DIRECT UTILIZATION OF SOLAR ENERGY by kajahussain

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									                       DIRECT UTILIZATION OF SOLAR ENERGY




                                           CHAPTER-1
                                   THE SOLAR RESOURCE


                  Solar energy—power from the sun—is free and inexhaustible. This vast,
clean energy resource represents a viable alternative to the fossil fuels that currently
pollute our air and water, threaten our public health, and contribute to global warming.
Failing to take advantage of such a widely available and low-impact resource would be a
grave injustice to our children and all future generations.
                  The aim of this work is to create an awareness among the students about
the abundant renewable energy(mainly solar energy) available and about the methods by
which this energy can be effectively utilized.
                  In the broadest sense, solar energy supports all life on Earth and is
the basis for almost every form of energy we use. The sun makes plants grow, which can
be burned as “biomass” fuel or, if left to rot in swamps and compressed underground for
millions of years, in the form of coal and oil. Heat from the sun causes temperature
differences between areas, producing wind that can power turbines. Water evaporates
because of the sun, falls on high elevations, and rushes down to the sea, spinning
hydroelectric turbines as it passes. But solar energy usually refers to ways the sun’s
energy      can      be     used      to    directly    generate      heat     and        lighting.
                  The amount of energy from the sun that falls on Earth’s surface is
enormous. All the energy stored in Earth's reserves of coal, oil, and natural gas is
matched by the energy from just 20 days of sunshine. Outside Earth's atmosphere, the
sun's energy contains about 1,300 watts per square meter. About one-third of this light is
reflected back into space, and some is absorbed by the atmosphere (in part causing winds
to blow). By the time it reaches Earth's surface, the energy in sunlight has fallen to about
1,000 watts per square meter at noon on a cloudless day. Averaged over the entire surface
of the planet, 24 hours per day for a year, each square meter collects the approximate
energy equivalent of almost a barrel of oil each year, or 4.2 kilowatt-hours of energy.
every day




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               Our campus is 30 acres(121405.68 square meter) of land. So the sunlight
falling on our campus per day is approximately equivalent to 509.903 mega-watts of
energy.
               The present situation of power crisis can be overcome by depending on
renewable energies like solar energy, which finds a range of applications on various
fields. India must take serious steps for adopting technologies in the renewable energy
field so as to meet the increasing power demands in future.




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                                     CHAPTER –2
              NATURAL TRANSFORMATION OF SOLAR ENERGY


               Natural collection of solar energy occurs in the Earth’s atmosphere,
oceans, and plant life. Interactions between the Sun’s energy, the oceans, and the
atmosphere, for example, produce the winds, which have been used for centuries to turn
windmills. Modern applications of wind energy use strong, light, weather-resistant,
aerodynamically designed wind turbines that, when attached to generators, produce
electricity for local, specialized use or as part of a community or regional network of
electric power distribution.
               Approximately 30 per cent of the solar energy reaching the outer edge of
the atmosphere is consumed in the hydrological cycle, which produces rainfall and the
potential energy of water in mountain streams and rivers. The power produced by these
flowing waters as they pass through modern turbines is called hydroelectric power.
               Through the process of photosynthesis, solar energy contributes to the
growth of plant life (biomass) that can be used as fuel, including wood and the fossil
fuels that are derived from geologically ancient plant life. Fuels such as alcohol or
methane can also be extracted from biomass.
               The oceans also represent a form of natural collection of solar energy. As
a result of the absorption of solar energy in the ocean and ocean currents, temperature
gradients occur in the ocean. In some locations, these vertical variations approach 20° C
(36° F) over a distance of a few hundred metres. When large masses exist at different
temperatures, thermodynamic principles predict that a power-generating cycle can be
created to remove energy from the high-temperature mass and transfer a lesser amount of
energy to a low-temperature mass. The difference in these two heat energies manifests
itself as mechanical energy (for example, output from a turbine), which can be linked
with a generator to produce electricity. Such systems, called ocean thermal energy
conversion (OTEC) systems, require enormous heat exchangers and other hardware in the
ocean to produce electricity in the MW range.




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2.1 Direct collection of solar energy
   2.1.1 Passive Solar Systems
   2.1.2 Solar Heat Collectors
   2.1.3 Thermal Concentrating Systems


These methods are discussed in detail in the following chapters.




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                                       CHAPTER-3
                                 PASSIVE SOLAR SYSTEMS


               Passive solar energy systems involve designing the structures themselves
 in ways that use solar energy for heating and cooling. Passive solar systems capture and
 use solar energy without the aid of mechanical or electrical devices.
               One simple, obvious use of sunlight is to light our buildings. If properly
designed, buildings can capture the sun's heat in the winter and minimize it in the
summer, while using daylight year-round. Buildings designed in such a way are utilizing
passive solar energy—a resource that can be tapped without mechanical means to help
heat, cool, or light a building. South-facing windows, skylights, awnings, and shade trees
are all techniques for exploiting passive solar energy. Buildings constructed with the sun
in mind can be comfortable and beautiful places to live and work.
3.1 Direct Gain Passive Solar Design Techniques
               Passive solar design strategies vary by building location and regional
climate, but the basic techniques remain the same-maximize solar heat gain in winter and
minimize it in summer.
Specific techniques include:
• Start by using energy-efficient design strategies.
• Orient the house with the long axis running east/west.
• Select, orient, and size glass to optimize winter heat gain and minimize summer heat
gain for the specific climate.
• Consider selecting different glazings for different sides of the house (exposures).
• Size south-facing overhangs to shade windows in summer and allow solar gain in
 winter.
• Add thermal mass in walls or floors for heat storage.
• Use natural ventilation to reduce or eliminate cooling needs.
• Use daylight to provide natural lighting.


These techniques are described in more detail :


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3.1.1 Cutting Losses: A passive solar home should start out well sealed and well
insulated. By reducing heat loss and gain, remaining energy loads can be effectively met
with passive solar techniques. Approaches that contribute to minimizing heating and
cooling loads include using advanced framing guidelines , properly installing insulation,
using recommended insulation levels (International Code Council’s International Energy
Conservation Code, (703) 931-4533, or the U.S. Department of Energy’s Insulation Fact
Sheet,DOE/CE-0180, (800) DOE-EREC),reducing duct losses, and tightening the
building envelope.
3.1.2 Site Orientation: The building’s southern exposure must be clear of large obstacles
(e.g., tall buildings, tall trees) that block the sunlight. Although a true southern exposure
is optimal to maximize solar contribution, it is neither mandatory nor always possible.
Provided the building faces within 30° of due south, south-facing glazing will receive
about 90 percent of the optimal winter solar heat gain.
3.1.3 Window Selection: Heating with solar energy is easy: just let the sun shine in
through the windows. The natural properties of glass lets sunlight through but trap long-
wave heat radiation, keeping the house warm (the greenhouse effect). The challenge often
is to properly size the south-facing glass to balance heat gain and heat loss properties
without overheating. Increasing the glass area can increase building energy loss. New
window technologies, including selective coatings, have lessened such concerns by
increasing window insulation properties to help keep heat where it is needed.
In heating climates, reduce the window area on north-, east-, and west-facing walls, while
still allowing for adequate daylight.
3.1.4 Shading: The summer sun rises higher overhead than the winter sun. Properly sized
window overhangs or awnings are an effective option to optimize southerly solar heat
gain and shading. They shade windows from the summer sun and, in the winter when the
sun is lower in the sky, permit sunlight top as through the window to warm the interior.
Landscaping helps shade south-, east-, or west-facing windows from summer heat gain.
Mature deciduous trees permit most winter sunlight (60 percent or more) to pass through
while providing dappled shade throughout summer.
3.1.5 Heat Storage: Thermal mass, or materials used to store heat, is an integral part of
most passive solar design. Materials such as concrete, masonry, wallboard, and even


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water absorb heat during sunlit days and slowly release it as temperatures drop. This
dampens the effects of outside air temperature changes and moderates indoor
temperatures. Although even overcast skies provide solar heating, long periods of little
sunshine often require a back-up heat source. Optimum mass-to-glass ratios, depending
on climate, may be used to prevent overheating and minimize energy consumption (The
Sun’s     Joules,http://solstice.crest.org/renewables/SJ/passive-solar/136.html).      Avoid
coverings such as carpet that inhibit thermal mass absorption and transfer.
3.1.6 Natural Cooling: Apt use of outdoor air often can cool a home without need for
mechanical cooling, especially when effective shading, insulation, window selection, and
other means already reduce the cooling load. In many climates, opening windows at night
to flush the house with cooler outdoor air and then closing windows and shades by day
can greatly reduce the need for supplemental cooling. Cross-ventilation techniques
capture cooling, flow-through breezes. Exhausting naturally rising warmer air through
upper-level openings (stack effect; e.g., clerestory windows) or fans (e.g., whole-house
fan) encourages lower-level openings to admit cooler, refreshing, replacement air.
3.1.7 Natural Lighting: Sometimes called day lighting, natural lighting refers to reliance
on sunlight for daytime interior lighting. Glazing characteristics include high-VT glazing
on the east, west, and north facades combined with large, south-facing window areas. A
day lit room requires, as a general rule, at least5 percent of the room floor area in glazing.
Low-emissivity (low-E) coatings can help minimize glare while offering appropriate
improved climatic heat gain or loss characteristics. Sloped or horizontal glass (e.g.,
skylights) admit light but are often problematic because of unwanted seasonal
overheating, radiant heat loss, and assorted other problems.

               Solar design, better insulation, and more efficient appliances could reduce
this demand by 60 to 80 percent. Simple design features such as properly orienting a
house toward the south, putting most windows on the south side of the building, and
taking advantage of cooling breezes in the summer are inexpensive yet improve the
comfort and efficiency of a home. In India some people are not yet aware of these simple
techniques that helps them to save power.




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3.2 Five elements of passive solar design




Here are the five elements that constitute a complete passive solar design, using a direct
gain design as an example. Each performs a separate function, but all five must work
together for the system to be successful.
Aperture (collector) -- the large glass window.
Absorber             -- masonry wall, floor.
Thermal mass         -- wall, floor
Distribution          -- conduction, convection, radiation
Control               -- roof overhangs


               So it is clear that by making small modifications in the building design, as
discussed above, the energy consumption (mainly electrical energy) can be reduced to
large extend. The other two methods for direct collection of solar energy are discussed in
the following chapters.




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                                       CHAPTER-4
                               SOLAR HEAT COLLECTORS

                Besides using design features to maximize their use of the sun, some
buildings have systems that actively gather and store solar energy. Solar collectors, for
example, sit on the rooftops of buildings to collect solar energy for space heating, water
heating (Fig 4.1), and space cooling. Most are large, flat boxes painted black on the
inside and covered with glass. In the most common design, pipes in the box carry liquids
that transfer the heat from the box into the building. This heated liquid—usually a water-
alcohol mixture to prevent freezing—is used to heat water in a tank or is passed through
radiators that heat the air.
                Oddly enough, solar heat can also power a cooling system. In desiccant
evaporators, heat from a solar collector is used to pull moisture out of the air. When the
air becomes drier, it also becomes cooler. The hot moist air is separated from the cooler
air and vented to the outside. Another approach is an absorption chiller. Solar energy is
used to heat a refrigerant under pressure; when the pressure is released, it expands,
cooling the air around it. This is how conventional refrigerators and air conditioners
work, and it’s a particularly efficient approach for home or office cooling since buildings
need cooling during the hottest part of the day. These systems are currently at work in
humid southeastern climates such as Florida.

                Solar collectors were quite popular in the early 1980s, in the aftermath of
the energy crisis. Federal tax credits for residential solar collectors also helped. In 1984,
for example, 16 million square feet of collectors were sold in the United States, but when
fossil fuel prices dropped and tax credits expired in the mid-1980s, demand for solar
collectors plummeted. By 1987, sales were down to only four million square feet. Most
of the more than one million solar collectors sold in the 1980s were used for heating hot
tubs and swimming pools.

                The number of Indians choosing solar hot water could rise dramatically in
the next few years. With Liquified Petroleum Gas (LPG) prices at historically high levels,
solar water and space heaters have become much more economic. According to the

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Indian Renewable Energy Development Agency (IREDA), water heating accounts for
about 15 percent of the average household’s energy use. As LPG and electricity prices
continue to rise, the costs of maintaining a constant hot water supply will increase as
well. Homes and businesses that heat their water through solar collectors could end up
saving as much as Rs.5000 to Rs.10000 per year depending on the type of system being
replaced.

       .




                             Fig4.1 (Solar Water Heater)




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                                         CHAPTER-5
                 SOLAR THERMAL CONCENTRATING SYSTEMS


                By using mirrors and lenses to concentrate the rays of the sun, solar
thermal systems can produce very high temperatures—as high as 3,000 degrees Celsius.
This intense heat can be used in industrial applications or to produce electricity. Solar
concentrators come in three main designs: parabolic troughs, parabolic dishes, and central
receivers.
5.1 Parabolic Troughs
                Long, curved mirrors that concentrate sunlight on a liquid inside a tube
that runs parallel to the mirror. Parabolic troughs are the only commercially available
solar concentrator that can be used to deliver high temperature thermal energy. Industrial
Solar Technology is one of the few companies in the world that manufactures parabolic
trough concentrators.
                Parabolic troughs are the most utilitarian of solar collectors in terms of the
markets they can serve. IST troughs can deliver heat at temperatures ranging from 40 C-
300 C for applications such as hot water, space heating, air-conditioning, steam
generation, industrial process heating,
desalination and power generation.
It is a principle of geometry that a
parabolic reflector pointed at the sun will
reflect parallel rays of light to the focal
point of the parabola. A parabolic trough
is a one-dimensional parabola that
focuses solar energy onto a line.
Physically, this line is a pipe with a
flowing liquid inside that absorbs the
                                                           Fig: 5.1
heat transmitted through the pipe wall and delivers it to the thermal load. A trough
captures sunlight over a large aperture area and concentrates this energy onto a much
small receiver area, multiplying the intensity of the sun by a concentration ratio in the


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range of 30-80. It is the process of concentration that allows troughs to delivery high
temperature thermal energy. However, to achieve such concentration, a trough tracks the
sun in one axis continually throughout the day. The required tracking accuracy is within a
fraction of a degree.
               Establishing the concentration ratio is the major tradeoff in designing a
trough concentrator. The goal is to balance the interception of solar energy at the receiver
against heat losses from the receiver. The larger the absorber diameter the greater the heat
loss from the absorber area. However, the absorber must be large enough to intercept
most of the sunlight reflected from the mirror. This intercept is affected by factors such as
the accuracy of the parabola, the size of the solar disk (the sun is not a point source), the
quality of the reflector, the accuracy of collector tracking and location of the receiver
with respect to the true focal point. IST's contribution to the development of parabolic
trough concentrators is a patented design concept by which a concentrator that is
accurate, lightweight and strong enough to survive in the outdoor environment can be
built at a reasonable cost. To maximize the sunlight incident on the absorber, the
reflectance of the parabolic reflector must be as high as possible. Aluminum or silver
reflectors are used. Silver has the higher reflectance, but is harder to protect against the
corrosive effects of the outdoor environment. It is also important to keep the reflectors
clean since dirt will degrade the reflectance of light from the parabola.
               The receiver of a trough concentrator is typically a metal absorber
surrounded by a glass tube. The absorber is coated with a selective surface. This is a
surface that has a high absorptance for incoming light in the visible range, and a low
emittance (or radiative loss) in the infrared wavelength. The surrounding glass insulates
the pipe from the effects of the wind and greatly reduces convective and conductive heat
loss. The gap between the absorber tube and the inside of the glass is sized to minimize
heat loss across the air gap. Glass is also a radiation barrier to infrared light so it reduces
heat loss due to radiation. Since the light from the parabola must first pass through the
glass before it hits the absorber, the glass is a source of optical inefficiency since some
light is reflected from the inside and outside glass/air surfaces, and absorbed in the glass
itself. IST reduces the negative effect of the glass tube by coating it with an anti-
reflective surface to minimize optical losses due to reflectance. Taking all these factors


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into account, the peak optical efficiency of a parabolic trough is in the range of 70-80%.
Since thermal losses from the receiver are relatively small and increase only moderately
as operating temperatures increase, at peak conditions, a trough can be expected to
deliver 60+% of the radiation incident on the collector even when taking into account
heat losses in the solar field piping.
                Parabolic troughs are highly modular. IST troughs are aimed at
commercial and industrial markets, but they can be configured in any reasonable
collector area to meet the desired load. Though east-west or north-south orientation of the
collector axis is typically specified for year-round or summer-peaking loads, respectively,
troughs can actually be oriented in any direction. The arrangement of troughs in parallel
rows simplifies system design and field layout, and minimizes interconnecting piping.
IST has trough models that can be mounted on the ground or on a roof.
                Tracking of a parabolic trough involves fixed costs associated with the
drive and control system. In large systems for commercial and industrial applications,
costs for the drive and control system are relatively less pronounced and the cost of the
collectors dominates the overall system cost. Materials are a major component of
collector costs. IST's contribution to the progression of parabolic trough technology
includes the development of a lightweight solar concentrator. Compared to a flat plate
collector, an IST parabolic trough module is 3 to 4 times less weight, and consequently
large trough systems are less costly that equivalent flat plate or evacuated tube collector
installations. Though the tracking of troughs involves more maintenance compared to flat
plate and evacuated tube collectors, the cost of electricity to power trough systems is less
because pumping power to circulate the collector fluid is reduced several times.
Importantly, troughs can meet temperature demands for energy far beyond the
capabilities of none tracking collectors.


5.2 Parabolic Dish
                These concentrators are similar to trough concentrators, but focus the
sunlight on a single point. Dishes can produce much higher temperatures, and so, in
principle, should produce electricity more efficiently. But because they are more
complicated, they have not succeeded outside of demonstration projects.


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                                Fig 5.2(Parabolic Dish)




              The fluid in the receiver is heated to very high temperatures of about
750oC. This fluid is then used to generate electricity in a small Stirling Engine, or
Brayton cycle engine, which is attached to the receiver. Parabolic dish systems are the
most efficient of all solar technologies, at approximately 25% efficient, compared to
around 20% for other solar thermal technologies. The Australian National University and
Wizard Information Systems have negotiated the terms of a licence to commercialise the
Big Dish solar concentrator technology and is working towards construction of a
demonstration plant in Whyalla, South Australia(Fig 5.3) .




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                Fig 5.3 (Demonstration Plant in Whyalla, South Australia)




               A more promising variation uses a stirling engine to produce power.
Unlike a car’s internal combustion engine, in which gasoline exploding inside the engine
produces heat that causes the air inside the engine to expand and push out on the pistons,
a stirling engine produces heat by way of mirrors that reflect sunlight on the outside of
the engine. These dish-stirling generators produce about 30 kilowatts of power, and can
be used to replace diesel generators in remote locations.


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5.3 Central Receiver
               The third type of concentrator system is a central receiver. Central
receivers (or power towers) use thousands of individual sun-tracking mirrors called
"heliostats" to reflect solar energy onto a receiver located on top of a tall tower.




                         Fig: 5.4(Solar Two Power Tower System)


The receiver collects the sun's heat in a heat-transfer fluid (molten salt)            that flows
through the receiver. The salt's heat energy is then used to make steam to generate
electricity in a conventional steam generator, located at the foot of the tower. The molten
salt storage system retains heat efficiently, so it can be stored for hours or even days
before being used to generate electricity. Therefore, a central receiver system is
composed of five main components: heliostats, receiver, heat transport and exchange,
thermal storage, and controls.
               One such plant in California features a "power tower" design in which a
17-acre field of mirrors concentrates sunlight on the top of an 80-meter tower. The


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intense heat boils water, producing steam that drives a 10-megawatt generator at the base
of the tower. The first version of this facility, Solar One, operated from 1982 to 1988 but
had a number of problems. Reconfigured as Solar Two(Fig-5.5) during the early to mid-
1990s, the facility is successfully demonstrating the ability to collect and store solar
energy efficiently. Solar Two’s success has opened the door for further development of
this technology. The parabolic trough has had the greatest commercial success of the
three solar concentrator designs, in large part due to the nine Solar Electric Generating
Stations (SEGS) built in California’s Mojave Desert from 1985 to 1991. Ranging from 14
to 80 megawatts and with a total capacity of 354 megawatts, each of these plants is still
operating effectively.
               Solar energy premiums and other incentives under review in Spain create
an attractive market opportunity, providing the economic incentives needed to reduce the
initial high cost and risk of commercializing a new technology. The Spanish project,
called "Solar Tres" or Solar Three, will use all the proven molten-salt technology of Solar
Two, scaled up by a factor of three. Although Solar Two was a demonstration project,
Solar Tres will be operated by industry as a long-term power production project. This
utility-scale solar power could be a major source of clean energy world wide, offsetting
as much as 4 million metric tons of carbon equivalent through2010.




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 Fig 5.5(Solar Two near Barstow, California.)




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                                      CHAPTER-6
                         THE FUTURE OF SOLAR ENERGY


               Developing countries in Asia, Africa, and Latin America-where half the
population is currently without electricity and sunlight is usually abundant-represent the
biggest and fastest growing market for power producing technologies. A number of
projects are being developed in India, Egypt, Morocco, and Mexico. In addition,
independent power producers are in the early stages of design and development for
potential parabolic trough power projects in Greece (Crete) and Spain. If successful, these
projects could open the door for additional project opportunities in these and other
developing countries.
               Solar energy technologies are poised for significant growth in the 21st
century. More and more architects and contractors are recognizing the value of passive
solar and learning how to effectively incorporate it into building designs. Solar hot water
systems can compete economically with conventional systems in some areas. And as the
cost of solar PV continues to decline, these systems will penetrate increasingly larger
markets. In fact, the solar PV industry aims to provide half of all new U.S. electricity
generation by 2025.Aggressive financial incentives in Germany and Japan have made
these countries global leaders in solar deployment for years. But the United States is
catching up thanks particularly to strong state-level policy support. The rolling blackouts
and soaring energy prices experienced by California in 2000 and 2001 have motivated its
leaders to create new incentives for solar and other renewable energy technologies. In
January 2006, the California Public Utility Commission approved the California Solar
Initiative, which dedicates $3.2 billion over 11 years to develop 3,000 megawatts of new
solar electricity, equal to placing PV systems on a million rooftops.
               As the solar industry continues to expand, there will be occasional bumps
in the road. For example, demand for manufacturing-quality silicon from the solar energy
and semiconductor industries has led to shortages that have temporarily driven up PV
costs. In addition, some utilities continue to put up roadblocks for grid-connected PV
systems. But these problems will be overcome, and solar energy will play an increasingly


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integral role in ending our national dependence on fossil fuels, combating the threat of
global warming, and securing a future based on clean and sustainable energy.
              The methods by which the solar energy can be utilized directly were
discussed in the above chapters. At present India is far behind in the field of utilizing
renewable energy resources compared to countries like Germany and America.
If India adopts these methods discussed above and other improved technologies, the
country can overcome the present situation of power crisis.




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                                    REFERENCES


Books and Journals:
1. J.D. Balcomb, (1992), “ Passive Solar Buildings” , MIT Press, 528 pp

2. M. Freeman, (1994), “The Solar Home: How to Design and Build a House
   You Heat with the Sun”, Stackpole Books , 240 pp.

3. Power Towers: Proving the Technical Feasibility and Cost Potential of Generating
   Large-Scale Electric Power from the Sun When It Is Needed, produced by NREL for
   DOE, August 2000.
4. Solar Trough Power Plants: Concentrating Power Plants Have Provided Continuous
   Generation Since 1984, produced by NREL for DOE, August 2000.


Related Websites:
5. Distributed Power Technologies—Concentrating Solar Power
   www.eren.doe.gov/distributedpower/pages/tech_csp.html


6. DOE Office of Building Technology, State and Community Programs
   www.eren.doe.gov/buildings/tools_directory


7. National Renewable Energy Laboratory
   www.nrel.gov/buildings_thermal


8. Parabolic Troughs: Solar Power Today
   www.eren.doe.gov/success_stories/opt_parabolic.html




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