[ExI] ExI] eroei forward for kennedy, p.e.

[Keith Henson]

On Sun, Dec 23, 2012 at 4:00 AM,  Robert G. Kennedy III. wrote:

snip

> So, for crude oil, we are fast approaching the "EROI cliff".
>
> I find that significant. Anyone can repeat this calculation
> themselves, from open sources. Yet other than specialty textbooks, it
> is almost entirely unremarked on.
>
> Here's the wiki on the subject of EROI:
> http://en.wikipedia.org/wiki/EROEI . The chart is roughly correct, but
> the value for PV is too low, should be more like 8-12. Nuclear's
> all-in EROI about equal to the figure of low teens which I derived.
> However, the chart does not depict trends. If it did, you'd see some
> first-derivative vectors for traditional energy resources pointing to
> the left, a few would be invisible b/c they're stationary, e.g.
> hydro's almost fully built out; and some such as PV would be pointing
> to the right, and the second derivative even more strongly so.
>
> The chart does not display the useful life of the particular
> technologies, a critical assumption in developing EROI. Hydroelectric
> dams last far longer, with far less O&M, than wind turbines, say.
> Again for PV, results from the field suggest that "hard" mono- &
> polycrystalline PV might last a century in service, so an assumption
> of 25 years' economic lifetime would undercut PV's EROI by a factor of
> 4.

A related concept for renewable sources is the energy payback time.
http://en.wikipedia.org/wiki/Energy_pay-back#Sustainables   PV, for
example, takes about 1-4 years to pay back the energy needed to put it
in place.

If 100% of the energy from PV were fed back into making more PV, the
doubling time would be in the vicinity of 1-4 years.  See also
http://en.wikipedia.org/wiki/Energy_cannibalism

Power satellites look fairly good in this light.  At 5 kg/kW and a
lift energy cost 7 kg of hydrogen (at 50 kWh) per kg of payload the
payback time is a bit over 3 months.  (This assumes that the lions
share of the energy cost is in lifting parts to GEO.)  Most of the
hydrogen isn't burned, it's just used for reaction mass, with the
energy coming from lasers powered by the first power satellite.

Keith