Environmental Science, 10th Edition (Cunningham)

Chapter 20: Sustainable Energy

GE Exercise: Solar Facility, Barstow, California

<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=jpg::::/sites/dl/free/8888888555/484165/google.jpg','popWin', 'width=210,height=178,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (34.0K)</a>

Take a virtual field trip with Google Earth!
Google Earth is a free, online application that uses satellite imagery to allow the user to zoom across the globe in a realistic, virtual environment. Downloading Google Earth is free at http://www.earth.google.com.

An overview manual is available by clicking here... Google Earth Overview (342.0K)

To continue:
- Make sure you have the Google Earth software installed and running.
- Copy the following latitude and longitude and paste into the "Fly to" field under the Search tab.
- Hit "Enter" for Google Earth to take you to the specified coordinates, then come back here and read the following overview.

Latitude/Longitude: 34.8658, -116.835

Overview: Solar Facility, Barstow, CA, p. 455

This experimental solar facility near Barstow , CA , has three different types of concentrated solar power (CSP) collectors. This site in the California desert captures abundant sunlight year-round and has been used to develop experimental, large-scale solar energy collectors:
  1. The shiny oval structure on the left (west) is a solar pond. This is a relatively low-tech, low-cost approach to harvesting solar energy. The principle is to fill a pond with three layers of water:
    1. A top layer with a low salt content
    2. An intermediate insulating layer with a salt gradient, which sets up a density gradient that prevents heat exchange by natural convection in the water.
    3. A bottom layer with a high salt content which reaches a temperature approaching 90 degrees Celsius

    4. The different densities in the layers due to their salt content prevent convection currents developing, which would normally transfer the heat to the surface and then to the air above. The heat trapped in the salty bottom layer can be used for different purposes, such as heating of buildings, industrial processes, or generating electricity.
  2. The rectangular arrays (bottom right) are parabolic trough systems (see figure 20.11 in the text). The reflective surface of a parabolic trough concentrates sunlight onto a receiver tube located along the trough's focal line, heating the fluid flowing in the tube to as much as 400 degrees C. This heated fluid is then transported through pipes to a steam turbine/generator. The troughs are normally designed to track the sun along one axis, predominantly north-south. Parabolic troughs assembled in collector fields are responsible for almost all commercially produced solar thermal power, with a total installed capacity of more than 350MWe in California , representing over 90% of the world's installed solar capacity.


  3. The concentric circles (top center) are rows of mirrors surrounding a central power tower (also know as a "heliostat" power plant). This design uses many flat, moveable mirrors (called heliostats) to focus the sun's rays upon a collector tower (the target). The high energy at this point of concentrated sunlight is transferred to a substance that can store the heat for later use. That energy can, in turn, be used to boil water for use in steam turbines that generate electricity.
    Solar One, which operated at this site from 1982 to 1988, was the world's largest power tower plant. In this plant, water was converted to steam in the receiver and used directly to power a conventional steam turbine generator. The heliostat field consisted of 1,818 heliostats of 39.3 m reflective area each. The project met most of its technical objectives by demonstrating (1) the feasibility of 2 generating power with a power tower, (2) the ability to generate 10 MW for eight hours a day at summer solstice and four hours a day near winter solstice. During its final year of operation, Solar One's availability during hours of sunshine was 96% and its annual efficiency was about 7%.
    Solar Two—to absorb and store energy effectively, the facility was modified in 1996 to a more advanced molten-salt heat-transfer system. The Solar One heliostat field, the tower, and the turbine/generator required only minimal modifications. The salt storage medium is a mixture of 60% sodium nitrate and 40% potassium nitrate. It melts at 220 o C (428 o F) and is maintained in a molten state (290 o C/554 o F) in the "cold" storage tank. Molten salt can be difficult to handle because it has a low viscosity (similar to water) and it wets metal surfaces extremely well. Consequently, it can be difficult to contain and transport. All tubing, valves, and storage tanks must be made of leak-proof, corrosion-resistant metals. Solar Two has produced 10 MW of electricity with enough thermal storage to continue to operate the turbine at full capacity for three hours after the sun has set.
A more recent heat transfer material that has been successfully demonstrated at other facilities is liquid sodium. Sodium is a metal with a high heat capacity, allowing that energy to be stored and drawn off throughout the evening. It is highly toxic, flammable, explosive, corrosive, and dangerous, however.

1
Why do you suppose this facility was located where it is?
A)Barstow is an extremely progressive, "green" city that enjoys being on the environmental cutting edge.
B)Arnold Schwarzenegger visited there once and made a promise.
C)In a strange twist of fate, the remains of a previous civilization provide the exact rectangular measurements needed for this facility, greatly facilitating its construction as well as reducing costs significantly.
D)The owners wanted access to a relatively less expensive regional labor pool
E)This area of California has a dry, sunny climate.
2
Which of the three solar arrays most closely resembles that on Aero Island from the air?
A)The round solar array that looks like a giant, segmented pond
B)The rectangular solar arrays
C)The arrays of parabolic troughs
D)The giant array disguised to appear like an arid, dry field
3
Describe the placement of the mirrors in Solar Two.
A)The mirrors are arranged in parallel lines.
B)The mirrors are arranged in concentric rings around a central tower.
C)The mirrors are pointed outward, away from the central tower.
D)The mirrors are placed haphazardly, at best.
E)The mirrors are arranged in no particular order whatsoever.
4
Why is the solar pond separated by horizontal dikes into five compartments?
A)Each compartment has its own salinity.
B)Each compartment has its own pH.
C)There are mathematical advantages inherent to this shape and size.
D)Some of the compartments contain toxic waste from solar power production.
E)Separating the solar pond into long, narrow compartments minimizes wind mixing of the water layers.
5
Why might these three different types of solar collectors be placed so close together?
A)They benefit synchronistically from each other's radiant heat.
B)They benefit synergistically from each other's radiant heat.
C)This is a research facility; the different types of collectors are placed close together so their output can be compared more accurately (all are affected equally by cloud cover, air temperature, solar input) as well as to be more convenient for researchers.
D)No other place would allow them to be sited.
E)Decades of research has proven that this is the hottest spot on earth.
Environemental Science Cover
Glencoe Online Learning CenterScience HomeProduct InfoSite MapContact Us

The McGraw-Hill CompaniesGlencoe