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Solar Panel Efficiency
Name: Nick
Status: Educator
Grade: 9-12
Location: CA
Country: United States
Date: November 2007
Question:
I heard a rumor that the process of making a solar panel actually
requires more energy than you could ever get out of a solar panel. True?
Replies:
This is an "it all depends" question. If you consider the energy on a "cradle to
the grave" basis, solar panels require more energy than they produce (depending
upon how long the panel remains active). This is because they require components
that must be purified, and that requires energy, but that is a "one time charge",
not an on-going expense. But if the solar panel can operate under conditions that
other energy sources cannot, then that is OK. Many power sources require more
energy to produce than they ultimately produce themselves. So I do not think that
is just a rumor. All "engines", whatever their function, produce less "work" than
they require to run. That is the Second Law of thermodynamics. Specifically,
"useful work (W)" and required energy, say in the form of heat (Q) are related by
the simple equation:
W/Q = 1 - T(cold)/T(hot). That is, the efficiency W/Q depends only on the "hot"
temperature and the "cold' temperature, and that is as good as it gets. It does
not matter what complex machinery you have between the heat source T(hot) and the
heat sink T(cold), it only depends upon the two temperatures (expressed in degrees
kelvin).
Vince Calder
The rumor is wrong.
You can think of a solar photovoltaic panels as having two "costs." One is
the amount of energy required to make the panel. The "payback" time for
energy for a solar panel is only about two years, or maybe a bit longer,
depending on climate or location.
The other cost is the actual dollar cost. For this, the "payback" time is
longer, perhaps a couple of decades. If the solar panel is installed where
conventional electric energy is inexpensive, the panel may never be able to
pay back its dollar cost, but it does quickly pay back the energy cost.
Robert Erck
Solar panels can be tricky and expensive to make, and their efficiency is
not as good as we want it to be. In very cloudy places, solar panels are not
cost-effective energy solutions. In other high-sun locations, solar panels
are definitely worth the investment. Their low cost to operate and long life
spans overcome this initial cost. The "break-even" point depends on the type
of panel and where it is located.
To answer your specific question, it is possible for a solar panel to
generate more energy than was used to create it. It depends on the type of
panel and where it is installed.
The overall energy generation question is more complicated than that,
though.
One big advantage of solar panels is that they can make energy accessible in
places where energy is scarce, expensive, or unavailable. Some areas do not
have access to power grids. Other areas experience outages during peak usage
times. Also, power transmission is very inefficient. All of these are
reasons to use solar power.
There is a lot of research being put into solar panels now as well.
Researchers have found ways to increase by a factor of 5 the efficiency of
solar panels, and are working on making commercial products from the new
panels. By increasing efficiency, the number of places and applications that
would benefit from solar energy will increase.
With today's technology, solar power is not the answer to all our power
needs. I cannot predict the future, but I would guess we will continue to use
a number of sources of power, including renewable energy like wind, solar,
and geothermal along with traditional sources like fossil fuels and nuclear
energy for some time to come.
Hope this helps,
Burr Zimmerman
Up-date Winter 2009-2010
As of 2010, "total life cycle analysis" (TLCA) of solar cells has become a
well-researched topic. TLCA studies add up all the inputs into making a solar
cell, ranging from mining special minerals to the costs of installation and
maintenance. With modern solar cell designs and optimum weather, energy payback
can be well under 1 year. Over a range of solar cell technologies, weather
conditions, sizes and installation types, energy payback estimates generally
range from 1 to as many as 6 years. Since cells are expected to operate for
30 years, this means that today's solar cells are generating much more energy
than was required to manufacture them. The financial payback is a different
issue, but purely in terms of energy, solar cells definitely can produce more
energy than was required to manufacture them. TLCA analysis has been performed
around greenhouse gas (GHG) and other emissions as well.
There are tons of studies that have been published using various methods of
estimating payback periods. I'll refer to a pamphlet from the National
Renewable Energy Laboratory that is a little old (2004), but gives a good
general overview:
http://www.nrel.gov/docs/fy04osti/35489.pdf
Burr Zimmerman
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