Re: Advice re solar power? - One More Parameter, Temperature


Bob Ballard
 

Jim,

 

LOL!  Danged Engineers … I had to deal with a raft of you guys during my almost 40 years in Aerospace Defense.  The sad reality is that the bulk of Engineers actually believe that they are so much smarter than non-Engineers that they consistently fail to consider anything they don’t initiate.  They also “Doan need no stinkin’ Instructions!” (consider the scene from “The Treasure of the Sierra Madre”) and wouldn’t follow the Instructions if they read them anyway!

 

 

You did put the attached file in PowerPoint Presentation mode per my initial message’s clearly stated Instruction, right? -“(put it into Presentation mode to run the animations properly)”.    

 

If you (unlike most Engineers) did follow the Instructions and the animations simply didn’t work which is a likely event because the initially attached file left my computer at 712 KBs,

attached above is a non-animated version of the presentation that should address the failure of the initial attachment (hopefully this one will arrive intact).

 

I concede; you win the hottest and coldest environment descriptions contest.      

 

 

As far as nurse behavior,  I’ll refrain from describing my brain tumor removal on June 5, 2020 beyond the 6.5 hour surgery, 3 days in ICU, 10 days in rehab with incredibly caring nurses that treated me like a beloved member of their family.  However, I still have low energy output that they tell me will take a few more months to return to “normal” (no permanent brain damage though thank God).

 

 

FWIW – I think we both have wasted enough time with our respective rants so I’m ending my participation with this one unless the attached file also fails to function normally.  Feel free to fire the final “get the last laugh” round and/or carry on all by yourself if you like.  Your great sense of humor and the laughter is certainly worth the time it takes to read it.

 

 

73,

Bob – KG5SQJ

 

From: QRPLabs@groups.io <QRPLabs@groups.io> On Behalf Of Jim Manley
Sent: Saturday, August 1, 2020 1:50 AM
To: QRPLabs@groups.io
Subject: Re: [QRPLabs] Advice re solar power? - One More Parameter, Temperature

 

Hi Bob,

 

When I tried to open your presentation, which shows here that it's 306 KBs, there was only one page.  It had a static chart showing panel power horizontally, and it had the 100 watt column circled in red.  Not exactly the most informative and exciting PowerPunt presentation I've ever seen, and I've seen some doozies.  I've been using PP since it first ran only on Macs in black and white (not even gray-scale), well before its inventors-founded Forethought was bought by Microsloth.  So, no, I didn't get to witness any whiz-bang animations or much more information than the numbers and letters on that chart.

 

As far as the connecting cable goes, it doesn't contribute to the warming of the cells, just a reduction in the power delivered, which will vary all over the place with the in situ setup.  So, it's not a factor for this discussion.

 

I don't doubt that high temperatures reduce output - I can vouch that my output goes to about zero in anything hotter than about 75 F, or lower then about 65 F, as I have low blood pressure and high metabolism.  When I was in an ICU overnight, the nurses told me to breath faster, because I kept setting off the low-breathing-rate alarm that could only be set down to 10 breaths/minute.

 

I was asleep when it was happening, and I asked them how I was supposed to breath faster while I was asleep.  They said that they didn't care how I did it, just do it!  When I proposed certain kinds of strenuous exercise with them in positions detailed in the Kama Sutra, they suddenly didn't seem so interested in my well-being.  Never tick off a nurse, especially ones monitoring you in an ICU when you're asleep!

 

If you want to try hot, go to the Persian/Arabian Gulf on a haze-gray Navy ship with black carborundum non-skid deck areas, or anywhere on the black, six-inch thick, HY-120 steel hull of a submarine.  The seawater injection temperature into the condenser of the engineering plant in that bathtub of a body of "water" is routinely well above 90 F, and that's the source of "cooling" for the vast majority of equipment on the ship .. including the crew!

 

On the other hand, we have five fingers (for now - the night is young), and there are some places I can invite you to visit in Montana in the Winter, and stick your tongue on the frame of a solar panel while witnessing the cells' vastly-improved performance.  Can you spell "Ralphie" from "A Christmas Story", in the scene with the flagpole out in front of the school?  Actually, it gets cold enough there that your tongue can get stuck to the cold air if you stick it out!

 

 

Jim  KJ7JHE

Lame Deer Montana High School Amateur Radio Club  KJ7JKU

 

 

On Fri, Jul 31, 2020 at 9:43 PM Bob Ballard <bobnmarji@...> wrote:

LOL!  Please note my comments below.  No whining nor griping … just all in fun!!!  😊

 

73,

Bob – KG5SQJ

 

From: QRPLabs@groups.io <QRPLabs@groups.io> On Behalf Of Jim Manley
Sent: Friday, July 31, 2020 7:52 PM
To: QRPLabs@groupsio
Subject: Re: [QRPLabs] Advice re solar power? - One More Parameter, Temperature

 

Hi Bob,

 

I assume that the temperatures are ambient _at_the_cells_ and not the ambient air temperature around the outside of the panel, which could easily be two very different things, depending on a lot of other very different things.  Being under glass, and with the cells made of a darker material (mounted on a dark background?), you could have quite a little oven cooking things.

Oh c’mon Jim!  You didn’t really fail to read what the presentation said, did you?     

The presentation indicates the cell temperature in several places.  For example, note the text highlighted in the first animation -  “the solar cell itself, not the surrounding.”.

  

Also, although I suspect it's a much smaller contribution, the current flowing through the cells and the connecting conductors have their own resistances, which means they're each also a contributor to heat, and it's all under that glass, so the air surrounding the cells will get that much warmer.

Yup!  And so do the losses attributable to the 40’ of AWG 10 solar system cable necessary to keep the solar cells out in the sun as long as possible and me and my radio under the trees and in the shade!

  

Being an engineer, I realize that the thermodynamic model for this is already the kind of thing that a massively-parallel, high-performance computing system was built to execute.  So, the $64,000 / 64 KW question is, has anyone done that, or at least done in situ measurements at enough points in a typical assembled panel to provide yet-another interesting graphic?

I’m not an Engineer so I obviously yield to your educated and experienced expertise on this subject.  Nevertheless, with the ambient air temperature above 95°F I have tested my two 100 Watt solar panels that I use to charge 12v Bioenno BLF-1220A 20aH  Lithium batteries.  I use the twin 100 Watt panels to charge each battery one at a time while the other battery is running my 100 Watt Kenwood TS-690SAT radio on Field Day.  When aligned directly at the sun, each solar panel produces approximately 65-70 Watts to an 80% discharged battery using Genasun GV-10-Pb-12V MPPT charge controllers (no RFI).  And yes, I know this system is a ridiculous overkill for this QRP thread but that is the only solar system I currently use.

If you think the solar panels won’t get hot enough to reduce their 100 Watt rated output that much, try briefly touching one of those shiny aluminum solar panel frames after it has been sitting in the hot Texas sun at 95°F (or more) air temperature for 2-3 hours.  And, as you stated above, the much darker Monocrystalline cells will absorb even more heat than the shiny aluminum frame.  And heaven help you if the frame you touch is one of the black powder-coated models (sizzle!)!  FWIW - If the wind is blowing they do work somewhat better because the air flow will slightly reduce the cell’s temperature.

  

Another brain fart that just escaped my cranium is, could small(er) fans be used to circulate cooler air (the ambient air has to be cooler than what's under the glass, even in 100 F Texas conditions, right)?  For a big enough solar panel array, could pumping subterranean-cooled water up (and warmed water back down) further increase the efficiency of the panels?

Yes that would work but what is the “big enough” point of diminishing returns where the cooling system consumes more energy cooling the cells than the cells produce to meet the need?  And this rabbit hole declines even more considering we should be focused on just enough solar power to charge batteries required to run QRP radios.

 

  

If this is feasible and hasn't been patented, I hereby lay claim to this being original prior art, with complete drawings, specs, computer models, etc., available for inspection at my QTH (I'm also a patent-holder :)  Now, you just need to figger out where, exactly, I am to see it all! 😃

Sounds good to me!

 

Thanks and  

Jim  KJ7JHE

Lame Deer Montana High School Amateur Radio Club  KJ7JKU

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