[ExI] Small scale solar payback time (was Re: Planetary defense)

[Keith Henson]

On Tue, May 17, 2011 at 7:01 AM, Eugen Leitl <eugen at leitl.org> wrote:
> On Tue, May 17, 2011 at 06:50:52AM -0700, Keith Henson wrote:
>
>> If you had a polymer PV that had an energy payback time of a couple of
>> months and lasted 2 years, that would be possible to grow energy on
>
> Great if you roll it out in the desert, and weigh down with stones.
> Total deployment time: <30 min. And you can always drive down
> to Walmart and get another roll of polycells-last-all-summer-long.
>
> Not so great if your home's outer skin is made from it. Here
> you'd want to go for 40+ years. (Yes, houses and people will
> be still around in 40+ years).

Roof's seldom last 40 years.  And if a house is painted, the paint
isn't likely to last more than ten years.

But that's not the point.

The use of solar energy needs to expand upwards of 128 times.  That's
7 doublings.  Consider PV systems limited by energy, one that lasts 2
years and had a payback in 2 months and one that lasts 24 years and
has a payback of two years.

If you are feeding all the energy produced into making new systems,
the first would take a year and two months years to grow by 128 times,
the second would take 14 years.

The fast payback would be an incredible economic bonanza.

Of course a system that had an energy payback time of two months and
lasted 50 years would be even better.

That's about what SBSP looks like with 6% efficient transportation to GEO.

Keith

>> the energy harvested, i.e., short doubling time.  PV that takes years
>> to pay back the energy used to make it has a slow doubling time.
>
> When PV panes are autopoietic, yes. As long as you put them up
> by people, not so great.
>
> Apropos solar: http://postbiota.org/pipermail/tt/2011-May/009071.html
>
>> I would rather have a short EPBT.  YMMV.
>
> --
> Eugen* Leitl <a href="http://leitl.org">leitl</a> http://leitl.org
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