How Viable is a Solar Trough?

Q: I have been hearing on and off about the Solar Tower project, first in India and then in Australia, which envisages the construction of a gigantic 1000 m tall chimney around a green house. Is this concept viable and has there been any significant progress on this project in Australia?

Chandra S.
Tamil Nadu, India

A: Chandra, Concepts to utilize large-scale base load solar abound.

The most noted successes start with the 350 MW in the Southern California desert by nine electric generation plants that began operating in the mid-1980s. These concentrated solar plants use troughs (concave glass mirrors) to heat a synthetic fluid to over 700 degrees C and create steam for electric generation. Natural gas supplies 25 percent of the energy, with solar thermal supplying the remaining 75 percent. Solargenix Energy of North Carolina announced a 50 MW power purchase agreement for Boulder City, Nevada to build another solar trough project under the State's Renewable Energy Portfolio Standard. This plant will have less than 5 percent natural gas as a backup and more advanced solar concentrating trough technology.

Another solar trough generation facility is being constructed by Solargenix Energy that incorporates concentrated solar power and external combustion engines. The 1 MW small generation facility for Arizona Public Service will have technology from Ormat of Nevada, and utilize organic Rankine engines and non-imaging solar trough technology. Also, SES of Arizona will be installing a series of Stirling engines driven by concentrated solar dishes, which was funded by the Department of Energy as a 1 MW demonstration project. The solar tower technology has yet to be demonstrated in large scale, but the goal is to produce 200 MW by convecting desert heat up a multi-storied tube, which turns 32 turbines within the tube.

According to a recent story in The New Zealand Herald, the Australian development company, Enviromission (whose major investor is US-based Solar Mission), is about to buy the land (10,000 ha) in Buronga, Australia for AUD 1.1 million -- so the project appears early in the development stages.