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

[Tom Elliot, Guffey Energy Works]

Todd,

>From my quick read of that post I get the impression that they assume that
all PV is manufactured with fossil fuel generated power.  Their
calclulations won't be valid for Wind or Hydro generated power.

Plus, it strikes me as yet another argument that assumes zero impact as the
ideal (which is impossible) in order to denigrate a technology that in
reality reduces impact in a very huge way.

Also, the shift between paragraphs 2 and 3 strike me as not logical.  It is
irrelevant, ISTM, what the original embedded energy is for the panels needed
to produce enough power to run a fab plant, once that power capacity is
produced it will continue to produce its output, powering the plant and
producing PV.  It strikes me that they are assuming the output of the PV
panels gets "used up" somehow.

The logic of the entire piece bothers me as well but the above is my quick
response.

Tom Elliot


> 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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