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Introduction

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A solar power tower is a type of indirect solar power technology. Solar power is electricity produced from the radiation of the sun. The energy of the sun can be captured and converted into power directly with Photovoltaic solar panels (PV) or indirectly by solar thermal conversion using Concentrated solar power (CSP) technology. [1] CSP technology uses thermal energy from the sun to heat a liquid, such as water or molten salt. This heat transferring liquid is used to vaporize water to the point of steam, which is then used to generate electricity in a traditional turbine-generator. Power plants using CSP technology include parabolic trough, parabolic dish and solar power tower systems. [2]

Background

Energy Collection

The PS10 Solar power plant
Heliostats

In order to concentrate the solar radiation from a very large area to a much smaller panel, an array of highly reflective heliostats reflect the sunlight to the thermal heat receiver or receivers located on the top of the tower. The arrangement of heliostats may vary between crescent shaped or radial arrays depending on how many receivers there are on a tower and where they are located[3]. In order for the receiver to collect full sun, 1000W/m2, they are programmed to follow the movement of the sun. Another important factor to obtain optimal radiation is to keep the heliostat panels clean and reflective[4].

Power to Energy Conversion

thumb Power Tower System Diagram

The thermal heat collected from the receiver can get up to temperatures of about is used to heat molten salt to exceedingly high temperatures of nearly 300°C. This thermal liquid is then circulated through water via pipes which then creates steam. That steam is used to turn turbines in electrical generators to produce the electricity that will then enter the surrounding grid. [5]

Storage

One of the most challenging issues with any form of renewable energy is energy storage. With a solar powered system for example, once the sun goes down you have no more electricity production. However if you have a thermal storage medium such as molten salt, heat can be stored for hours after the sun goes down. At the moment the PS10 solar power tower plant stores heat in tanks as steam, which only gives a storage time of about an hour. Future projects such as the Solar Tres power tower in Andalusia, Spain, are now storing heat in storage tanks of molten salts such as sodium and potassium nitrate. A variety of fluids have been tested for the transport and storage of the sun's heat, including water, air, oil, and sodium, but molten salt was determined the most efficient. Molten salt is usually made up of 60% sodium nitrate and 40% potassium nitrate which may also be referred to as saltpeter. This salt has a melting point of 220 °C or 430 °F and is kept liquid at 290 °C or 550 °F. Molten salt is an ideal material for storage in solar power tower systems because it is efficient and inexpensive. The benefit of having this kind of long term heat storage system is that even with an intermittent renewable energy like solar, you can constantly be providing power to the grid.

Advantages

  • Provides large amounts of electricity daily
  • Power can constantly be produced and provided to the grid
  • Clean energy for commercial use

Disadvantages

  • Takes up a lot of land
  • Solar technology is still very expensive
  • Daily Maintenance

Previous

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Solar One

The first CSP tower plant was the Solar One with a power capacity of 10MW.[6] The plant was located in the Mojave Desert, California near the town of Barstow.[7] The purpose of this solar power project was to show the potential of a large scale solar power tower plant. Solar one successfully produced over 38 million KWh of electricity in the 6 years it was operational in 1982-1988.[8]



Solar Two

After Solar One ceased operation, in 1995 the plant was renovated and reopened utilizing new technology to increase the efficiency of its' storage system[9]. Thus the Solar Two was born. The Solar Two plant utilized a molten-salt energy storage system that is still used for current solar power tower projects[10]. The Solar One and Two demonstration plants were very successful in encouraging countries all over the world to pursue and improve the technology of solar power tower plants.



Current

Planta Solar 10

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Planta Solar 10 is the first CSP system producing grid-connected power for commercial use. The PS10 was completed in 2008 and manufactured by Abengoa. The system uses 624- 120m2 glass metal heliostats over a 75,000m2 with a net turbine capacity of 11MW. With this 11MW, the PS10 is able to generate enough energy to power about 5,500 households a day. 115m tower, 250c receiver to turn steam 35 million euro project by albengoa and solucar.[11]





Planta Solar 20

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Planta Solar 20 is the sister plant to the PS10 with technological advancements. This system utilizes a more efficient solar receiver on the tower and molten salt storage. The PS20 has a power capacity of 20MW and is able to power over 10,000 households a day. The field holds 1,255 heliostats, each with a surface area of 1202, the same as the PS10. [12]




Sierra SunTower

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The Sierra SunTower project is a solar power tower operating in Lancaster, CA. This is the only operating plant in North America and occupies around 20 acres or 80,000m2 in the Mojave Desert [13] . This system consists of 24,360- 1.136m2 heliostats, giving a net power capacity of 5.0 MW [14]. Sierra was completed in 2009 by eSolar and is selling their electricity to Southern California Edison. [15]





Future

Gemasolar

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17MW 2011 Fuentes de Andalucia, Seville for villanueva del rey or andalusia, spain Central tower and heliostat tech Molten salt storage system, temps of 500 degree celsius in the storage tank gives about 15 hours of extra electricity generation = 6,500 hours a year of energy prod do math??? 2,500 helio's on 185 hectares=1.85 km2 110 GWh/year receiver 95% of solar radiation 25,000 homes of energy

Solar Tres

2493- 96m2 glass-metal heliostats Storage of 6,250 T of molten nitrate salt so 16 hours, 600 MWH Solar Tres, which is located in the city of Écija, in Andalusia, Spain and received a subsidy of five million Euro from the European Commission, follows the Solar Two in using molten salt but is designed to be three times of it in size.

Ivanpah

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BLM and CEC Release Draft EIS for the 400-MW Ivanpah Solar Project [16]

Further Reading

Miyares, Dave. "Concentrated Solar Power Projects Receive $62 million From DOE". Solar Power Engineering. June 12, 2010 [17]

U.S. Department of Energy: Energy Efficiency and Renewable Energy News [18]

References

  1. Robles, Pedro. "Power Tower". Abengoa. June 12, 2010 [1]
  2. Richter, Dr. Cristoph. "CSP- Technology". SolarPACES. June 12, 2010. [2]
  3. Arvizu, Dan. "Concentrating Solar Power". National Renewable Energy Laboratory. June 12, 2010 [3]
  4. Arvizu, Dan. "Concentrating Solar Power". National Renewable Energy Laboratory. June 12, 2010 [4]
  5. Robles, Pedro. "Power Tower". Abengoa. June 12, 2010. [5]
  6. Robles, Pedro. "Power Tower". Abengoa. June 12, 2010 [6]
  7. Robles, Pedro. "Power Tower". Abengoa. June 12, 2010 [7]
  8. U.S. DOE. "Solar Power Towers Deliver Energy Solutions." Waste Isolation Pilot Plant. June 12, 2010. [8]
  9. U.S. DOE. "Solar Power Towers Deliver Energy Solutions." Waste Isolation Pilot Plant. June 12, 2010. [9]
  10. U.S. DOE. "Solar Power Towers Deliver Energy Solutions." Waste Isolation Pilot Plant. June 12, 2010. [10]
  11. Robles, Pedro. "PS10: The first commercial tower of the world". Abengoa Solar. June 12, 2010. [11]
  12. Robles, Pedro. "PS20 Tower". Abengoa Solar. June 12, 2010. [12]
  13. Arvizu, Dan. "Concentrating Solar Power Projects". National Renewable Energy Laboratory. June 12, 2010 [13]
  14. Arvizu, Dan. "Concentrating Solar Power Projects". National Renewable Energy Laboratory. June 12, 2010 [14]
  15. Arvizu, Dan. "Concentrating Solar Power Projects". National Renewable Energy Laboratory. June 12, 2010 [15]
  16. Energy Efficiency and Renewable Energy Network News. "BLM and CEC Release Draft EIS for the 400-MW Ivanpah Solar Project". June 12, 2010. [16]
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