Guide to Solar Batteries: Are They Worth It? (March 2024)

All solar batteries have the same basic function, but each type is suited for different applications. Your solar battery will offer higher reliability and return on investment when its chemistry is suitable for the application at hand.

For example, some electricity consumers are subject to higher kWh prices at certain times of the day, or additional charges for sudden peaks in consumption. In this case, you need a battery bank capable of delivering large amounts of electricity in a short time. Lithium-ion batteries are suitable for this task, but not redox flow batteries.

Regardless of the battery type, you also need to consider the depth of discharge (DoD), which indicates a battery’s usable capacity. The service life of a battery can be drastically shortened if you exceed the DoD, or you can even cause permanent damage. For example, using 70% of the stored energy is acceptable with a solar battery rated for 80% DoD, but not a 50% DoD battery.

Lead-Acid

Lead-acid batteries are an established technology, commonly used by off-grid solar energy systems in remote locations. Lead-acid batteries are affordable and have a well-established supply chain due to their popularity, so you can easily find vendors and technical support.

In spite of their low cost, lead-acid batteries have some technical limitations you should consider:

• Lead-acid batteries typically have a charging life of 500 to 1000 cycles.
• Batteries should be fully recharged after each use, or the lifespan is drastically reduced.

An absorbed glass mat or AGM battery is an improved version of the traditional lead-acid battery. They can charge faster while having a spill-proof design and more durability. You can also find AGM deep cycle batteries that are designed for 80% DoD.

Using lead-acid batteries along with solar panels requires charge controllers to sustain a suitable charging current. These batteries should not be wired directly to your solar array, or your system may be damaged by excessive current.

Lithium-Ion

Lithium-ion batteries have become very popular in recent years since they can achieve synergy with solar panels and wind turbines. For example, the Tesla Powerwall and Enphase IQ are two types of lithium-ion batteries commonly used in home solar applications. You can also find smaller lithium batteries from brands like Renogy and WindyNation, which are portable and better suited for DIY solar projects.

Lithium iron phosphate or LFP batteries are a subtype of lithium batteries, characterized by a superior service life. The best LFP batteries offer a service life of over 4,000 cycles at 80% DoD, which means they can last for over 10 years on a daily charging cycle. This makes LFP batteries the ideal complement to solar installations. Unlike lead-acid batteries, which need separate charge controllers, many of the lithium battery models that are commercially available come with built-in chargers and controls.

The main drawback of lithium-ion batteries is the high price, but this could change in the near future — the U.S. Department of Energy is targeting a 90% energy storage cost reduction by 2030. Lithium batteries can also suffer a phenomenon called thermal runaway when used at high temperatures, which causes them to catch fire. You can prevent thermal runaway by making sure your batteries are high-quality and installed by qualified electricians.

Nickel-Cadmium

Nickel-cadmium batteries are characterized by their durability, tolerance to high temperatures and simple maintenance needs. Thanks to these performance features, nickel-cadmium batteries are popular in industrial and utility applications. Unfortunately, cadmium is highly toxic to humans, so nickel-cadmium batteries are not recommended in homes.

Flow

Flow batteries store energy by separating positive and negative electrical charges in chemical solutions, which are stored in separate tanks. When these two solutions interact, they undergo a reduction-oxidation reaction (redox) and the battery releases energy. This battery technology is also referred to as “redox flow” for this reason.

The main disadvantage of redox flow batteries is their space requirement, and they are not cost-effective for small-scale projects. Even a small redox flow battery system can be the size of a shipping container, so using flow batteries in home solar systems is not viable.

Before deciding whether you want to install a battery now or in the future, ask yourself: Why do I want a battery? Do I need one?

A battery is a big purchase – one that typically adds more than $10,000 to your overall cost to go solar. And in some areas of the country, you may not see a financial return on that upfront investment.

A solar battery can help you save money if your utility has demand charges, time-of-use rates, or doesn't offer net metering. By storing solar electricity onsite in a battery, you can avoid pulling expensive electricity from the grid when your solar panel system isn't generating enough power to meet your needs (like at night).

Resiliency is another good reason to add a battery to your solar panel system. If you experience frequent power outages and want to keep your lights on when the grid goes dark, a battery can help you do just that. Installing a solar battery for home backup may not save you money in the long run, but that doesn't mean it's not worth it: After all, you can't put a price on peace of mind, right?

If none of these reasons jump out at you as compelling enough to add a battery, that's okay! It probably means you shouldn't install one right now. But if you know you want a battery, just need an answer on timing, read on.