Saltwater batteries: What you need to know

Lithium-ion batteries dominate the energy storage market with their proven technology and continuously falling costs. Lithium-ion isn’t the only storage technology available, however: saltwater batteries are another option that has been around in some form for years now and have the potential to impact the energy storage landscape in a big way in the coming years.

Just like any battery technology, saltwater batteries store electricity for use at a later time. The main difference between saltwater batteries and other energy storage options (for example, lithium-ion and lead-acid batteries) is their chemistry. In saltwater batteries, a liquid solution of salt water is used to capture, store, and eventually discharge energy. Whereas a traditional lithium-ion battery uses lithium as its primary ingredient for conducting electricity, a saltwater battery uses sodium, the same element found in table salt.

Saltwater batteries have many advantages as a result of their chemistry. Here are a few that have helped make them a potential energy storage technology of the future, including when paired with a solar panel system:

Safety

While commercially-available batteries (like the Tesla Powerwall or LG Chem RESU) are safe for use, saltwater batteries excel in this category. The saltwater in the system means that there is essentially no fire risk with saltwater battery technology. Additionally, saltwater batteries don’t use the same toxic metals and other materials that most lead-acid or lithium-ion batteries use.

Easily recyclable

Another advantage of the lack of heavy metals and toxic materials in saltwater batteries is that they’re easier to recycle. As the use of batteries continues to increase worldwide, having plans for recycling used battery components will be essential to making batteries a truly sustainable energy technology.

Long lifecycle

Saltwater batteries have long lifecycles, which means they can be used for longer periods than many other battery options on the market. This has many implications - for example, you likely wouldn’t have to replace a saltwater battery as often as you would with most lithium-ion batteries, which can save you money in the long run.

With so many advantages to this technology, you’d think that saltwater batteries would be installed with every residential solar panel system and widely used for utility-scale storage projects. However, that’s not the case, and there are a few key reasons why.

The biggest hurdle for saltwater batteries reaching the mass market is upfront cost - specifically, their cost compared to the established market-leading technology: lithium-ion batteries. The cost of lithium-ion batteries has fallen exponentially over the past several years while we’re just beginning to experiment with saltwater battery options.

One of the most apparent problems related to the cost of saltwater batteries is their size. Saltwater batteries have a lower energy density than lithium-ion batteries, meaning they store less energy in the same amount of space. This is problematic because a lower energy density means a larger physical battery, and larger batteries use more materials and cost more to produce. As lithium-ion battery prices continue to fall, the cost challenge for saltwater batteries will only become more prevalent. Until saltwater batteries are produced at a large scale, the price will likely continue to be the largest barrier to their commercial availability.

This problem played out with saltwater battery manufacturer Aquion, a company that raised significant funding from Bill Gates and other impressive investors before collapsing into bankruptcy in 2017. Aquion promised all the benefits of saltwater batteries mentioned above and even installed a few battery systems before the financial challenge of scaling fast enough took down the company.

The future is uncertain for saltwater batteries. Their lower energy density means that one potentially more practical application is in larger grid storage systems where space is less of a concern than with smaller residential and commercial storage setups. Still, these costs will be a huge challenge to any saltwater battery companies that pop up.

Luckily, there are plenty of proven and available energy storage options that you can buy and install on your property. With any large purchase like solar and batteries (paired or separately), you want to consider your options. You can sign up on the EnergySage Marketplace to receive turnkey quotes for solar installation from pre-screened local solar installers. If battery storage is something you’re interested in pairing with your system, we recommend adding a note in your account preferences specifying you’re interested in pricing and information about batteries. Even if a solar installer doesn’t install batteries themselves, they can design a solar panel system so that you can add a battery later down the line.