Renogy pulled their flexible panels from the market

[arctictraveller]

I now have three 100w panels and the performance has been kinda poor. Granted, it's winter and the sun angle is low, but the most I've seen out of them in direct sun has been about 12A, most times I average about 5 to 6. I'd hoped for better, but perhaps the summer output will be better.

[gcvt]

Jeff, I got 11.9 amps (max) from my two 100w panels last Summer, so you might see an increase here in a few months.

[Overlandsolar]

We tried and tested multiple flexible cells for over a year to see if it was something we would offer but the output per watt was significantly lower than the standard panels. Within the year all of them dropped even further with delamination and the heat was a factor I did not want to be a part of. There was another product that was pulled with a sticky backing about two years ago and I heard the similar issues we saw. I am always looking for the "next thing" but with flexible I think it's just not going to work reliably without some new technology that deals with initial low output issues and the heat they go through on the roof. I try not to do forums as a business owner with skin in the game with my own products but many of you know me from the Overland shows and know I am happy to point you away from even my stuff if it is not the best solution for an application. If I can help with something you are working on in the solar field I am happy to do so here or in person at the Overland Expos. See you at Overland West, as always the cooler will be full!

Brian

[arctictraveller]

Overland solar, Thanks for clearing that up. Perhaps you can clear up another question I have. If a panel is rated at say 100w, I would expect to see about 7A at 14v or even 8A at 12v in direct overhead sun with no clouds. At best, I'm seeing about 4A from each of my three panels, for a real world output of about 50W. Could you explain how the 100W rating is derived, and under what conditions? Thanks for your comments.

[Scalf77]

While not in the Solar business, I do have a basic understanding of Solar Power. It is a very common misconception that if I purchased a 140 Watt solar panel, that I will be getting 140 watts of charge for my house battery. It comes down to how the output of a panel is specified, and while you may feel short changed, be happy that their is at least a common spec.

Panels are rated at Standard Test Conditions (STC) STC = 1000 W/M2 irradiance, 25° C (77 ° F) module temperature, Air Mass 1.5 spectrum. First these are pretty unrealistic conditions in the real world and rarely achieved. So from the start you would rarely get the stated output of panel during actual use.

Many Panel manufacturers will also state something called Nominal Operating Cell Temperature Conditions (NOCT) NOCT = 800 W/M2 irradiance, 20° C (68 ° F) ambient temperature, AM 1.5 spectrum. Please see the tables below of a common panel provider.

Standard Test Conditions (STC)
STC = 1000 W/M2 irradiance, 25°C module temperature, AM 1.5 spectrum


Pmp 140 W
Vmp 17.7 V
Imp 7.91 A
Voc 22.1 V
Isc 8.68 A
P tolerance +7/-0 %

Nominal Operating Cell Temperature Conditions (NOCT)
NOCT = 800 W/M2 irradiance, 20°C ambient temperature, AM 1.5 spectrum

TNOCT 45 °C
Pmax 101 W
Vmp 16.0 V
Imp 6.33 A
Voc 20.2 V
Isc 7.03 A
PTC 124.9 W

Temperature Coefficients
Pmax -0.46 %/°C
Vmp -0.52 %/°C
Imp 0.0066 %/°C
Voc -0.36 %/°C
Isc 0.06 %/°C
Operating Temp -40 to +90 °C

From these specifications we can see that at NOCT the output of that same 140 Watt panel is really 101 Watts. That is a sizable difference in output of the panel. Even with the NOCT ratings the actual module temperature is about 48 °C (118.4 °F), solar panels operating on the top of a van can reach much higher temperatures. Flexible panels have even less cooling as they are generally mounted directly to the roof, with no airflow underneath the panels. Then take into account your location and time of year, flat panels, and you may not be even close to NOCT levels.


Now that we see that a panel will not really produce the rated wattage, we can dig a little deeper and find the next area for some loss. That is going to revolve around the controller, and the specifics of your controller. We certainly can’t take 16 Volts out of the panel and apply it directly to the battery, for this reason we need some kind of controller. Are choices are PWM and MPPT, PWM is the most common for RV. Take into account that all controllers are going to have some form of power loss during the conversion or regulation process, but there are still differences in the controllers available. Looking at the 140 Watt panel under NOCT we are getting out about 101 Watts or Vmp of 16.00 Volts and an Imp of 6.33 amps, the best that we can do with a PWM controller 6.33 amps X Battery set point voltage 13.5 Volts. Disregarding any loss for conversion this would yield us about 85 watts (6.33 X 13.5). So now in reality your 140 Watt Panel is really yielding you 85 Watts.

In theory the MPPT controller will try to take the extra head room in voltage and apply it to the overall available current so you would still be getting closer to the 101 Watts of power at 13.5 volts. Obviously the conversion cost are higher than with the PWM. In the cases of our platforms (the top of a van) with heat having a direct effect on the Vmp voltage, sometimes the output of the panel is not even high enough for a MPPT controller to take advantage of it. MPPT controllers are great if your installation can take advantage of it.

The next area for power loss comes from the cabling in the installation, voltage drops from the panel to the controller can reduce the output even more.

Hope this helps.

-Greg

[arctictraveller]

Thanks Greg, that confirms my initial suspicion that ratings are acheaved under conditions impossible to get in the real world I have a 60 mile radar on my boat, that under real world conditions will see perhaps 40. Years ago I wrote that off as advertising hype. It seems like the solar industry is following a similar formula. Actually I'm sure a lot of other industry's do too. Thanks again for an excellent explanation that I'll have to read again, but prior to any beers.

[Overlandsolar]

Greg has a better understanding than many in the "solar business" Arctic and can't say much more. Ratings are based on conditions that assume a lot in the real world. Websites will say 100 watt panels give you 6 amps with no qualifiers and there are many before and after the charge controller. China has flooded the U.S. with a sea of pretty poorly made and inefficient cells, the anti dumping tax finally imposed on imports for Chinese solar last year should start to limit the cheap stuff and let those of us who don't sell it show what better solar production means in amps to the battery.

Start with a decent monocrystaline panels, keep wire size thick enough for the length of the run, crimp connections well, have the panels tilt appropriately for location and time of year, and use decent charge controllers. Mppt controllers in small systems are kind of a waste of money especially when the controller is exposed to higher heat on the panel or in the van. I keep a few on hand when customers insist on them but just having panels tilt and move will set you up well.

[sbgrimm]

Check out AM Solar for the SF160 panel. 160 watt panel with a small footprint, so you may be able to get by with fewer panels.

[gcvt]

Originally Posted by sbgrimm

Check out AM Solar for the SF160 panel. 160 watt panel with a small footprint, so you may be able to get by with fewer panels.

In terms of a ~300 watt setup, it'd be 3 lbs less than a Renogy setup, but quite a bit more expensive, with no controller included from AM. Could be a good option for people with real estate issues...small roof rack, etc.

[sbgrimm]

Originally Posted by gcvt

In terms of a ~300 watt setup, it'd be 3 lbs less than a Renogy setup, but quite a bit more expensive, with no controller included from AM. Could be a good option for people with real estate issues...small roof rack, etc.

Yes, that was my situation exactly. I needed to save room on the roof for a cargo box and kayak(s), so I was willing to pay the premium for the higher output panel from AM Solar. BTW, they are a great company to deal with. (No financial interest, just a happy customer).