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

[matthew tritt]

Todd,

As I remember from the late 70's when the "renewable" term was being tossed
around, it originally was referring to trees as a replacement for fossil
fuels when used to produce heat. Trees, if given the opportunity, will
indeed be replaced with another generation of their kind, whereas fossil
fuels are a one-shot deal. PV, wind and hydro were referred to as
"alternative" energy generators, not renewables - a distinction I take pains
to make when dealing with potential customers or people at parties!

WECS and hydro obviously could (considering the jerk's arguments you
forwarded) be considered as "renewables" because of the vastly greater
amount of energy produced versus energy consumed in producing the generator
in the first place. Also, Tom's comments are relevant especially if PV
equipment is produced from energy generated by wind or hydro.

So, does the nay-sayer suggest that we continue using-up fossil fuels
instead of actually doing something to ease the problem?

Matt T
----- Original Message ----- 
From: "Todd Cory, Mt. Shasta Energy Services" <toddcory at finestplanet.com>
To: "Wrenches" <RE-wrenches at topica.com>
Sent: Thursday, July 03, 2003 10:39 AM
Subject: energy "payback" of PV's [RE-wrenches]


> 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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