I had a thought about this last night. There are two entirely separable questions. One is whether the maxSolarRad value is correct, and the other is what your sensor is measuring. I think the "is the max correct" can be answered (and should be) without considering your data at all.
First, I think we're talking about radiation incident on a horizontal surface. I didn't level my sensor carefully, but it's within a few degrees. I see in the defautl config file that maxSolarRad is set to prefer_hardware, but I am guessing VP2 does not actually output that. For theory, there seem to be multiple approaches, and notions include not only the in-space radiation of 1353 W/m^2, but some contribution from diffusion as well as air-mass attenuation and pollution (but northeast air quality is pretty good) https://en.wikipedia.org/wiki/Air_mass_(solar_energy) {The rest of the specific numbers I mention in this post assume 42.5 latitude, which is more or less where Tom and I are.) At 42.5 degrees and the winter solstice, the sun elevation is 20. In the summer, it's 65. So that's 70 and 25 in terms of zenith angle. Interpolating by guessing from the table, that leads to 1017 W/m^w summer solstice 710 W/m^2 winter solstice but as I understand it, that is radiation at the arrival angle, not radiation horizontally. It just does not make sense to me that there would be 710 W/m^2 on horizontal panel when the sun is 20 degrees up - but my intuition has not been working well so far on this subject. Tom's graph shows 461 for yesterday's peak theoretical and I'd expect 243 horizontal for 710 at 20 degrees. Except that the diffuse component would not be reduced, just the direct, from the angle. For 1017 incident , basically discounting air mass and keeping the 10% gain, I'd expect 347. So I have no idea where that 461 is coming from. Looking back near the solstice at a cloud-free day (June 17), I see a nice sine-ish curve over the day peaking at about 941 W/m^2. If I take 1017 and multiple by sin(65deg) I get 922. So I guess the big point is that this is much harder than I thought it was going to be when I started looking it up! This may be useful, but it seems to be about daily energy https://naldc.nal.usda.gov/download/34980/PDF This might have some data from calibrated instruments: https://www.ncdc.noaa.gov/data-access/land-based-station-data/land-based-datasets/solar-radiation -- You received this message because you are subscribed to the Google Groups "weewx-user" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/weewx-user/rmipn347b6r.fsf%40s1.lexort.com.
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