Salt is one of the most important materials in the energy industry, especially in concentrated solar power (CSP) systems, where it is used as a means of storing thermal energy. CSPs are technologies that concentrate solar radiation through mirrors or lenses to produce heat, which is then converted into electricity. Unlike photovoltaics (PV), which directly convert sunlight into electricity, CSP utilises thermal energy, offering the advantage of heat storage for use even when there is no sunshine, thus addressing the significant problem of intermittent production which is common in renewable energy sources.
How the system works
In a typical CSP system, solar radiation is concentrated through mirrors or lenses onto a receiver, where salt is heated until it melts. The molten salt flows in a closed circuit and is stored in specially designed high-temperature tanks. When electricity is needed, the hot salt transfers heat to water through a heat exchanger, producing steam that drives turbines to generate electricity.
Advantages of using salt
High Heat Capacity: Salt can store large amounts of heat at high temperatures (400 - 600°C), making it ideal for energy storage.
Stable and Continuous Energy Supply: Thermal storage allows electricity to be generated even at night or on cloudy days, providing stability to the system.
Economic Sustainability: Inorganic salts, such as sodium nitrate and potassium nitrate, are relatively inexpensive and available in large quantities.
Safety: Most of the salts used are non-toxic and environmentally friendly, with a low risk of ignition compared to other storage fluids.
Technological developments
Research is focused on improving the properties of the salts used in CSP systems. The aim is to reduce the melting point to prevent the salt from solidifying at lower temperatures and to increase the operating temperature range for greater efficiency. New salt mixtures are also being developed offering better thermal performance and reduced corrosion of the metal parts of the facilities.
Challenges and limitations
Despite the significant advantages, there are also some challenges:
Material Corrosion: The high temperatures and chemical nature of molten salt can cause corrosion of the metal parts of the system, requiring durable materials and frequent maintenance.
Freezing Management: If the salt cools below its melting point, it solidifies, causing operational problems and increasing maintenance costs.
Initial Installation Costs: The construction of storage tanks and heat transfer systems requires significant investment, although operating costs remain low.
Future prospects
The international energy community expects significant growth in the CSP sector. According to the International Energy Agency (IEA), global installed CSP capacity is expected to increase dramatically in the coming decades, from ~6.5 GW today to 73 GW in 2030 and 281 GW in 2040. At the same time, the integration of CSP with photovoltaic (PV) systems in hybrid installations is emerging as a critical strategy for achieving continuous 24-hour power generation.
These systems combine direct electricity generation from PV during the day with the heat storage capacity of CSP for night-time use. Advanced integration technologies, such as the use of superheated salt for storage and the utilisation of excess PV energy to heat the salt, offer reduced production costs compared to stand-alone systems. The development of such hybrid solutions, combined with improvements in salt technologies, creates a promising future for thermal storage.
Salt has emerged as a strategic material for the energy industry, offering efficient, safe and economically viable solutions for thermal energy storage in concentrated solar power systems. With the continuous evolution of technology and the growing need for stable and clean energy, the role of salt is expected to be further strengthened in the future.