Solar power tower

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).

A solar power tower, also known as 'central tower' power plant or 'heliostat' power plant, is a type of solar furnace using a tower to receive focused sunlight. It uses an array of flat, movable mirrors (called heliostats) to focus the sun's rays upon a collector tower (the target). Concentrating Solar Power (CSP) systems are seen as one viable solution for renewable, pollution-free energy.^[1]

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 (left) and Ashalim Power Station in Negev, Israel (right)
• 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. Storing the heat energy for later recovery allows power to be generated continuously, while the sun is shining, and for several hours after the sun has set (or been clouded over).

Cost

In 2021, the US National Renewable Energy Laboratory (NREL) estimated the cost of electricity from concentrated solar with 10 hours of storage at $0.076 per kWh in 2021, $0.056 per kWh in 2030, and $0.052 per kWh in 2050.^[2] 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.^[3] 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.^[4]

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 (CSP) towers are air-cooled instead of water-cooled, to avoid using limited desert water^[5]
• Flat glass is used instead of the more expensive curved glass^[5]
• 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 (932 °F) 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).

In 2023, Australia's national science agency CSIRO tested a CSP arrangement in which tiny ceramic particles fall through the beam of concentrated solar energy, the ceramic particles capable of storing a greater amount of heat than molten salt, while not requiring a container that would diminish heat transfer.^[6]

Environmental concerns

There is evidence that such large area solar concentrating installations can burn birds that fly over them. Near the center of the array, temperatures can reach 550 °C (1,022 °F) which, with the solar flux itself, is enough to incinerate birds. More distant birds' feathers can be scorched, leading to the eventual death of the bird. Ivanpah reported one bird scorching in every two minutes. 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.^[7]

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.^[8]

Commercial applications

Several companies have been involved in planning, designing, and building utility size power plants. There are numerous examples of case studies of applying innovative solutions to solar power. Beam-down (a variation of central receiver plants with Cassegrainian optics^[9])^{[clarification needed]} tower application is also feasible with heliostats to heat the working fluid.^[10]

Novel applications

Pit Power Tower concept in Bingham Canyon mine

The Pit Power Tower^[11][12] combines a solar power tower and an aero-electric power tower^[13] 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

Name	Developer/Owner	Completed	Country	Town	Height m	Height ft	Collectors	Installed maximum capacity *(MW)	Yearly total energy production (GWh)
Dawn[14]	Synhelion	2024	Germany	Jülich	20 m	65.6 ft
Noor Energy 1	ACWA Power	2022	United Arab Emirates	Saih Al-Dahal, Dubai	262.44 m	861 ft
Ashalim Power Station	Megalim Solar Power	2019	Israel	Negev Desert	260 m	853 ft	50,600	121 MW	320
Ouarzazate Solar Power Station	Moroccan Agency for Sustainable Energy	2019	Morocco	Ouarzazate	250 m	820 ft	7,400	150 MW	500
Cerro Dominador Solar Thermal Plant[15]	Acciona (51%) and Abengoa (49%)	2021	Chile	Calama	250 m	820 ft	10,600	110 MW
Redstone Solar Thermal Power	ACWA Power	2023	South Africa	Postmasburg, Northern Cape Province				100 MW[16]
Shouhang Dunhuang 100 MW Phase II[17]	Beijing Shouhang IHW	2018	China	Dunhuang	220 m	722 ft	12,000	100 MW	390[18]
Qinghai Gonghe CSP[19]		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[20]	Supcon Solar	2016	China	Delingha	200 m	656 ft		50 MW	146
Haixi 50 MW CSP Project[21]	Luneng Qinghai Guangheng New Energy	2019	China	Haixi Zhou	188 m	617 ft	4,400	50 MW
Hami 50 MW CSP Project[22][23]	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[24]		2018	China	Dunhuang	138 m	453 ft	1,525[25]	10 MW
Sundrop Farms	Aalborg CSP	2016	Australia	Port Augusta	127 m	417 ft	23,712[26]	1.5 MW
Dahan Power Plant[27]	Institute of Electrical Engineering of Chinese Academy of Sciences	2012	China	Dahan	118 m	387 ft	100	1 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[28] (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	Albuquerque, New Mexico	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	Greenway CSP	2013	Turkey	Mersin	60 m	200 ft	510	1 MW (5 MWt)
ACME Solar Tower[29]	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[30]	24,000	5 MW	na, demolished
Jemalong CSP Pilot Plant[31]		2017	Australia	Jemalong	5x 27 m	5x 89 ft	3,500	1.1 MW (6 MWt)

See also

• Concentrated solar power
• Particle receiver
• Feed-in tariff
• List of concentrating solar thermal power companies
• List of solar thermal power stations
• National Solar Thermal Test Facility (NSTTF)
• Solar furnace
• Solar thermal energy