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

[Todd Cory, Mt. Shasta Energy Services]

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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