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Best Batteries for Solar Energy Storage

By April 23, 2021Blog

The core of a solar storage system is the battery array that takes excess charge and contains it for later use, or distribution across the electric grid. There are several options for the type of battery used in systems like this, each with its own advantages and disadvantages. Since this is one of the earliest and most important decisions that must be made about solar battery storage, let’s take a closer look at the various battery options and why they are the current popular choices in commercial solar installations.

Lead-Acid Batteries

Lead-acid batteries are some of the oldest options for solar energy storage – and that comes with certain advantages. These deep cycle batteries use a well-known sulfate chemical reaction between an acid present in the electrolyte and lead dioxide materials within the battery’s plates. When working with a technology that’s been around for more than 100 years, you know that you are dealing with a dependable solution. The limits, uses, and maintenance requirements for lead-acid batteries are very well understood.

There are two types of lead-acid batteries used for storage projects: Flooded and sealed. Flooded batteries have the simplest design and can be regularly maintained so they stay optimal but need a lot of attention when it comes to adding water to the electrolyte mixture, avoiding leaks, and so on. Sealed batteries use glass mats or gels and have very few relative maintenance requirements, but they may not be as efficient, and they can’t be maintained over time like flooded batteries. Flooded batteries tend to be the most common choice for large solar storage projects.

Some owners still prefer lead-acid batteries to other options, for several important reasons. They are by far the cheapest option for setting up solar storage, and their simple design means they are less likely to face mechanical error than some options. Many materials in lead-acid batteries are fully recyclable as well.

However, these batteries do require significant, regular maintenance to keep work, and installation requirements may be more rigorous than other battery options. They tend to last between 5 to 10 years before needing to be replaced, one of the shorter lifespans for solar storage.

Lithium-Ion Batteries

Today, lithium-ion batteries are used in everything from your smartphone to electric vehicle. They are one of the newer forms of electricity storage, and very good at what they do: The battery depends on transferring charged lithium ions, which products free electrons that generate a charge. So many of our modern devices – especially mobile devices – use this technology because it’s incredibly efficient and very easy to recharge. When it comes to energy density, few batteries can perform as well as lithium-ion options.

A couple of specific lithium-ion battery types are used for solar storage – as lithium-ion technology continues to improve, new versions occasionally enter the market, and a particularly popular field concerns lithium-ion battery arrays that are specialized for vehicles or electric grids. These compact batteries have several significant advantages: While they do require periodic maintenance, they have nothing near the requirements of lead-acid batteries, so upkeep is much easier. Their innate efficiency and depth of discharge (in other words, the vast majority of the battery’s charge can be used before a recharge is necessary) also gives lithium-ion batteries longer lives, with most large application versions rated for at least 10 years.

So why are lithium-ion batteries not the default choice for all solar storage? While they are certainly common, lithium-ion technology tends to be significantly more expensive than other storage options, so you are indeed paying for what you get. There are also occasional concerns about lithium-ion batteries catching fire, although with proper manufacturing quality and professional installation this is not really a concern.

Nickel Cadmium Batteries

Nickel cadmium batteries are an interesting alternative to the common lead-acid and lithium-ion storage systems. These batteries are similar to sealed lead-acid batteries but made of rarer elements with a more precise design that allows the battery to easily absorb gases created during the charging process.

Nickel cadmium batteries have a very high capacity, which makes them a favored pick for particularly challenging tasks, which is why they are still used in medical equipment, aircraft technology, and some power tools. It also helps that these are some of the most durable rechargeable batteries in existence, able to handle extreme temperatures with the correct design and installation. They need very little maintenance, too.

All of these benefits are well-suited to commercial solar installation projects, which is why you sometimes see them in the solar industry. The significant downside to nickel cadmium batteries, however, is that cadmium is highly toxic, difficult to dispose of, and banned by some governments, which makes it a poor choice for organizations working to meet sustainability goals and a headache to replace.

Saltwater/Flow Batteries

The final option for solar storage is called saltwater or flow batteries. They use a water-based electrolyte (which is, yes, frequently a saltwater mixture) suspended between two different chambers. It’s a relatively new design that takes up a lot of room but has several innate advantages. The incredible depth of discharge allows these batteries to be fully discharged without damaging the battery, which is ideal in a situation where ongoing variable charges are managed like a solar installation.

Flow batteries also skip the use of heavy metals, so they are seen as a greener option compared to lead-acid, and their simple design makes them extremely durable, able to last up to 30 years with proper care.

The downside to flow batteries is that they are still extremely expensive, and they can’t hold as much of a charge as alternative batteries, especially at the same size. However, they can be a viable option for large, commercial solar installations, where we expect to see a growing number of these batteries in the coming years.

If you are interested in planning or upgrading a solar installation, contact us at Coldwell Solar today to schedule a consultation. We offer consulting, design and engineering, financing options, construction, maintenance and monitoring services for commercial solar energy installations. We also can help you choose and install the right battery array for your solar energy storage.