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Weather station - sunshine?

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Posted by John W. Hall on May 10, 2004, 2:17 pm
I'm looking into setting up a weather station to record data for
planning solar thermal panels (& because it's an interesting project,
& a friend wants me to introduce him to microprocessors, 1-wire
sensors etc).

Some low-cost kits, e.g. AAG's 1-wire weather station:
measure wind speed & direction, and one can add instruments for
rainfall & some other criteria.

But I don't see any low-cost stations that measure hours of sunshine,
and I don't know what constitutes "sunshine" when it comes to
measuring/recording it. I suppose one needs to measure direct sunlight
if interested in concentrating collectors, or diffused for flat-panels
(my interest is primarily DHW pre-heating).

I could perhaps find a nearby weather station and get their data, but
we're close to the mountains here, and micro-climates vary
significantly over short distances.

Suggestions or comments welcomed.

I just remembered that a high school here is setting up some solar-PV
panels, and will contact them to see if/what they are measuring. The
school is about 25 km from our proposed solar site, but I might
consider doing a joint weather station project with them.

Cochrane, Alberta, Canada.
"Helping People Prosper in the Information Age"

Posted by Ecnerwal on May 10, 2004, 3:02 pm

I don't think the standard instruments for this are made in enough
volume to ever be low-cost. However, you could probably get a very
acceptable qualitative measurement by dumping a small PV cell into a
resistor and measuring the voltage across (or current through) the
resistor. If you have several channels available, you could put several
cell/resistor combinations in several different orientations
(horizontal/angled at latitiude/vertical - for vertical and angled, you
could also have South, and other directions (probably not a lot of point
in going too far off South for a solar application in the northern
hemisphere, but perhaps 22.5 and 45 degrees to East and West of South).
If you plan to track you could also put one on a tracker.

Voltage across the resistor should give you a pretty good idea of direct
.vs. diffuse radiation. You could probably process the data to strip
that information out without too much fuss.

Cats, Coffee, Chocolate...vices to live by

Posted by nicksanspam on May 10, 2004, 8:31 pm

You might want to measure W/m^2 or Wh/m^2-day.
You can do that with a "pyroheliometer" or a
calibrated photodiode. Edmund Scientific used to
sell photodiodes for about $ uncalibrated or
$0 with a NIST calibration certificate. The
solar intensity is proportional to the diode
current at 0 V, ie into a short.

Daystar (www.raydec.com/daystar) makes a $34
solar meter with a digital output. Kipp and Zonen
(www.kippzonen.com) and Eppley (www.eppleylab.com)
sell more expensive versions, up to about $0K.

The 1981 Solarium Workbook (which may be hard to
find since the National Research Council of Canada
ordered them all destroyed :-) says a south wall
in Lethbridge gets 2578 Wh/m^2 on an average -4 C
December day...


Posted by John W. Hall on May 10, 2004, 8:40 pm
 On 10 May 2004 16:31:04 -0400, nicksanspam@ece.villanova.edu wrote:

Thanks for the info, Nick.
Yup, southern Alberta seems to be the sun & wind capital of Canada.
It's also got LOTS of bullshit, from the cattle feedlots - that's
another interest.

Cochrane, Alberta, Canada.
"Helping People Prosper in the Information Age"

Posted by Duane C. Johnson on May 11, 2004, 3:30 am
 Hi John;

This is a nice circuit for using a small
solar cell as a pretty good insolation sensor.

It is quite linear. See:


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