energy "payback" of PV's [RE-wrenches]

[Ian Woofenden, Home Power]

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Todd,

See the first link at 
http://www.homepower.com/magazine/downloads_solar_power.cfm for an 
article on PV energy payback. Payback is two to four years on the 
modules, depending on module and site. Old myths die hard.

Ian

>Sorry to raise this ugly issue again, but I am dialoguing with some
>folks that insist that PV's never recoup their embedded energy. Can this
>possible have merit?
>
>Pasted text follows.
>
>Todd
>
>
>RENEWABLE ENERGY SYSTEMS
>
>So-called "renewable" energy systems are evaluated differently
>than "non-renewable" energy systems. In order to be "renewable",
>an energy system must produce enough net energy to reproduce
>itself.
>
>A BTU of sunlight is fundamentally different than a BTU of fossil
>fuel. Directly and indirectly it takes about 1,000 kilocal of
>sunlight to make a kilocalorie of organic matter, about 40,000 to
>make a kilocalorie of coal, about 170,000 kilocal to make a
>kilocalorie of electrical power, and 10 million or more to support
>a typical kilocalorie of human service. So when renewable energy
>systems are evaluated, both inputs and outputs must be converted
>to solar eMjoules (or "sej") and compared. (There are ten
>different sets of equations to convert energy to sej:
>http://dieoff.com/emergy.pdf ) The difference between the sej
>input and sej output is known as the "net sej".
>
>Calculations show that solar cells consume twice as much sej as
>they produce. http://dieoff.com/pv.htm So even if all the energy
>produced were put back into production, then one could build only
>half as many cells each generation -- they are not sustainable.
>Even if the sej efficiency of solar cells doubled, ALL of the
>energy produced would have to be used to manufacture new cells,
>which still leaves a zero net benefit to society!
>
>Traditional measures of "net energy" for solar cells may be
>improving but "net sej" may be getting worse because there are ten
>different sets of equations to convert energy to sej. The only way
>to know is to DO THE MATH. http://dieoff.com/emergy.pdf
>
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-- 

Ian Woofenden <ian.woofenden at homepower.com>
Senior Editor, Home Power magazine, The Hands-On Journal Of Home-Made Power
My use of words is just some antics.

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