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Introduction

The PS10 and PS20 solar power towers together produce a total energy of over 16,000KWh in a day

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

Aerial view of the PS10.
Heliostats are highly reflective and are usually made out of metal and or glass.

In order to concentrate the solar radiation from a large area to a much smaller area, an array of highly reflective heliostats are faced towards 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 way to obtain optimal radiation is to keep the heliostat panels clean and reflective[4].

Power to Energy Conversion

A simple diagram of a solar power tower system.

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 liquid is then circulated through water creating steam from the boiling temperatures???fix. That steam is then utilized to turn turbines in electrical generators to produce the electricity that will then enter the surrounding grid. [5]

thermal fluids are use to vaporize water into steam which turn turbine-generators. drives a steam turbine

Storage

Heat is transferred to a thermal storage medium in an insulated reservoir during the day, and withdrawn for power generation at night. Thermal storage media include pressurized steam, concrete, a variety of phase change materials, and molten salts such as sodium and potassium nitrate.

Steam accumulator The PS10 solar power tower stores heat in tanks as pressurized steam at 50 bar and 285°C. The steam condenses and flashes back to steam, when pressure is lowered. Storage is for one hour. It is suggested that longer storage is possible, but that has not been proven yet in an existing power plant. Molten salt storage A variety of fluids have been tested to transport the sun's heat, including water, air, oil, and sodium, but molten salt was selected as best.

Molten salt is used in solar power tower systems because it is liquid at atmosphere pressure, it provides an efficient, low-cost medium in which to store thermal energy, its operating temperatures are compatible with today's high-pressure and high-temperature steam turbines, and it is non-flammable and nontoxic.

The molten salt is a mixture of 60 percent sodium nitrate and 40 percent potassium nitrate, commonly called saltpeter. The salt melts at 430 °F (220 °C) and is kept liquid at 550 °F (290 °C) in an insulated storage tank.

The uniqueness of this solar system is in de-coupling the collection of solar energy from producing power, electricity can be generated in periods of inclement weather or even at night using the stored thermal energy in the hot salt tank. Normally tanks are well insulated and can store energy for up to a week.

As an example of their size, tanks that provide enough thermal storage to power a 100-megawatt turbine for four hours would be about 30 feet tall and 80 feet in diameter.

Advantages

Provides large amounts of energy energy can be stored for overcast days and night clean energy for commercial use

Disadvantages

need lots of land expensive initial cost

Previous

Solar two.jpg

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, the plant was renovated with 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.

  • Later, in 1995 it was converted into Solar Two, with the addition of a second ring of 108 larger heliostats around the existing Solar One. The total number of heliostats became 1926 on an area of 82,750 m². Solar Two used molten salt, which is a combination of 60% sodium nitrate and 40% potassium nitrate, instead of water.

Current

Planta Solar 10

PS10 solar power tower wikimedia.jpg

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. 115m tower, 250c receiver to turn steam 35 million euro project by albengoa and solucar.[11]




Ps20.jpg


Planta Solar 20

Planta Solar 20 is the new and improved version of the PS10???. This system is also located in Seville, Spain next to the PS10 and was also built by Abengoa. The PS20 consists of 1,255 heliostats each with a surface area of 1202. Improvements to the PS20 include a higher-efficiency receiver, better thermal energy storage, and other operational changes resulting in a 20MW power capacity. [12]

160m tower 10,000 home




Sierra SunTower

Sierra esolar.jpg

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

First solar system to use molten salt to store heat and produce electricity for about 15 hours without sunlight.

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

Ivanpah.jpg

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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