Newsgroups: sci.energy
Subject: Renewable Energy - solar
From: spang@calstatela.edu (Sue Pang 10-16-91)
Date: 12 Nov 92 17:16:11 PST
Reply-To: spang@calstatela.edu
Distribution: world
Organization: Cal State University, Los Angeles

As I have promised, here is something which may interest you.  If you feel I have an error, please let me know by email at:
spang@atss.calstatela.edu

I will post any corrections if needed.

Sue

P.S.  Warning!!!  This is a big file approx more than 110 lines.



RENEWABLE ENERGY
Written by:  Sue Pang on January 1992
===================================================================
	Michael Faraday built the first generator in 1871.  He 
called it the dynamo, for making electric current. Since then, 
electricity, our most prized tool, is there for us at the flick 
of a switch. The invention of new energy-intensive appliances 
such as the air-conditioner and refrigerator added to the challenge 
of the ever demanding electricity. The world of electronic goods 
also depends on electricity as a major source of power. As our 
population continues to grow in numbers, electricity is more 
than ever in demand.

	Many energy sources have been used to generate electricity 
on a large scale basis to supply the electrical demand, but non-
renewable energy resources such as fossil fuels are being depleted. 
Their usage have also caused a price to be paid on our environment, 
which requires us to find alternative ways to generate electricity 
to satisfy the people's growing demand. Our planet has only a limited 
amount of energy sources such as fossil fuels to supply the next few 
generations. We have used up much of these energy sources. Although 
alternative renewable energy sources in the non-solar category such 
as hydro energy, ocean thermal energy, and wind power have been used, 
some people have expressed negative opinions toward their usage due 
to their negative environmental impacts, high construction costs, and 
operational and maintenance expenses. Renewable energy sources, 
including solar energy, are sources which are inexhaustible, in the 
sense that little change in their energy output is expected over a 
span of millions and trillions of years. They are energy sources which 
do not depend on the extraction of fossil resources, but on naturally 
occurring energy flows.

	One form of renewable energy in the nonsolar category is 
"Hydro energy", which is a form of energy using water power as a driving 
force to turn the hydraulic turbine to create electricity. Its cycle 
is very inefficient, because 50% of the input energy is lost in the 
process while generating electricity. Another form is "Ocean thermal 
energy", which is a limited heat source with only about 2% to 3% 
efficiency. It is determined by the temperature difference of warm 
ocean surface water and the cold ocean floor water. If it is used for 
a large scale generation, the aquatic life in the ocean will 
certainly be disturbed from the water flow while electricity is being 
generated. Unlike "Ocean thermal energy", "Geo-thermal energy" comes 
from the heat of the earth and decay of radioactive minerals. It is 
used to generate power at hot springs, Geysers, and near volcanoes, 
and it is quite dangerous. For instance, if the underground pressure 
is not maintained properly, the earth's surface might cave in. Also, 
the impurities in the steam from the earth can corrode and clog 
pipe-lines while bringing up this energy, making it economically 
inefficient. "Wind energy", on the other hand, generates electricity 
using wind power, but the wind can be unpredictable; long transmission 
lines will make this renewable energy quite expensive. Building 
a power plant using wind to generate electricity requires special 
planning. Its usage also requires backup generating system. 
Renewable resources such as hydro, ocean thermal, geo-thermal, and 
wind energy achieve very low efficiency, and it is economically 
expensive to construct and to operate on a large scale basis. An 
alternative renewable energy source would be the use of solar 
energy.

	The sun's supply of solar energy is everlasting. Solar 
energy is very abundant and inexhaustible. It has been burning for 
almost 6 billion years. On a clear day, sunlight can produce the 
power of approximately one kilowatt per square meter. Energy is 
transmitted to us by sunlight. The sun's energy arrives as rays. 
Most of all, 51% of the sun's energy arrives as the long infrared 
ray of heat or thermal energy, while 40%of its energy comes to us 
a light, the visible spectrum that we see. Lastly, the dangerous 
short waves in the form of ultra-violate (UV) make up of only 9% 
of the sun's energy.

	The sun's energy can be converted into useful energy with 
the use of solar cells or photovoltaic cells by means of a non-
thermal process. ...

	Pure silicon can achieve about 16% to 18% efficiency, while 
amorphous silicon can only achieve 9% to 11% efficiency.

	A solar power plant located near Barstow, California, and 
Phoenix, Arizona uses the sun's thermal energy to generate 
electricity. "Solar One" was a Ten Mega-Watt power plant which 
operated between 1982 and 1988. Based upon research to date, it was 
a highly successful pilot plant which established the technical 
feasibility of central receiver technology in a six year test 
program, and it will be put into use for another experimental 
project named "Solar Two".

	"Solar Two" is a solar thermal electric power system 
which is located at the "Solar One" site. The new technology of 
"Solar Two" over "Solar One" will be its usage of molten salt, which 
is known as a saltpeter. 

	Molten salt is a liquid at atmospheric pressure made up of 
60% sodium and 40% potassium nitrate. It has a melting point of 
450 degrees Fahrenheit, and it is a nonflammable and nontoxic liquid. 

	Molten salt technology is the most cost effective and safe 
method to convert solar thermal energy into electrical energy. By 1994 
the construction phase of this four-year project will begin and 
"Solar Two" will begin its operation by 1995.

	The "Solar Two" will have much more benefit to the environment 
and advantages over most types of electrical power plants. It will use 
clean solar energy and will emit no pollution to our environment. This 
power plant will be very reliable, safe, efficient and modular. 
Electricity can be produce during cloudy periods or in the evening 
after sunset, using a two-tank (hot and cold) storage system. This 
storage system will produce 99% efficiency, the ratio of its useful 
energy output and energy input. The annual capacity factor of 60% to 
80% will make "Solar Two" as an efficient large-scale solar thermal 
electric power plant. There will also be a low energy cost in the long 
run for this type of power plant, because the sun will continue to 
supply a free source of energy. Very little maintenance will be needed. 
Solar thermal electric power plants such as this one will benefit 
consumers as well.

	Many people may believe that solar energy is very inefficient, 
because they don't believe the heat intensity of sunlight have much 
energy. They are wrong. If we look further into the future, we will 
realize that the resources available now, such as coal, may become 
scarce or depleted in the few generations from now. Renewable energy 
resources such as hydro-power energy, ocean-thermal energy, geo-thermal 
energy and wind energy are not as reliable and cost effective as solar 
energy on a long term basis. Many other energy sources now available 
are considered economical now, but the cost will add up as our environment 
will share the price, such as the global warming effects and other 
environmental problems which we are beginning to notice.

	The solar energy the sun sends to earth is free and everlasting. 
Our technologies have taught us how to catch this abundant energy 
sources by the use of photovoltaic cells or collector systems on 
large scale studies such as "Solar One". Solar central receiver systems 
have also been studied and put into use worldwide. 

	"Solar Two" is a large scale project to study the new technology 
of molten salt in conjunction with solar central receiver systems. 
Projects such as this will benefit the safety of future large-scale 
solar thermal power plants. As more and more people live in this world, 
our dependency on electricity will increase. Majority of our home 
lighting systems and appliances rely on electricity as a source of 
power which is generated by our utility company on large scale systems. 
The growing worldwide demand for energy, its increasing cost, and the 
depletion of nonrenewable energy reserves make solar power systems an 
attractive alternative for supplying electricity for a wide range of 
uses. Renewable energy such as solar thermal energy to generate 
electricity will be one of the best ideas man has captured and put 
into use; it is a great plus for our future and the generations to come.


Newsgroups: sci.energy,sci.environment