Posted by nicksanspam on August 26, 2006, 2:23 pm
Oops... per hour.
Posted by Gary on August 26, 2006, 2:34 pm
This may be more than what you had in mind, but Apogee pyranometers are designed
and calibrated to read the full spectrum solar intensity.
I use the amplified one with a multimeter or my Onset data logger. It appears
to work well. They start around $40. The amplified ones put out 1 mv per 0.5
watt/m^2 of sunlight, or about 2.0 volts for full sun -- so, they work well with
Apogee uses silicon cell that senses radiation from 350 to 1000 nm and
calibrates this to the full solar spectrum. They also use a light gathering
dome that handles cosine effects. The page below has some info on the ins and
outs of measuring solar radiation.
One thing that I thought about doing, but never got there, was to use something
like the PV cells discussed in the posts above, and do the calibration (which is
the hard part) by getting the hour by hour solar isolation data from the our
nearest weather station.
"Build It Yourself" Solar Projects
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Posted by daestrom on August 26, 2006, 3:50 pm
Yes, I agree about the 'calibration is the hard part'.
But even uncalibrated, a datalogger monitoring the output of a PV cell could
be 'interesting'. It could show hourly (or better) changes in output in a
given location. This could give one a lot of information about the mean
time between sunny days throughout a heating season. And that could go a
long way towards calculating storage and backup heater requirements.
Posted by schooner on August 26, 2006, 4:43 pm
Our main use is just to get some sort of reading, as meaningless as it might
be on its own, for use to compare one day to the next and one panel to
another. When building new panels and measuring their temp diff and air
output it is hard to compare one panel to another without knowing what the
solar radiation level was on a given day.
I just created a simple "meter" using a small solar panel cell from radio
shack, a 10 ohm resister, and a millimeter to read to voltage across the
resistor. Seems to do the trick. Amazing just how it varies from minute to
minute even when the sky looks clear and the big drops when a cloud appears.
Since the panel is rated for 0.55V at high noon in direct full sun there is
some basic level of calibration, knowing when you are getting near the max
From the comments maybe I should use the resistor but some sites seem to say
to use one such as this one:
Posted by SJC on August 26, 2006, 6:07 pm
be on its own, for use to compare one day to the next
diff and air output it is hard to compare one panel
shack, a 10 ohm resister, and a millimeter to read to
varies from minute to minute even when the sky looks
some basic level of calibration, knowing when you are
to use one such as this one:
If your multimeter can read D.C. current up to an amp, then you could just
read the current through the meter as a shorted load. You should get a very
linear response and no temperature coefficient through the external resister.
It would be interesting to see the results of the relative test when it looks
a bit overcast in the winter. The current reading will be only a fraction of
your "calibrated" current under full sun , but IR strength may be enough to
create more heat than you thought.
solar radiation levels for checking solar hot air
available on a given day to compare panel output
be 'interesting'. It could show hourly (or better)
information about the mean time between sunny days
calculating storage and backup heater requirements.