The energy tower is a device for producing

electrical power Electric power is the rate of transfer of electrical energy within a electric circuit, circuit. Its SI unit is the watt, the general unit of power (physics), power, defined as one joule per second. Standard prefixes apply to watts as with oth ...

. The brainchild of Dr. Phillip Carlson, expanded by Professor Dan Zaslavsky from the Technion. Energy towers spray water on hot air at the top of the tower, making the cooled air fall through the tower and drive a turbine at the tower's bottom.

Concept

An energy tower (also known as a downdraft energy tower, because the air flows down the tower) is a tall (1,000 meters) and wide (400 meters) hollow cylinder with a water spray system at the top. Pumps lift the water to the top of the tower and then spray the water inside the tower. Evaporation of water cools the hot, dry air hovering at the top. The cooled air, now denser than the outside warmer air, falls through the cylinder, spinning a turbine at the bottom. The turbine drives a generator which produces the electricity. The greater the temperature difference between the air and water, the greater the

energy efficiency Energy efficiency may refer to: * Energy efficiency (physics), the ratio between the useful output and input of an energy conversion process ** Electrical efficiency, useful power output per electrical power consumed ** Mechanical efficiency, a rat ...

. 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 Desalination is a process that removes mineral components from saline water. More generally, desalination is the removal of salts and minerals from a substance. One example is Soil salinity control, soil desalination. This is important for agric ...

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

solar power Solar power, also known as solar electricity, is the conversion of energy from sunlight into electricity, either directly using photovoltaics (PV) or indirectly using concentrated solar power. Solar panels use the photovoltaic effect to c ...

. Energy production continues at

night Night, or nighttime, is the period of darkness when the Sun is below the horizon. Sunlight illuminates one side of the Earth, leaving the other in darkness. The opposite of nighttime is daytime. Earth's rotation causes the appearance of ...

, because air retains some of the day's heat after dark. However, power generation by the energy tower is affected by the

weather Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloud cover, cloudy. On Earth, most weather phenomena occur in the lowest layer of the planet's atmo ...

: it slows down each time the

ambient Ambient or ambiance or ambience may refer to: Arts and entertainment * ''Ambiancé'', an unreleased experimental film * ''Ambient'' (novel), a novel by Jack Womack Music and sound * Ambience (sound recording), also known as atmospheres or backgr ...

humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation (meteorology), precipitation, dew, or fog t ...

increases (such as during a

rain Rain is a form of precipitation where water drop (liquid), droplets that have condensation, condensed from Water vapor#In Earth's atmosphere, atmospheric water vapor fall under gravity. Rain is a major component of the water cycle and is res ...

storm), or the

temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...

falls. A related approach is the

solar updraft tower The solar updraft tower (SUT) is a design concept for a renewable energy, renewable-energy power plant for generating electricity from low temperature solar heat. Sunshine heats the air beneath a very wide greenhouse-like roofed collector struct ...

, 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% 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 and by Czisch about conversion efficiency and about cost of energy (cents/kWh) are based only on model calculations, no data on a working pilot plant have ever been collected. Actual measurements on the 50 kW Manzanares pilot solar updraft tower found a conversion efficiency of 0.53%, although SBP believe that this could be increased to 1.3% in a large and improved 100 MW unit. This amounts to about 10% of the theoretical limit for the

Carnot cycle A Carnot cycle is an ideal thermodynamic cycle proposed by French physicist Nicolas Léonard Sadi Carnot, Sadi Carnot in 1824 and expanded upon by others in the 1830s and 1840s. By Carnot's theorem (thermodynamics), Carnot's theorem, it provides ...

. It is important to note a significant difference between the up-draft and down-draft proposals. The usage of water as a working-medium dramatically increases the potential for thermal energy capture, and electrical generation, due to its specific heat capacity. While the design may have its problems (see next section) and the stated efficiency claims has yet to be demonstrated, it would be an error to extrapolate performance from one to the other simply because of similarities in the name.

Potential problems

* In salty humid air corrosion rates can be very high. This concerns the tower and the turbines. * The technology requires a hot and arid climate. Such locations include the coast of

West Africa West Africa, also known as Western Africa, is the westernmost region of Africa. The United Nations geoscheme for Africa#Western Africa, United Nations defines Western Africa as the 16 countries of Benin, Burkina Faso, Cape Verde, The Gambia, Gha ...

Western Australia Western Australia (WA) is the westernmost state of Australia. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to the south, the Northern Territory to the north-east, and South Australia to the south-east. Western Aust ...

, northern

Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

Namibia Namibia, officially the Republic of Namibia, is a country on the west coast of Southern Africa. Its borders include the Atlantic Ocean to the west, Angola and Zambia to the north, Botswana to the east and South Africa to the south; in the no ...

, the

Red Sea The Red Sea is a sea inlet of the Indian Ocean, lying between Africa and Asia. Its connection to the ocean is in the south, through the Bab-el-Mandeb Strait and the Gulf of Aden. To its north lie the Sinai Peninsula, the Gulf of Aqaba, and th ...

Persian Gulf The Persian Gulf, sometimes called the Arabian Gulf, is a Mediterranean seas, mediterranean sea in West Asia. The body of water is an extension of the Arabian Sea and the larger Indian Ocean located between Iran and the Arabian Peninsula.Un ...

, and the

Gulf of California The Gulf of California (), also known as the Sea of Cortés (''Mar de Cortés'') or Sea of Cortez, or less commonly as the Vermilion Sea (''Mar Vermejo''), is a marginal sea of the Pacific Ocean that separates the Baja California peninsula from ...

. Most of these regions are remote and thinly populated, and would require power to be transported over long distances to where it is needed. Alternatively, such plants could provide captive power for nearby industrial uses such as

desalination plant Desalination is a process that removes mineral components from saline water. More generally, desalination is the removal of salts and minerals from a substance. One example is soil desalination. This is important for agriculture. It is possible ...

aluminium production Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

via the Hall-Héroult process, or to generate

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

for

ammonia production Ammonia production takes place worldwide, mostly in large-scale manufacturing plants that produce 240 million metric tonnes of ammonia (2023) annually. Based on the annual production in 2023 the major part (~70%) of the production facilities are b ...

. * 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). 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 Brine (or briny water) is a high-concentration solution of salt (typically sodium chloride or calcium chloride) in water. In diverse contexts, ''brine'' may refer to the salt solutions ranging from about 3.5% (a typical concentration of seawat ...

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 Infrastructure is the set of facilities and systems that serve a country, city, or other area, and encompasses the services and facilities necessary for its economy, households and firms to function. Infrastructure is composed of public and pri ...

, increasing capital requirements and overall risk.

Demonstration project

Maryland-based Solar Wind Energy, Inc. was developing a 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.

References

# # # Zaslavsky, Dan; Rami Guetta et al. (December 2001). . Technion Israel, Israel - India Steering Committee. Retrieved on 2007-03-15. # # # # # # # # Zwirn, Michael J. (January 1997). Energy Towers: Pros and Cons of the ''Arubot Sharav'' Alternative Energy Proposal. Arava Institute for Environmental Studies. Retrieved on 2006-12-22. # Zaslavsky, Dan (November, 1996)
"Solar Energy Without a Collector"
''The 3rd Sabin Conference''.

External links