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From: amirza@silver.ucs.indiana.edu (anmar mirza)
Newsgroups: sci.energy,sci.electronics,sci.physics
Subject: Re: solar cells
Message-ID: <1990Dec31.173248.24523@bronze.ucs.indiana.edu>
Date: 31 Dec 90 17:32:48 GMT
References: <1990Dec28.210436.10601@zoo.toronto.edu> <939@venice.SEDD.TRW.COM> <1990Dec29.063939.20478@zoo.toronto.edu>
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In article <1990Dec29.063939.20478@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes:
>In article <939@venice.SEDD.TRW.COM> ries@venice.sedd.trw.com (Marc Ries) writes:

>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.
Never ever rule out other reasonable forms of power. We do not want to
get into the trap of relying on one source again.
>> 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
I have said it before, and I'll say it again, polycrystalline cells,
made in the early 50's, have shown no significant deterioration in
power output. Amorphous cells degrade comparatively quickly.

>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.
This is a problom that some of the people who I deal with share. 
What I have a problem with is people who refuse to consider building
passive solar heating or cooling systems into their house, when it
costs little or no extra, and the long term payoffs are significant.
Right now though, solar cells offer an easy way for people to generate
power on a small scale, a way for them to be independant. It is
also a good way to make use of space that is wasted (rooftops).

>
>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.
Pardon me, but on the average, when I do a site survey for
photovoltaics in a retrofit installation, I can usually reduce a
households power consumption by 30% without major redesign, or loss of
comfort. I can usually drop it 50% by redesigning lighting schemes and
refrigeration and the like. This is assuming they do not heat with
electric. If they do, and they switch to a combination
geothermal/passive or active solar, the savings can be even greater.
What is really good about passive solar heating and geothermal systems
is that they *will* pay for themselves in savings compared to the old
system. The turn around time can be as little as 10 years.
If the house is being built, then the extra cost is minimal.




--
Anmar Mirza   # If a product is good, # I speak only my   # Space, humans next
EMT-A         # they will stop making # opinions on these # goal in the race 
N9ISY (tech)  # it. Unless it is      # subjects, IU has  # for immortality.
Networks Tech.# designed to kill.     # it's own.         # --- me