Energy tower (downdraft)

The energy tower is a device for producing

The greater the temperature difference between the air and water, the greater the energy efficiency. Therefore, downdraft energy towers should work best in a hot dry climate. Energy towers require large quantities of water. Salt water is acceptable, although care must be taken to prevent corrosion; desalination can help solve this problem.

The energy that is extracted from the air is ultimately derived from the sun, so this can be considered a form of

A related approach is the solar updraft tower, which heats air in glass enclosures at ground level and sends the heated air up a tower driving turbines at the base. Updraft towers do not pump water, which increases their efficiency, but do require large amounts of land for the collectors. Land acquisition and collector construction costs for updraft towers must be compared to pumping infrastructure costs for downdraft collectors. Operationally, maintaining the collector structures for updraft towers must be compared to pumping costs and pump infrastructure maintenance.

Cost/efficiency

Zaslavsky and other authors estimate that depending on the site and financing costs, energy could be produced in the range of 1-4 cents per kWh, well below alternative energy sources other than hydro. Pumping the water requires about 50% of the turbine's output. Zaslavsky claims that the Energy Tower would achieve up to 70-80% ^[3] of the Carnot limit. If the conversion efficiency turns out to be much lower, it is expected to have an adverse impact on projections made for cost of energy.

Projections made by Altmann^[4] and by Czisch^[5][6] about conversion efficiency and about cost of energy (cents/kWh) are based only on model calculations^[7], no data on a working pilot plant have ever been collected.

Actual measurements on the 50 kW

• In salty humid air corrosion rates can be very high. This concerns the tower and the turbines.[9]
• The technology requires a hot and arid climate. Such locations include the coast of
  Hall-Héroult process, or to generate hydrogen for ammonia production
  .
• Humidity as a result of plant operation may be an issue for nearby communities. A 400 meter diameter powerplant producing wind velocity of 22 meters per second, must add about 15 grams of water per kilogram of air processed. This is equal to 41 tonnes of water per second (m³s⁻¹).[1] In terms of humid air, this is 10 cubic kilometers of very humid air each hour. Thus, a community even 100 kilometers away may be unpleasantly affected.
• Brine is a problem in proportion to the humidity created, since water's vapor pressure decreases with salinity, it is reasonable to expect at least as much brine as water in humidity. This means that a river of brine flows away from the powerplant at 41 tonnes per second (m³s⁻¹), along with a river of saline water flowing in with 82 tonnes of water per second (m³s⁻¹).

Large industrial consumers often locate near cheap sources of electricity. However, many of these desert regions also lack necessary infrastructure, increasing capital requirements and overall risk.

Demonstration project

Maryland-based Solar Wind Energy, Inc. was developing a 685 metres (2,247 ft) tower. Under the most recent design specifications, the Tower designed for a site near San Luis, Arizona, has a gross production capacity on an hourly basis, of up to 1,250 megawatt hours. Due to lower capacities during winter days, the average hourly output per day for sale to the grid for the entire year averages approximately 435 megawatt hours/hr.^[2][3]

See also

• Psychrometrics (not to be confused with Psychometrics)
• Solar updraft tower

References