Deployment of solar power to energy grids

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Deployment of solar power to energy grids depends largely upon local conditions and requirements. Many industrialized nations are installing significant solar power capacity in their grids as a reliable economic supplement or alternative to other power sources. Long distance transmission allows remote renewable energy resources to be used to displace fossil fuel consumption. Solar, hydro and wind sources can't be moved closer to high population cities, and solar costs are lowest in remote areas where local power needs are the least. Connection costs alone can determine whether any particular renewable alternative is economically sensible. Costs can be prohibitive for transmission lines.

Most electrical grids are relatively local, as transporting electricity more than about 350 miles (560 km) was not efficient. However, newer, higher voltage lines now make possible transmission over 4,000 miles (6,400 km), allowing the development of a global energy grid.

A global energy network makes enormous sense if we are to meet global energy needs with a minimal impact on the world's environment. Such advances (in long distance transmission) may even make possible the visionary suggestion ... that the Eastern and Western hemispheres be linked by underwater cable to assist each other in managing peak energy demand, since the high daytime use in one hemisphere occurs at precisely the low night time consumption by the other.
Nobel Laureate, and former U.S. Vice President Al Gore[1]

A global energy grid will allow bringing solar power from the sunny Middle East and Mexico to Europe and North America.

Solar power plants use one of two technologies

  • Arrays of photovoltaic (PV) modules, mounted on buildings or ground mounted 'solar parks'
  • Solar thermal energy plants, using concentrated solar energy to make steam. The steam is converted by a turbine to electricity.
  • Another solar thermal technology approach uses concentrated solar energy to drive a Stirling engine which then powers a generator.

Contents

[edit] Africa

June 7, 2007 Rwanda formally opened Africa's largest solar energy plant, Kigali Solaire, on Mount Jali, 250 kW, near the city of Kigali.[2]

[edit] Asia

[edit] China

[edit] India

Government support and subsidies have been major influences in its progress.[3] India's very long-term solar potential may be unparalleled in the world because it is one of the few places with an ideal combination of both high solar power reception and a large consumer base in the same place. India's theoretical solar potential is about 5000 trillion KW·h per year (i.e. 600 TW), far more than its current total consumption. The Rajashtan government has set aside a 35,000 km² area of the Thar desert for solar power.[4]

The grid-connected solar power as of June, 2007 was 2.12 MW.[5]

[edit] Israel

In 2005, the Israeli government announced an international contract for building a 100 MW solar trough plant to supply the electricity needs of more than 200,000 Israelis living in southern Israel. The plan may eventually allow the creation of a gigantic 500 MW power plant, making Israel a leader in solar power production.[6]

[edit] Japan

As of 2004, Japan had 1200 MWe installed. Japan currently consumes about half of worldwide production of solar modules, mostly for grid connected residential applications.

[edit] South Asia

Solar power in South Asia

[edit] South Korea

South Korea installed about 21 MW of photovoltaics in 2006, mostly because of feed in tariffs.[7]

[edit] Australia

The largest solar power station in Australia is a 400 kW (peak) photovoltaic array at Singleton, New South Wales.

Other significant solar arrays include the 220 kWp array on the Anangu Pitjantjatjara Lands in South Australia, the 200kWp array at Queen Victoria Market in Melbourne and the 160kWp array at Kogarah Town Square in Sydney.

A 30 MWe solar thermal `coal saver' system is currently under construction at Liddell power station by Macquarie Generation and Solar Heat and Power. The system used `compact linear Fresnel reflector' technology developed in Australia. It will provide solar-powered steam to the 600 MW black coal power station's boiler feedwater heater. The project is funded by Macquarie Generation in order to meet its requirements under the Australian Mandatory Renewable Energy Target (MRET) scheme.

A 154 MW (peak) solar power station in Victoria will soon begin construction.[8][9]

A building-integrated photovoltaic (BIPV) installation of 60 kW in Brisbane (at the Hall-Chadwick building) has an uninterruptible power supply (UPS) which gives around 10–15 minutes worth of emergency power in the event of the loss of electricity supply. Any power not used by the UPS is connected to the grid and goes towards reducing the building's overall power bills.

Numerous smaller arrays have been established, mainly in remote areas where solar power is cost-competitive with diesel power.[10]

[edit] Europe

[edit] Belgium

In October 2009, the city of Antwerp announced that they want to install 2 500 m² of solar panels on roofs of public buildings, that will be worth 265,000 kwh per annum. [11]

In December 2009, Katoen Natie announced that they will install 800 000m² of solar panels in various places, including Antwerp. [12] It is expected that the installed solar power in the Flemmish Region will be increased by 25%, when finnished. [13] That will be the largest installation in Europe.[14] The total cost will be 166 million euros. [15]

[edit] Crete

A large solar PV plant is planned for the island of Crete. Research continues into ways to make the actual solar collecting cells less expensive and more efficient.

[edit] Germany

Germany was the fastest growing major PV market in the world in 2005, particularly because of implementing a Feed in Tariff. In 2005, 837 MWp of PV were installed. The German PV industry generates over 10,000 jobs in production, distribution and installation. Over 90% of solar PV installations are in grid-tied applications in Germany. The balance is off-grid (or stand alone) systems.[16]

Completed in 2006, the 12 MW Solarpark Gut Erlasee photovoltaic system, near Arnstein in Bavaria, Germany, is currently Germany's largest PV system.[17] The 10 MW Solarpark Bavaria in Germany was also the largest PV installation when completed in 2005, covering 25 hectares (62 acres) with 57,600 photovoltaic panels.[18]

[edit] Portugal

On April 27, 2006, GE Energy Financial Services, PowerLight Corporation and Catavento Lda announced that they will build one of the world’s largest solar photovoltaic power projects. The 11-megawatt solar power plant, comprising 52,000 photovoltaic modules, will be built at a single site in Serpa, Portugal, 200 kilometers (124 miles) southeast of Lisbon in one of Europe’s sunniest areas.[19]

[edit] Spain

In March 2007, Europe's first commercial concentrating solar power tower plant was opened near the sunny southern Spanish city of Seville. The 11 megawatt plant known as PS10, produces electricity with 624 large heliostats. PS10 is the first of a set of solar electric power generation plants to be constructed in the same area that will total more than 300MW by 2013. This power generation will be accomplished using a variety of technologies.[20]

Two 50 MWe solar thermal trough power plants, AndaSol-1 and AndaSol-2, are being built in the region of Andalucia, each with a 510,120 m² solar collector field and six hours’ thermal storage. The AndaSol-1 project obtained financial closure in May 2006 and has received a €5 million grant from the European Commission’s (EC) Fifth Framework Programme, along with financial support from the German Federal Ministry for Environment. Construction started in July 2006 and will be completed in 2008.[21]

A 15 MWe solar-only power tower plant, the Solar Tres project, is in the hands of the Spanish company SENER, employing United States molten salt technologies for receiver and energy storage.

The Plataforma Solar de Almería (PSA) in Spain, part of the Center for Energy, Environment and Technological Research (CIEMAT), is the largest center for research, development, and testing of concentrating solar technologies in Europe.[22]

[edit] United Kingdom

In the United Kingdom, the second tallest building in Manchester, the CIS Tower, was clad in photovoltaic panels at a cost of £5.5 million and started feeding electricity to the national grid on November 2005.[23]

[edit] North America

[edit] United States

A laundromat in California supplements water heating with solar panels on the roof.

The world's largest solar power plant, the solar trough-based Solar Energy Generating Systems (SEGS), is located in the Mojave Desert. Solel,[24] an Israeli company, operates the plant, which consists of 1,000 acres (4.0 km2) of solar reflectors and produces 354 MW (compared to the largest PV plant of 12 MWp). At the beginning of 2005, this plant was estimated to produce 90% of the world's commercially produced grid-connected solar power,[6] however the rapid growth of photovoltaics has increased the percentage generated with photovoltaics. By the end of 2006 624 megawatts of photovoltaics had been installed in the US,[25] and 830 megawatts by the end of 2007.[26] In the near future, very large scale photovoltaic projects are proposed which "could generate many times the current primary global energy supply".[27] To compensate for night time energy needs large pumped storage capacity would also be needed.

In some areas of the United States, PV electric systems are already competitive with utility systems. As of 2005, there is a list of technical conditions that factor into the economic feasibility of going solar: the amount of sunlight that the area receives; the purchase cost of the system; the ability of the system owner to sell power back to the electric grid; and most important, the competing power prices from the local utility. For example, a photovoltaic system installed in Boston, Massachusetts, produces 25% less electricity than it would in Albuquerque, New Mexico, but yields a greater savings on utility bills since electricity costs 60% more in Boston.

In addition to these considerations, many states and regions offer substantial incentives to improve the economics for potential consumers. Up until December 31, 2008 homeowners can claim one federal credit of up to $2,000 to cover 30% of a photovoltaic system's cost and another 30% credit of up to $2,000 for a solar thermal system. After that there is no limit on the 30% credit through the end of 2016. Fifteen states also offer tax breaks for solar, and two dozen states offer direct consumer rebates.[28] In October 2009 California passed into law the first feed-in tariff for solar energy in the United States. This law (AB 920) requires electric utilities to pay private households and companies for excess power generated. [29]

Solar One was a pilot solar thermal project in the Mojave Desert near Barstow, California. It used heliostats, and molten salts storage technology, to achieve longer periods of power generation. It was rebuilt as Solar Two, which elaborated on the success of Solar One. It was an R&D project, partly financed by the US federal Department of Energy. Solar Two used liquid salts as a storage medium in order to continue to provide energy for much of the time when sunlight is not available. Its success has led to the larger Solar Tres project in Spain.

Nevada Solar One is the third largest solar power plant in the world, generating 64 MW. It is being built in Boulder City, Nevada.[30] Nevada Solar One will use parabolic troughs as thermal solar concentrators, heating tubes of liquid (solar receivers), instead of the power tower concentrator (as Solar One used).

On August 11, 2005, Southern California Edison announced an agreement to purchase solar-powered Stirling engines from Stirling Energy Systems over a twenty year period and in quantities (20,000 units) sufficient to generate 500 megawatts of electricity.[31] These systems — to be installed on a 4,500 acres (18 km2) solar farm — will use mirrors to direct and concentrate sunlight onto the engines which will drive generators. Less than a month later, Stirling Energy Systems announced another agreement with San Diego Gas & Electric to provide between 300 and 900 megawatts of electricity.[32]

On January 12, 2006, the California Public Utilities Commission approved the California Solar Incentive Program,[33] a comprehensive $2.8 billion program that provides incentives toward solar development over 11 years.

A survey conducted in May 2007 showed that 87% of Americans think that solar electricity should be an option for all new home construction, up from 77% a year earlier.[34]

In April 2007 MMA Renewable Ventures, a MuniMAE company, announced they will be leasing 140 acres (0.57 km2) at the western edge of Norris Air Base in Nevada to build a 15 MW PV system by the end of the year, slated to be the countries biggest, and is expected to generate over 25 million KWh/year.[35] The power plant, Nellis Solar Power Plant, was completed in December, 2007.

On July 25, 2007, PG&E signed an agreement with Solel, the same firm that runs the SEGS plants (see above), for 553 megawatts of solar power in the Mojave Desert.[36] If completed on schedule (2011), it will displace SEGS as the largest solar power plant in the world.

[edit] Mexico

Mexico is already the greatest solar energy producer in Latin America and it is planning a solar trough based plant with 30MW which will use a combined cycle gas turbine about 400MW to provide electricity to the city of Agua Prieta, Sonora. The World Bank has financed this project with US$50 million.

[edit] Worldwide installed photovoltaic totals

Produced, Installed & Total Photovoltaic Peak Power Capacity (MWp) as of the end of 2007
Country or Region
Report Nat. Int.
off
grid
Δ
on
grid
Δ
Installed
2007
off
grid
Σ
on
grid
Σ
Total
2007
Wp/capita
Total
Module
Price
/Wp
kW·h/kWp·yr
Insolation
Feed-in Tariff
EU¢/kW·h
 World 127.9 2,130 2,258 662.3 7,178 7,841 2.5–11.2 800–2,902 0–59.3
 Germany[37][38] 35 1,100 1,135 35 3,827 3,862 46.8 4.0–5.3 1,000–1,300[39] 51.8–56.8
 Japan[38][40] 1.562 208.8 210.4 90.15 1,829 1,919 15 2.96 1,200–1,600 Ended(2005)
 United States[38][41] 55 151.5 206.5 325 505.5 830.5 2.8 2.98 900–2,150[39] 1.2–31.04(CA)
 Spain ?[38] 22 490 512 29.8 625.2 655 15.1 3.0–4.5 1,600–2,200 18.38–44.04
 Italy[38][42] 0.3 69.9 70.2 13.1 107.1 120.2 2.1 3.2–3.6 1,400–2,200 36.0–49.0
 Australia[38][43] 5.91 6.28 12.19 66.45 16.04 82.49 4.1 4.5–5.4 1,450–2,902[44] 0–26.4(SA'08)
 South Korea[38][45] 0 42.87 42.87 5.943 71.66 77.60 1.6 3.50–3.84 1,500–1,600 56.5–59.3
 France[38][46] 0.993 30.31 31.30 22.55 52.68 75.23 1.2 3.2–5.1 1,100–2,000 30.0–55.0
 Netherlands[38][47] 0.582 1.023 1.605 5.3 48 53.3 3.3 3.3–4.5 1,000–1,200 1.21–9.7
 Switzerland[38][48] 0.2 6.3 6.5 3.6 32.6 36.2 4.9 3.18–3.30 1,200–2,000 9.53–50.8
 Austria ?[38] 0.055 2.061 2.116 3.224 24.48 27.70 3.4 3.6–4.3 1,200–2,000 >0
 Canada[38][49] 3.888 1.403 5.291 22.86 2.911 25.78 0.8 3.76 900–1,750 0–29.48(ON)
 Mexico ?[38] 0.869 0.15 1.019 20.45 0.3 20.75 0.2 5.44–6.42 1,700–2,600 None
 United Kingdom[38][50] 0.16 3.65 3.81 1.47 16.62 18.09 0.3 3.67–5.72 900–1,300 0–11.74(exprt)
 Portugal ?[51] 0.2 14.25 14.45 2.841 15.03 17.87 1.7 1,600–2,200
 Norway[38][52] 0.32 0.004 0.324 7.86 0.132 7.992 1.7 11.2 800–950 None
 Sweden[38][53] 0.271 1.121 1.392 4.566 1.676 6.242 0.7 3.24–7.02 900–1,050 None
 Denmark[38][54] 0.05 0.125 0.175 0.385 2.69 3.075 0.6 5.36–8.04 900–1,100 None
 Israel[38][55] 0.5 0 0.5 1.794 0.025 1.819 0.3 4.3 2,200–2,400 13.13–16.40
Country or Region
Report Nat. Int.
off
grid
Δ
on
grid
Δ
Installed
2007
off
grid
Σ
on
grid
Σ
Total
2007
Wp/capita
Total
Module
Price
/Wp
kW·h/kWp·yr
Insolation
Feed-in Tariff
EU¢/kW·h

Notes: Off grid refers to photovoltaics which are not grid connected. On grid means connected to the local electricity grid. Δ means the amount installed during the previous year. Σ means the total amount installed. Wp/capita refers to the ratio of total installed capacity divided by total population, or total installed Wp per person. Module price is average installed price, in Euros. kW·h/kWp·yr indicates the range of insolation to be expected. While National Report(s) may be cited as source(s) within an International Report, any contradictions in data are resolved by using only the most recent report's data. Exchange rates represent the 2006 annual average of daily rates (OECD Main Economic Indicators June 2007).
Module Price: Lowest:2.5 EUR/Wp[38] (2.83 USD/Wp[56]) in Germany 2003. Uncited insolation data is from maps dating 1991-1995.
PV Power (2007-June)[51][57] IEA PVPS website.

[edit] See also

[edit] References

  1. ^ New Power for the Planet
  2. ^ Rwnda installs "Africa's biggest" solar plant
  3. ^ Solar energy heats up India is Rapidly Developing Solar Energy via Photovoltaic & Thermal Systems
  4. ^ Rajasthan's Solar Revolution
  5. ^ Estimated medium-term(2032) potential and cumulative achievements on Renewable energy as on 30-06.2007
  6. ^ a b IsraCast: Technology in Israel
  7. ^ PV Power June 2007
  8. ^ 154MW Victorian Project
  9. ^ PM turns up heat on solar power | The Australian
  10. ^ AGO - Renewable Energy - Power Stations
  11. ^ http://www.standaard.be/artikel/detail.aspx?artikelid=DMF30102009_046
  12. ^ http://www.standaard.be/artikel/detail.aspx?artikelid=DMF05122009_014
  13. ^ ibid
  14. ^ ibid
  15. ^ http://www.demorgen.be/dm/nl/5376/Planet-Watch/article/detail/1038201/2009/12/05/Belgie-heeft-grootste-installatie-zonnepanelen-van-Europa.dhtml
  16. ^ German PV market
  17. ^ SunPower Announces the Opening of SOLON's Solarpark Gut Erlasse
  18. ^ Solarpark Bavaria
  19. ^ WORLD’S LARGEST SOLAR PHOTOVOLTAIC POWER PLANT TO BE BUILT
  20. ^ http://www.ens-newswire.com/ens/mar2007/2007-03-30-02.asp
  21. ^ http://spider.iea.org/impagr/cip/pdf/issue36solarp.pdf
  22. ^ Plataforma Solar de Almería - Facilities and Infrastructure
  23. ^ Building converts to solar power
  24. ^ Solel
  25. ^ National Survey Report of PV Power Applications in The United States Of America 2006
  26. ^ National Reports
  27. ^ http://www.iea-pvps.org/products/rep8_02s.htm
  28. ^ Database of State Incentives for Renewable Energy (DSIRE)
  29. ^ Governor Signs Two Big Solar Bills
  30. ^ "ACCIONA invests 220 million euros in a solar thermal electric power plant in Nevada (USA)" (in Spanish). 2006-02-13. http://www.acciona.es/default.asp?x=0002060101&z=000105&item=152&bus=1. Retrieved 2006-10-23. 
  31. ^ World's largest solar installation to use Stirling engine technology
  32. ^ World's Largest Solar Energy Farm to be built in Southern California
  33. ^ California Solar Incentive Program
  34. ^ Roper: Business Survey
  35. ^ Air Force takes step forward toward renewable energy Nellis expects to save $1 million/year ($0.04/kWh price savings)
  36. ^ PG&E Signs Agreement With Solel for 553 Megawatts of Solar Power
  37. ^ Dr. Wissing, Lothar; Jülich, Forschungszentrum & Jülich, Projektträger (May 2007). "National Survey Report of PV Power Applications in Germany 2006 - Version 2" (PDF). IEA - PVPS Programme - NSRs for Germany. http://www.iea-pvps.org/countries/download/nsr06/06deunsr.pdf. Retrieved 2007-10-20. 
  38. ^ a b Sherwood, Larry; Les Nelson, Fred Morse, Jeff Wolfe, Chris O’Brien (2006). "US Solar Industry - Year In Review - 2006" (PDF). Solar Energy Industries Association (SEIA) & The Prometheus Institute for Sustainable Development. http://www.seia.org/Year_in_Solar_2006.pdf. Retrieved 2007-10-20. 
  39. ^ Ikki, Osamu; Matsubara, Koji (2007-05-25). "National Survey Report of PV Power Applications in Japan 2006" (PDF). IEA - PVPS Programme - NSRs for Japan. http://www.iea-pvps.org/countries/download/nsr06/06jpnnsr.pdf. Retrieved 2007-10-20. 
  40. ^ Pedigo, Susannah; Maycock, Paul D. & Bower, Ward (2007-08-30). "National Survey Report of PV Power Applications in The United States Of America 2006 - Version 14" (PDF). IEA - PVPS Programme - NSRs for The USA. http://www.iea-pvps.org/countries/download/nsr06/06usansr.pdf. Retrieved 2007-10-20. 
  41. ^ Guastella, Salvatore; Castello, Salvatore & Anna De Lillo (May 2007). "National Survey Report of PV Power Applications in Italy 2006" (PDF). IEA - PVPS Programme - NSRs for Italy. http://www.iea-pvps.org/countries/download/nsr06/06itansr.pdf. Retrieved 2007-10-20. 
  42. ^ Watt, Muriel (May 2007). "National Survey Report of PV Power Applications in Australia 2006" (PDF). IEA - PVPS Programme - NSRs for Australia. http://www.iea-pvps.org/countries/download/nsr06/06ausnsr.pdf. Retrieved 2007-10-16. 
  43. ^ Blakers, Andrew W. (2000). "Solar and Wind Electricity in Australia" (pdf). Australian Journal of Environmental Management, Vol 7, pp 223-236, 2000. http://solar.anu.edu.au/pubs/papers/Solar&Wind.pdf. Retrieved 2008-09-03. 
  44. ^ Yoon, Kyung-Hoon; Kim, Donghwan & Yoon, Kyung Shick (May 2007). "National Survey Report of PV Power Applications in Korea 2006" (PDF). IEA - PVPS Programme - NSRs for The Republic of Korea. http://www.iea-pvps.org/countries/download/nsr06/06kornsr.pdf. Retrieved 2007-10-20. 
  45. ^ Claverie, André; Equer, Bernard (2007-07-15). "Solar Photovoltaic Electricity Applications in France National Survey Report 2006" (PDF). IEA - PVPS Programme - NSRs for France. http://www.iea-pvps.org/countries/france/FRANCE%20NSR%20PV%202006.pdf. Retrieved 2008-03-13. 
  46. ^ Swens, Job (May 2007). "National Survey Report of PV Power Applications in The Netherlands 2006" (PDF). IEA - PVPS Programme - NSRs for The Netherlands. http://www.iea-pvps.org/countries/download/nsr06/06nldnsr.pdf. Retrieved 2007-10-20. 
  47. ^ Hüsser, Pius; Hostettler, Thomas (May 2007). "National Survey Report on PV Power Applications in Switzerland 2006" (PDF). IEA - PVPS Programme - NSRs for Switzerland. http://www.iea-pvps.org/countries/download/nsr06/06chensr.pdf. Retrieved 2007-12-11. 
  48. ^ Ayoub, Josef; Martel, Sylvain & Dr. Dignard-Bailey, Lisa (May 2007). "National Survey Report of PV Power Applications in Canada 2006" (PDF). IEA - PVPS Programme - NSRs for Canada. http://www.iea-pvps.org/countries/download/nsr06/06cannsr.pdf. Retrieved 2007-10-16. 
  49. ^ Davidson, Sarah (2007-October). "National Survey Report of PV Power Applications in the United Kingdom 2006" (PDF). IEA - PVPS Programme - NSRs for The United Kingdom. http://www.iea-pvps.org/countries/uk/UK_IEA_PVPS_NSR_2006.pdf. Retrieved 2008-03-16. 
  50. ^ a b EurObserv'ER, (Includes Some Discredited/Preliminary Sources) (2007-April). "EurObserv’ER - Photovoltaic Energy Barometer" (PDF). Systèmes Solaires - Le Journal des Énergies Renouvelables n° 178: pp. 49–70. http://www.energies-renouvelables.org/observ-er/stat_baro/observ/baro178.pdf. Retrieved 2007-09-07. 
  51. ^ Bugge, Lars; Salvesen, Fritjof (2007-05-30). "National Survey Report of PV Power Applications in Norway 2006" (PDF). IEA - PVPS Programme - NSRs for Norway. http://www.iea-pvps.org/countries/download/nsr06/06nornsr.pdf. Retrieved 2007-10-20. 
  52. ^ Malm, Ulf; Stolt, Lars (May 2007). "National Survey Report of PV Power Applications in Sweden 2006" (PDF). IEA - PVPS Programme - NSRs for Sweden. http://www.iea-pvps.org/countries/download/nsr06/06swensr.pdf. Retrieved 2007-10-20. 
  53. ^ Ahm, Peter (May 2007). "National Survey Report of PV Power Applications in Denmark 2006 - Version 04" (PDF). IEA - PVPS Programme - NSRs for Denmark. http://www.iea-pvps.org/countries/download/nsr06/06dnknsr.pdf. Retrieved 2007-10-20. 
  54. ^ Dr. Siderer, Yona; Dann, Roxana (May 2007). "National Survey Report of PV Power Applications in Israel 2006 - Version 14" (PDF). IEA - PVPS Programme - NSRs for Israel. http://www.iea-pvps.org/countries/download/nsr06/06isrnsr.pdf. Retrieved 2007-10-20. 
  55. ^ FRB: G.5A Release-- Foreign Exchange Rates, Release Dates
  56. ^ EurObserv'ER, (Includes Some Discredited/Preliminary Sources) (2007-April). "EurObserv’ER - Photovoltaic Energy Barometer" (ASP). Systèmes Solaires - Le Journal des Énergies Renouvelables n° 178: pp. 49–70. http://www.energies-renouvelables.org/observ-er/stat_baro/erec/baro178.asp. Retrieved 2007-09-07.