Solar Batteries: Pros, Cons, How to Choose

Solar batteries store solar energy for use at another time. Manufactured by companies including Panasonic, LG, Generac and Tesla, a solar battery typically costs $12,000 to $22,000. Solar batteries may be a good choice if you’re looking to use less grid electricity or go off-grid completely^[0]

Solar battery pros and cons

How do solar batteries work?

When you pair your solar energy system with a solar battery, the surplus energy your system generates goes straight to the battery, where it’s stored for later use (as opposed to that surplus automatically being returned to the grid)^[0]

.The energy stored in your battery bank can then be used later when you need it most, such as during a power blackout. Here’s how it works:

• Solar panels use photons from the sun to knock electrons away from atoms and generate an electrical flow.

• The excess electricity generated by the solar panels is stored as direct current (DC) energy in the solar battery.

• An inverter converts the DC energy to alternating current (AC) energy for home use — either as needed, if you have a DC-coupled conversion system — or immediately for instant use if you have an AC-coupled conversion system. Excess power in this type of system can be converted back to DC to charge the battery.

A solar system with a solar battery may include these basic components:

• Ground or roof-mounted solar panels.

• Inverter that converts DC energy into AC energy for home use.

• Junction box to connect solar panel wiring to the home breaker panel.

• Charge controller to prevent battery overheating.

• Utility meter for the battery bank.

• Disconnect switch to prevent islanding (continuing to generate electricity and push it onto the grid) during blackouts. This protects electrical workers trying to restore power.

If your solar system is connected to the grid, you’ll also have an interconnection agreement with your utility provider.

Here are some of the main types of batteries commonly used in solar systems.

These reliable staples are the oldest type of solar batteries, and they are often used for off-grid applications. They’re the most affordable solar battery option, but they have a low energy density, meaning they can’t hold a lot of energy for their weight. Compared to other options, they’re large and heavy.

• Dependable, time-tested technology.

• Lower priced than other types of solar batteries.

• Compatible with most systems.

• Heavier and bulkier than other types of solar batteries.

• To preserve battery life, it’s recommended that you don’t let the battery capacity drop below 50%. Other types of batteries can drop to 10% capacity — and sometimes lower — without damaging the system.

• Generally need maintenance such as adding water (unless sealed).

• Shorter life span than other types of solar batteries.

• Take longer to recharge than other types of solar batteries.

• Contain harmful chemicals and they require proper disposal.

Well-suited to residential solar systems, lithium-ion batteries offer a small, light and long-lasting solar battery option with a high energy density. This newer technology lets you access more of the battery’s stored energy before needing to recharge it, which is why this type of battery is common in laptops and mobile phones. If they’re not installed properly, however, lithium-ion batteries can catch fire. They’re also pricier than some other types of batteries.

• Smaller and lighter than other battery types; work well in tight spaces.

• Newer technology with improved battery capacity and efficiency.

• Little or no maintenance required.

• Fewer batteries needed for power.

• Lithium-ion batteries have a high depth of discharge, meaning if the battery capacity drops to 10%, it won’t strain the system or cause the system to degrade.

• Can catch fire if improperly installed.

• Special equipment required for installation.

Designed mostly for commercial solar systems, nickel-cadmium batteries are rare in smaller residential applications. Because some manufacturers are testing ni-cads for home systems, we may see more of them in the future. Nickel-cadmium batteries use older technology, are low maintenance and long-lasting, have a high discharge capacity and can work efficiently even in extreme temperatures. However, they’re also heavy and bulky, lose charge when they’re not used, are costly and contain toxins that are harmful to the planet when not properly disposed of. Some countries have banned their use.

• Long life span of up to 20 years or more.

• Nickel-cadmium batteries have a high depth of discharge, meaning if the battery capacity drops to 20%, it won’t strain the system or cause the system to degrade.

• Perform well under extreme weather conditions.

• Power retention is lower than other battery types.

• Not environmentally friendly.

• Not typically available for residential solar systems.

Engineered for large-scale use with very limited availability to homeowners, this new technology uses water-based electrolytes that flow between two internal tanks. Charging and discharging takes place through chemical reactions within the battery, and increasing the number of tanks can increase total energy storage capacity. Flow batteries are very efficient and have a 100% discharge capacity. They’re also long-lasting and use nontoxic, nonflammable materials. Unfortunately, they’re also heavy, large and expensive. They require a lot of maintenance and have a low power density.

• Long life span of 20 years or more.

• Nonflammable and nontoxic materials.

• High efficiency with 100% discharge capacity.

• Considered too expensive for residential use.

Final considerations and how to choose a solar battery

Here are a few important factors to consider and compare:

• Budget. Weigh affordability and durability, and be aware that less expensive lead-acid batteries won’t last as long as lithium-ion batteries, which are more expensive upfront.

• Space. Choose batteries that fit in your available space.

• Warranty: Look for a solid warranty from a reputable manufacturer.

• Battery capacity. For maximum efficiency, be sure this is appropriate for your solar system’s energy production. There are two measurements to consider: Storage capacity is how much energy the battery can hold; usable capacity is the energy the battery can provide minus the energy needed to operate the battery.

• Battery life span. Longer life spans save on battery replacement costs over time and lessen the impact on the environment.

• Round-trip efficiency. This is the measure of how well your battery stores and retrieves energy and how efficient its operation is after it’s charged. The industry standard for this is about 80%^[0]

• Depth of discharge: This is how much power a battery uses before you need to recharge it.

• Maintenance. Lower-priced battery options such as lead-acid typically require more maintenance, and you’ll need to decide how much maintenance you’re willing and able to perform.

• Your system’s voltage requirements. Make sure your battery is compatible with the voltage requirements of your solar panels.