Solar power tower

 
 
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)

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.

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

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](dead link). Companies such as ESolar (backed by Google.org) are continuing development of cheap, low maintenance, mass producible heliostat components that will reduce costs in the near future.[2] ESolar's design uses large numbers of small mirrors (1.14 m²), which reduce costs for installing mounting systems such as concrete, steel, drilling, and cranes.

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

The decommissioned Solar Two in California

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. After adjusting the standby position to not focus all the solar energy into a single point, during the following 6 months of operations, a total of 321 birds were killed.[4] However newly developed technique is available to prevent further bird fatalities.[4]

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.[5]

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.[6]

Examples of heliostat power plants

Power plants Installed
capacity
(MW) 		Yearly
production
(GWh) 		Country Developer/Owner Completed
Ivanpah Solar Power Facility 392 (U/C) 650 United States BrightSource Energy 2013
Crescent Dunes Solar Energy Project 110 (U/C) 500 United States SolarReserve 2015
PS20 solar power tower 20[7] 44 Spain Abengoa 2009
Gemasolar[8] 17 100 Spain Sener 2011
PS10 solar power tower 11[9] 24 Spain Abengoa 2006
Sierra SunTower 5[10] United States eSolar 2009
Jülich Solar Tower 1.5[11][12] Germany 2008
Greenway CSP Mersin Solar Tower Plant 5[13] Turkey Greenway CSP 2013

Novel applications

Pit Power Tower concept in Bingham Canyon mine

The Pit Power Tower[14][15] combines a solar power tower and an aero-electric power tower[16] 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.

See also

References

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