Renewable Energy Questions/Discussion > Automation, Controls, Inverters, MPPT, etc
Battery voltage sensor placement TrisStar 45 MPPT
ChrisOlson:
--- Quote from: Rover on January 26, 2012, 06:05:56 pm ---Don't think there is an easy answer here. In order to come up with a conclusion you will need to data log your sources over a large period of time (large enough that you can average out and hope you have a decent best day / worst day comparison)
--- End quote ---
I got that for the last five years. But stuff changed in the meantime. We put in a whole new system last March and it's 24 volt, where our old system was 12.
The Schott panels were just added in September in the hopes they would help out more in the winter. The Sharp panels are 5 years old. All the solar now runs thru the same shunt that measures and logs the data in my APRS logger. So I would have to get another shunt and separate the two arrays out for logging purposes.
Looking back thru my logs from the last five years I see there was many times in January I got more power from the Sharp panels on 12 volt than I'm getting from all of them this January. But that doesn't mean the weather wasn't different back then. I remember in 2009 the lake (Superior) was froze over and we had more clear days then.
The only way I will really know is to put a different controller on and see what it does. I can easily wire the two strings of Sharp panels from parallel to series to get the voltage up to 218 just by changing a couple wires around in the combiner box during the night when they're dead. But re-wiring them in pairs for series parallel would be a chore to try them direct-hooked on 24 volt. But I think on 24 volt they would be not as good as they are on 12 because Vmp is like 17 point something.
So I don't know for sure. I was curious what you are seeing. I'm going to try a different controller.
--
Chris
rossw:
--- Quote from: Rover on January 26, 2012, 06:05:56 pm ---Don't think there is an easy answer here. In order to come up with a conclusion you will need to data log your sources over a large period of time (large enough that you can average out and hope you have a decent best day / worst day comparison) .
--- End quote ---
Add a pyranometer to your solar logging and you start to get some reasonable data fairly quickly.
If the pyro tells you there are (x) watt-seconds per square metre of available power during the day, it's a fairly simple calculation of the area of your panels * their efficiency compared to the pyro's output, to see how you're going.
This can be done over fairly short periods of time (minutes even), to give an indication of how your arrays are working under different lighting, temperature, load and controller conditions.
ChrisOlson:
--- Quote from: rossw on January 26, 2012, 06:22:53 pm ---If the pyro tells you there are (x) watt-seconds per square metre of available power during the day, it's a fairly simple calculation of the area of your panels * their efficiency compared to the pyro's output, to see how you're going.
--- End quote ---
Whoaa here, Bessy!
This is the kind of info I'm looking for. <light bulb comes on over noggin> My weather station has one of those but I don't have it hooked up and it's still in the box. Mainly because I don't know what the data means even if I had it. It measures UV and a bunch of other stuff too.
Thanks! That's something I could do that would probably be a lot better than making stabs in the dark trying to figure it out.
--
Chris
Rover:
I agree with Ross .. to a degree.. thing is you have other sources boosting battery bank voltage, all of the solar controllers (mppt) will plot against some form of algorithm based on the voltage.
You have other things conflicting.... yes you can put up a solar sensor.... but you are trying to evaluate a complex equation, it is not longer how much from solar .. because you can't isolate. Ross suggestion gives you potential.. but cannot take into account the SOC of the bank etc for what you are looking for.
Rover
rossw:
On re-reading that, I've missed a couple of words. They make a change mostly to the accuracy of my terms.
The pyro output is usually watts per square metre.
Your panels also produce power, in watts.
However since you will be recording over time, not instantaneous output (I infer that from the use of a logger), then using instantaneous values over a period of time is largely meaningless.
If you monitor every second and accumulate, you get instantaneous-watts, every second, which is close enough for our purposes to being "watt seconds". Add them up and store the values every minute or 5 minutes or whatever, and you get a reasonably accurate "watt seconds" per unit time.
Here's a graph from my own from yesterday and today:
The blue area is the number of watt-seconds in each 5 minute period.
The red line is the PEAK watts during each 5 minute period.
The black line is a calculated estimate of the total incident radiation that would be available to a perfectly aligned array.
To explain some things that are evident.
1. The dips in the blue, where the red appears more-or-less unchanged is from something casting a shaddow. Possibly a bird sitting on the sensor, or a small cloud.
2. Dips in the blue, with an accompanying spike in the red line shows the cloud-edge effect, magnifying the sun causing a higher "peak" power, but then the shaddow causing a reduced total watt-seconds in the interval.
3. The black line is complex. My pyranometer is a cosine-corrected instrument. It takes into account the angle of the sun.
Some of my arrays track the sun, so I want to know how much "should" be available to them. This black line is calculated backwards from the power measured and corrected, and the calculated position of the sun.
Tip for you, chris - when you install your weather station sensor, install it close to your solar panels, and most critically - install it facing exactly the same way. That will NOT be the way they tell you to install it, which will be perfectly level. If you want to use it for this purpose, you want to know the sun relative to the panels, not relative to the ground.
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