Start-up company exploring the use of molten salt to store renewable energy

14-12-2021 | By Robin Mitchell

A new start-up tech company is developing molten salt technology to store excess energy from renewable sources. Why do renewables face challenges with energy storage, what is the company’s proposed solution, and is molten salt a new technology?

Why do renewable energies face challenges with energy storage?

Before the widespread of renewable energy, the addition of a wind farm or solar panels would be hailed as a major victory for the integration of green technology. Many environmentalists would talk about a renewable future where coal and oil plants would no longer be needed, and the idea of burning any fossil fuel would be considered archaic. In fact, some of these environmentalists would go one step further and target nuclear energy as also not being needed; the entire world would run on solar and wind.

There is no doubt that wind and solar, the largest two renewable sources of energy in the UK, are plentiful sources of energy; the UK is very windy and very bright. Interestingly, many would assume that deserts would be the best place for solar panels. Still, the intense heat and lack of clouds can degrade their performance (UK solar panels boost energy during intermittent days where sunlight shines on a panel and reflects off clouds).

However, many people were unaware of the dependability of energy sources and how to deal with excessive power when it occurs. The wind doesn’t always blow, and the sun doesn’t always shine, meaning that there are times when renewable sources are not producing power. Then there are times when there is too much wind, and the sun is exceptionally bright, but there is not enough demand for the generated power.

Coal and oil plants have the major advantage of being fast to switch on and off, allowing them to react to real-time demand on the electrical grid. This is important because a grid that provides too much or too little power can experience over-voltage, under-voltage, and changes in powerline frequency, which are essential for modern life.

Trying to store excess energy from renewable sources is a significant challenge simply because of the sheer amount of energy produced during peaks. Many power storage technologies such as pumped hydro require vast amounts of space that simply don’t exist. Power storage such as batteries are costly, have low charge/discharge cycle numbers, and can be potentially dangerous (i.e. major fire risk). The perfect energy storage solution for renewables would be cheap, compact, and able to respond quickly to demand to ensure power supply stability.

Start-up company Hyme raises funds for molten salt storage

Recently, a Danish company called Hyme announced that it has received $12 million in funding for research into renewable energy storage technologies. One technology that the start-up is particularly interested in is molten salt as an energy storage medium.

Their system would essentially consist of two vats containing molten salt. The first vat would use energy from the grid to heat up salt to 700˚C, while a second return vat would keep the salt at 350˚C. When energy is required by the power grid, the first vat will pump its molten salt through a boiler that would then generate electricity via a steam turbine.

The second vat is the return feed from the now cooled molten salt, where it is kept as a liquid and re-pumped back into the first vat. The system would generate electricity, and the waste heat can also be used for district heating of homes which would help to increase efficiency further.

The start-up hopes that its technology will benefit Denmark, especially when considering that 40% of Danish energy comes from wind which is often wasted. Furthermore, Hyme expects its energy storage technology to retain its heat significantly for up to 14 days, enabling long-term energy storage.

Is molten salt a new technology?

While molten salt energy storage hasn’t practically been done before, solar installations use it a lot. Solar power technology falls under two main types; photovoltaic and thermal. Photovoltaic devices directly convert sunlight into electricity, while thermal solar panels instead reflect light onto a target that is then heated.

Salt is melted in the heated target, which can then be pumped through heat exchangers and turbines to generate electricity, essentially identical to what the Hyme company is planning to do. Hyme would do this through electric heaters while a thermal solar power plant heats up salt from sunlight.

One significant advantage of Hyme using molten salt is that it is a tried and tested technology that operates well. As the technology is already established in solar thermal plants, Hyme simply needs to adapt the design for use with electric heaters and develop efficient district heating.


By Robin Mitchell

Robin Mitchell is an electronic engineer who has been involved in electronics since the age of 13. After completing a BEng at the University of Warwick, Robin moved into the field of online content creation, developing articles, news pieces, and projects aimed at professionals and makers alike. Currently, Robin runs a small electronics business, MitchElectronics, which produces educational kits and resources.