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Topic ClosedRenogy RipOff - please tell me otherwise
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offgrid View Drop Down
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Posts: 5290 		Direct Link To This Post Topic: Renogy RipOff - please tell me otherwise
    Posted: 18 Jul 2020 at 7:02am
You are certainly getting a typical battery charging output for a nominal 200 watt solar array, so that's good. Also, those look to be 5 inch cells which are typically about 3 watts each, so 64 x 3 = 192 walls.

And, your two modules certainly appear to be connected in series, so that would imply that the modules are 6V nominal. Voc (open circuit voltge) of the cells should be around 0.6V so your 10V per module measurement would imply that there is a 16S by 2P  series/parallel cell configuration internal to the modules. 


Can you take  a photo of the front of one of the modules and post it? It should be possible to trace the internal cell connections if the resolution is good enough.

But yes, if you wanted to reconfigure the two modules in series to reduce voltage drop and then step the voltage down with an MPPT you will be disappointed. I can only speculate why Renogy would do that. They want to be able to supply modules for 6V applications also and are trying to keep their parts count low? They feel that parallel cell connections help mitigate shading issues (they can)?  
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Posts: 1014 		Direct Link To This Post Posted: 18 Jul 2020 at 7:14am
Good catch on the cell size! 
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Posts: 6288 		Direct Link To This Post Posted: 18 Jul 2020 at 7:28am
Originally posted by offgrid

They feel that parallel cell connections help mitigate shading issues (they can)?

What meant by "they can." or "they can?"? The sentence is a bit ambiguous. Please clarify how that works. I have the 100W setup, so mine is 32 cells. 32x3=96 watts, which rounds to 100. I am guessing from what you wrote that my modules are also 6V nominal and the two panels connected in series would make the kit 12V. Am I correct in my understanding?
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fwunder View Drop Down
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Posts: 1676 		Direct Link To This Post Posted: 18 Jul 2020 at 7:47am
Some additional pics...
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Posts: 1676 		Direct Link To This Post Posted: 18 Jul 2020 at 7:58am
Originally posted by offgrid

But yes, if you wanted to reconfigure the two modules in series to reduce voltage drop and then step the voltage down with an MPPT you will be disappointed.

This was whole whole point of me bringing this up in the first place. Thank you.
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offgrid View Drop Down
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Posts: 5290 		Direct Link To This Post Posted: 18 Jul 2020 at 10:38am
Ok, these are SunPower back contact cells (meaning that both the cell + and - connections are on the backs of the cells. Makes it hard to tell how they're interconnected. We can only surmise bv your electrical measurements that they are 16S x 2P for a nominal 6V 100 watt module. 

Yes I was deliberately vague about how paralleling cells can reduce shading impacts, because its a little complicated. What happens is that if you have a long string of cells in series, shading one cell can block current flow through all the other cells in that string. So, imagine a leaf that covers one cell, that can take out the whole module, or more than one module in a higher voltage system. That's what bypass diodes are for (the devices in the photos of the module jboxes). They allow current to bypass around shaded cells or groups of cells. 

By placing the cells in parallel you reduce the impact of shading individual cells, because the cells can share current between them. This works especially well if the parallel cells aren't directly next to each other so it becomes less likely to shade both of them at once. There are drawbacks too, the currents are higher so the bypass diodes (the devices in the photos of the module junction boxes) have to be larger. 

That's probably enough solar 202 (you already passed 101!) unless you really want more. Sorry you can't do the MPPT controller and use a lighter gauge wire. But, at least you are getting a reasonable output from your system. To answer your original question personally don't use Renogy stuff because I think its overpriced for what you get. If the size works for you, the best deals in solar are going to be standard 60 or 72  6 inch cell residential or industrial modules. with an MPPT to take that down to 12V. Often those can be had from CL or Ebay for less than 50 cents a watt. 
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Posts: 1676 		Direct Link To This Post Posted: 18 Jul 2020 at 11:20am
Thanks offgrid!! I am learning a lot. Prolly should have studied more before I jumped into this...Oh well...money under the bridge. I am having fun with it. In fact, I did order another panel - from HQST. Looks like the exact same panel Renogy sells for $40.00 more. Will Prowse did a good side by side comparison. I bought it because the dimensions are perfect for want I want to use it for (TV roof rack).

Back to my suitcase...It's really not all bad news. These panels really do perform.

I just did a load test with a 331 watt AC load (wife's hair dryer) via 1500 watt inverter. Battery bank is two one year old 220ah GCs fully charged. Midday sun and panels 12 feet from PWM controller w/ 10 AWG. Panels had no problem keeping up with the load pumping in as much as 11.8 A @ 150+ watts. After ten minutes or so battery voltage measured @ inside panel leveled out @ 12.3v. So, I would say they certainly performed within spec.

My beef is I wanted to get the panels further away from controller without using humongous wire so I planned on buying a MPPT controller and 100 watt series connected 12v panels (which I thought these were). I cannot do that with these panels. Really, that's my only beef. (besides spending much more money than I really needed to)

Thanks for the education! Still learning!
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Posts: 6288 		Direct Link To This Post Posted: 18 Jul 2020 at 12:03pm
+1. I also appreciate the information I have learned here. I had not thought about 6V vs. 12V panels. I bought the 100W kit with the assumption that I would be using it as a set since that is the way it is made. I had not thought about adding any additional panels.
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Posts: 5290 		Direct Link To This Post Posted: 18 Jul 2020 at 12:09pm
I agree those modules are fine power wise. At 150 watts you're running at about 75% of nominal rated power. The 200 watt rating is under full sun at 25C (77F) module temperature (aka STC = Standard Test Conditions). PV modules drop off in voltage by about 0.4% per degree C, and heat up by about 25-30C under full sun. So lets's say its 85F (about 30C) where you are then your module will be at about 60C and will lose about 14-15%. Then you'll have additional losses from the PWM cointroller from not runningy the module at max power point like an MPPT would. Then you have a little wiring loss and as its East Coast summer some haze and humidity so you're not at full sun. Overall I'd say you're right about where you should be. 

Sorry about not being able to convert to an MPPT for those modules, but maybe you'll make up for it a bit when're camping in partial shade someday. Wink
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