Solar energy is a clean energy source which, unfortunately, can only be harvested during the day. Researchers have experimented with different mediums to find a way of storing the energy, so that it can be used at any time. SolarReserve has developed a method of using molten salt as both a heat transfer unit, and a thermal energy storage medium. This has proven to be a flexible, cost effective, and efficient method of large scale energy storage, creating an entirely new way in which solar plants can operate. Molten salt has revolutionized the solar power industry by allowing the energy to be stored and dispatched, without the need for back up fossil fuel energy storage, keeping both the harvesting and the storage of the energy clean.
Solar energy plants have a 30+ year lifespan, during which the molten salt will not need to be replace or topped up. It is made from an environmentally friendly mixture of sodium and potassium nitrates, which can be used as a high grade fertilizer once the plant has been decommissioned. The salt is stored in tanks at atmospheric pressure, and about 566°C. The sunshine is reflected by a field of mirrors onto a tower, which heats the salt up. Using the molten salt for both heat transfer and energy storage means that the number of storage tanks and the salt volumes can remain relatively low. The salt is circulated through highly specialized piping in the receiver, during the day, and kept in storage tanks at night.
Once electricity is required, the salt is dispatched from the hot tank though a heat exchanger to create steam. This powers a conventional steam turbine, which then provides the electricity needed. Molten salt energy storage is currently the most cost effective way to store clean energy, and it is expected that the costs will continue to decrease. There are a significant amount of other benefits to using molten salt for energy storage, including:
- It facilitates thermal power plants operating in the same way as fossil fuel or nuclear power plants, without the associated harmful emissions as well as eliminating the cost for the fuel. These plants can also operate around the clock, providing power for both on-grid and off-grid applications.
- Energy generation can be adapted to meet different needs, using the integrated energy storage method. This also enables the delivery of reliable power at high capacities, where and when it is needed.
- Each plant that has a molten salt storage facility can double its energy output every year.
- The storage capabilities make the transport system more stable and secure.
SolarReserve has begun using molten salt to store energy in their 110-megawatt Solar Energy Facility in Nevada, which has the ability to power 75000 homes. The company also has similar projects planned for other countries, where they will be capable of storing up to 10 hours of energy.