Cooling PVs
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nick pine
Mar 16, 2012, 3:59:00 AM3/16/12
to sunspace, jkpr...@verizon.net
I like these $159.99 500 W Chinese grid-tie inverters
http://www.amazon.com/Small-Inverter-Converter-24-52v-90v-130v/dp/B005N2B0C2/ref=sr_1_1?ie=UTF8&qid=1331847121&sr=8-1
The least expensive PVs I've found so far are AUO panels which make
240 watts at 44 C in 1kW/m^2 sun with a 14.4% efficiency and a -0.44%
power tempco and an 80 C max operating temp, for $1.28/Wp, including
shipping. I'd like to raise their output to at least 250 watts so 2
panels can drive a 500 watt inverter. I could lay them flat on the
north edge of a deck and lay a piece of greenhouse poly film on top to
make a shallow water trough. At my 40 N lat, 6/21 beam sun at noon has
a 90-40+23.7 = 73.5 degree elevation.
In July, Phila has an average 0.0133 outdoor humidity ratio, with Pa =
29.921/(0.62198/0.0133-1) = 0.654 "Hg. At the wet bulb temp, Bowen's
1926 equation says 100(Pw-Pa)/(Twb-Td) = -1, ie Twb = 9621/(22.47-
ln(Td-Twb+100Pa) = 9621/(22.47-ln(606.8-Twb), with Td = 460+81.4 R and
Twb (R). Plugging in Twb = 70 F (530 R) on the right makes Twb = 530.7
on the left. Repeating makes Twb = 530.4, then 530.5 R, ie 70.5 F or
19.2 C, so the panel output would increase by 100(46-19.2)0.0044 =
11.8% if cooled at the wet bulb temp, eg 240x1.118 = 268 watts under 1
kW/m^2 sun.
How tall should the reflector be to make 250 watts per panel at noon
on 6/21? If P = (800+1.9h800)268/1000 = 214(1+0.9h) with h in meters,
h = 0.0052P-0.9 meters, eg 0.39 meters for 250 watts or 0.826 for 333
watts. A 4' (1.22 m) reflector would make 450 watts peak, or 2.7 real
kW for 6 panels, enough for 4 or 5 $159.99 500 W grid tie inverters.
They have overcurrent protection, so they probably don't mind
overdriving.
With 5 inverters, this system would cost about $2638.60/2.5kW = $1.06
per real peak watt.
I see 240 watt panels at 80 cents/watt at http://www.soldist.com/clearance/
Nick
http://www.amazon.com/Small-Inverter-Converter-24-52v-90v-130v/dp/B005N2B0C2/ref=sr_1_1?ie=UTF8&qid=1331847121&sr=8-1
The least expensive PVs I've found so far are AUO panels which make
240 watts at 44 C in 1kW/m^2 sun with a 14.4% efficiency and a -0.44%
power tempco and an 80 C max operating temp, for $1.28/Wp, including
shipping. I'd like to raise their output to at least 250 watts so 2
panels can drive a 500 watt inverter. I could lay them flat on the
north edge of a deck and lay a piece of greenhouse poly film on top to
make a shallow water trough. At my 40 N lat, 6/21 beam sun at noon has
a 90-40+23.7 = 73.5 degree elevation.
In July, Phila has an average 0.0133 outdoor humidity ratio, with Pa =
29.921/(0.62198/0.0133-1) = 0.654 "Hg. At the wet bulb temp, Bowen's
1926 equation says 100(Pw-Pa)/(Twb-Td) = -1, ie Twb = 9621/(22.47-
ln(Td-Twb+100Pa) = 9621/(22.47-ln(606.8-Twb), with Td = 460+81.4 R and
Twb (R). Plugging in Twb = 70 F (530 R) on the right makes Twb = 530.7
on the left. Repeating makes Twb = 530.4, then 530.5 R, ie 70.5 F or
19.2 C, so the panel output would increase by 100(46-19.2)0.0044 =
11.8% if cooled at the wet bulb temp, eg 240x1.118 = 268 watts under 1
kW/m^2 sun.
How tall should the reflector be to make 250 watts per panel at noon
on 6/21? If P = (800+1.9h800)268/1000 = 214(1+0.9h) with h in meters,
h = 0.0052P-0.9 meters, eg 0.39 meters for 250 watts or 0.826 for 333
watts. A 4' (1.22 m) reflector would make 450 watts peak, or 2.7 real
kW for 6 panels, enough for 4 or 5 $159.99 500 W grid tie inverters.
They have overcurrent protection, so they probably don't mind
overdriving.
With 5 inverters, this system would cost about $2638.60/2.5kW = $1.06
per real peak watt.
I see 240 watt panels at 80 cents/watt at http://www.soldist.com/clearance/
Nick
barbara deane-gillett
Mar 16, 2012, 8:48:50 AM3/16/12
to suns...@googlegroups.com, jkpr...@verizon.net
amazing what the chinese can do with 70% of the worlds pv production!
one caution, the extra radiation from the reflector needs to be evenly distributed over the module since the cells are in series and current is limited to that of the least irradiated cell. some newer modules get around this a bit with special wiring, but not the cheap ones.
also saw enphase grid tie inverters 200 watts for $167 with individual panel monitoring.
no problem with "overdriving" i.e. 2700 watts of panel for 2000 watts of inverter since the ratings are based on different things . also the inverter should harmlessly receive max power from panel , if more is available than inverter rating, it should clip at that level by simply allowing panel volts to go up and amps down. should this occur during peak sun or additional reflection from passing clouds, no problem should result other than losing slight amount of energy.
my 240w panels in fl have yet to peak out its 200watt inverter. i expect that in summer a bit. there is a tracker in wisc that regularly peaks at 10am-2pm clipping about 5% of the annual energy.
google" enphase enlighten live public sites "for more info.
> Date: Fri, 16 Mar 2012 00:59:00 -0700
> Subject: Cooling PVs
> From: pine...@gmail.com
> To: suns...@googlegroups.com
> CC: jkpr...@verizon.net
> Subject: Cooling PVs
> From: pine...@gmail.com
> To: suns...@googlegroups.com
> CC: jkpr...@verizon.net
nick pine
Mar 17, 2012, 7:59:35 AM3/17/12
to sunspace, jkpr...@verizon.net
PE Drew Gillett writes:
>one caution, the extra radiation from the reflector needs to be evenly distributed over the module since the cells are in series and current is limited to that of the least irradiated cell. Some newer modules get around this a bit with special wiring, but not the cheap ones.
A 48" vertical Mylar reflector would illuminate less than a 39" panel
width when the sun elevation is higher than atn(48/39) = 51 degrees,
but that seems OK with water cooling under 2 suns. I'd mainly like
more summer energy to power my AC and walk-in cooler. Should I paint
the reflector white instead of using Mylar?
Looking closer at the AUO PM240P00 data sheet, it only produces 240
watts under Standard Test Conditions (STC), ie 25 C in 1 kW/m^2 sun.
Astronergy's CHSM6610P looks like a better bargain, producing 235
watts at 25 C STC with a -0.469%/K Pmpp tempco, at a cost of $1.10/
watt, including shipping. It's rated at 176.3 watts at the 43 C (109
F) Normal Operating Condition Temperature (NOCT.)
The panel output would only increase by 100(25-21.4)0.469 = 1.7% if
cooled to the wet bulb temp, eg 235x1.017 = 239 watts under 1 kW/m^2
sun.
If P = (800+1.9h800)239/1000 = 191(1+0.9h), an h = 1.22 m (4') 10 cent/
ft^2 vertical Mylar film north reflector would make P = 401 watts
peak, or 2.4 real kW for 6 panels. The inverter spec on Ken's blog
http://ken-nect.blogspot.com/2011/12/how-to-use-three-spare-solar-pv-modules.html
says the max AC output is 600 W at 92% max efficiency, so I'd only
need 4 inverters, lowering the cost to $2191/2.4kW = 91 cents per real
peak watt, or 91/0.92 = 99 cents, including inverter efficiency.
Seems like a nice 15% tax-free investment.
Nick
>one caution, the extra radiation from the reflector needs to be evenly distributed over the module since the cells are in series and current is limited to that of the least irradiated cell. Some newer modules get around this a bit with special wiring, but not the cheap ones.
A 48" vertical Mylar reflector would illuminate less than a 39" panel
width when the sun elevation is higher than atn(48/39) = 51 degrees,
but that seems OK with water cooling under 2 suns. I'd mainly like
more summer energy to power my AC and walk-in cooler. Should I paint
the reflector white instead of using Mylar?
Looking closer at the AUO PM240P00 data sheet, it only produces 240
watts under Standard Test Conditions (STC), ie 25 C in 1 kW/m^2 sun.
Astronergy's CHSM6610P looks like a better bargain, producing 235
watts at 25 C STC with a -0.469%/K Pmpp tempco, at a cost of $1.10/
watt, including shipping. It's rated at 176.3 watts at the 43 C (109
F) Normal Operating Condition Temperature (NOCT.)
The panel output would only increase by 100(25-21.4)0.469 = 1.7% if
cooled to the wet bulb temp, eg 235x1.017 = 239 watts under 1 kW/m^2
sun.
If P = (800+1.9h800)239/1000 = 191(1+0.9h), an h = 1.22 m (4') 10 cent/
ft^2 vertical Mylar film north reflector would make P = 401 watts
peak, or 2.4 real kW for 6 panels. The inverter spec on Ken's blog
http://ken-nect.blogspot.com/2011/12/how-to-use-three-spare-solar-pv-modules.html
says the max AC output is 600 W at 92% max efficiency, so I'd only
need 4 inverters, lowering the cost to $2191/2.4kW = 91 cents per real
peak watt, or 91/0.92 = 99 cents, including inverter efficiency.
Seems like a nice 15% tax-free investment.
Nick
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