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What is a lead-acid solar battery?

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    solar panel connected to a battery

    Technically speaking, a lead-acid solar battery, also referred to as a lead-acid deep cycle battery, is a type of rechargeable battery commonly used in solar energy systems to store excess electricity for later use.

    That definition isn’t entirely helpful, though; you probably could have guessed as much from context clues. Keep reading to find out what you need to know about lead-acid solar batteries, including how they work, how they’re different from their main competitor and whether one is right for your energy storage needs.

    Key insights 

    • Lead-acid batteries are an established option for storing energy produced by solar panels.
    • These batteries store energy using a chemical reaction that takes place inside their cases.
    • While lead-acid batteries are affordable and time-tested, they don’t last as long as lithium-ion batteries, and they require more space and maintenance.
    • Whether a lead-acid battery is right for you depends on your needs and preferences, and you can consult with a solar energy company if you need more specific guidance.

    Understanding lead-acid batteries

    For context, there are many different types of batteries that can store solar energy, and lead-acid batteries are just one option. More specifically, lead-acid batteries are a mature battery technology widely used due to their reliability, ability to deliver high current and cost-effectiveness.

    However, lead-acid batteries do have some disadvantages, such as shorter life spans, relatively low energy density (meaning they can’t store as much energy in a given amount of space) and the need for regular maintenance to keep their electrolyte levels correct and prevent sulfation (a buildup of lead sulfate crystals that can reduce the battery's effectiveness).

    How does a lead-acid battery work?

    It’s easiest to understand how a lead-acid solar battery works if we break its operation down into two functions: charging and discharging.

    1. Charging: During the day, sunlight hits your solar panels, creating direct current (DC) electricity. This DC electricity travels to a solar charge controller, which regulates the amount of current flowing to the battery to prevent overcharging. The electricity then flows into the battery, initiating a chemical reaction that stores the energy. The battery's lead plates (electrodes) react with the sulfuric acid electrolyte inside of it, converting lead and sulfuric acid into lead sulfate and producing electrons, which provide the electrical current.
    2. Discharging: When you need power later on, such as at night or on cloudy days when your panels aren't actively producing enough electricity to meet your demands, the process is reversed. The lead sulfate breaks down, returning to its original state of lead, lead oxide and sulfuric acid, which generates electricity you can draw on to power your home (after it passes through your inverter).

    » LEARN: How solar energy is stored

    Are lead-acid batteries better than lithium-ion batteries?

    If you’re shopping for a way to store your excess solar energy, there’s a good chance your choice will come down to either a lead-acid or lithium-ion battery. However, whether lead-acid or lithium-ion batteries are "better" really depends on your situation and preferences because each type of battery has its own advantages and disadvantages.

    Pros and cons of lead-acid batteries

    Check out the pros and cons of lead-acid batteries below to see if they’re right for you.

    • Pros: Lead-acid batteries are typically less expensive upfront, well-understood and recyclable at the end of their life spans. They also have a high power output, which can be good for systems with high surge loads.
    • Cons: Lead-acid batteries tend to have shorter life spans than lithium-ion batteries (typically three to seven years under normal use). They are also bulkier and heavier for the amount of energy they store, and they require regular maintenance to keep them working efficiently. Additionally, their efficiency decreases as they discharge, meaning they provide less energy when they're close to being out of power.
    It’s smart to consider the total cost of ownership over the life of the battery instead of just the upfront costs.

    Pros and cons of lithium-ion batteries

    Now, compare and contrast the pros and cons of lithium-ion batteries below to see if they sound like a better option for your needs.

    • Pros: Lithium-ion batteries can last 10 years or more, making them more cost-effective over the long run despite their higher upfront cost. They are more efficient at storing and discharging energy, have a higher energy density (they can store more energy in the same amount of space), and require virtually no maintenance. They can also withstand more charge/discharge cycles than lead-acid batteries and can run lower on power without being damaged.
    • Cons: Lithium-ion batteries have a higher upfront cost than lead-acid batteries. As one ConsumerAffairs reviewer mentioned during an unpublished portion of their phone interview, “I do not have the lithium because my pockets aren't that deep.” Also, while lithium-ion batteries can be recycled, the recycling process is less established and more complex than the process for lead-acid batteries. Finally, while rare, these batteries can pose a fire risk if damaged or improperly charged.

    Ultimately, the decision between these types of batteries will depend on your budget, how long you need your batteries to last, how much space you have for battery storage and how much maintenance you're willing to do. If you need help making a decision, a solar energy company can provide the expertise and experience you need to make the right choice for your home.

    » MORE: Best solar batteries

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      Are lead-acid batteries still used?

      Lead-acid batteries are still widely used despite the advent of newer battery technologies. They are often employed in applications where cost is a significant factor and where the battery isn’t cycled (charged and discharged) very frequently. Outside of the solar industry, lead-acid batteries are commonly used in automobiles, backup power supplies, recreational vehicles, marine applications, industrial equipment and mobility aids like wheelchairs and scooters.

      How long do lead-acid solar batteries last?

      As a rule of thumb, you can expect a lead-acid solar battery to last anywhere from three to seven years, but the life span of a lead-acid solar battery can depend on a number of factors, including the quality of the battery itself, the depth of discharge, the ambient temperature and how well it's maintained.

      What’s bad about lead-acid batteries?

      While lead-acid batteries have served us well for over a century and continue to be widely used, they do have some drawbacks, including:

      • Limited life spans
      • Above-average maintenance requirements
      • Low energy density
      • Possible environmental damage (when improperly disposed of)
      • Relatively slow charging
      • Declining performance in cold weather
      • Worse efficiency than other types of batteries
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