How solar energy is stored

Examining solar storage technology, its uses and benefits

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    Wondering how you can store the energy produced by your solar energy system? We’ll cover everything you need to know about how solar energy is stored so you can make an educated decision on whether a solar battery is right for you.

    Key insights

    • Storing your solar energy has a lot of benefits, but it’s not always necessary.
    • Most solar energy systems with storage capabilities use lithium-based batteries to store energy electrochemically.
    • Given the relatively large upfront costs involved, choose a storage solution you expect to last a long time.

    Do you have to store solar energy?

    Because larger solar energy systems for homes and businesses are often connected to the power grid, solar energy storage is not always necessary. That’s because grid-tied systems can send the excess power they produce out to the utility grid, potentially netting their owners a profit through net metering. However, if you have a solar energy system that’s not connected to the power grid, storing the electricity generated by your panels is practically essential.

    Without some way to store or export the energy your solar panels produce, you’ll likely waste a large portion of the electricity they generate. Solar storage lets you capture the power produced by your photovoltaic (PV) system and access it later, like after the sun goes down.

    Installing a grid-tied system without battery storage can help save you money initially, and you still have the option of adding solar storage in the future.

    Larry, a ConsumerAffairs reviewer from California, initially purchased a grid-tied system but eventually wanted to add storage for emergencies, explaining: “We've been satisfied with going solar, but we still want to figure out how we can go off-grid by adding a battery component. When the power goes off, our system also goes off because it's a grid tie.”

    Benefits of solar energy storage

    If you’re wondering why anyone spends their money on an energy storage system when it’s not necessary, the answer is that having storage capabilities can unlock several benefits beyond the cost savings and environmental benefits of solar panels alone.

    The most common benefits of solar energy storage include:

    • Islanding: With enough solar battery storage, you can pivot your home to run (temporarily) without help from the power grid. This can not only keep your lights and appliances running during local electrical outages, but it can also help you avoid expensive utility energy rates during peak demand hours.
    • More independence: Although going solar is a great first step to energy independence, adding battery storage is one of the best things you can do to have more power and control over your home’s electricity. By storing excess solar power in your battery, you get a source of emission-free power that you can tap into anytime.
    • Future-proofing: As the energy grid continues to grow and advance, having solar battery storage can put you ahead of the curve in terms of adopting the right technology. While there are plenty of incentives designed to reduce the costs of battery storage today, there are also lots of new programs being created to help solar battery owners share and sell their energy on the open market.

    » LEARN: Are solar panels worth it?

    How is solar energy stored?

    Like all electricity, solar energy can be stored in a variety of ways. To get a bit technical, solar power may be stored either:

    • Thermally (by retaining heat from the sun)
    • Mechanically (by using compressed air, pumped hydropower or another active element)
    • Electrochemically (by using a battery)

    While mechanical solar energy storage is more common at large scales, the majority of homes and commercial buildings utilize batteries for their size and convenience. And, thanks to decades of growth in the renewable energy industry, there are multiple types of batteries available today that are specifically designed for solar energy storage.

    How solar energy is stored in batteries

    Whenever new energy is generated in a set of solar panels, it has to be sent through a charge controller before it can be stored. (Charge controllers, also known as regulators, are sometimes built into solar batteries with the purpose of preparing the incoming energy so it can be stored efficiently.)

    Once the electricity reaches your solar battery, a chemical reaction converts it into a form suitable for dormant storage. Whenever energy is released from the battery and discharged to power your electronics, this chemical reaction is reversed.

    Types of solar batteries

    A solar battery’s “type” is usually defined by its chemical composition. In general, lithium-based batteries are seen as the best solar batteries for residential and small-scale commercial energy storage because of their efficiency and availability.

    Alternatively, lower-cost options, such as lead-acid-based batteries, can be useful to run simple devices like solar gate openers, well pumps or lights. (Lead-acid batteries have been used to store solar for decades. However, the technology is neither as efficient nor as long-lasting as today’s lithium counterparts.)

    » LEARN: How do solar panels work?

    How much does solar energy storage cost?

    The cost of solar energy storage mostly depends on two main factors: the battery’s chemistry and its approximate storage capacity. However, several other factors can also come into play, like build quality, warranty periods and installation expenses.

    We included prices for three popular batteries in the table below to give you a better idea of how much solar energy storage costs.

    BatteryChemistryCapacityApproximate price per battery
    Tesla Powerwall Lithium-ion 13.5 kWh $11,500
    Renogy 12V 200Ah Lithium iron 2.5 kWh $1,000
    Grainger Approved 33Ah Sealed lead-acid 0.5k Wh $200

    » MORE: How much do solar panels cost?


    How long can solar energy be stored?

    The length of time you can store solar energy depends on the chemistry and quality of the battery you use. While small, do-it-yourself solar batteries tend to hold their charge for up to five days, large home residential batteries can store solar without any significant power losses for a full week or even longer.

    How long do solar batteries last?

    Depending on its quality, a solar battery can last anywhere from a few years to two decades. On average, most solar batteries last between five and 15 years, with some low-quality and high-end products appearing as outliers on either side of this range.

    How many solar batteries do I need?

    The amount of solar batteries you need depends on the output of your solar panel system and the wattage capacity of each battery.

    Let’s say you have a small solar energy system that outputs an average of 2 kilowatt-hours (or 2,000 watt-hours) of electricity per day. If you're purchasing 1,000-watt-hour batteries, you would probably want to buy two of them to capture the approximate average daily production of your solar array. Solar panel production isn’t stable year-round, though, so you may need even more storage capacity if you want to capture all of your system’s potential production on long summer days.

    What’s the cheapest way to store solar energy?

    The cheapest way to store solar energy is with a high-efficiency battery (like a lithium-ion option) that is rated to last for a long time.

    Although purchasing a less-efficient battery (like a lead-acid-based unit) will be cheaper upfront, investing slightly more can help you save money in the long run with increased amounts of storage potential and fewer part replacements.

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      Bottom line

      Ultimately, our methods of storing solar energy will continue to evolve as more creative solutions emerge in an increasingly renewables-powered world. For now, purchasing a high-quality lithium-based battery is the best way to store your solar power, whether you're purchasing a home system or designing a DIY project.

      If you’re considering solar storage for your home, talk to your solar installer about different system sizes and price points to find the best fit for your energy demands. As John Ytterberg, a former solar energy consultant, put it for us: “My advice would be to talk to your installer about batteries. You don’t necessarily need to buy one that is big enough to go off the grid permanently – that can get pretty pricey. Sometimes, a smaller battery may be the answer if it is just to maintain power during blackouts.”

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