

How Do Solar Panels Work With Batteries?

Solar panels work with batteries by sending the excess energy they produce to the battery instead of the grid. 

Then, when solar energy isn’t available for use such as during dark hours, you can use the energy stored in the battery rather than having to take energy from the grid.

Can Solar Batteries Be Retrofitted Onto Existing Solar Systems?

Solar batteries can be retrofitted onto existing solar systems quite easily. Your solar developer will be able to recommend the best battery storage system for your solar installation.

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