Green energy seems to be the buzzword lately. We constantly hear about solar, wind, even tidal power and the great promises they hold, but we never hear about new technologies to store this abundance of clean energy. Rather, we hear that these technologies are unreliable and work only during a given time of the day/year.
That is because battery technology, in comparison to green energy generation, is lagging in development. This is obvious in many places like California, which at the moment has many solar installations, but not enough utility-scale storage infrastructures. This seems to be one of the main problems that users run into when trying to install solar panels on their homes. The panels are becoming more efficient each year, but battery technology is staying static. Even Elon Musk pointed out in an interview a few years ago that the greatest hurdle for producing the Model 3 is manufacturing and integrating the battery.
The molten salt battery has the capacity to change the whole game. It’s an old technology first developed in WW2 by German scientist Georg Otto Erb for the use of the famous V2 rocket starter. He later was captured by the Allies and started working for them. The technology started to get incorporated in all kinds of weapons, including a detonator for atomic bombs in the 50s and a power source for the Tomahawk missile.
Most military exploitations of the technology involved its use as a blast generator to set up explosions or other reactions. During the 60s, different universities began to test the molten sodium battery as a reusable solid-state battery. The technology was promising because the material (sodium) was abundant and cheap. It also seemed the energy output could be much higher than that from the standard lithium-ion batteries. The biggest problem was that sodium based batteries operate at temperatures between 470 and 660°F (245 and 350°C). This meant special insulation and wiring was needed, making the battery very expensive and bulky, practically unusable in today’s applications. Despite the impracticality, plans of battery usage continued and included ideas of use in space; one was even made for a Space Shuttle mission in 1997, but was never used.
Molten Salt as a Thermal Energy Storage
Molten salt can be used in solid state batteries (like the batteries in our phones) or as a thermal energy storage (a big container usually placed underground). Stored heat in the molten salt can later be used for generating electricity through steam generators or other technology.
Thermal energy storage is used in concentrated solar plants, such as Ivanpah in the Mojave Desert (image above) between California and Nevada Concentrated solar operates by joining hundreds (or even thousands) of mirrors that reflect sun rays into a central tower that receives heat and transforms it into thermal energy. Water is typically used as a medium to absorb heat and later produce electricity through a steam turbine. If energy needs to be stored for a given time, a heat saving material, like molten salt, can be used.
The molten salt is placed in large containers, usually half or completely buried in the earth, which allows for temperature to be maintained for days, weeks or sometimes even months. The same molten salt can be used repeatedly without much degradation for as long as 50 years. This makes molten salt thermal energy very affordable and attractive for big solar power stations. For example, the Solana Generating Station in the U.S. can store up to six hours worth of generating capacity by utilizing molten salt. During the summer of 2013, the Gemasolar Thermosolar power plant with molten salt in Spain achieved continuous production of electricity for 36 days straight.
New Research into Solid Salt Batteries
In February of this year, a team of researchers at the Sandia National Laboratories in Albuquerque managed to lower the operating temperature of a molten sodium battery to just 230°F (110°C). They charged and discharged a single battery 400 times in the span of eight months. The sodium battery ran on 3.6 volts, which is 40% more than other molten salt batteries that existed. This breakthrough demonstrated that the battery can use fewer cells and have a higher energy density than anything we have right now.
Due to COVID restrictions and lab closure, they froze the battery for a month and heated it back up in an oven. The battery functionality returned without any damage to the internal chemistry.
This is all great news; battery development is back in vogue. The Sandia experiment means that the next generation of molten salt batteries can be small in size and lighter, without the need for expensive insulation. They will also be very powerful. This opens up a bevy of applications for green technology and grid scale storage. It shows great promise to be a backup grid scale solution that will turn on quickly when power is down and last for days or even months. This could lead to greater adoption of both renewable resources and electric transportation.
How do Molten Salt Batteries Work?
Typical lead acid batteries (used as a car battery) have a lead plate on one side, a lead dioxide plate on the other and sulfuric acid in the middle. When the lead plates react with the sulfuric acid, sulfate and electrons are produced, thus generating electricity. These electrons start the car and then return to the other side of the battery.
The molten salt battery works on the same principle, substituting the lead plate for liquid sodium metal and the lead dioxide plate for a liquid mixture containing sodium iodide and a small amount of gallium chloride. Instead of sulfuric acid in the middle, there is a separator made of ceramic.
Molten Salt vs Lithium-ion Battery
The main advantage of the molten salt battery is its liquid component. Because there are no hard materials to react with the liquid, the battery remains in a state of constant reaction, with the parts undamaged despite time or use. Since there is no degradation of materials, like in traditional lithium-ion batteries, the salt battery can last for a very long time. Studies suggest life spans of up to 10-15 years, compared to the lithium-ion battery that can last only 2-3 years. That is an equivalent of 300 to 500 charge cycles.
Another advantage of salt batteries is the safety demonstrated by the chemistry of the battery. In the event of a malfunction, the battery will simply stop working. Though the chemicals inside mix, they are not volatile. In lithium-ion batteries, failure usually results in overheating and the battery catching fire; that’s why there are so many videos of iPhones and other small devices in flames
The only drawback of the salt battery is timing. It will probably take another ten years for full commercialization. Although there are big salt batteries now, we will have to wait probably a decade to get them for our phones, devices and cars.
The Future of Salt Batteries
The future of salt batteries looks bright. The main component in these batteries is sodium, which is widely available all over the world and relatively inexpensive. Production of sodium batteries can thus be conducted globally. The Sandia experiment used a sodium iodide and gallium chloride mixture termed “catholyte.” Gallium chloride has a higher price, which makes it commercially unavailable; however, researchers are hoping to find a new material with comparable properties.
If we manage to keep salt batteries at a cooler temperature around 230°F, then they could provide universal application. One of the most urgent use cases may involve connecting them to solar photovoltaics to store energy during the night or times of cloudy weather. This could benefit both individual household power systems and wider grid scale storage solutions.
California, in particular, could benefit from deployment of these batteries. The state is experiencing what is known as the ‘Duck Curve’. While the state installed significant solar capacity, there was a lack of focus on storage installation. This has caused a giant ‘U’-shaped curve between peak generation when the sun is up and peak demand when the sun goes down, at which time the grid electricity is in high demand.
Texas has the same problem with storage of wind energy, a weakness which contributed to the February 2021 Texas Power Crisis we’ve written extensively about. During a massive storm with low temperatures statewide, many of the renewable sources did not provide electricity because there was not enough stored energy. This contributed to power shortages that lasted for days.
Another intriguing application for salt batteries is sea transport and machinery, especially the maritime transport business. The installation and use would allow the cost of transport to be massively reduced.
The non-reactiveness of these batteries make them suitable for vehicles in terms of safety because the risk of fire is mitigated. This is good news for heavy machinery used during construction, mining, and even in space exploration. In space, you can harness pure solar power which is more potent than the sort that is available on earth. Salt batteries could provide a more energy dense storage solution that what is currently available.
Molten salt batteries hold great promise. As we move toward greener energy consumption, we will need to produce better energy storage solutions to remediate undesirable features (like the Duck Curve) and reduce the risks involved with relying on renewable generation. It’s possible we may soon see molten salt batteries playing a larger role for peak-shaving and grid reliability applications, getting us closer to achieving a zero emission future.
Andrew Schaper is a professional engineer and principal of Schaper Energy Consulting. His practice focuses on advisory in oil and gas, sustainable energy and carbon strategies.