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re: solar water heater sources
4 apr 1996
hla tin   wrote:

>if anybody knows the sources for 50 gallon solar water heaters 
>please let me know. i have a need for these for a developing country.
>i am located in california and would prefer a calif. source.

how about combining pv and water heating?

                               .
clear corrugated         . i   t   i .  
  polycarbonate-->  .  .                   .
              .  . <--pv panel                   .
        .  .                                           .

in other words, use 4' x 12' dynaglas polycarbonate "shingles" from sps in
san jose, ca (408) 997-6100 or replex (800) 726-5151 for the roof with
stanford ovshinsky's new 5%-efficiency "pv shingles" in long strips under the
rafters, and put some insulation up in the ridge peak, with an 8' long x 6"
diameter galvanized steel or pvc pipe water tank up there under the insulation,
with no insulation underneath the tank, so the tank is heated by solar hot air
from the shingle-pv cavity, or say, 2 gpm of water trickling over the 6 m^2 (?)
of pvs, collecting in a small gutter and being pumped back up to the tank,
with a tiny pv-powered pump, when the tank water temp is low, with some sort
of damper with a bimetallic spring that opens near the top of the cavity to
let the pvs run cooler, when the tank is warm enough, eg the $11 afv-1b
automatic foundation vent made by leslie-locke of atlanta (gee, what a run-on
sentence :-)

except for the pv part, this is cheaper than conventional roof construction,
and in a cold climate, it could provide daylighting and space heat for the
house beneath, if a reflective motorized return air damper in the insulated
attic floor, hinged on the north side, tilted up to the south and a fan blew
air down from the attic peak through one of the pv cavities, in sunny times.

ovshinsky shingles are made in california, and make about 50 w/m^2 in peak sun
at 25 c, according to engineer jim young at united solar (800) 397-2083, who
says this only decreases to 45 w/m^2 at 60 c. he says the current retail price
of their least expensive product is about $4.50/peak watt.

nick

ps: i would guess these shingles won't get cheaper quickly, from this email
dialog with villanova university's professor singh, posted with permission. 

date: fri, 29 mar 1996 10:08:16 -0500
to: nick@ece.vill.edu (nick pine)
from: "dr. p. singh" 
subject: re: inexpensive pvs...

nick:

        i am glad to see that you are getting some opportunities to contribute
to a few solar home designs. i have still not found a student group to work
on the solar shed - as soon as i do we'll follow up on that project. 

>he didn't mention that it was that complex, and i'd gotten the impression
>somehow that the substrate was ordinary cheap mild steel...

        ovshinsky's panels used to use a japanese steel because they could
not find an american steel manufacturer that made steel with a smooth enough
morphology to make good devices !! the process is complicated because the
amorphous silicon needs to have a low enough density of impurities and
defects in order to make devices. the amorphous silicon solar panels
actually start off as 8-10% efficiency and drop down to 5% because of
optical generation of defects in the amorphous silicon material. in
research, non-degraded 10% amorphous silicon cells have been demonstrated
but i don't think that they have reached production yet. 

        it is actually quite difficult to make solar cells that are 10%
efficient - especially over large areas. imagine making square feet of solar
panels that are low in defects and impurities - it's not easy !! 

        the only company electrodepositing solar panels is bp solar in
england. i'm not sure of the status of their production. 

        i hope that this information is useful to help you understand a
little more about pv processing. please feel free to disseminate this
information to whomever you wish - but i would like you to mention me as the
source in case others wish to contact me for more information (especially on
my research work). 

        hope we see some sun again soon - it's quite dreary outside today.

        pali
         
at 04:08 pm 3/28/96 -0500, you wrote:
 
 hi pali,
 
 >        i have a couple of corrections to make to your statements about my
 >pv research and ovshinsky's panels.
 
 thank you.
 
 >i am working on electroplated solar cells on transparent substrates.
 
 sorry, i guess i missed that when you explained to me what you were doing.
 
 >the electroplating process is a low temperature process (60 c) and so could
 >potentially be used on plastic substrates with a transparent conducting
 >oxide (such as tin oxide or indium tin oxide) as the transparent contact.
 >this would allow potentially low cost devices to be manufactured since the
 >process and materials costs could both be very low. the transparent substrate
 >would also allow heat to pass through so that the use of these devices in
 >a hybrid electrical/thermal system would be a great idea. it also makes
 >a lot of sense to use these types of pv cells in a hybrid solar collector
 >with a heat exchanger because that would allow the cells to operate a
 >little more efficiently !!
 
 i do recall your mentioning that a little company in maryland was actually
 producing these... ovshinsky pvs make 50 w/m^2 in peak sun at 20 c, and 45 w
 at 60 c. i wonder about the efficiency of your plated cells might be at
 40-60 c, ie water heating temps... or will that damage them?
 
 in ovshinsky's case, the pvs would absorb 90% of the sun as heat, which might
 heat air or water directly, but in your case, i guess that 90% would shine on
 through the  cell to strike a dark surface, perhaps behind another transparent
 layer with an air gap on each side, so your cells would run cooler in this
 application, i guess. 
 
 >i will keep you informed as to how the research is going but don't hold
 >your breath - after all it is research and may take a few years to get to
 >a point before it is commercially viable. 
 
 sure... altho you seem to be more interested in coming up with a practical
 product than many other scientists and professors... i'd be happy to post 
 some edited version of this email of yours to our ae list, about 500 amateurs
 worldwide, and a few professionals, with your permission, anon if you like.
 most of the info they get about pvs comes from fairly slanted advertising and
 press releases.
 
 >        in terms of ovshinsky's cells, these are amorphous silicon alloys
 >that are made by a plasma assisted chemical vapor deposition process. those
 >big chambers that you have seen that look like a newpaper press are in fact
 >evacuated chambers in which gases of sih4, geh4, ch4, ph3 (phosphine),
 >ash3(arsine) and b2h6 (diborane) flow. an rf plasma is used to break down
 >these gases and the silicon, germanium, carbon, hydrogen and dopant
 >components are driven to the stainless steel substrate by the capacitive dc
 >self-bias between anode and cathode capacitor plates.
 
 he didn't mention that it was that complex, and i'd gotten the impression
 somehow that the substrate was ordinary cheap mild steel...
 
 >the multiple chambers are used to deposit individual layers of a device
 >that may have as many as 10-12 layers !! this is not an inherently cheap
 >process in small scale production (<10mw/yr.) and so the selling price of
 >$4.50 a peak watt is about the production price of these cells.
 
 i wonder why this has to be so complicated, if they are only aiming at
 5% efficiency? these things are basically just large area pn junctions
 with carefully non-shading top electrode, no? not cmos microprocessors...
 
 >(ussc is very secretive about its books and so the exact production price
 >is generally not known
 
 jim young of ussc gave me that "retail price." i assumed these things cost
 them a lot less to make, at 5% efficiency, and that ussc was charging what
 the market will bear, and making lots of money competing against crystalline
 cells, where mounting area is not a big factor. john page also mentioned
 that ovshinsky seemed to leave out some details in his talk. 
 
 >but solarex's
 >thin film division makes a similar product and they are selling the cells
 >for more than it costs to make them). as far as i am aware only the solarex
 >polycrystalline silicon cell division is making money as a solar cell
 >manufacturer and they are selling at about $3.50 a peak watt for large
 >orders. there is a joint venture between enron corp. and amoco (solarex's
 >parent company) to make a 10 mw/yr. thin film pv manufacturing facility in
 >virginia. until now the amorphous silicon community has said that the cost
 >of amorphous silicon pv will drop dramatically (down to less than $1/wp) if
 >they could take advantage of economies of scale and produce at least 10mwp/yr.
 
 seems like they have been saying that for 30 years :-) i read a paper
 by ovshinsky in physics review in about 1966...
 
 >enron has called their bluff and so let's see what happens !! keep posted.
 
 ok...
 
 >in the meantime solarex's polycrystalline silicon cell division is
 >ramping up to increase their production capacity three-fold and siemens
 >solar (what used to be arco solar) is also increasing production. so there
 >is a growing market for pv but primarily for remote applications in
 >developing countries. 
 
 the figure i heard is that 80% of our pv production goes overseas, a lot
 of that to the 2 vbillion people  in the world who have no elecrcity at all. 
 just mud and tin huts with dry cells and candles, i guess.
  
 >        i agree that we should start any solar home design with trying to
 >meet the heating load of a house through good passive solar design (after
 >insulating the house as well as possible) and then look to fund pv to supply
 >the necessary but small electric load (if economically justified). 
 
 good. would you still like a solar shed in your yard?
 
 >        i'm still looking for students for solar homes projects - i'll let
 >you know if i get any bites. 
 
 thanks. i'm going to try to show up for the second day of the current
 senior project talks. dr. k sent me a schedule. meanwhile, i'm helping
 design a 100% solar house in lebanon, pa, and it looks like i might
 be helping design another in seattle, where they have no sun :-), and my
 episcopal friend father jim evans from phoenixville, who has built about
 500 low income houses in this area over the last 10 years or so, some with
 his own hands, says he'd like me to help figure out how to make cheaper
 electricity for people in st kitts, which has lots of wind, 16 mph average
 in some places, and some dormant volcanos with geothermal potential. he's
 building a conference center surrounded by 50 new vacation homes, which
 may want solar water heaters in the roofs, combined with pvs?

nick




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