Giant Arizona Solar Tower: High Energy with Hot Air

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It was love when I first saw the 200-meter-tall Spanish structure in a Youtube video. At that time, it was called a “Solar Chimney.” The same video now has an “EnviroMission Ltd.” label attached. On their website, Enviromission claims worldwide rights to this technology.

Confusing Names:
Chimney’s have been used for centuries to remove smoke from fireplaces, furnaces and boilers. The solar chimney power plant was first proposed in 1903 by a Spanish Colonel in a magazine article. Unfortunately, the term “Solar Chimney” also describes a type of construction sometimes used with Earth tubes to promote natural ventilation. Common to both is the chimney or stack effect which is driven by buoyancy and enhanced by the shape of the chimney. In deciding to change the name to “solar tower,” EnviroMission chose a name in conflict with the more popular concentrated solar power technology that uses heliostats for focusing the sun’s heat on a central target. The Pickens Plan used the name “Solar updraft tower.” (Not to be confused with down draft towers being built in Israel) and a well-informed website calls them Meteorological Reactors.

Not Your Typical Tech Company:
EnviroMission Ltd., an Australian development company, has had previous connections/incarnations as SolarMission and Energen Global. Both of these names have been used by other companies as well. EnviroMission is run by Mr Roger Davey, whose vision has been slowly moving the company along. Davey, a former stock broker and accountant, has planned building the tower in various locations and has been setting dates of completion for over 10 years. In each case, financing such a huge project has been an ongoing issue. Presently, EviroMission has a power purchase agreement and an engineering team.

The design of a Solar Chimney is simple with few moving parts.

The EnviroMission Plan is simple. The idea is a marriage between the chimney effect and the greenhouse effect that produces wind. The wind is used to run turbines and give us electricity. A roughly circular greenhouse area has a roof that is pitched to a central chimney. The rising hot air can only escape through the chimney, where it turns the turbines. It is a man-made wind machine on a huge scale.

Unlike other concentrated solar power technologies, it uses a minimum amount of water. The ground under the greenhouse heats up as well and allows the unit to operate 24/7. Solar concentrators and even PV collectors must be spaced to avoid shading but the greenhouse completely covers the target area. Condensation under the greenhouse promotes plant growth. Few moving parts and internal heat storage allows the design a higher capacity factor than other wind technologies (up to 60% vs 20 to 30%), and the power plant could easily be designed to last 80 to 100 years.

Hot-air solar panels are commonly made by DIY builders. Although the principles behind the solar chimney are very similar to hot-air solar panels, we don’t hear of many farmers converting an old silo into a solar chimney. (Let me know if you do.) This is because the design works more efficiently on a large-scale. EnviroMission wants to build a tower in Quartzsite, Arizona that is 2,600 feet tall by 2015. It would be designed to produce 200 MW and cost about $750 million for the facilities.

Solar updraft tower

The road not taken:
Alternative possibilities exist to produce the necessary solar chimney effect, and some may be less expensive. This is not to say the that EnviroMission’s existing plans are not sound. On the contrary, here is a favorable comparison of a solar updraft tower to coal mining. Technology has a way of moving forward. Just because we have a plan today does not mean that it can’t be completed in a better way tomorrow. This is rather hard on human institutions where financing, permits, expertise and contracts may take some time to carry out. It is also difficult for a patent holder or licensee who may find that their rights are made obsolete by subsequent technology. Alternatively, a licensee may not want to promote any technology where they don’t hold the rights.

There are many interesting alternatives to the EnviroMission Plan. The chimney could be made out of fabric instead of concrete and steel. The fabric would be held up by lighter-than-air collars and guyed to the ground. The lifespan would be shortened but the overall cost could be substantially reduced. This has been compared favorably to a coal-fired power plant. The author claims it is patented technology.

The chimney might be replaced in whole or part with a vortex, a kind of tornado in reverse. Either of these implementations might be set up more quickly and might therefore satisfy emergency or military needs.

Yet another design suggests a closed system that incorporates a regenerator. The covering and experience in Spain gives us some suggestion that condensation effects should be interesting both under the canopy and coming out of the top of the chimney. Capitalizing on this, there is yet another design that adds water vapor to the system, increasing the greenhouse effect, and then recycles the water back into the system.

There has been discussion about building a tube going up a mountain. In this case, the construction might also be less costly. But you won’t see any of these innovations on the Enviromission website. You will find these and much more on a website hosted by a supporter of the technology here.

There are several drawbacks mentioned in related literature in addition to the massive cost of a very tall concrete chimney. The first is the overall efficiency of the system (around 5%). Another is that increased condensation exiting the chimney may create an unknown (though possibly beneficial) microclimate. Condensation may also be responsible for a significant drop in efficiency. Someday, devices such as these may be used to intentionally create a microclimate from which we can extract energy.. at which point the name Meteorological Reactors would be somewhat prophetic.

Top Photo Credits: EnviroMission
Bottom Photo Credit: Schlaich J, Bergermann R, Schiel W, Weinrebe G (2005). “Design of Commercial Solar Updraft Tower Systems—Utilization of Solar Induced Convective Flows for Power Generation”(PDF). Journal of Solar Energy Engineering 127 (1): 117–124. doi:10.1115/1.1823493

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