Author Topic: Pro 2 with UV and Solar Sensors  (Read 1070 times)

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Offline JRHill

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Pro 2 with UV and Solar Sensors
« on: October 02, 2022, 12:18:18 PM »
We've had our Pro2 for over 13 years. We sent it for a refurb at the 10 year mark and it came back like new. A bit after that in celebration I bit the bullet and added the UV and Solar Radiation sensors. After adding the sensors it was interesting to compare the harvest of our solar panels with the Radiation sensor especially on cloudy days or times when we experience 'cloud edge' generation (when there is no direct sunlight but refraction from moisture actually increases panel harvest).

But there are two things about these sensors that keep me wondering:
  • The formula Davis uses for EvapoTranspiration (ET). I have looked and I can not find it. Maybe its proprietary to them?
  • ET trueness. Are there limitations regarding location, run off (grade), soil type, vegetation or anything else?
  • ET is logged through the calendar year while the Rain year is Oct 1 through Sept 30. Well, that's clumsy for comparative purposes. Maybe that's a standard for the weather data but for my use having the periods correlate would be much more useful.

For example, for the rain year that just ended we logged 16.99" (which is actually around a inch more than several of the past years during these drought times). However the ET as of Sept 30 was 24.87" and that's :shock: for the calendar year. Since we added the UV and SR sensors 2 years ago its been like this. Gee, no wonder the trees around us in the forest are dying?

Any input on the precision, accuracy and trueness of ET in general or on anything else I have mentioned here?

Best, Jim
KWALYLE28

Offline mcrossley

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Re: Pro 2 with UV and Solar Sensors
« Reply #1 on: October 02, 2022, 01:36:54 PM »
The ET is semi propriety - see their application note on derived variables
Mark

Offline JRHill

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Re: Pro 2 with UV and Solar Sensors
« Reply #2 on: October 02, 2022, 01:55:56 PM »
Thank you, Mark. That helps bunches!

Offline Buick

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Re: Pro 2 with UV and Solar Sensors
« Reply #3 on: November 18, 2022, 04:24:40 PM »
It looks like your location is in the vicinity of The Dalles? I would think ET would always be in excess of precip on an annual/water year timescale given the semiarid climate of that area and that your water year precip and calendar year ET seem to make sense. The calculated reference ET is typically ~27"/calendar year at my location and is usually less than water year (or calendar year) precip.
VP2 (6163) w/ 7345.425 & 24hr FARS
6410 @ 26' AGL, 12' above rooftop
6415 @ 12' AGL
7714
Rainwise 111
Stratus
WiFiLogger2
WeatherLink Live

Offline JRHill

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Re: Pro 2 with UV and Solar Sensors
« Reply #4 on: January 02, 2023, 02:05:51 PM »
Buick, that is really surprising to me at your location.

Darn. Just asked the DW if she wrote the ET down on 12/31/22 and she said she thought it was the same as the rain year. Oops. The last notation on the calendar was Sept 30 and it was 24.87" so it was probably pretty close to yours. I'm still up in the air about the darn subscription to WeatherLink.

Offline JRHill

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Re: Pro 2 with UV and Solar Sensors
« Reply #5 on: January 02, 2023, 02:46:53 PM »
Bit the bullet and bought the subscription. It hurt. I'm a cheapskate.

Offline Buick

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Re: Pro 2 with UV and Solar Sensors
« Reply #6 on: January 02, 2023, 04:21:45 PM »
Hi JRHill,

Could you explain what you find surprising about my response to your post regarding the Davis ET calculation?
VP2 (6163) w/ 7345.425 & 24hr FARS
6410 @ 26' AGL, 12' above rooftop
6415 @ 12' AGL
7714
Rainwise 111
Stratus
WiFiLogger2
WeatherLink Live

Offline JRHill

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Re: Pro 2 with UV and Solar Sensors
« Reply #7 on: January 02, 2023, 05:07:36 PM »
Hi JRHill,

Could you explain what you find surprising about my response to your post regarding the Davis ET calculation?

Nope. It makes full sense. I didn't catch my screw-up it until I posted it I realized your ET was less than the precipitation. Being an A$$****I let it go to see if anyone caught it.

You were right on top of it.

I just can't handle that much precipitation. My hat is off to you. And not just because I had a '71 Skylark convertible and like your handle.

Offline Buick

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Re: Pro 2 with UV and Solar Sensors
« Reply #8 on: January 02, 2023, 05:38:05 PM »
Gotcha. Thanks for clarifying and the kudos!

Bellingham is definitely gloomy (perhaps even a touch more so than average for interior Western Washington) but at least it reliably gets relatively cold and snowy compared to areas further south along Puget Sound or the Willamette Valley.

Honestly, it's not the actual amount of precip that the area receives, it's the persistent cloudiness combined with the short days leading to a merciless lack of sunlight during the rainy season even for the latitude. I would imagine, say, International Falls to be much more agreeable in that regard and doubt the hardy inhabitants of that area have the same vitamin D supplementation needs as the sad, soggy residents of the northern PNW.

I actually spent my childhood in the greater Atlanta area and my hometown receives substantially more precip than Bellingham - but it also receives immeasurably (not really, but it sure seems like it  :lol:) more sun. Down there an inch or 2 of rain that falls during the course of a day might all come down in an hour or two leaving the remainder of the day sunny (if muggy). Here an inch or 2 of rain in a day means that just about every second of every minute of every hour of the day is plagued by continuous rainfall.

I could cite some WeatherLink calculated values for accumulated solar radiation at my site that would make you shudder...for instance, December 2022 managed just 63.26MJ/m^2 of accumulated solar energy for the entire month (about what one would expect during 3 typical midsummer days) along with 0.375" of ET. There was 4.43" of precipitation including about 12" of snowfall and around .5" of ice/freezing rain with a monthly mean temp of 34.2F.
VP2 (6163) w/ 7345.425 & 24hr FARS
6410 @ 26' AGL, 12' above rooftop
6415 @ 12' AGL
7714
Rainwise 111
Stratus
WiFiLogger2
WeatherLink Live

Offline Buick

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Re: Pro 2 with UV and Solar Sensors
« Reply #9 on: January 02, 2023, 05:39:20 PM »
Apologies for the long-windedness. I should've just kept it at "Don't get me started on the weather here!"
VP2 (6163) w/ 7345.425 & 24hr FARS
6410 @ 26' AGL, 12' above rooftop
6415 @ 12' AGL
7714
Rainwise 111
Stratus
WiFiLogger2
WeatherLink Live

 

anything