The Technology behind Solar Reserve – The Rankine Cycle and Molten Salt Energy Storage

SolarReserve is designing power plants using Solar Power Towers.

This configuration captures and focuses the sun’s thermal energy with thousands of tracking mirrors (called heliostats) in a two square mile field. A tower resides in the center of the heliostat field. The heliostats focus concentrated sunlight on a receiver which sits on top of the tower. Within the receiver, the concentrated sunlight heats molten salt to over 1000 degrees Fahrenheit.

The heated molten salt then flows into a thermal storage tank where it is stored, maintaining 98% thermal efficiency, and eventually pumped to a steam generator. The steam drives a standard turbine to generate electricity. This process, also known as the “Rankine cycle” is similar to a standard coal-fired power plant, except it is fueled by clean and free solar energy. Other than the few unique components noted below, SolarReserve’s power plants are comprised of available materials, such as mirrors, and established technologies, such as steam generators and turbines.

According to the company this will enable SolarReserve to provide electricity at or below prices from traditional sources such as coal or natural gas.

The unique components in SolarReserve’s power towers are the molten salt storage loop and the power tower central receiver. The molten salt storage loop enables the plant to generate electricity whenever it is needed – 24 hours per day or during “peak demand” periods. Molten salt is an efficient and inexpensive medium to store energy.The salt used in the process is an environmentally friendly mixture of sodium and potassium nitrate, the same ingredients used in garden fertilizer. The other unique component is the power tower central receiver. This high heat flux hardware represents a unique blend of liquid rocket engine heat transfer technology and molten salt handling expertise. United Technologies has decades of experience with these technologies in both land-based and space applications, and its support will be invaluable to SolarReserve in developing power plants utilizing this revolutionary technology

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