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groingo
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# Posted: 20 Aug 2025 02:54pm - Edited by: groingo
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Not being one to see something useful just do nothing I put the old 6 Renogy 100 watt panels back to work and got some pleasing results.
First, they look old, 2 BB, snail trails all over the place
and overall under the glass kinda gungy.
So, I plugged them into my new 8 awg wire onto my new Shengen MTTP (undersized 20 amp) charge controller and was blown away how well they performed, easily pulling 19.7 amps at 20.4 volts where all the time prior regardless the controller never higher than 13 amps at best! These numbers were also limited due to the 20 amp controller and the battery now being full charged to 14.5 volts while the controller throttled down as it should.
The controller (provided it lasts) may be one of those odd gems, with it's smoked see through case, readouts you can read from odd angles and accuracy with zip heat output...panels still kicking after 14 years!
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Steve_S
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# Posted: 21 Aug 2025 12:00pm
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Pleasant Surprise indeed and I'm willing to bet, you had serious doubts about those old "crusty" panels eh. Do you have a link for that MPPT Solar Controller ? I'm curious about it.
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travellerw
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# Posted: 21 Aug 2025 03:01pm
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I had 18 year old Shell solar panels on our boat. They had begun to get the brown spots of death. Yet they still produced more than their rating on some days.
Another cruiser we were friends with "rescued" 1000s of watts of panels out of the garbage that big boats threw away because they were bad. Pretty much every one of them was a wiring issue or dead bypass diode. MC4 connectors suck, especially if you mix different brands of use off brands.
Panels last a lot longer than people think.
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gcrank1
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# Posted: 21 Aug 2025 05:03pm
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Yet I suspect the power companies with the solar fields will mass replace at a point in time, likely keep a replacement rotation going on, just like big business replaces all their light bulbs rather than just replace as they go bad.
Where will they end up? My guess is a panel graveyard rather than the secondary market.
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groingo
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# Posted: 21 Aug 2025 06:46pm - Edited by: groingo
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Steve_S
Keep in mind these are sold under many different names but the real manufacturer is Shengen.
https://www.amazon.com/dp/B0DZ29WBVR?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1
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groingo
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# Posted: 21 Aug 2025 06:49pm - Edited by: groingo
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travellerw
Mine looked like they were rusting yet never leaked and all are thick with snail trails, according to various sources online they were toast and I too had issues with the MC4 connectors cracking, leaking and shorting so I manually tied the wires and sealed, no more MC4's.
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gcrank1
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# Posted: 21 Aug 2025 10:51pm
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Think my old panels have MC3's!!!, well, the few that are left. Last time used a few years ago they were working to rating on a fine day. They are sitting inside storage now, dont think they deteriorate stored well do they?
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paulz
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# Posted: 25 Aug 2025 07:09pm
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My shop roof contains all my old panels. That rack of 12 panels, I was buying something else off CL and he said he’d sell that rack for next to nothing, so long ago I forget. Don’t know how it’s wired, comes out in two pairs of leads. Have all this junk charging my shop leds and yard cam, does that ok. Guess I could measure them, probably 20 years old.
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gcrank1
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# Posted: 25 Aug 2025 09:34pm
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That is a Nasty Looking array!
Cant help but wonder what king of output you'd get if you cleaned em off and re-did all the connections.
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paulz
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# Posted: 26 Aug 2025 12:08pm
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I plan to clean and test them today. What’s the test, open voltage, amps?
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gcrank1
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# Posted: 26 Aug 2025 01:55pm
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I suggest not even testing, just clean (cause ya know ya need to) then redo ALL the elec connections you see and can get at, they are probably all in poor shape.
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paulz
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# Posted: 26 Aug 2025 07:42pm
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Went down and blew them off then played around. Whole array comes out in two pairs. Both measured equally 34 volts. Label says 17v so they must be paired up. Nicely put together with copper stranded. Only took one cover off. My VOM didn’t have dc amp fitting so couldn’t check that.
So, be better to run more in series? What about those Schengen SCCs, good?
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groingo
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# Posted: 27 Aug 2025 08:29pm - Edited by: groingo
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Typical older panels, that's some beefy wiring, are they wired in Series or Parallel, (looks like Series on the tag) From your tags looks like a 40 amp SCC would do fine.
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travellerw
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# Posted: 27 Aug 2025 10:43pm
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Parallel is MUCH better for shade. Based on your location they are probably configured pretty decent. I wouldn't change them.
I mean we can get into semantics. 34V is pretty low and a quality MPPT wants more voltage... bla bla bla..
But you have been using them so far and things are good. Sure you might get more with some tweaking, but will the juice be worth the squeeze for your use? Probably not!
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paulz
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# Posted: 28 Aug 2025 12:47pm
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Yes these must be 2 parallel,3 pairs in series, two sets, 12 panels total. This morning, in total shade, as they always are for about 23 hours a day, one measured .3 amps, the other .2xx. If I happen to be down there and catch in the sun I will measure.
But again all it has to do is keep my trail cam going and a couple shop LEDs when I go for a tool. One 12v car battery.
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groingo
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# Posted: 28 Aug 2025 01:36pm - Edited by: groingo
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Just got my 40 amp replacement SCC for the problem child 60 amp SCC (which was putting out half of the 40 amp) and all is well in the world, output is back up where it should be, for $60.00 all in I couldn't ask for more and if it doesn't perform send it back!
https://www.amazon.com/dp/B0DZ2CYXWD?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1&tag=smaca b-20
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paulz
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# Posted: 29 Aug 2025 06:09pm - Edited by: paulz
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Caught my old shop panel in the sun today so grabbed my volt meter with a dc amp setting. One pair of the output wired read 7 amps, other 3x amps, just open circuit with the vom leds touching. Again without tracing the wiring I'm assuming its got 8 panels on one string and 4 on the other. Total a bit over 10 amps, good enough to keep my car battery/leds charged when it gets sun. Panels say 75 watts so its way below that. I still havent washed them, just air blew the duff of.
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gcrank1
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# Posted: 29 Aug 2025 06:18pm
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Ive read that especially with old panels you are more likely to get only 60% of the rating even in good conditions.
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groingo
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# Posted: 29 Aug 2025 06:18pm
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Paulz,
Sounds like money in the bank to me, something you had pretty much written off is now paying back!
What kind of charge controller you using, just curious.
Might try what I did, because of having so many trees mucking things up I aimed my straight (almost flat) aimed at the sky, amazing how much they pull when we have bright cloudy days !
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paulz
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# Posted: 29 Aug 2025 07:42pm - Edited by: paulz
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Yeah i read about your controller the other day and looked them up, great price. These panels are just connected to the one that came with the Harbor Freight cheapo solar kit, my first delve into solar back when. But its working..
Not sure I'm even measuring amps right, just open circuit. Im used to measuring in line with something running at the other end.
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gcrank1
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# Posted: 29 Aug 2025 10:46pm
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A too small scc will limit the output harvest to whatever the scc is rated at; imo yer always better off to go a higher rating on it than what you calc the array should put out.
That little HF unit is the most basic switching on/off scc that there is.
I only check the voc from the panels to be sure they make that rating. The amps from the scc to bat (load) is where I measure that.
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paulz
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# Posted: 30 Aug 2025 01:14am
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The little HF controller says its 10 amp so i could overdo it i suppose. I might pop for one of groingos sccs. Although after hearing so much good about Victrons i owe it to myself to try one. But that’s more suited to cabin use, I have seen close to 40a out of that solar.
At the end of the day the one 12v FLA in the shop stays charged with the little output it does. Maybe I should put a microwave down there, get away from the blabbing wife for a bit. 
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groingo
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# Posted: 31 Aug 2025 12:08am - Edited by: groingo
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paulz
Maybe just try a cheap PWM controller to see if it makes a difference, it will show you your volts, amps and battery charge levels and is programable, should be around ten bucks....if it shows promise then try and MPPT controller or it may work great!
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Nobadays
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# Posted: 31 Aug 2025 10:20am
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Quoting: paulz hearing so much good about Victrons i owe it to myself to try one.
From what I understand Victron has the best algorithm in the business for collecting energy , especially in cloudy/shady and low intensity sunny conditions (light clouds). That said, nearly any MPPT Controller is going to out perform a PWM controller in the conditions you face.
Gcrank1 hit the nail on the head... that HF controller you're using is almost certainly drastically reducing the energy you could be harvesting off those shop panels.
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groingo
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# Posted: 31 Aug 2025 12:39pm
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Nobadays,
My suggestion was to see IF another controller would improve his power production at minimal cost, basically a throw away item, but if it does improve his power situation then graduate to the more expensive MPPT, also those are SEIMENS panels which should be top of the line regardless of age, did you see the cables coming out of them?
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Nobadays
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# Posted: 1 Sep 2025 10:26am
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Groingo... smart... my comments were directed toward Paul's thought of getting a Victron SCC. Knowing his very shaded conditions I'm certain an MPPT would benefit him immensely.
I did see the cables but uncertain what I am seeing. I am used to the standard 10awg, ~24" cables terminating in MC4 connectors. These look like almost water tight connections with flex conduit. Not seen that before.
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Nobadays
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# Posted: 1 Sep 2025 10:42am
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Quoting: travellerw I mean we can get into semantics. 34V is pretty low and a quality MPPT wants more voltage... bla bla bla..
Interesting! I just ran into this the other day. I'm considered "the solar guy" in our little cabin community. I buy solar panels and other equipment (only Victron) nearly every winter when we are in AZ then bring it up here and resell it to our cabin friends.
One neighbor I sold some panels to just wasn't getting good performance out of his system. He has 1000w of solar in a great location running through a Victron 150/35 SCC yet never seeing above 250w and not getting a full charge without using his generator. NOTE, he has an older model chest freezer that runs all day long sitting on his porch.
His 4 panels were wired parallel and only bringing ~32v to the SCC. On a whim I suggested we rewire 2s2p and double the voltage coming to the SCC. Like magic this basically solved his issues. Now he regularly sees +800w coming in on the meter and floats his batteries nearly every day! At that time I was not aware MPPT controllers liked higher voltage.... that said I still have a hard time understanding why paralleling the panels didn't deliver the same wattage. Oh well, it worked!
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MtnDon
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# Posted: 1 Sep 2025 03:58pm
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Quoting: paulz Both measured equally 34 volts. Label says 17v so they must be paired up
If you are getting 34 volts coming out of the panel array, and IF you are using a PWM charge controller like the ones HF supplies in their kits, and IF the battery bank is 12 volts, then your system is wasting over half the available energy.
That is the fault of the way a PWM charge controller works. All PWM charge controllers clip off the incoming voltage that is higher than what is required to charge the battery and disposes of that energy as heat.
Simply put, an MPPT charge controller contains magic parts and software that can convert the excess voltage and turn it into amperes to add to the charge of the battery.
If those batteries are being sufficiently charged the way the system is, I guess you can say it works, so it does not need changing. However, if you would like to charge more batteries, use more energy for something, then some changes might be beneficial. But that is a project needing more complete information before tossing money at it, IMO.
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MtnDon
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# Posted: 1 Sep 2025 04:06pm - Edited by: MtnDon
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Quoting: Nobadays I was not aware MPPT controllers liked higher voltage
It depends a lot on how close the panel voltage is to the battery voltage. If that system was based on a 24 volt battery, with a Vmp of 32 volts it would be more susceptible to underperform than if the voltage difference was higher. And it especially makes more difference in conditions of less than ideal sunshine, partial shading or cloudy weather for example.
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Nobadays
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# Posted: 1 Sep 2025 07:27pm
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Quoting: MtnDon If that system was based on a 24 volt battery, with a Vmp of 32 volts it would be more susceptible to underperform than if the voltage difference was higher.
Yep, 24v system.
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