Author Topic: Panel Cooling.  (Read 416 times)

glort

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Panel Cooling.
« on: December 29, 2018, 02:43:30 AM »

Way too hot here to go work in the shed on any engines but I have  been playing with the solar stuff again and thought I'd start another topic on that to bore you all.

I have set up 5 x 250w panels on a garden bed I just stripped, ploughed and leveled. They are in series so I could test an inverter I ( successfuly ) repaired.
Being 40+ here today, I noticed my inverter was only outputting about 840W.  seemed a bit low for 1.25 Kw of panels in the middle of summer at close to midday.

With the garden hose nearby I decided to put something to the test and gave them a good spray.  Going straight back to the meter I noticed I was now getting about 1030W although it was falling pretty fast.  Go back out 20 Min later and I'm back down to 840w again.  There sure is a fall off when these panels get warm.

I have read people saying that this is due to the magnifying effect of the water droplets but I don't think there is much to that.  I spose I could set up a test and spray the back of a panel and see the difference in output but I think I'd still see a significant jump.  I did not think I'd see a near 200W jump though.

This solar generation has so many inefficiency it's a wonder it works at all. If they can in years to come  overcome a lot of these things there will be great gains to be made.

old seagull man

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Re: Panel Cooling.
« Reply #1 on: December 29, 2018, 08:50:28 AM »
My best output days in Brisbane are cool clear sunny days when the panels are cold or only warn, the hotter the panels the less the output.
Remember the specifications output is at 20C on a perfect day, when the panel is new and you have just won the lotto for the third time this week.
Plus most inverters don't like to be over about 35 C or they cut output.
Today the highest output from the 3060 watt array on the back of the house was 2876 watts,  18 x 170 watt panels,  making 19.7 kwh so it not bad.

glort

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Re: Panel Cooling.
« Reply #2 on: December 29, 2018, 09:52:44 AM »

Yeah I always thought the temp rating was farcical. I know they have to pick some number as the standard and i know not every place is as hot as Oz BUT....  A lot are.  besides that, i have picked up panels laying in the sun in the middle of winter and going by my temperature pain threshold which is well tested, the things have to be nudging 50 even then.  Only way they are going to be 20 is someplace where it's -20 ambient.

I have a large Tube fan on top of my main inverter. it has a small temp switch that cuts in at 40o and runs through a relay to switch on the fan. the switch is stuck to the lower part of the inverter with some thermal grease for good contact. When the inverter gets warm the fan kicks in and helps cool the thing off.

I made a mistake today and unplugged the temp switch instead of something else. When I went back up later and was surprised the fan wasn't running, I felt the inverter it was damned hot.  Way too hot for any electronic appliance even though it's completely shaded in the shed and the shed itself has big fans in the window keeping it very cool for the ambient conditions.  Saw what I had done and plugged the relay in. the heat coming out of that inverter was incredible.  Much more than any fan heater will do.  Thing was still running at 7:30 this evening.

How these things survive without cooling I'll never know but I'm quite sure mine will do a lot better than most with the forced air cooling it has.

mike90045

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Re: Panel Cooling.
« Reply #3 on: December 30, 2018, 01:58:13 AM »
The amperage of solar panels is dependent on the "brightness" of the sun
The Voltage is dependent on the temperature, cooler is higher voltage, warmer is lower voltage.

That's why all the panel "string calculators" want to know the record low temps in your area, as the temps drop, the voltage of a string can go way up - enough to fry a controller.

glort

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Re: Panel Cooling.
« Reply #4 on: December 30, 2018, 09:15:09 AM »

The Voltage is dependent on the temperature, cooler is higher voltage, warmer is lower voltage.


I have been wondering if the string voltage has any effect on the AC output Voltage.
I notice some days I'm maxing out on the AC voltage even though the wattage being generated is not that much. Other days like the last week or so, the thing is cranking out far more power but the AC voltage is relatively low.

I have been wondering if I reduced the number of panels in my strings if this would have any influence but i cannot think how it could.  The line voltage needs to be raised in order to back feed the power which should be nothing to do with the DC side.

Been going to test the theory but seeing no reason it would work and the effort involved in re configuring the strings has put me off. I'm only running about 350V on an inverter that's good for 600V so plenty of headroom there. Each string only has 8 Panels.

I do have a test array going atm. Spose I could throw another set of panels down and see the voltage difference on the AC side with them in series and in parallel.

Couple of amusing observations with this test setup. it's right outside my office window.  In the morning, my cats like to get underneath them where I have them slightly raised for a bit of tilt.  as the morning wears on and the sun gets more direct, the pusses obviously get a bit too warm and head for the cool of the verandah where I have been putting the fans on for them given the days have been 40o for the last 4 days on the trot.  In the late evenings, they come back and sleep on top of them.
The first day they were down I saw them walking on them then jumping up and prancing off as their feet got too hot.

The birds, mainly those Indian minor pests seem attracted to them. Haven't seen the native noisy minors, the rainbow lorikeets or the parrots go near them.  Stupid Indian minors come round and mid day and land on them and can't seem to figure out what is going on when clearly their feet are being cooked on the things.  i can see them jumping about and squawking in distress but takes some of them a long time to fly off.

mike90045

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Re: Panel Cooling.
« Reply #5 on: December 31, 2018, 03:44:14 AM »
AC line voltage variation is mostly about local generation, local consumption , and the resistance in the run from the inverter to the pole transformer.
 Low local consumption on a cool sunny day, will produce higher line voltage.  Add some local usage, and the line voltage will go down.
  This is becoming a problem with neighborhoods with lots of solar, nobody really cares/notices with low line voltage, your fridge does not fault out, but the safeguards in GT inverters, when the line voltage goes up, they start shutting down as individual voltage sense goes over the threshold.

AdeV

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Re: Panel Cooling.
« Reply #6 on: December 31, 2018, 10:27:16 AM »
The birds, mainly those Indian minor pests seem attracted to them. ...  I can see them jumping about and squawking in distress but takes some of them a long time to fly off.

Doesn't that lead to a bit of a bird shit problem (I presume the crap when in distress, like most animals  :o); given the high temperatures, I imagine it gets baked on in seconds....
Cheers!
Ade.
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1x Lister CS Start-o-Matic (complete, runs)
0x Lister JP4 :( - Sold to go in a canal boat.

glort

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Re: Panel Cooling.
« Reply #7 on: December 31, 2018, 12:32:38 PM »

Funny enough, over the last 4 days haven't seen a spec on them. Lots of leaves and dirt however.

I did notice walking down the yard this morning, a couple of great White coloured skid marks on the west roof panels that looked like an Emu had been up there.

Gone this afternoon due to the fierce but short live rain storm we had.