Solar Tower Technology 2006
Solar tower technology is positioned to be the next medium size (50-200 MW) electricity generating technology on the renewable market. Investors will have two different technology choices, a solar updraft tower design and a mirror tower design.
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The particulars of the process start with the sun heating the air in the greenhouse. As air warms, it naturally gets channeled up the tower. As the air moves through the tower it passes through an electricity generating turbine.
The design plan is relatively simple and currently an Australian company, EnviroMission, has a license to the technology and plans to break ground on the first large scale commercial plant. The project's dual construction needs, a large tower and a large glass enclosed greenhouse area, make it a challenging. If and when built, it will be the largest ever man-made structure. A 1,600 foot tall tower will site on an almost football field sized site and will have a 25,000 acre greenhouse surrounding it.
Mirror tower designs are the second type of solar power tower technology. The design is based on solar thermal principles, mainly the idea that the sun's heat could be collected and used to drive electricity generating turbines. A couple of demonstration plants built around the world have used this basic design.
One of the better documented projects was originally funded by the United States Department of Energy. The demonstration of this technology went through three phases called Solar One, Solar Two and Solar Tres.
The first two phases of the technology demonstration took place at a solar power plant in Daggett, CA. In 1981 the Solar One plant was built. The central part of the design was a tower. This time it functioned as a receiver, collecting heat produced by a field of mirrors (heliostats) at its base.
The two phases of the project differed in their use of heat storage and transfer processes. Solar One used water tanks as the steam conductor driving the electricity turbines. Solar II switched to a molten-salt conductor. Storage tanks of molten salt were heated and then that heat was used to generate steam for the turbines. The advantage molten salt designs is that they retain heat longer than water and thus provide for more flexible electricity generation planning.
In 2002, a National Academy of Science Committee reviewed both the Solar One, Solar Two project and the independent review of it. As to the cost effectiveness of the plant they say,
"The committee notes... and S&L concludes in the executive summary section that to achieve the cost reductions of scale-up, a total redesign and optimization of the field, the tower, and receiver are required. This implies considerable engineering development by commercial developers with commensurate risk to investors."
Solar Tres addressed these issues and others. It completed its demonstration phase in June 2006. Apart from some yet unknown technology tweaks that might be made following a full review of all the data, it appears that the molten-salt tower plants could be commercially viable in the next couple of years.
© 2006 Patricia A. Michaels.