Solar updraft towerFrom Wikipedia, the free encyclopedia

This article is about a type of power plant. For other uses, see Solar tower (disambiguation).

Schematic presentation of a Solar updraft tower

The solar updraft tower is a renewable-energy power plant for generating electricity from solar power.

Sunshine falling on a greenhouse-like collector structure around the base of a tall chimney heats the air

within it. The resulting convectioncauses air to rise up the tower by the chimney effect. This airflow

drives wind turbines to produce electricity.

Contents

  [hide]

1 Design

o 1.1 Hybrid

2 History

o 2.1 First prototype

o 2.2 Jinshawan tower

o 2.3 Ciudad Real Torre Solar

o 2.4 Australian proposal

o 2.5 Botswana test facility

o 2.6 Namibian proposal

o 2.7 Turkish model

o 2.8 Arizona projects

o 2.9 Mountainside tower

2.9.1 Arctic tower

3 Efficiency

4 Related ideas and adaptations

5 Financial feasibility

6 See also

7 References

8 External links

[edit]Design

Power output depends primarily on two factors: collector area and chimney height. A larger area collects

and warms a greater volume of air to flow up the chimney; collector areas as large as 7 kilometres

(4.3 mi) in diameter have been discussed. A larger chimney height increases the pressure difference via

the stack effect; chimneys as tall as 1,000 metres (3,281 ft) have been discussed.

Telescopic collapsible features can enable chimneys to be lowered to prevent storm damage.

Heat can be stored inside the collector area. A saltwater thermal sink in the collector could 'flatten' the

diurnal variation in energy output, while airflow humidification in the collector and condensation in the

updraft could increase the energy flux of the system.[1][2]

Turbines can be installed in a ring around the base of the tower, with a horizontal axis, as once planned

for an Australian project and seen in the diagram above; or—as in the prototype in Spain—a single

vertical axis turbine can be installed inside the chimney.

Carbon dioxide is emitted only negligibly[citation needed] as part of operations. Manufacturing and construction

require substantial power, particularly to produce cement. Net energy payback is estimated to be 2–3

years.[2]

Since towers occupy significant amounts of land, deserts and other low-value sites are most likely.

A small-scale solar updraft tower may be an attractive option for remote regions in developing countries.[3]

[4] The relatively low-tech approach could allow local resources and labour to be used for construction and

maintenance.

[edit]Hybrid

Solar updraft towers can be combined with other technologies to increase output. Solar thermal

collectors or photovoltaics can be arranged inside the collector greenhouse. This could further be

combined with agriculture.[citation needed]

[edit]History

In 1903, Isidoro Cabanyes, a colonel in the Spanish army, proposed a solar chimney power plant in the

magazine La energía eléctrica.[5] Another early description was published in 1931 by German

author Hanns Günther.[6] Beginning in 1975, Robert E. Lucier applied for patents on a solar chimney

electric power generator; between 1978 and 1981 patents (since expired) were granted in Australia,

[7] Canada,[8] Israel,[9] and the USA.[10]

[edit]First prototype

SUT as seen from La Solana

SUT powerplant prototype in Manzanares, Spain, seen from a point 8 km to the South

Solar Chimney Manzanares view through the polyester collector roof

Solar Chimney Manzanares-view of the tower through the collector glass roof

View from the tower on the roof with blackened ground below the collector. One can see the different test materials for canopy

cover, and 12 large fields of unblackened ground for agricultural test area.

In 1982, a small-scale experimental model of a solar draft tower[11] was built in Manzanares, Ciudad Real,

150 km south of Madrid, Spain at 39°02′34.45″N 3°15′12.21″W. The power plant operated for

approximately eight years. The tower's guy-wires were not protected against corrosion and failed due to

rust and storm winds. The tower blew over and was decommissioned in 1989.[12]

Inexpensive materials were used in order to evaluate their performance. The solar tower was built of iron

plating only 1.25 millimetres (0.049 in) thick under the direction of a German engineer, Jörg Schlaich. The

project was funded by the German government.[13][14]

The chimney had a height of 195 metres (640 ft) and a diameter of 10 metres (33 ft) with a collection area

(greenhouse) of 46 hectares (110 acres) and a diameter of 244 metres (801 ft), obtaining a maximum

power output of about 50 kW. Various materials were used for testing, such as single or double glazing or

plastic (which turned out not to be durable enough). One section was used as an actual greenhouse.

During its operation, 180 sensors measured inside and outside temperature, humidity and wind speed

data was collected on a second-by-second basis.[15] This experiment setup did not sell energy.

[edit]Jinshawan tower

In December 2010, a tower in Jinshawan in Inner Mongolia, China started operation, producing

200 kilowatts.[16][17] The 1.38 billionRMB (USD 208 million) project was started in May 2009 and intends to

cover 277 hectares (680 acres) and produce 27.5 MW by 2013. The greenhouse is expected to improve

the climate by covering loose sand, restraining sandstorms.[18]

[edit]Ciudad Real Torre Solar

A proposal to construct a solar updraft tower in Ciudad Real, Spain, entitled Ciudad Real Torre

Solar would be the first of its kind in the European Union [19]  and would stand 750 metres (2,460 ft) tall[20] –

nearly twice as tall as the continent's tallest structure, theBelmont TV Mast [21]  – covering an area of 350

hectares (860 acres).[22] It is expected to produce 40 MW.[23]

[edit]Australian proposal

EnviroMission in 2001,[24] proposed to build a solar updraft tower power generating station known as Solar

Tower Buronga nearBuronga, New South Wales.[25] The company did not complete the project and now

plans a similar plant in Arizona.[26]

[edit]Botswana test facility

Based on the need for plans for long-term energy strategies, Botswana's Ministry of Science and

Technology designed and built a small-scale research tower. This experiment ran from 7 October to 22

November 2005. It had an inside diameter of 2 metres (6.6 ft) and a height of 22 metres (72 ft),

manufactured from glass-reinforced polyester, with a area of approximately 160 square metres

(1,700 sq ft). The roof was made of a 5 mm thick clear glass supported by a steel framework.[27]

[edit]Namibian proposal

In mid 2008, the Namibian government approved a proposal for the construction of a 400 MW solar

chimney called the 'Greentower'. The tower is planned to be 1.5 kilometres (4,900 ft) tall and 280 metres

(920 ft) in diameter, and the base will consist of a 37 square kilometres (14 sq mi) greenhouse in which

cash crops can be grown.[28]

[edit]Turkish model

A model solar updraft tower was constructed in Turkey as a civil engineering project.[29] Functionality and

outcomes are obscure.[30][31]

[edit]Arizona projects

In October 2010, EnviroMission announced further plans to build two 200 MW Solar Updraft Towers in

Western Arizona. Southern California Public Power Authority (SCPPA) has agreed to negotiate a power-

purchase agreement with EnviroMission. The project has been listed by the SCPPA.[32] As of January

2011, the company had secured $29.8 million in financing from AGS Capital Group.[33] In August 2011,

United States construction services contractor, Hensel Phelps Construction Co. was engaged for delivery

of a construction schedule and cost estimate of a 200 MW tower.[34] A potential construction roadblock to

is its potential environmental impact. Environmental concerns have arisen over desert solar panel arrays

in the US Southwest.[35](registration required) The desert tortoise (Gopherus agassizii) is an endangered

species in the area. [citation needed]

[edit]Mountainside tower

In 1926 Prof Engineer Bernard Dubos proposed to the French Academy of Sciences the construction of a

Solar Aero-Electric Power Plant in North Africa with its solar chimney on the slope of a large mountain.[36]

[37] A mountainside updraft tower can also function as a vertical greenhouse. [citation needed]

[edit]Arctic tower

Locating a tower at high latitudes could produce up to 85 per cent of the output of a similar plant located

closer to the equator, if the collection area is sloped significantly southward. The sloped collector field is

built on suitable mountainsides, which also functions as a chimney. A short vertical chimney on the

mountaintop to accommodate the vertical axis air turbine. The results showed that solar chimney power

plants at high latitudes may have satisfactory thermal performance.[38]

[edit]Efficiency

The solar updraft tower has a power conversion rate considerably lower than many other designs in the

(high temperature) solar thermal group of collectors. The low conversion rate is balanced to some extent

by the lower cost per square metre of solar collection.[39][40][12]

Model calculations estimate that a 100 MW plant would require a 1,000 m tower and a greenhouse of 20

square kilometres (7.7 sq mi). A 200 MW tower with the same tower would require a collector 7 kilometres

in diameter (total area of about 38 km²).[2] One 200MW power station will provide enough electricity for

around 200,000 typical households and will abate over 900,000 tons of greenhouse producing gases from

entering the environment annually. The collector area is expected to extract about 0.5 percent, or 5 W/m²

of 1 kW/m², of the solar energy that falls upon it. Concentrating thermal (CSP) or photovoltaic (CPV) solar

power plants range between 20% to 31.25% efficiency (dish Stirling). Overall CSP/CPV efficiency is

reduced because collectors do not cover the entire footprint. Without further tests, the accuracy of these

calculations is uncertain.[41]

The performance of an updraft tower may be degraded by factors such as atmospheric winds,[42][43] by

drag induced by the bracings used for supporting the chimney,[44] and by reflection off the top of the

greenhouse canopy.

Carnot's theorem reveals the absolute limit of efficiency:

For example, if the air entering the base of the tower was 353 K (80 °C;

176 °F) and the surrounding air at the top of the tower was 283

K (10 °C; 50 °F), then the maximum efficiency would be ~20%. For the

above 100 MW plant, assuming peak solar radiation of ~1 kWm−2, and

efficiency of 0.5%, output would be 5 Wm−2. Thus, 39 units of

potentially available energy are available for every unit captured. For

perspective, PV panels providing the same amount of energy

(assuming they operate at ~20%), would occupy 2.5% as much land.

Conversely, covering the same acre with PV panels would produce

4,000 MW.

[edit]Related ideas and adaptations

The inverse of the solar updraft tower is the downdraft-

driven energy tower. Evaporation of sprayed water at the top of the

tower would cause a downdraft by cooling the air and driving wind

turbines at the bottom of the tower.[45]

The atmospheric vortex proposal[46] replaces the physical chimney

by a controlled or 'anchored' cyclonic updraft vortex. Depending on

the column gradient of temperature and pressure, or buoyancy,

and stability of the vortex, very high-altitude updraft may be

achievable. As an alternate to a solar collector, industrial and

urban waste-heat could be used to initiate and sustain the updraft

in the vortex.

Release of humid ground-level air from an atmospheric vortex or

solar chimney at altitude could form clouds or precipitation,

potentially altering local hydrology.[47] Local de-desertification, or

afforestation could be achieved if a regional water cycle were

established and sustained in an otherwise arid area.

Fitted with a vortex chimney scrubber, the updraft could be cleaned

of particulate air pollution. The solar cyclone distiller[48] could

extract atmospheric water by condensation in the updraft of the

chimney.

This solar cyclonic water distiller with a solar collector pond could

adapt the solar collector-chimney system for large-scale

desalination of collected brine, brackish- or waste-water pooled in

the collector base.[49]

A form of solar boiler technology placed directly above the turbine

at the base of the tower might increase the up-draught.[citation needed]

If the chimney updraft is an ionized vortex, then the electro-

magnetic field could be tapped for electricity, using the airflow and

chimney as a generator.[citation needed]

Energy production and water desalination[49] could be used to

support carbon-fixing or food-producing local agriculture,[50] and for

intensive aquaculture and horticultureunder the solar collector as a

greenhouse.

If land is at a premium then collection area can be increased by

means of a multi-layer greenhouse at the base, sealed at alternate

ends to force air to flow over the whole of it. [citation needed]

[edit]Financial feasibility

A solar updraft power station would require a large initial capital outlay,

but would have relatively low operating cost.[2]

Capital outlays would be roughly the same as next-generation nuclear

plants such as the AP-1000 at roughly $5 per Watt of capacity. As with

other renewable power sources, towers have no need for fuel. Overall

costs are largely determined by interest rates and years of operation,

varying from 5 eurocent per kWh for 4% and 20 years to 15 eurocent

per kWh for 12% and 40 years.[51]

Estimates of total costs range from 7 (for a 200 MW plant) and 21 (for a

5 MW plant) euro cents per kWh to 25-35 cents per kWh.[52] Levelized

cost are approximately 3 Euro cents per KWh for a 100 MW wind or

natural gas plant.[53] No actual data are available for a utility scale

power plant.[54]

As with other solar technologies, some mechanism is required to mix its

varying power output with other power sources. Heat can be stored in

heat-absorbing material or saltwater ponds. Electricity can be cached in

batteries or other technologies.[55]

[edit]See also

Solar pond

[edit]References

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[edit]External links

video link Spanish solar updraft tower

video link Australian tower proposal

video link Solar Updraft Tower — a small model with various

substrates

The Floating Solar Chimney Technology

Solar Nozzle

CNN money article  2006-10-26

Mildura Solar Tower  at Structurae

University of Stellenbosch study

U.S. Department of Energy's Solar Energy Technologies program

Atmospheric Vortex alternative to Solar Chimney

2nd International Conference on Solar Chimney Power

Technology[[fi:Aurinkotorni]

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