Molten salts: a key solution for energy storage
The molten salts They are a product with a wide range of applications, such as high-temperature process heating, heat treatment and annealing of steel, and thermal storage in solar thermal power plants. These salts consist of fluoride, chloride and nitrate, and their versatility has made them key elements within the renewable energy sector.
Given their relevance, this article explores in depth what molten salts are, what their characteristics are, and how they are currently used to contribute to energy storage, an increasingly crucial aspect in the global energy transition.
Features and advantages of molten salts
Molten salts stand out for their ability to store large amounts of thermal energy due to their high operating temperatureThey can reach up to 566 °C, making them an efficient means of heat storage and transfer.
Unlike other heat transfer media, such as synthetic oils or water systems, molten salts do not generate significant vapor pressure, which allows safe operation at high temperatures and is therefore ideal for use in solar thermal plants and industrial processes.
Despite its many advantages, it is important to note that one of its disadvantages is its high freezing point, which can range from 120°C to 220°C, depending on the specific composition of the salts. This requires storage and circulation systems to keep the salt in a molten state to prevent solidification, which increases complexity and costs.
Applications of molten salts
There are multiple industrial and energy applications of molten salts. They are mainly used in:
- Process heating: Due to their ability to operate at high temperatures, molten salts are used in heat treatments such as annealing of steel and other metals.
- Heat transfer: In industrial heat transfer systems, molten salts can replace synthetic oils, offering a more efficient and sustainable solution.
- Energy storage: In concentrated solar thermal plants, salts are used to store the sun's thermal energy and convert it into electricity when there is no sunlight, such as at night or on cloudy days.
Molten salt storage systems
The most prominent use of molten salts today is in the energy storage systems of solar thermal plants. Concentrated solar power systems store large amounts of energy during the day, which can then be used at night or on days without sun.
A typical molten salt storage system consists of two tanks: one for hot salt and one for cold salt. During the day, solar energy concentrates heat on the cold salt, raising its temperature and transforming it into hot salt. This hot salt is stored and later used to generate steam, which powers an electricity-generating turbine.
This system is safe, efficient and widely used in large solar thermal plants, such as those that Spain leads internationally, with important advances in storage technologies to improve the efficiency and duration of the process. This type of plant can store energy for more than ten hours, generating electricity during times of low production, such as at night or on cloudy days.
Challenges and solutions in the use of molten salts
One of the main challenges of using molten salts for energy storage is the corrosion to which construction materials are exposed, especially at temperatures above 700 ºC. Molten salts are highly reactive with common metals, which can accelerate their oxidation and compromise the integrity of storage tanks.
However, innovations have been developed such as the use of graphite-based anticorrosive methods. This material, when locally decomposed in the contact area between the tank and the molten salt, generates a protective layer that reduces oxidation and decreases localized corrosion. This advancement has improved the viability of molten salts as a high-temperature thermal storage medium.
Strategic projects and the future of molten salts
Spain is currently consolidating its position as a world leader in the use and development of solar thermal plants with molten salt storage. There are 50 solar thermal plants in operation in the country, with an installed capacity of 2,3 GW, which represents one third of the global capacity. This experience positions Spain as an international reference in thermal storage.
The National Energy and Climate Plan (PNIEC) projects the incorporation of up to 5 additional GW in the next ten years. This measure aims to consolidate the use of molten salts not only in solar thermal plants, but also in other industrial sectors, helping to decarbonization of industries such as steel, cement and others that require intensive thermal processes.
Furthermore, the future of molten salts may also include their integration with hybrid renewable energy, such as green hydrogen, to achieve more efficient and sustainable storage systems. The combination of molten salts with emerging technologies offers a promising horizon for the energy industry.
Every day, there is more progress in the development of new technologies that can extend the useful life of salts and improve the efficiency of large-scale energy storage. This, combined with constant research into methods that reduce costs and corrosion problems caused by high temperatures, makes the future of energy storage in molten salts increasingly attractive and viable.
In short, molten salts have proven to be one of the most promising solutions on the road to energy sustainability. Their ability to store energy and contribute to the decarbonisation of industrial and energy sectors gives them a crucial role in the fight against climate change.