PV module temp [RE-wrenches]

Tue Sep 25 23:24:14 PDT 2001

I ought to get some sleep!

80 F. (26.6 C.) ambient temperature will result in approx. 115 F. (46.6 C.) cell
temperature.

Travis' 80 F. (26.6 C.) ambient temperature and 140 F. (60 C.) cell is high but
possible.

Here's some more empirical data. In Los Angeles, on August 1, 1999, at 1PM PDT at 870
watt/m2 insolation and ambient temperature 77.5 F. (25.3 C.), an SP70 cell in a 10
degree tilt solar array mounted 3.5 inches above a composition roof measured 111.2 F
(44 C.).

jay peltz wrote:

> Hi Joel,
>
> I think you had better check your math.
>
> A difference of 20 degrees C is   36 degrees F.
>
> The difference is that if the air temp is 20 degrees C, then that does equate to 68
> degrees F, but thats not what is being discussed.
>
> jay
>
> Joel Davidson wrote:
>
> > The formula for converting C. to F. is ((C + 40)1.8) - 40 = F.
> >
> > The formula for converting F. to C. is ((F + 40)0.555) - 40 = C.
> >
> > Cell temperature is approx. 20 degrees C. (68 F.) above ambient air temperature.
> > If ambient air temperature is 80 F., I expect cell temperature to be approx. 148
> > F and find it to be so. An open rack PV system in Pasadena receiving 700 to 900
> > W/m2 at ambient 33 C. consistently measures 55 C. cell temperature since 1996.
> >
> > In Tokyo, a roof mounted single crystal array with black tedlar and black frame
> > raised and boxed in over an existing roof with no air circulation measured 83 C.
> > cell temperature in September. (The IEEE report on this test is somewhere in my
> > office, but I can't put my hands on it. I think the testing was done in 1993 or
> > 1994.) For many years, I told engineers in Japan not to use black tedlar or box
> > in the array. They said that the customer wants a uniform all black appearance
> > and does not want to provide bird nesting places.
> >
> > If the peak voltage of a solar module at 25 C. is 17 volts, at 83 C. module
> > voltage is 12.62 volts.
> > 83 C - 25 C = 58 C difference in temperature x 0.0021 generic voltage
> > coefficient for single crystal cells x 36 cells = 4.38 volts drop.
> >
> > Bill Brooks wrote:
> >
> > > Joel,
> > >
> > > Careful with your units. The boys on the other side of the globe might get a
> > > little testy. You are referring to 20C hotter than ambient temp (probably
> > > more than that for roof mounted arrays) which is only 36F hotter than
> > > ambient (not 68F--68F=20C when we are talking actual temperatures, not
> > > temperature difference). Degrees C is 1.8 times degrees F when looking at
> > > differences.
> > >
> > > On a 40C day in full sun (1000 W/m2), I measured 70C (158F) on an open rack
> > > array. That's 30C which is worst case rather than 20C which might be an
> > > annual average.
> > >
> > > Bill.
> > >
> > > > -----Original Message-----
> > > > From: Joel Davidson [mailto:joeldavidson at earthlink.net]
> > > > Sent: Tuesday, September 25, 2001 2:53 PM
> > > > To: RE-wrenches at topica.com
> > > > Subject: Re: PV module temp [RE-wrenches]
> > > >
> > > >
> > > > Single crystal and polycrystalline cell temperature is approx. 20
> > > > degrees C. (68 F.)
> > > > above ambient air temperature. The sensor should measure the cell
> > > > temperature, not
> > > > the atmosphere at the back of the panel.
> > > >
> > > > Smitty wrote:
> > > >
> > > > > Trav, the insulation is probably giving you a high reading. The
> > > > sensor should be
> > > > > exposed to the same atmosphere that the back of the panel is. Smitty.
> > > > >
> > > > > "Travis Creswell, Ozark Solar" wrote:
> > > > >
> > > > > > Hey Gang,
> > > > > >
> > > > > > I have hooked up a Heliotrope Quadra Temp four channel temp
> > > > monitor that
> > > > > > uses 10k sensors.  One of the channels is monitoring temp on
> > > > the back of a
> > > > > > module in my roof mounted PV array.  I'm seeing temps of
> > > > nearly 140 F on
> > > > > > sunny days that the ambient temp doesn't get past 80 F.  That
> > > > seems pretty
> > > > > > high.  The sensor is fine as it reads ambient temp accurately
> > > > after sunset
> > > > > > plus I checked it before I installed it.  I siliconed the
> > > > sensor along with
> > > > > > a small piece of Armaflex insulation on the back
> > > > approximately in the center
> > > > > > of the module.
> > > > > >
> > > > > > I insulated it so the temp would be more accurate but now I
> > > > am wondering if
> > > > > > I'm not holding heat in with the insulation causing the temp
> > > > to be too high?
> > > > > >  But if I don't insulate it won't it read too cool?
> > > > > >
> > > > > > Suggestions?
> > > > > >
> > > > > > Thanks in advance.
> > > > > >
> > > > > > Travis Creswell
> > > > > > Ozark Solar
> > > > > >
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