World’s First Molten Salt Solar Plant Produces Power at Night

by Philip Proefrock

Sicily has just announced the opening of the world’s first concentrated solar power (CSP) facility that uses molten salt as a heat collection medium. Since molten salt is able to reach very high temperatures (over 1000 degrees Fahrenheit) and can hold more heat than the synthetic oil used in other CSP plants, the plant is able to continue to produce electricity even after the sun has gone down.

While photovoltaic solar panels work by directly producing electricity from sunlight, CSP plants use mirrors to concentrate sunlight and produce high temperatures in order to drive a turbine to generate electricity. CSP plants have been in existence for many years, but the Archimede plant is the first instance of a facility that uses molten salt as the collection medium.
Heat from the molten salt is used to boil water and drive the turbines, just like other fossil fuel plants. CSP plants use the same kind of steam turbines as typical fossil fueled power plants. This makes it possible to supplement existing power plants with CSP or even to retrofit plants to change over to clean energy producing technology. Some existing CSP plants have used molten salt storage in order to extend their operation, but the collectors have relied on oil as the heat collection medium. This has necessitated two heat transfer systems (one for oil-to-molten-salt, and the other for molten-salt-to-steam) which increases the complexity and decreases the efficiency of the system. The salts used in the system are also environmentally benign, unlike the synthetic oils used in other CSP systems.

Since molten salts solidify at around 425 degrees F, the system needs to maintain sufficient heat to keep from seizing up during periods of reduced sunlight. The receiver tubes in the Archimede facility are designed to maximize energy collection and minimize emissions with a vacuum casing that enables the system to work at very high temperatures required with molten salts. By using the higher temperatures of molten salts, instead of oil, which has been used in other CSP plants until this point, the plant is able to maintain capacity well after the sun sets, allowing it to continue generating power through the night.
The Archimede plant has a capacity of 5 megawatts with a field of 30,000 square meters of mirrors and more than 3 miles of heat collecting piping for the molten salt. The cost for this initial plant was around 60 million Euros.

Commercializing Solar Power with Molten Salt

by Karim Yergaliyev, 01/14/08

Solar power might be the most up-and-coming renewable energy source, but one of the biggest drawbacks to solar power plants is their inability to generate electricity at night or during cloudy days. But now, a new venture called SolarReserve hopes to change all that using salt! Their program would save and store captured solar energy in molten salt, the new solar plant will produce up to 500 megawatts of peak power — comparable to what a regular coal power plant can produce, only with no greenhouse gas emissions.

Unlike other solar power plants, SolarReserve’s will be able to produce electricity at night or in inclement weather. You can see the commercial potential here if you note that just one megawatt is enough power roughly 1,000 U.S. households. The company hopes to build 10 plants over the next 10 to 15 years.
The concept behind new concentrated solar power plant is very similar to Seville’s solar power tower where hundreds of solar panels reflect the sun’s light to heat the water inside the tower, which later evaporates into steam that passes through series of turbines to generate electricity. However, instead of tower that holds water, SolarReserve’s holding tank will have molten salt. Huge array of mirrors will reflect light onto the tank; heated 1,000 degrees Fahrenheit liquid is then pumped into a steam generator that will turn a turbine to make electricity.
“Due to the unique ability of the product to store the energy it captures, this system will function like a conventional hydroelectric power plant, but with several advantages,” says Lee Bailey, managing director of US Renewables Group, SolarReserve parent company. “This product is more predictable than water reserves, the supply is free and inexhaustible, and the environmental impact is essentially zero.”
SolarReserve says that their use of molten salt, a mixture of sodium and potassium nitrate, instead of water or oil, allows the heat to be stored for use when sun is not present. The National Solar Thermal Test Facility conducted several studies and concluded that molten salt is the most efficient fluid when it comes to transporting sun’s heat. The study states, “molten salt is used in solar power tower systems because it is liquid at atmosphere pressure, it provides an efficient, low-cost medium in which to store thermal energy, its operating temperatures are compatible with today’s high-pressure and high-temperature steam turbines, and it is non-flammable and nontoxic.”
+ SolarReserve (US Renewables Group, parent company)

Read more: Commercializing Solar Power with Molten Salt | Inhabitat - Green Design Will Save the World