The Gemasolar Concentrating Solar Power plant (Gemasolar) is under construction by Torresol Energy in Sevilla, Spain. The project represents a major leap forward in solar power technology.

The solar power plant promises to outdate conventional processes and will feature major technological breakthroughs in solar heat reception and storage systems.

The concept

Gemasolar incorporates 2,650 heliostats – tracking reflectors – situated around a central tower.

They act to concentrate the sun’s rays onto a receiver placed at the top of a tower, which is capable of absorbing 95 percent of the heat energy.

Molten salts acting as the working fluid are passed through the receiver and become heated. These are used to generate water vapor for steam turbines that drive electric generators.

With 17 megawatts of nameplate power, Gemasolar will generate enough electricity to power 30,000 homes.

This renewable solar power project will annually offset 30,000 metric tons of carbon dioxide emitted into the atmosphere.

Gemasolar will be the first commercial central tower-heliostat plant in the world. It will be fitted with a heat storage system where the hot molten salts are stored in special tanks at temperatures exceeding 500 °C.

This system will allow Gemasolar to operate for up to 15 hours without solar radiation.

Gemasolar will feature extraordinary energy efficiency, more than double that of conventional solar power technology. It will accomplish this with only two-thirds of the investment required for older technology.

Hailing Gemasolar as the most advanced technological venture in solar energy to date, Torresol Energy remains true to its commitment to making solar power increasingly affordable and accessible.

The new technology has been developed by SENER, a Spanish engineering and technology group and a 60 percent owner of Torresol Energy.

The problem

To be able to build the innovative hot salts tanks for the heat storage system, SENER needed a tank material able to handle the task.

Stainless steel was the ideal material because of its ability to withstand elevated temperatures. SENER specified a standard heat resistant grade, 347H (EN 1.4550), but needed more information about the behavior of this grade at the operating temperatures of the tanks.

SENER contacted Outokumpu’s Spanish sales and technical team for the materials expertise they needed. Specialists provided SENER with information about the grade’s behavior at 550 °C and above, the corrosion and stress relief tests to be applied, and welding procedures, as well as possible alternatives to 347H.

The results

Outokumpu kept an early and deep involvement with the Gemasolar project. This was instrumental in securing the stainless steel supply for the hot salts tanks, which consisted of 347H plates.

The contract for the fabrication of the largest tank (23 meters in diameter and 14 meters high), went to the Barcelona-based tank fabricator Emypro. This tank represents continued successful cooperation between Emypro and Outokumpu in building industry-leading storage tanks in Spain.

Images of Gemasolar. Courtesy of Torresol Energy

Gemasolar under construction. The foundations of the cold and hot molten salts tanks next to the central tower are in place. Courtesy of Torresol Energy