Measuring available solar energy

[Gerriko]

Russ
these look good, I am tempted to buy one.
Do you have any idea of the accuracy of the above pyronometer, over time? The BPW34 photo-diode listed in the parts (I have some) and these have a polymer lens which might be affected over long-term by UV exposure. The data-sheet for the sensor, made by Temik Semiconductors, provides no relevant data to the long-term accuracy.
Any body out there owned one for a few years? Comments?

Mr. Gerriko's initial idea of using a resistive shunt, in series with a resistive load element, is indeed an accurate way to measure delivered power. Accurate current shunts are not too expensive and available from electronics suppliers. What you will need a a pair of reasonable resolution multimeters. (Or a 2-ch data-logger) One to measure the voltage delivered to the load, and another to measure the voltage across the current-shunt.
Instantaneous power : Wdelivered = Vload x (Vshunt/Rshunt)

M

Would the resistive shunt work? What I'd want measure is the available power from the solar panel - not necessarily the actual power drawn through a set resistor, which would be related to the value of the resistive load connected. If I wanted to check the max power available from a solar panel how would you do that? The power that you measure with the resistive shunt suggested would only measure the power drawn - proportional to the resistive connected. Therefore - if you had a smaller resistive load, the solar panel would generate a smaller power output? Does that sound right, or am I missing the point?
Generally, what I want to measure & compare the varying power of 2no. solar panels - with various inclinations & directions etc. Put I wouldn't be able to do this, if the resistive load attached were identical - and power was available from both solar panels regardless of the inclination & direction. I would still only measure the the set power output - relative to the resistor. Does that sound correct anyone?

[mountain]

SP1.JPG
In general, electrical resistivity of metals increases with temperature. This means that by simply measuring the voltage across your non-precise resistive load, ohms law will not really help you, since the resistance will change with heat. Any affordable test-load will not be a precision device, it

[RifRaf]

mountain that was very informative and made things work alot better for me testing current and output. also learnt how to test very small resistances alot more accurately. for a shunt i used what was laying around, 4 x 0.1% 5W wire wound resistors and put them in parallel, the resistance was tested by putting a known voltage and current though it until such a time as it had heated to a working temperature(still cool to touch), at 2A the resistance started at 0.0252R cold and stabilised at 0.0248R, so i'm just going to refer to it as a 0.25R shunt from here.

the image here http://rifraf.dyndns.org/solar/40-vo...re_current.jpg shows it with a 1.82A current going though it at 12.0V, the voltage drop across the shunt is 45.2mV. knowing these 3 things i can now say the shunt is 0.2483R, the power loss in the resistor is 0.082w (easy load) and the power used by the test light globe is 21.84W. this would equate to a small solar panel, for testing my larger cells have now been able to easy calculate power output at the panels if i can measure in this way, more accurate than the analogue ammeters but they have their place still. cheers
41-shunt_resistor.jpg

[russ]

You guys play with some interesting stuff! Well done and thanks to Gerriko, RirRaf & Mountain!

Russ

[avandalen]

Hi Guys,
Working on a project with regards to solar energy at present, and was hoping to get some input from you.
Basically I want to measure the available solar energy at a solar panel location, at a particular tilt etc..

Although not designed for this purpose my solar cell curve tracer could be used for accurate measuring available solar energy, see here

http://avdweb.nl/arduino/solar-cell-curvetracer.html

For the latest hardware and software contact me please.

[russ]

Just out of general interest - another device I came across in my web travels -

Daystar's DS-05A solar meter brings 'point and read' simplicity to the measurement of solar irradiance. Just turn the meter on, point the sensor at the sun and obtain a reading in Watts/m2.

http://www.zianet.com/daystar/solarmeter.html

Russ

[avandalen]

Just out of general interest - another device I came across in my web travels -

Daystar's DS-05A solar meter brings 'point and read' simplicity to the measurement of solar irradiance. Just turn the meter on, point the sensor at the sun and obtain a reading in Watts/m2.

http://www.zianet.com/daystar/solarmeter.html

Russ

Hey, that is easy! Thanks.