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The model for the fusion power plant, the sun, is a source
of practically unlimited energy, most of which is wasted but
nevertheless provides us with millions of kilowatts of power,
keeps us warm, and grows all our food. To top it off, solar energy
is safe, pollution-free energy on and in which living things
have thrived since they first appeared on earth.
Every day the sun showers Earth with several thousand times
as much energy as we use. Even the small amount that strikes
our roof is many times as much as all the energy that comes in
through electric wires. With the sun straight overhead, a single
acre of land receives some four thousand horsepower, about equivalent
to a large railroad locomotive. In less than three days the solar
energy reaching Earth more than matches the estimated total of
all the fossil fuels on Earth!
The logical question at this point is, Why are we not making
use of this incredible bonanza in the form of solar energy? The
answer, of course, is that we are using it, and have been from
the beginning. All our energy-except nuclear- comes originally
from the sun. A solar-powered radio draws on the sun directly,
but a gasoline fueled automobile also uses solar energy-stored
solar energy, in which the sunshine of ages ago was trapped in
the earth until reclaimed by oil drillers. The challenge is to
make use of solar energy directly and in a non-polluting fashion.
The Russian philosopher, Kuzma Prutkov, decided that the moon
is more useful than the sun, since it shines at night when light
is needed; while the sun is of little use in the daytime since
it is light anyway! In such a fashion we, too, have dismissed
the importance and potential of the sun. It appears that the
fruitful application of solar energy is destined to wait until
the bottom of the energy stockpile the sun has willed us is depleted.
Now is the time to make realistic goals and strategies to
harness the power of the sun.
The harnessing of solar energy is not new in fact, development
of solar energy dates back more than 100 years, to the middle
of the industrial revolution. Several pioneering solar power
plants were constructed to produce steam from the heat of the
sun, which was used to drive the machinery of the time. At the
same time, Henri Becquerel discovered the photovoltaic effect;
that is, the production of electricity directly from the sun.
Becquerel's research was investigated and extended by, among
others, Werner Siemens. Photovoltaic power remained a curiosity
for many years, since it was very inefficient at turning sunlight
into electricity.
Early photovoltaic applications were geared more towards sensing
and measuring light (such as a camera's light meter) than towards
producing power. With the advent of the transistor and accompanying
semiconductor technology, however, the efficiency of photovoltaic
power increased dramatically. Photovoltaic power became more
practical. Over the years, many companies, including Siemens
Solar, have worked to increase the efficiency of photovoltaic
power. Today, commonly available solar panels are 12% efficient,
which is four times greater than only a few years ago. Today,
solar power is still used in two primary forms: thermal solar,
where the heat of the sun is used to heat water or another working
fluid, which drives turbines or other machinery to create electricity;
and photovoltaic, where electricity is produced directly from
the sun with no moving parts. Siemens Solar manufactures photovoltaic
panels which produce electricity directly from the sun.
 Solar Technology
Today
Photovoltaic power can be produced in many ways, with widely
varying efficiency and costs. They can be divided into two basic
groupings: discrete cell technology and integrated thin film
technology.
Discrete Cell Technology
Single-crystal silicon
Sliced from single-crystal boules of grown silicon, these wafers/cells
are now cut as thin as 200 microns. Research cells have reached
nearly 24-percent efficiency, with commercial modules of single-crystal
cells exceeding 15-percent.
Multicrystalline silicon
Sliced from blocks of cast silicon, these wafers/cells are both
less expensive to manufacture and less efficient than single-crystal
silicon cells. Research cells approach 18-percent efficiency,
and commercial modules approach 14-percent efficiency.
Dendritic web
A film of single-crystal silicon pulled from a crucible of molten
silicon, like a soap bubble, between two crystal dendrites. Gallium
Arsenide (GaAs) A III-V semiconductor material from which high-efficiency
photovoltaic cells are made, often used in concentrator systems
and space power systems. Research cell efficiencies greater than
25 percent under 1-sun conditions, and nearly 28 percent under
concentrated sunlight. Multijunction cells based on GaAs and
related III-V alloys have exceeded 30-percent efficiency.
Integrated Thin Film Technology
Copper Indium Diselenide (CuInSe2), or CIS
A thin-film polycrystalline material, which has reached a research
efficiency of 17.7 percent, delivers the highest completed module
efficiency for full sized power modules, reaching over 11 percent.
Amorphous Silicon (a-Si) Used mostly in consumer products for
solar watches and calculators, a-Si technology is also used in
building-integrated systems, replacing tinted glass with semi-transparent
modules. The primary issue with a-Si technology remains the low
efficiency and associated greater requirement for space and higher
array installed cost and weight
Cadmium Telluride (CdTe)
A thin-film polycrystalline material, deposited by electrodeposition,
spraying, and high-rate evaporation.Small laboratory devices
approach 16-percent efficiency, with commercial-sized modules
(7200-cm2) measured at 8.34-percent (NREL-measured total-area)
efficiency and production modules at approximately 7 percent.
Advantages
of Photovoltaic Power
Photovoltaic solar power is one of the most promising renewable
energy sources in the world. Compared to nonrenewable sources
such as coal, gas, oil, and nuclear, the advantages are clear:
it's totally non-polluting, has no moving parts to break down,
and does not require much maintenance. A very important characteristic
of photovoltaic power generation is that it does not require
a large scale installation to operate, as different from conventional
power generation stations. Power generators can be installed
in a DISTRIBUTED fashion, on each house or business or school,
using area that is already developed, and allowing individual
users to generate their own power, quietly and safely.
Rooftop power can be added as more homes or businesses are
added to a community, thereby allowing power generation to keep
in step with growing needs without having to overbuild generation
capacity as is often the case with conventional large scale power
systems But even when photovoltaic power is compared to other
renewable energy sources such as wind power, water power, and
even solar thermal power, there are some obvious advantages.
First, wind and water power rely on turbines to turn generators
to produce electricity. Turbines and generators have moving parts
that can break down, that require maintenance, and are noisy.
Even solar thermal energy needs a turbine or other mechanical
device to change the heat energy of the sun into mechanical energy
for a generator to produce electric power. Photovoltaic power,
by contrast, is generated directly from the sun. PV systems have
no moving parts, require virtually no maintenance, and have cells
that last for decades.
Uses of Solar
How practical is solar for home and mobile home/marine use?
These days, it's pretty practical, especially for remote homes.
Until solar power came along, people who wanted to live in remote
areas frequently had to pay large fees to have a power cable
run to their house. Now, a remote home can be virtually self-sufficient
with solar power. Even in areas where power lines are nearby,
solar may be a viable alternative to being connected to a power
company. An average home has more than enough roof area to produce
enough solar electricrity to supply all of its power needs. With
an inverter, which converts direct current (DC) power from the
solar cells to alternating current (AC), which is what most home
appliances run on, a solar home can look and operate very much
like a home that is connected to a power line. For recreational
vehicles, solar power provides the freedom to go to more remote
locations, without relying on a plug-in power source or a noisy
electric generator. Systems for RVs can be small for charging
batteries only or large enough to power the entire vehicle for
a period of time. Similarly, boats can use solar power for many
of their power needs, rather than a generator or engine.
Solar PV Power in Industry
Some of the most important applications of solar energy are
nearly invisible.
Telecommunications, oil companies, and highway safety equipment
all rely on solar power for dependable, constant power, far from
any power lines.
Call Boxes: look at any California
roadside call box, and you'll see a solar panel. California standardized
on the use of solar power and cellular phones to eliminate the
need for any buried cable connections to these phones. Given
the sometimes literally life-saving nature of these call boxes,
dependability is a must.
Roadside signs: solar power
is used for many lighted highway signs, eliminating the need
for diesel generators.
Telecommunications installations:
when you need a microwave repeater on a remote mountaintop, the
last thing you want to do is run a power line up to it. For reliable
power, many communications repeaters in remote areas use solar.
Siemens Solar alone has shipped over 130 megawatts of modules
since its inception, and the use of solar power is projected
to grow at 10-15% per year from now until the year 2010. This
is over three to five times the rate of growth of the Gross National
Product of the United States!
Given this growth, solar power will be a much larger part
of our lives in 2010 than it is today. Homes could incorporate
solar power at the time that they are built, dramatically reducing
both the cost of buying solar power and the cost of utility bills.
New communications technology may make living in remote areas
a practical reality given the availability of solar power. Mobile
uses will undoubtedly increase. And industrial applications will
continue to enjoy the versatility of solar power.
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