Mountain Solar Updraft Chimneys

By: Paul Klinkman | 12-Dec-2014 | 5:12 am | Mail idea | Print idea | RSS

Solar updraft towers work well, but they aren't economical. From an engineering standpoint, building and maintaining any structure 1 or 2 kilometers high is expensive. Such structures can also be aviation hazards.

The clear solution is to build the updraft towers on mountain sides. A chimney was first built up a Vermont hillside in the 19th century to take smelter fumes out of an enclosed valley. The ground-level slate chimney apparently worked well. The first modern mountain solar chimney was suggested in U.S. patent #7,026,723. I followed up with U.S. patent #8,823,197.

A prototype updraft tower running up a hill could be built with hoops and fabric, like a high hoop tunnel, except the tunnel need not be made of clear plastic. Any heat-resistant fabric or tarp could contain the chimney's air.

Increasing the chimney height of the Manzanares Solar Updraft experiment by a factor of ten, from 200m to 2000m, should increase electricity production by a factor of ten. 2000m peaks are common in the Western United States. Charleston Peak near Las Vegas, for example, runs rapidly from a base elevation of 4,000 feet to 12,000 feet.

Increasing the chimney's operating temperature by a factor of ten should increase electric production by one more factor of ten. Two standard ways of concentrating solar heat are using multiple layers of windows and using reflectors. If the price can in fact be reduced by two factors of ten, it's possible that a mountain solar updraft chimney is the least expensive way to generate electricity.

I find the method of solar heat collection in the Manzanares chimney to be fine for the 1980s but probably unacceptable today. Manzanares used plastic sheets held above the dirt on ten foot poles. To get hotter temperatures, we need to cheaply pre-warm the raw incoming air, then concentrate heat into the air. Pre-warming air can be as dirt-cheap as siphoning air off of a black parking lot, then running the air through a black-bottomed trench covered with a tilted layer of plastic or glass. For moderate heating of air I prefer to use linear troughs of mirrored surfaces.

In the 1970s it was discovered that rock bed and air storage systems produced radon and mold when used in houses. However, such a heat storage system should be fine for electricity production. Rocks can take almost any temperature. Spreading the airflow out within the rock bed is key. Otherwise, most of the chimney's latent energy is wasted on air friction within the rock bed. A well-managed rock bed is key to keeping the electric power output from a mountain chimney rock-steady.

Putting water vapor into a 2000 meter chimney, from a solar pond, from a geothermal warm spring, exhaust steam captured from an existing solar thermal plant or even slightly moister air siphoned out of a nearby town's sewer system, can result in distilled water condensation halfway up the chimney. Water vapor acts as hurricane fuel -- as it condenses it releases latent heat, driving the chimney with more power.

Comments:

By: Donald Ferguson | 29-Sep-2015 | 8:00 am

Such a system could not only produce power but could help solve California's drought problem. The introduced water should exit as snow during the winter months at those elevations.

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