Solar power tower

The solar power tower, also known as 'central tower' power plants or 'heliostat' power plants or power towers, is a type of solar furnace using a tower to receive the focused sunlight. It uses an array of flat, movable mirrors (called heliostats) to focus the sun's rays upon a collector tower (the target). Concentrated solar thermal is seen as one viable solution for renewable, pollution-free energy.

This article is about a particular design of Solar thermal energy using mirrors. For the astronomical instrument and other uses of the term, see solar tower (disambiguation). For other tall structures used for electricity power generation, see Energy tower (disambiguation).
 
 
Concentrating solar power towers:
  • Top: Solar towers of the Ivanpah facility, the world's largest solar thermal power station in the Mojave Desert, southeastern California
  • Middle: PS10, the world's first commercial solar power tower in Andalusia, Spain
  • Bottom: The THEMIS solar power tower in the Eastern Pyrenees, France (left) and the German experimental Jülich tower (right)

Early designs used these focused rays to heat water, and used the resulting steam to power a turbine. Newer designs using liquid sodium have been demonstrated, and systems using molten salts (40% potassium nitrate, 60% sodium nitrate) as the working fluids are now in operation. These working fluids have high heat capacity, which can be used to store the energy before using it to boil water to drive turbines. These designs also allow power to be generated when the sun is not shining.

Cost

In 2017, the US National Renewable Energy Laboratory (NREL) has estimated that by 2020 electricity could be produced from power towers for 5.47 cents per kWh.[1] In 2007, companies such as ESolar (then backed by Google.org) were developing cheap, low maintenance, mass producible heliostat components that were to reduce costs in the near future.[2] ESolar's design used large numbers of small mirrors (1.14 m²), to reduce costs for installing mounting systems such as concrete, steel, drilling, and cranes. In October 2017, an article in GreenTech Media suggested that eSolar ceased business in late 2016.[3]

Improvements in working fluid systems, such as moving from current two tank (hot/cold) designs to single tank thermocline systems with quartzite thermal fillers and oxygen blankets will improve material efficiency and reduce costs further.

Design
Ashalim Power Station, Israel, on its completion the tallest solar tower in the world.
The decommissioned Solar Two in California
  • Some concentrating solar power towers are air-cooled instead of water-cooled, to avoid using limited desert water[4]
  • Flat glass is used instead of the more expensive curved glass[4]
  • Thermal storage to store the heat in molten salt containers to continue producing electricity while the sun is not shining
  • Steam is heated to 500 °C to drive turbines that are coupled to generators which produce electricity
  • Control systems to supervise and control all the plant activity including the heliostat array positions, alarms, other data acquisition and communication.

Generally, installations use from 150 hectares (1,500,000 m2) to 320 hectares (3,200,000 m2).

Environmental concerns

There is evidence that such large area solar concentrating installations can kill birds that fly over them. Near the center of the array temperatures can reach 550 oC which, with the solar flux itself, is enough to incinerate birds while further away feathers are scorched leading to the eventual death of the bird. Workers at the Ivanpah solar power plant call these birds “streamers,” as they ignite in midair and plummet to the ground trailing smoke. During testing of the initial standby position for the heliostats, 115 birds were killed as they entered the concentrated solar flux. During the first 6 months of operations, a total of 321 birds were killed. After altering the standby procedure to focus no more than four heliostats on any one point, there have been no further bird fatalities.[5]

The Ivanpah Solar Power Facility is classified as a greenhouse gas emitter by the State of California because it has to burn fossil fuel for several hours each morning so that it can quickly reach its operating temperature.[6]

Commercial applications

Recently, there has been a renewed interest in solar tower power technology, as is evident from the fact that there are several companies involved in planning, designing and building utility size power plants. This is an important step towards the ultimate goal of developing commercially viable plants. There are numerous examples of case studies of applying innovative solutions to solar power.[7] Beam down tower application is also feasible with heliostats to heat the working fluid.[8]

Novel applications
Pit Power Tower concept in Bingham Canyon mine

The Pit Power Tower[9][10] combines a solar power tower and an aero-electric power tower[11] in a decommissioned open pit mine. Traditional solar power towers are constrained in size by the height of the tower and closer heliostats blocking the line of sight of outer heliostats to the receiver. The use of the pit mine's "stadium seating" helps overcome the blocking constraint.

As solar power towers commonly use steam to drive the turbines, and water tends to be scarce in regions with high solar energy, another advantage of open pits is that they tend to collect water, having been dug below the water table. The Pit Power Tower uses low heat steam to drive the pneumatic tubes in a co-generation system. A third benefit of re-purposing a pit mine for this kind of project is the possibility of reusing mine infrastructure such as roads, buildings and electricity.

Solar power towers

List of solar power towers
NameDeveloper/OwnerCompletedCountryTownHeight mHeight ftCollectorsInstalled maximum
capacity
*(MW)		Yearly total energy
production
(GWh)
Mohammed bin Rashid Al Maktoum Solar Park ACWA Power 2020 United Arab Emirates Seih Al-Dahal, Dubai 262 m 860 ft
Ashalim Power Station Megalim Solar Power 2018 Isreal Negev Desert 260 m 853 ft 50,600 121 MW 320
Ouarzazate Solar Power Station Moroccan Agency for Sustainable Energy 2009 Morocco Ouarzazate 250 m 820 ft 7,400 150 MW 500
Shouhang Dunhuang 100 MW Phase II[12] Beijing Shouhang IHW 2018 China Dunhuang 220 m 722 ft 12,000 100 MW 390[13]
Qinghai Gonghe CSP[14] 2019 China Gonghe 210 m 689 ft 50 MW 156.9
Khi Solar One Abengoa 2016 South Africa Upington 205 m 673 ft 4,120 50 MW 180
Crescent Dunes Solar Energy Project SolarReserve 2016 United States Tonopah 200 m 656 ft 10,347 110 MW 500
Supcon Solar Delingha[15] Supcon Solar 2016 China Delingha 200 m 656 ft 50 MW 146
Haixi 50 MW CSP Project[16] Luneng Qinghai Guangheng New Energy 2019 China Haixi Zhou 188 m 617 ft 4,400 50 MW
Hami 50 MW CSP Project[17][18] Supcon Solar 2019 China Hami 180 m 590 ft 50 MW
PS20 solar power plant Abengoa Solar 2009 Spain Sanlúcar la Mayor 165 m 541 ft 1,255 20 MW 48
Gemasolar Thermosolar Plant Torresol Energy 2011 Spain Sevilla 140 m 460 ft 2,650 19.9 MW 80
Ivanpah Solar Power Facility (3 towers) BrightSource Energy 2014 United States Mojave Desert 139.9 m 459 ft 173,500 392 MW 650
Shouhang Dunhuang 10 MW Phase I[19] 2018 China Dunhuang 138 m 453 ft 1,525[20] 10 MW
Sundrop Farms Aalborg CSP 2016 Australia Port Augusta 127 m 417 ft 23,712[21] 1.5 MW
PS10 solar power plant Abengoa Solar 2007 Spain Sanlúcar la Mayor 115 m 377 ft 624 11 MW 23.4
The Solar Project U.S. Department of Energy 1981 United States Mojave Desert 100 m 328 ft 1,818 later 1,926 7 MW, later 10 MW na, demolished
Supcon Solar Delingha 10MW[22] (2 towers) Supcon Solar 2013 China Delingha 100 m 328 ft 10 MW
National Solar Thermal Test Facility U.S. Department of Energy 1978 United States Mojave Desert 60 m 200 ft 1 MW (5-6 MWt) na, demonstrator
Jülich Solar Tower German Aerospace Center 2008 Germany Jülich 60 m 200 ft 2000 1.5 MW na, demonstrator
Greenway CSP Mersin Solar Tower Plant Greenway CSP 2013 Turkey Mersin 60 m 200 ft 510 1 MW (5 MWt)
ACME Solar Tower[23] ACME Group 2011 India Bikaner 46 m 150 ft 14,280 2.5 MW
Sierra SunTower (2 towers) eSolar 2010 United States Mojave Desert 46 m 150 ft[24] 24,000 5 MW na, demolished
Jemalong Solar Thermal Station[25] 2017 Australia Jemalong 27 m 89 ft 3,500 1.1 MW (6 MWt)

See also

References
  1. John Lowry (2017). Avoiding Carbon Apocalypse Through Alternative Energy: Life After Fossil Fuels. Springer. p. 33.
  2. Google's Goal: Renewable Energy Cheaper than Coal November 27, 2007
  3. Deign, Jason (12 October 2017). "Concentrated Solar Power Contender ESolar Goes AWOL". GreenTech Media. Retrieved 13 June 2019.
  4. "FAQs". Brightsourceenergy.com. Retrieved 2019-09-28.
  5. Kraemer, Susan (16 April 2015). "One Weird Trick Prevents Bird Deaths At Solar Towers". Clean Technica. Retrieved 20 February 2017.
  6. Danelski, David (21 October 2015). "It's not easy being green: Ivanpah solar plant near Nevada burns much natural gas, making it a greenhouse gas emitter under state law". Orange County Register. Santa Ana, California. Retrieved 14 September 2016.
  7. SOLAR POWER IN THE NEWS
  8. "Three solar modules of world's first commercial beam-down tower Concentrated Solar Power project to be connected to grid". Retrieved 18 August 2019.
  9. Pit Power Tower - Alternative Energy News Feb 2009
  10. Pit Power Tower US Patent
  11. Energy tower
  12. https://www.sh-ihw.es/dunhuang100
  13. https://solarpaces.nrel.gov/shouhang-dunhuang-100-mw-phase-ii
  14. http://www.supconsolar.com/en/cases/detail/id/12.html
  15. http://www.supconsolar.com/en/cases/detail/id/11.html
  16. https://solarpaces.nrel.gov/luneng-haixi-50mw-molten-salt-tower
  17. http://helioscsp.com/cpecc-hami-tower-concentrated-solar-power-project-to-be-completed-in-mid-2019/
  18. https://solarpaces.nrel.gov/hami-50-mw-csp-project
  19. https://solarpaces.nrel.gov/shouhang-dunhuang-10-mw-phase-i
  20. https://www.solarpaces.org/shouhang-and-edf-first-to-test-s-co2-cycle-in-concentrated-solar-power/
  21. https://solarpaces.nrel.gov/sundrop-csp-project
  22. http://www.supconsolar.com/en/cases/detail/id/10.html
  23. https://solarpaces.nrel.gov/acme-solar-tower
  24. https://www.pv-tech.org/editors-blog/esolar_sierra_suntower_project_offline_-_clarified
  25. https://vastsolar.com/portfolio-items/jemalong-solar-station-pilot-1-1mwe/
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