An Introduction to Hydrogen, Thermal, and Molten Salt Energy Storage

By Hope Wilder

Why energy storage is essential for renewable energy and carbon drawdown

Renewable energy such as solar power and wind don’t make power at convenient times. For example, solar power peaks during the middle of the day, whereas energy usage peaks in the evening. Wind power at ground level is reliant on the weather and is intermittent. Reliable and sustainable energy storage technologies are required to store energy when it is abundant and to give it out at times when people want to use energy. Popular lithium-ion batteries are expensive, toxic, and create environmental problems in mining. This article summarizes three renewable energy storage technologies that are cleaner than lithium batteries: hydrogen fuel cells, thermal energy storage, and salt batteries.

Hydrogen energy storage and fuel cells

Hydrogen itself can be used as energy storage. When renewable sources are creating excess electricity, an electric current can be used to split water into hydrogen and oxygen. The hydrogen can then be used to generate electricity at a later time in a hydrogen fuel cell.

In large-scale renewable operations, proponents of hydrogen as energy storage advocate storing hydrogen in underground caverns. The advantages of hydrogen power include that inputs (water) and outputs (heat and oxygen) are clean and safe. Currently, hydrogen fuel cell technology is available in limited demonstration sites on the grid, in hydrogen-fueled electric cars that are on the market, and in fairly expensive home technologies.

Thermal energy storage

Thermal energy storage is simply heating something and using the heat at a later time, and there are many varieties of thermal energy storage systems. An example of renewable technology would be a solar hot water heater where the water is directly heated by the sun. Other residential applications include pumping excess heat into the ground during the day and retrieving the heat at night. Thermal energy storage can even be used on seasonal cycles, storing heat during the summer and using it during the winter. The simplest thermal energy technologies are for heating and cooling applications, but thermal batteries that could store energy as heat and be used to create electricity later are also under development.

Molten salt batteries

One form of thermal energy storage is the molten salt battery. Molten salt batteries work by freezing and thawing a salt solution, and they can store energy for weeks or months at a time. This cheap and efficient technology could be used at scale for the power grid. Pros include affordable and abundant materials, high safety, long life cycles compared to chemical batteries, and safe disposal of materials. The major con is that these batteries must constantly be maintained at very high temperatures (~250 degrees Celsius) and therefore take up to 12 hours to charge. The best application for molten salt batteries is to be maintained at high heat by the power grid to even out power distribution daily and seasonally.

Conclusion

These are just some technologies under development to help store energy. Many different energy storage technologies need to be developed to tackle climate change head-on.