Posted by jacjentait on February 1, 2004, 8:59 am
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
Posted by Anthony Matonak on February 1, 2004, 12:53 pm
jacjentait wrote:
> 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 ?
...
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
Posted by nicksanspam on February 1, 2004, 2:59 pm
>...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?
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
Posted by nicksanspam on February 2, 2004, 9:52 am
>...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?
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'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*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 OHB0*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 %
Posted by George Ghio on February 3, 2004, 9:24 am
nicksanspam@ece.villanova.edu wrote:
>
> >...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?
>
> I can picture something like this on the ground, made from 12 18' pieces
> of Unistrut, viewed in a fixed font:
>
>At dawn, in full sun, the panels might
>see about 0.9x0.9x0.9x800W/m^2x16'/6' =
>1555 W/m^2... 6 62"x32.5" 165 W Sharp
>panels might produce 1539 watts, if
>they are cooled by a few inches of water
>flowing through plastic film ducts on top.
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?
>The panels would dissipate about 1539/0.15
>10.2K Btu/h of heat. A couple of Attwood
>V1250 24V 35W bilge pumps could move 42 gpm
>of pool water through the ducts, keeping the
>panels about 10.2K/(42x8x60) = 2 F above the
>24-hour shaded-pool wet bulb temp.
What is the duty cycle of these pumps?
>
> With a basement heat store, this might also provide some
> wintertime space heating or hot water for showers.
"Might" have several lbs of frozen water sitting on the panels.
>
> It could have a building underneath.
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
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> 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 ?
...