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Discussion in 'Photovoltaics' started by jacjentait, Feb 1, 2004.

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  1. jacjentait

    jacjentait Guest

    super conductors work at cold temps
    so
    would water cooling / refridgerating the back of the PV cell generate more
    current ?
    would backing the cell with a cold magnetic material to help electron jump ?

    some simple thought logic . william james tait
     
  2. ....

    I don't think super conductors or magnets are particularly related
    to PV's and probably wouldn't help here on Earth.

    PV cells do lose efficiency as their temperature rises. This means
    that you can get more power out by simply cooling them. The question
    is how much does this cooling equipment cost in materials, maintenance
    and energy to run vs. how much extra energy it helps to produce.

    I.e. If it takes a kilowatt to run the pumps to cool the panels and
    you only get half a kilowatt extra out of the panels then why do it?

    Anthony
     
  3. Guest

    I can picture something like this on the ground, made from 12 18' pieces
    of Unistrut, viewed in a fixed font:

    |
    . |
    F| At dawn, in full sun, the panels might
    . r| see about 0.9x0.9x0.9x800W/m^2x16'/6' =
    e| 1555 W/m^2... 6 62"x32.5" 165 W Sharp
    Dynaglas . s| panels might produce 1539 watts, if
    n| they are cooled by a few inches of water
    . e| flowing through plastic film ducts on top.
    18' l| 16'
    . | The panels would dissipate about 1539/0.15
    r| 10.2K Btu/h of heat. A couple of Attwood
    . e| V1250 24V 35W bilge pumps could move 42 gpm
    f| of pool water through the ducts, keeping the
    . | panels about 10.2K/(42x8x60) = 2 F above the
    duct duct | 24-hour shaded-pool wet bulb temp.
    . panel panel |
    -----------------|------evap pool-----
    | ~6' | ~8' | ~1'
    ......................................................


    --------------------------------------
    | | |
    | | |
    | P P | |
    |-----------------| |
    | V V | |
    | | |
    | P P | 10' wide |
    |-----------------| EPDM rubber | 16'
    | V V | |
    | | |
    | P P | |
    |-----------------| |
    | V V | |
    | | |
    | | |
    --------------------------------------

    With a basement heat store, this might also provide some
    wintertime space heating or hot water for showers.

    It could have a building underneath.

    Nick
     
  4. Guest

    I can picture something like this on the ground, made from 17 18' pieces
    of Unistrut, viewed in a fixed font:

    |
    . |
    F| At dawn, in full sun, the panels might
    Dynaglas . r| see about 0.9x0.9x0.9x800W/m^2x16'/6' =
    corrugated e| 1555 W/m^2... 6 62"x32.5" 165 W Sharp
    polycarb. . s| panels might produce 1539 watts, if
    n| they are cooled by a few inches of water
    . e| flowing through plastic film ducts on top.
    18'purlin l| 16'
    . | The floor would receive about 6x16x1555/10.76
    r| -1539 = 12.3kW of net heat. Two Attwood V1250
    . e| 24V 35W bilge pumps could move 42 gpm of
    purlin f| water through the ducts, keeping the panels
    . | about 12.3Kx3.41/(42x8x60) = 2 F above the
    duct duct | 24-hour shaded-pool wet bulb temp.
    . panel panel |
    -----------------|------evap pool-----
    | ~6' | ~8' | ~1'
    ......................................................


    --------------------------------------
    | | |
    | | |
    | P P | |
    |-----------------| |
    | V V | |
    | | |
    | P P | 10' wide |
    |-----------------| EPDM rubber | 16'
    | V V | |
    | | |
    | P P | |
    |-----------------| |
    | V V | |
    | | |
    | | |
    --------------------------------------

    With sun elevation theta, the panels would see approximately
    800x0.9x0.9/3.28(6+16x0.9) = 1185(sin(theta)+2.4cos(theta)) = 3082 W/m^2
    (3 suns max), when theta = 26.2 degrees, producing about 3051 watts
    of electricity with about 83.4K Btu/h of net heat on the floor, so
    the panels might be about 83.4K/(42x60x8) = 4.1 F warmer than
    the 68.4 F (20.2 C) 24-hour wet bulb temp in Phila in July.

    Nick

    10 PI=4*ATN(1)
    20 AXISELD=12'axis elevation above horizon (degrees)
    30 AXISEL=PI*AXISELD/180'axis elevation above horizon (radians)
    40 FL=6'focal length (feet)
    50 HEIGHT=1.33'reflector height (feet)
    60 N=9'number of strip reflectors
    70 PRINT"strip #","bottom (ft)","top (ft)","spacer (in)","tilt (deg)"
    80 PRINT
    90 A=ATN(HEIGHT/FL)'initial est angle to focus (rad)
    100 FOR STRIP=1 TO N'reflector strip # (from bottom)
    110 TILT=(A-AXISEL)/2'reflector tilt from vertical (rad)
    120 D=HEIGHT*SIN(TILT)'spacer (feet)
    130 TH=TB+HEIGHT*COS(TILT)'upper strip edge height (feet)
    140 AH=ATN(TH/(FL-D))'new estimate
    150 IF ABS((A-AH)/A)>.001 THEN A=AH:GOTO 110'iterate to 0.1%
    160 SPACER=12*D'spacer width behind top of strip (inches)
    170 PRINT STRIP,TB,TH,SPACER,180*TILT/PI
    180 TB=TH+D*TH/(FL-D)'next bottom edge height (feet)
    190 NEXT STRIP
    200 CONC=N*HEIGHT/FL'concentration ratio
    210 OHB=100*D/FL'overhead sun blocking (%)
    220 PRINT
    230 PRINT"height=";TH,"conc=";CONC,"ohb=";OHB;"%"

    strip # bottom (ft) top (ft) spacer (in) tilt (deg)

    1 0 1.329988 0.069425 0.2492357
    2 1.331271 2.653542 1.718152 6.180075
    3 2.718412 4.021652 3.185456 11.51298
    4 4.207816 5.485535 4.430827 16.11825
    5 5.845247 7.095126 5.455744 19.98893
    6 7.676832 8.899349 6.285437 23.19267
    7 9.75055 10.94771 6.952877 25.82627
    8 12.11791 13.29236 7.489846 27.98812
    9 14.83565 15.99017 7.923422 29.76574

    height= 15.99017 conc= 1.995 ohb= 11.00475 %
     
  5. Well, it's a long way from superconductor territory, but PV cell
    voltage does droop with increasing temperature, so there is some
    advantage to cooling the panels if ambient temperatures are high. A
    good PV controller can take advantage of this.

    Practical photovoltaics (Richard Komp) briefly describes a couple of
    home-brew hybrid panel ideas for shuffling heat off the back of the
    cells into air or fluid.

    I think this might be more common in commercial products except that
    linking the two functions together would narrow the market.

    The next few years may be interesting however.

    -=s
     
  6. George Ghio

    George Ghio Guest

    The clue to Nicks advice is the frequent use of the word "Might"

    Full sun at dawn? Not likely unless the array is mounted on top of a
    building with clear view of the horizon.

    What shape ducts?

    If they are tubular what is the effect of lens effect of the water on
    energy production?

    What are the losses through a couple of inches of water and two layers
    of plastic?

    How much energy is lost to pumping the water and moving the panels or
    mirrors?

    If moving the panels what about the transfer of weight of water?
    What is the duty cycle of these pumps?
    "Might" have several lbs of frozen water sitting on the panels.
    Love this bit. A building under the basement.

    I can picture something like this, Nick Pine in building under the
    basement with an automatic banana feed. Free hot air for heating.

    For a domestic installation the cost would exceed the gain. If it was at
    all an economical proposition it would be done everywhere.

    Nicks plan would have at least 3 motors running for the greater part of
    day light hours. Four motors if duel axis tracking was used.

    The number of moving parts of the drawn design would guarantee an
    unacceptable amount of maintenance.

    George
     
  7. Guest

    Flattish... 30" 6 mil UV poly film greenhouse air distribution ducts
    (about 40 cents per linear foot) laid flat on top of the PV panels
    so they are about 44" wide and 2" tall when the sun is shining, and
    empty at night.
    Almost none for the water itself. The air-plastic interface would have
    a Fresnel loss of about 4%, with a lot less for polyethylene-water and
    polyethylene-glass interfaces, with some sort of matching goo. You might
    look up the refractive indices and work this out.
    ....70 watts max, as mentioned below. The panels and mirrors don't move.
    Perhaps 8 hours per day in July. Less in winter, when more heat is needed.
    Intelligent control.
    You may be confused, my good man. Pick one:
    1. Basement heat store with PVs on a ground rack, or
    2. No basement heat store, with a building under the rack.

    Nick

    ....something like this on the ground, made from 15 18' pieces of Unistrut,
    viewed in a fixed font:

    |
    . |
    F| At dawn, in full sun, the panels might
    . r| see about 0.9x0.9x0.9x800W/m^2x16'/6' =
    e| 1555 W/m^2... 6 62"x32.5" 165 W Sharp
    Dynaglas . s| panels might produce 1539 watts, if
    n| they are cooled by a few inches of water
    . e| flowing through plastic film ducts on top.
    18' l| 16'
    . | The floor would receive about 6x16x1555/10.76
    r| -1539 = 12.3kW of net heat. Two Attwood V1250
    . e| 24V 35W bilge pumps could move 42 gpm of
    f| water through the ducts, keeping the panels
    . | about 12.3Kx3.41/(42x8x60) = 2 F above the
    duct duct | 24-hour shaded-pool wet bulb temp.
    . panel panel |
    -----------------|------evap pool-----
    | ~6' | ~8' | ~1'
    ......................................................


    --------------------------------------
    | | |
    | | |
    | P P | |
    |-----------------| |
    | V V | |
    | | |
    | P P | 10' wide |
    |-----------------| EPDM rubber | 16'
    | V V | |
    | | |
    | P P | |
    |-----------------| |
    | V V | |
    | | |
    | | |
    --------------------------------------

    With sun elevation theta, the panels would see approximately
    800x0.9x0.9/3.28(6+16x0.9) = 1185(sin(theta)+2.4cos(theta)) = 3082 W/m^2
    (3 suns max), when theta = 26.2 degrees, producing about 3051 watts
    of electricity with about 83.4K Btu/h of net heat on the floor, so
    the panels might be about 83.4K/(42x60x8) = 4.1 F warmer than
    the 68.4 F (20.2 C) 24-hour wet bulb temp in Phila in July.

    strip # bottom (ft) top (ft) spacer (in) tilt (deg)

    1 0 1.329988 0.069425 0.2492357
    2 1.331271 2.653542 1.718152 6.180075
    3 2.718412 4.021652 3.185456 11.51298
    4 4.207816 5.485535 4.430827 16.11825
    5 5.845247 7.095126 5.455744 19.98893
    6 7.676832 8.899349 6.285437 23.19267
    7 9.75055 10.94771 6.952877 25.82627
    8 12.11791 13.29236 7.489846 27.98812
    9 14.83565 15.99017 7.923422 29.76574

    height= 15.99017 conc= 1.995 ohb= 11.00475 %
     
  8. George Ghio

    George Ghio Guest

    Oh I am sorry I thought that the pumps ran for more than an hour.
    Explain this;

    At dawn, in full sun, the panels might see about
    0.9x0.9x0.9x800W/m^2x16'/6'

    If neither the panels or mirrors move it would perhaps be better that
    the panels face south. Faceing east to see sun rise?
    No that is the expected run time. What is the rated duty cycle of the
    named pump? 20%? 50%?
    Sorry but you said;

    With a basement heat store, this might also provide some
    wintertime space heating or hot water for showers.

    It could have a building underneath.

    All this aside what is the cost to set this up?

    Oh sorry, I forgot you don't know. You have never done this. Never will
    do it. If you want to sell this the materials will need to be new. It
    would also have to be cheaper than adding panels to the same energy
    value.

    When you get to the point where you can say;

    'I have built this and it supplies X amount of energy beyond panels
    without cooling at a cost this much less than adding panels to the same
    energy gain'

    then you may be taken seriously.

    George
     
  9. George Ghio

    George Ghio Guest


    Oh yeah, 70 watts is .56 kWh a day.

    70W X 8hours.
     
  10. Guest

    Glass is 1.526. Water is 1.33...
    Watts vs watt-hours makes it clear the pumps can return
    something like 50X more electrical power than they use.
    The polycarbonate cover transmission is 0.9, the mirror reflectance is
    about 0.92, and I underestimated the duct transmission as 0.9. The 16/6
    is the concentration ratio at dawn. How much sun bounces back out through
    the cover or off the reflective endwalls?
    Horizontal panels seem easy to mount and cool, with a vertical reflector
    facing south.
    ....100%, with a $33 price and a 3-year guarantee. They'll be in fairly clean
    cool fresh water most of the time, altho they're tested in hot salty mud,
    among other things.
    Here's a partial materials list:

    $3000(?) 6 Sharp 165 W PV panels
    2000 24 V grid-tie inverter
    800 280' of Unistrut
    12 32' poly film ducts
    66 2 24 V 21 gpm pumps
    300 pump controls, hoses, etc.
    400 288 ft^2 Dynaglas
    50 180 ft^2 EPDM
    88 256 ft^2 1" foil-faced foamboard
    20 192 ft^2 metalized Mylar film
    -----
    $6736 for 3 kW peak, with useful hot water, vs

    $5800 for 800 W peak, with no hot water, for
    a system with only the first three parts.

    Nick
     
  11. Guest

    The air-plastic interface would have a Fresnel loss of about 4%, with
    And low-density polyethylene is 1.51, so we have about 0.96 transmission
    into the poly, 1-((1.51-1.33)/(1.51+1.33)^2 = 0.996 from poly to water and
    water to poly, and almost nothing from poly to glass (compared to 0.96 with
    panels in air?), so it looks like the net penalty is less than 1%.

    Nick
     
  12. George Ghio

    George Ghio Guest

    So in 8 hours you use 560 Wh for a return of 28000 Wh
    I see the panels are fixed and the mirrors are fixed. So the mirrors
    will direct sun across the panels for what, An hour in the middle of the
    day, Maybe a whole ninty minutes and for the rest of the day the panels
    will recieve a fraction of the available energy due to poor angle.

    Anyway it is all a moot point until you build it. You can't, and even if
    you did it would cost at least twice what you quote and not perform to
    your claims. And the pump will last for about 5 months or less. 1000
    hours being about it for such a motor. You see Nick, you have no
    experience. Theory is great but more often than not fails to prove true.
    This is the difference between theory and fact.

    So just once in your life. Do it. Prove you're right. While most people
    here are doing things you are all talk. Hell, even Wayne has managed a
    working system even if he can't explain it.

    George
     
  13. Bill Shuler

    Bill Shuler Guest

    Yes,
    cooling a pv does cause it to harness more energy. I proved this with
    a pv b4 putting it up. Using a dmm, I checked the voltage and amperage
    on the warm, dry pv in the sun versus wetting it down. The power increased
    when the pv was water cooled. I do not recall how much, for I did not make
    note.
    I am thinking of building a system with pv s mounted on a heat collector
    with
    a liquid medium w/i to help heat water being circulated to a heat exchanger
    within a water heater tank- thereby harnessing
    more power- electric and heat.

    Bill

    Also, there is no such thing as a stupid question.
     
  14. wmbjk

    wmbjk Guest

    You might try talking about what *you're* doing, rather than criticizing
    others for using a discussion group for <gasp> discussion. I see that
    your web site has been expanded http://www.citlink.net/~wmbjk/tbfdu.htm.
    I guess you figured out that the more often the site gets mentioned, the
    sooner it will be on the top of any web search for your name. So your
    plan is to keep prodding me to mention the URL? I knew you must be doing
    something productive.

    Wayne
     
  15. George Ghio

    George Ghio Guest

    Well Wayne I do want people to look at your site. It is an interesting
    design you have chosen. People can learn a lot from your site. Of course
    they could learn a lot more if your site had realistic numbers that
    would add up. But still and all worth the study.
     
  16. George Ghio

    George Ghio Guest

    Been a while so here are some pics of my work for those that have not
    seen them before. Charts and circuits as well as some of my
    installations around central Victoria.

    George
     
  17. wmbjk

    wmbjk Guest

    And I think that your site http://www.citlink.net/~wmbjk/tbfdu.htm
    (updated for the second time this morning) is an excellent primer for
    anyone considering sending you money for your book.

    Wayne
     
  18. wmbjk

    wmbjk Guest

    Invisible pictures? Excellent strategy.

    Wayne
     
  19. ....
    How about using an airflow to cool this. With aluminum heat fins into a
    light aluminum channel to carry the air, you could arrange it to naturally
    convect, then just add a bit of forced air with a fan. Well, it's an idea.
    Easier to build than a water based system.
     
  20. Bughunter

    Bughunter Guest

    Good one!

     
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