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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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