Solar Radiation Sensor

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RandomJoe
RandomJoe Solar Expert Posts: 472 ✭✭✭
in General Solar Power Topics #1
Ah, new toys are always fun! :cool:

I added a solar radiation sensor to my Davis VP2 weather station. It supplies a watts/ sq. meter solar radiance level, and quite conveniently the range of frequencies it responds to is very close to what my panels use. (Its range is a little wider than the panels.) Got it connected a couple days ago right at sundown (darn it...) and had a fairly sunny day yesterday - some light milky high clouds - and it's almost gloomy this morning so a nice contrast to see how it does. For the past 24 hrs I have gotten this:

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I can now calculate expected solar array output with (so far) a fair amount of reliability. The calculation is a bit high in the morning, since most of my array faces west, but was quite close to actual yesterday afternoon as the sun set. My array size is 16 sq meters, so:

Sensor reading x 16 x 0.135 (panel efficiency) = expected max output

Now to find some good uses for the info...! :roll: :D
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
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    Re: Solar Radiation Sensor

    sounds pretty cool.
    don't forget the pv age efficiency factor.
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  • RandomJoe
    RandomJoe Solar Expert Posts: 472 ✭✭✭
    #3
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    Re: Solar Radiation Sensor

    True, although hopefully I'm not losing much to age yet, they aren't that old! :) Half were installed just last spring.

    Today was truly GLOOMY! The day is just about done:

    Attachment not found.

    Note the much reduced wattage scale! Not much happening today... A whopping 150W/m^2 max. Or about 300W peak from a 2160W array! :cry:

    I notice the sensor reads higher in the morning, is fairly even midday, and now (the sun just peeked out briefly down by the horizon) the sensor is actually below my panels' production. I'll have to think about that... Right now it's mounted on the weather station rain bucket, where it would normally go, but if I really want to use it for power production purposes I might get more accuracy by mounting it to one of the solar panel racks so it's at the same angle as the panels...

    It isn't that far off at any point, so probably not worth the hassle. I can be a bit of a control freak with my sensors though...! :D
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
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    Re: Solar Radiation Sensor

    as soon as you get a good sunny day, let's see the graph then.
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  • Ralph Day
    Ralph Day Solar Expert Posts: 1,019 ✭✭✭✭
    #5
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    Re: Solar Radiation Sensor

    Sounds neat, but I've got two solar radiation detectors...one on either side of my nose;).

    Ralph
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #6
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    Re: Solar Radiation Sensor
    Ralph Day wrote: »
    Sounds neat, but I've got two solar radiation detectors...one on either side of my nose;).

    Ralph

    If your nose is large enough to cast a good shadow, you can use the two sensors to construct a solar tracker! :-)
    SMA SB 3000, old BP panels.
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  • RandomJoe
    RandomJoe Solar Expert Posts: 472 ✭✭✭
    #7
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    Re: Solar Radiation Sensor
    Ralph Day wrote: »
    Sounds neat, but I've got two solar radiation detectors...one on either side of my nose;).

    Ralph

    Oh, sure, it isn't exactly an essential item. One reason I waited two (three?) years to get it! :p

    I haven't quite fully formed my ideas for using the data, but in general terms I'm hoping to get a better refined control algorithm for my "opportunity loads". Of course right now I can see that my PV array is at / near Voc when the system is floating and know I have surplus power, but I can't know just how much until I actually turn on a load. Since I didn't want things switching on and off repeatedly on an overcast day I've always run the opportunity loads manually but that requires I be here, which means I don't get to do them very often.

    With this, if its numbers track the actual production capability of the array consistently, then I'll know before throwing the switch whether I can run the opportunity loads or even in some cases how much - low/high on a space heater or mini-split. (I'm also considering a new mini-split, one of the inverter-driven heat-pump types. I'd especially love to find a model that lets me send a control signal from my automation system specifying max capacity.) Perhaps have the system "do laundry" for me. I could load the washer, then set the system to fire up off-grid if there is enough sun. (Can't tell you HOW MANY TIMES I've had sunny weekends, then right as I go to wash clothes off-grid clouds form! :roll: ) Too bad I don't have a way to automate loading the dryer from the washer...! :D

    Same thing as I lose sunlight. To reduce cycling of the inverter's transfer switch, right now if I drop back to grid due to lack of power I don't let it go back automatically. The system has no way of knowing if that max-voltage PV array is actually getting lots of sun again or if it is just barely bright enough to drive them to (close to) Voc. Now I can actually see that yes, it may have been cloudy earlier but now it's nice and sunny again, so go back off-grid.

    That's the general idea, anyway. Once I have enough data to see that yes, things track the way they seem to be, I can start trying it out!


    Looks like for me at this time of year, about 575W/m^2 is max. The past two days have been nice and clear, and I didn't quite get to 600. It just occurred to me today is winter solstice, so hopefully I'll start seeing the peak grow higher and especially wider soon!

    This is the past four days:
    Attachment not found.
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