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Re: Solar Panels
Actually I am amazed at how little light it appears to take for our
panel to charge the battery.
I was told they start to produce useful energy at about 50 w/m^2 and are
then linear up to rated power at 1 kW/m^2.
Actually my spreadsheet said that the total exposure above 50 for 1998
here in N. CA was about 1330 kWhr/m^2 and my panel is 11.2% efficient.
This would mean a 9 year payback - JUST about the time it needs to start
to be considered for replacement.
I have NO idea what the fall off is like once it starts.
BUT - it would seem we are in agreement about what one can expect per
day per sq meter.
(unless that number is for amorphous which is 50% less sensitive)
"Heinmiller, Bruce" wrote:
>
> I'd be interested in the number as well. I have an unofficial energy
> manufacturing cost of 1360 kWh/m^2 of photovoltaic panels. Assuming a very
> generous installed electricity production rate of 0.4 kWh/d.m^2, the energy
> payback time would be almost 10 years.
>
> But I'm skeptical about my 0.4 kWh/d.m^2. I was at Mountain Equipment Co-op
> in Toronto a couple years ago near noon on a largely cloudless day in June.
> This store touts there "1-kW" roof-mounted solar panel unit (with a power
> meter at street-level) as a model of environmental stewardship. When I was
> there, the display was, for some reason, cycling from zero W to about 250 W
> (plus or minus 30 W) when the sky was cloudless. When a puff of cumulous
> cloud intervened for a minute, the display read "sleeping", which I
> interpreted quantitatively as zero W. The following year (last year) I
> happened to be there again on a cloudless day in June (my records indicate
> Sunday, June 6, 12:00), and the unit was behaving more consistently - it
> continuously read "sleeping" on that beautiful day about two weeks shy of
> summer solstice.
>
> I wouldn't need a lot of convincing that these trinkets are a net energy
> drain. Furthermore, I'd like to see a comprehensive safety analysis report
> for this technology, including waste management, construction, and
> maintenance risks (even per unit gross energy produced).
>
> Bruce Heinmiller
> heinmillerb@aecl.ca
>
> > ----------
> > From: Ted de Castro[SMTP:tdc@xrayted.com]
> > Reply To: radsafe@romulus.ehs.uiuc.edu
> > Sent: Tuesday, May 02, 2000 2:16 PM
> > To: Multiple recipients of list
> > Subject: Solar Panels
> >
> > While on the subject of Solar Panels - or Photo Voltaics (PVs) I'd like
> > to see if anyone has hard information to settle a long standing
> > question.
> >
> > Of course we all know that the Si industry has somehow avoided general
> > knowledge of the extremely corrosive and hazardous chemicals they use.
> > That has already been mentioned here.
> >
> > BUT - I once read that it takes more energy to produce a PV than it will
> > EVER produce!
> >
> > Does anyone have the hard numbers on this?
> >
> > Currently I am persuaded this may be so. 10 or so years a ago I did a
> > simple calculation at the surplus price of solar panels and the time to
> > payback from the electricity they generated. The idea was that if
> > energy cost was a major part of the cost of producing a solar cell then
> > the time to cost recover from electrical generation alone would be very
> > long. This was NOT meant to be a definitive calculation - but just one
> > for plausibility - certainly other factors can raise the cost.
> > Conversely if the payback time was short - then obviously they could NOT
> > consume more energy than they could produce.
> >
> > The payback time calculated to about 60 years. Thus I concluded that it
> > certainly is possible that they COULD require more energy to produce
> > than they could ever put out.
> >
> > More recently I had a project for a remotely cited monitoring station
> > where a PV was THE answer for power! It is a temporary project and the
> > cost to get power to the site was high.
> >
> > BUT - to design the project to be SURE the PV and batteries where right
> > to carry the load year round I had to do some calculations. So - I did
> > a spreadsheet using actual hourly solar data for our site from the
> > previous year and calculated the charge state of the batteries hour by
> > hour. This allowed me to choose between panel and battery capacity and
> > minimize cost.
> >
> > The panel we use is a $615 120w crystalline panel. An amorphous panel
> > would have been about the same price but 50% larger.
> >
> > This panel was bought from Wind and Sun in Arizona - I found their web
> > site and excellent source of information (www.windsun.com).
> >
> > They made the observation that PVs really haven't come down much in 20
> > years - and as for the future ....Their opinion is to "not to hold your
> > breath". Pretty frank talk for someone making a living selling this
> > stuff!! They also say that PVs NOW do produce more than it takes to
> > make them (but no hard data).
> >
> > Anyhow - seeing this thread on alternative power sources I realized that
> > my spreadsheet designed to calculate battery charge could also calculate
> > total power output and I could redo the time to payback calculations I'd
> > scratched out before AND with current industry pricing for the largest
> > single PVs I could find.
> >
> > Guess what - once again the answer was 60 years!!!
> >
> > The guarenteed life of a PV to 80% capacity is 5 to 10 years depending
> > on the make and type (amorphous has a shorter life).
> >
> > So - it is still plausible in my mind that the power to produce a PV
> > could very well exceed its life time generating capacity - or be very
> > close to it.
> >
> > The argument is often made that PVs are too costly now for "normal"
> > installations - but as power costs go up - this will change. BUT it is
> > obvious that if power is a major cost to make PVs - then their price
> > will go up accordingly.
> >
> > Of course we could always wish for a new break through process that
> > makes them better and cheaper and more efficient. But that is NOT here
> > and now - or even in the visible future AND has been "promised" for
> > almost as long as nuclear power has been said to become "too cheap to
> > meter".
> >
> > Ted de Castro
> > ************************************************************************
> > The RADSAFE Frequently Asked Questions list, archives and subscription
> > information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html
> >
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