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From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: solar cells
Message-ID: <1990Dec29.063939.20478@zoo.toronto.edu>
Organization: U of Toronto Zoology
References: <1990Dec17.190857.16559@engin.umich.edu> <1990Dec28.210436.10601@zoo.toronto.edu> <939@venice.SEDD.TRW.COM>
Date: Sat, 29 Dec 90 06:39:39 GMT

In article <939@venice.SEDD.TRW.COM> ries@venice.sedd.trw.com (Marc Ries) writes:
>   Yet, the prices are falling as we speak...

They have been falling for a long time, actually, but they still have a
way to go before solar cells are very useful in the absence of constraints
that rule out other forms of power.

> There is no reason why the pure
> silicon-based PVs can not last "forever" -- there is nothing to break 
> down within the cell itself...

Oh yes there is:  the cell.  There is a common misconception that
semiconductor devices ought to be eternal; it is not true.  There are
a variety of failure mechanisms, including diffusion of the doping
elements within the silicon -- yes, diffusion happens in solids too,
it's just slow -- migration under electric fields, and infiltration
of contaminants from the outside.  These effects are not completely
insignificant for any semiconductor and are quite noticeable in those
that are being pushed hard under a severe cost constraint.  (A particularly
severe example is the laser diode in a CD player, whose lifetime is
measured in months if you run it 24 hours a day.)

> It's true that creating PVs are not
> 100% "clean", but then neither is any power generation source, from
> "hydro to nuclear." ...

Agreed; the point is that solar cells are not exempt from cost-benefit
calculations for environmental impact.  They are not the magic solution,
free of any environmental price, that some people think.

>     New battery storage technologies are being made, along with other methods
>  holding energy over time -- underground storage, etc...

At the moment, all are fearfully inefficient and tremendously costly if
used in bulk, barring extremely favorable circumstances.  The state of
battery technology in particular is a disgrace.

> PVs work in Alaska...

When the sun is shining.  I spent the last ten days at home on holiday in
central Saskatchewan; we saw the sun on maybe four of those days, tops.

> Very large collecting surfaces are only needed for
>  the production of very high amounts of energy.  A typical home could be
>  powered by PVs covering the roof area alone.

Numbers, please.  And state whether you assume massive redesign of the home
for minimum electrical use, including what alternate form of heating you
propose.  There is no prospect of redesigning any large fraction of the
homes in North America any time soon.

"Very high" amounts of energy are needed if we want a major fraction of
our total energy supply to come from solar.
-- 
"The average pointer, statistically,    |Henry Spencer at U of Toronto Zoology
points somewhere in X." -Hugh Redelmeier| henry@zoo.toronto.edu   utzoo!henry