The decommissioned Solar Two near Barstow, CA.

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.

Examples of heliostat power plants

The THEMIS Solar Power tower in the Pyrénées-Orientales, France.

Jülich solar tower power plant

Mersin Solar Plant 5MW Turkey 2013

Cost

The 11MW PS10 near Seville in Spain.

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.^[7] 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.^[8] ESolar's design uses large numbers of small mirrors (1.14m²), which reduce costs for installing mounting systems such as concrete, steel, drilling & 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

• Some Concentrating Solar Power Towers are air-cooled instead of water-cooled, to avoid using limited desert water ^[9]
• Flat glass is used instead of the more expensive curved glass ^[9]
• 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).

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 example of case studies of applying innovative solution to solar power.^[10]

Novel applications

Pit Power Tower concept in Bingham Canyon mine

The Pit Power Tower^[11] combines a Solar Power Tower and an Aero-electric Power Tower^[12] 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

	Energy portal
	Sustainable development portal

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

References

External links

• Cleantech Group picks winners and losers in concentrated solar thermal
• 'CSP' posts in Green Tech
• eSolar's demonstration plant in Lancaster, Calif.
• National Solar Thermal Test Facility
• Detailed Description of Central Receiver Systems
• Power Station Harnesses Sun's Rays BBC article about solar plant near Seville in Spain
• Description of first commercial Solar Power Tower
• vICERP A research cooperation with a demonstration plant in Juelich, Germany
• Solar Tower Plant Juelich Germany's first solar tower power plant in Juelich
• Heliostat fields on Google maps List of solar tower plants and solar furnaces with heliostat field on Google maps
• Zero Carbon Australia Stationery Energy Plan

Institutional links

• CSIRO > Divisions > CSIRO Energy Technology
• ESTELA > Technology > Tower Technology
• Promes Laboratory > Facilities > Solar concentrators > Themis
• PSA > Facilities > Central Receiver
• Sandia National Laboratory > National Solar Thermal Test Facility > Central Receiver Test Facility > Heliostats and tower capabilities
• Weizmann Institute > Environmental Sciences & Energy Research > Research > Energy Research

Commercial links

• Abengoa Solar > Technologies > Concentrating Solar Power > Power Tower
• Aora-Solar
• BrightSource Energy > Technology > How LPT Works
• Desertec > Concept > Technologies
• Device Logic
• eSolar > Our Projects
• Kraftanlagen München > Field of activities > Renewable energies > Solar thermal power plants > Jülich experimental power plant
• Nur Energie > Projects > Tunisia
• SENER > Projects > Gemasolar
• Solar Reserve > Technology
• Torresol Energy > Technologies > Own technologies > Central-tower technology
• Experimental Solar Thermal Power Plant Jülich (Kraftanlagen München) - YouTube