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Enel Archimede plant in Italy. Photo: Enel

This July the Italian utility Enel unveiled “Archimede”, one of the most important developments in the emerging field of concentrating solar power (CSP). The launch showcases this power plant as the first CSP  plant in the world to use molten salts for heat transfer and storage.

Archimede, a 5 MW plant located in Priolo Gargallo (Sicily). The breakthrough project was co-developed by the utility, Enel, and ENEA, the Italian National Agency for New Technologies, Energy and Sustainable Economic Development. The name, “Archimede,” refers to the rows of huge parabolic mirrors used to capture the sun’s rays, recalling the “burning mirrors” that Archimedes is said to have used to set fire to the Roman ships besieging Syracuse during the Punic War of 212 BC.

Energy writer Carlo Ombello writes that while several CSP plants already operate (see graphic above)  in the world, mainly in the US and Spain, they use synthetic oils to capture the Sun’s energy in the form of heat, using mirrors that beam sunlight onto a pipe where pressurized oil heats up. A heat exchanger is then used to boil water and run a conventional steam turbine cycle. Older CSP plants only operate at daytime – when direct sunlight is available.

In its press release, Enel writes that the Archimede plant is “the first in the world to use molten salts as the heat transfer fluid and is also the first in the world to integrate a combined-cycle gas facility and a solar thermal power plant for electricity generation.”

Because molten salts can operate at higher temperatures than oils (up to 550°C instead of 390°C), they increase efficiency and power output of a plant. With the higher-temperature heat storage that is allowed, the plant can also extend its operating hours to a 24-hour day. From an environmental and cost perspective, this news is good. A simplified plant design that does not use avoids the need for oil-to-salts heat exchangers eliminate the safety and environmental concerns of using oils. Molten salts are inexpensive and do not catch on fire like synthetic oils currently that are used in current CSP plants. In addition, the high temperatures of molten salts enable the use of steam turbines at the standard pressure/temperature parameters as used in most common gas-cycle fossil power plants. Translated, this means that conventional power plants can be integrated replaced with this technology without expensive retrofits to the existing assets.

Carlo Rubbia -- Molten salt pioneer. Source: Enel

The concept for using molten salts dates back to 2001. The Italian nuclear physicist and Nobel Prize winner, Carlo Rubbia (left photo), ENEA’s President at the time, started research and development on molten salt technology. One problem encountered in using molten salts is that they freeze pr solidify at around 220°C.

ENEA and Archimede Solar Energy, a private company focusing on receiver pipes, have developed several patents in order to improve the pipes’ ability to absorb heat and maximize the heat transfer to the fluid carrier.

Insiders believe the result of these and several other technological improvements create a state-of-the-art CSP plant at a price 60 million Euros. While the price is high for a 5 MW power plant, energy officials believe this model is scalable for a roll-out there is overwhelming scope for a massive roll-out in sunny regions like Northern Africa, the Middle East, Australia and the United States.