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Researchers have for the first time deployed molten salt as the heat transfer medium at the Puerto Errado 1 (PE1) Fresnel solar thermal power plant.
© Novatec Solar GmbH
Solar thermal power plant

The image shows the demonstration plant that has recently commenced operation at the PE1 Fresnel power plant in southern Spain.
© Novatec Solar GmbH

Molten salt transfers heat

At the PE1 power plant in southern Spain, a demonstration plant has gone into operation that uses inorganic molten salt as the heat carrier. The advantage: Salt is inexpensive and can also be used as a heat storage medium. In addition, operating temperatures above 500 degrees Celsius can be achieved, which increases the efficiency by ten per cent.

Until now, most solar thermal power plants have used thermal oils as the heat transfer medium – while salt has been used as a storage medium. However, the application temperature is limited to 390 degrees Celsius. Molten salt is now being used and tested for the first time in a European demonstration project as both the heat transfer and storage medium in a Fresnel collector. For this purpose, Novatec Solar has integrated a molten salt circuit in an existing solar thermal plant, Puerto Errado 1 (PE1). Through operating the so-called Direct Molten Salt collector (DMS collector), the researchers want to gain important insights and lay the foundation for future applications of this power plant technology. In order to investigate the performance of the salt in the collectors, they have installed a 540-metre-long test section with a maximum thermal output of up to 1.8 megawatts.

Integrated salt-based storage system planned

Molten salt is already being successfully used in several solar thermal power plants as a storage medium. The use of molten salt as a heat transfer medium enables higher process temperatures of about 550 degrees Celsius to be achieved. Dr Max Mertins, responsible for research and development at Novatec, explains: “When properly handled, nitrate and nitrite salts also remain stable above 500 degrees Celsius and can be used as a medium for 25 years. They are used worldwide as fertiliser and are therefore environmentally compatible even if there is an accidental discharge.”
In the DMS project, it is intended to use solar salt not just as a heat transfer medium but also as a storage medium. The scientists are currently developing in parallel a salt-based latent heat storage system called SALSA. In order to combine the DMS collector and storage system together in one circuit, the researchers are considering using sodium and potassium nitrate in future. “However, to enable us to exploit this potential, the DMS technology must first be developed to market maturity and demonstrated,” explains Max Mertins.

Base load capacity of the Fresnel power plant increased

By integrating the DMS technology and storage system, the intention is to increase the annual operating hours of solar thermal power plants and – depending on the application – their base load capacity. “Just raising the upper process temperature relative to plants with thermal oil increases the efficiency by up to 10 per cent,” adds Mertins. As a result, the electricity generation costs for solar thermal power plants based on the DMS technology are also significantly reduced.

The German Federal Ministry for Economic Affairs and Energy is contributing around 1.8 million euros to fund the DMS demonstration plant until the end of 2014. Subsequent power plant generations are intended to benefit from the test results.



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Solar thermal power plants
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 Project SALSA
Researchers are currently developing a salt-based latent heat storage system as part of the SALSA project. This is intended to be deployed, for example, for utilising waste heat in industrial processes. The storage system will be installed and tested in the PE1 power plant at the end of 2016.

Energy storage systems
Recent reports on research, development and demonstration of energy storage systems