On August 5th, the company eSolar opened the Sierra Sun Tower, the newest example solar power towers. According to the website of esolar, the Sierra facility supplies 5 MW of clean, renewable energy to the grid. As the only commercial CSP tower in the United States, supplies electricity to Southern California Edison (SCE) and will power up to 4,000 homes. Many bloggers and journalists welcome it as a promising development.

UBS Wealth Management, moreover, is predicting that the relatively small market for concentrated solar power tends to expand, with projected growth of almost 20 gigawatts in new capacity over the next decade.  UBS analysts Gianrento Gamboni and Christoph Hugi, refers to the new projects in the United States and Spain as they say “After a long period of stagnation, the market is evolving more dynamically.”

• What is a solar power tower?

One square kilometer of land holds the capacity – depending on the specifities of location – to  generate as much as 100 gigawatt hours (GWh) of electricity per year through solar thermal technology. To make it clear, this amount is enough to run 50,000 residences.

One option to produce this energy is the solar power tower, which is a type of solar thermal plant that uses a tower to receive the sunlight, focused  upon it via an array of flat, movable mirrors (ie. heliostats). These focused rays heats the water and the steam produced powers a turbine. As you see, no pollutants are emitted in producing the electricity.

Today liquid sodium is commonly used instead of water to store the energy during brief interruptions in sunlight or in night time.

• A major advantage: Solar thermal plants produce electricity whose current and future costs are known.

It is a fixed-cost generation resource know to the consumer in advance and it decreases consumers’ exposure to market fluctuations and the volatile cost of natural gas (which solar thermal typically replaces in the portfolio).

• A major disadvantage: Solar thermal power plants are huge

It uses a huge land desirably less than 3 percent slope. With respect to the electricity output versus total size, they make use of the land more effectively than coal plants or hydroelectric dams, though.

The best locations for solar power plants are massive lands, such as deserts, for which there might be few other uses; but again, then comes the problem of how to provide the necessary water.

The factsheet in the released in the webpage of governement of CA, claims that as experience is gained with this technology, the acreage requirements
will likely be reduced due to more efficient placement of the heliostats.

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• Five Earlier Examples:

1. Solar One, a pilot solar-thermal project built in the Mojave Desert (CA, USA) was the first test of a large-scale thermal solar power tower plant. It was designed by the Department of Energy (DOE), Southern California Edison, LA Dept of Water and Power, and California Energy Commission. Solar One’s method of collecting energy was based on producing heat to drive a steam turbine.
2. Later, in 1995 it was converted into Solar Two, with the addition of a second ring of 108 larger heliostats around the existing Solar One. The total number of heliostats became 1926 on an area of 82,750 m². Solar Two used molten salt, which is a combination of 60% sodium nitrate and 40% potassium nitrate, instead of water.
3. Solar Tres, which is located in the city of Écija, in Andalusia, Spain and received a subsidy of five million Euro from the European Commission, follows the Solar Two in using molten salt but is designed to be three times of it in size.
4. Europe’s first commercial solar tower PS10 is located near the Southern Spanish city of Seville. It produces electricity of 11 MW with 624 large heliostats with surfaces of 120 square meters each.  The height the tower is 115 meters.
5. The PS20 solar power tower is also near Seville. The capacity is 20 megawatt.  The  tower is taller than PS10, it is 160 meters.
6. The THEMIS solar power tower, located near the village of Targassonne, in the département of Pyrénées-Orientales, South of France, is a R&D center focused on solar energy, as well as a photovoltaic power facility and a solar thermal energy plant. It had a power output of 2 MW in 1983.