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

[Eugen Leitl]

On Tue, May 24, 2011 at 07:41:12AM -0700, Keith Henson wrote:
> On Tue, May 24, 2011 at 7:01 AM, Eugen Leitl <eugen at leitl.org> wrote:
> 
> snip
> 
> > gas network. Anaerobic digesters could cover probably up to 20%.
> 
> I worked out trash to syngas to liquid fuel some years ago and came up
> with less than 5% of the demand.

No, I meant 20% of natural gas demand. The estimate being a bit
on the high side, admittedly. In general, the only other options
are hydrogen from water electrolysis (from renewable electrical 
surplus) and synmethane (Sabatier, H2+CO2).
 
> If you consider the thermal value of the stuff that goes down the
> drain vs the trash . . . I don't think so.

It seems it's better to use the trash organics rather then losing
them. Most economic digester sizes would be municipality-scale.
There's not enough waste organics in a typical household to make
much with it -- farmers being a notable exception.

-- 
Eugen* Leitl <a href="http://leitl.org">leitl</a> http://leitl.org
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