Combining "new" 160W solar with "old" 95W? - Escape Trailer Owners Community

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Old 07-19-2014, 06:56 PM   #1
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Combining "new" 160W solar with "old" 95W?

Many of us have the 95W solar panel and (maybe) a little bit jealous of those who have the newer, more efficient 160W panel. I was wondering if it would be feasible (and how complex it may be [other than roof attachment]) to combine the new 160W panel with our existing 95W unit two into a "mega" 255W charger? Would it be necessary to make any changes to the controller or other electronics? Would it be a parallel or series connection? (Clearly, electrical mods are not my strong suit.)
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Old 07-19-2014, 07:13 PM   #2
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Or, two 160's for those getting the new set-up?
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Old 07-19-2014, 07:24 PM   #3
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Quote:
Originally Posted by pkgman51 View Post
Or, two 160's for those getting the new set-up?
I think then it becomes a build sheet question since ETI would handle the combination. I'm interested in retrofitting.
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Old 07-19-2014, 07:33 PM   #4
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I was at ETI last Friday and checked out the installation of the panels; they've epoxied the panel mounting rails onto the trailer surface. There are no holes drilled through the glass to screw things down, so a retro shouldn't be hard IF you have the roof area - the 160W panels are BIG; ETI mounts them behind and below the AC on the 21 to minimize turbulence that could produce an uplift effect.
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Old 07-19-2014, 08:15 PM   #5
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Mounting issues aside, the electrical side can be easy: you can just parallel the two panels together. How optimally this works depends on the charge controller: the more basic the controller the less it matters that two panels are sharing one controller.
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Old 07-19-2014, 08:59 PM   #6
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I don't see where the 160's are any more efficient then the 95's (17.8% vs 17.4%), just proportionally bigger. You need somewhere on the 19 that has space for a 26x58" panel. If you have MC4 connectors you can buy T's to combine the 2 panels on the roof. The only issue may be the size of the cable and the distance the total run will be. The 30A gopower solar controllers will handle both. If the run is fused you probably need to up it's value.
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Old 07-19-2014, 10:00 PM   #7
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I previously telephoned Go Power and asked if the 160 and 95 could be connected together. I was told no. If I remember correctly, because it was several months ago, they said the units are grounded differently and therefore cannot connect together.
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Old 07-19-2014, 11:08 PM   #8
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[QUOTE=...they said the units are grounded differently and therefore cannot connect together.[/QUOTE]

They might have given you the correct answer, but for the wrong reason.

For a solar panel, a ground is a ground. But if you try to hook them in parallel and one is a different voltage than the other, the higher voltage unit will try to discharge through the lower voltage unit - unless blocking diodes were used in the correct location. But the resulting combination would be very inefficient with the higher voltage unit providing the bulk of the power, and the lower voltage unit contributing almost nothing most of the time.

If they are the same voltage output then absolutely no problems with a parallel connection. Just connect a blocking diode to each panel and connect the ground to ground and the positive to positive, and consider the two panels as a single panel.

If you were trying to hook them in series the voltages combine because the ground of one panel connects to the positive of the other, just like two batteries in a flashlight. No blocking diodes needed. But the problem with series is that the combined voltage may exceed the limits of the controller in the worst case. And in a common scenario, the combined voltage would just be converted to wasted heat if the controller is a linear device (as opposed to a DC-DC converter). Should the controller be in fact a DC-DC converter and be able to function with 50 volts input, then this would be a very nice setup.

Obviously the correct answer depends on the specifics of each panel plus the controller, for which I have no first hand knowledge.
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Old 07-20-2014, 12:46 AM   #9
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I agree with alanmack's description of the electrical situation. I was assuming a parallel connection, because these panels are both clearly the same nominal voltage.

I am guessing - so corrections would be appreciated - that we're talking about
160 watt panel: CTI-160
95 watt panel: CTI-95
charge controller: GP-PWM-30

The operating voltage of the two panels looks pretty compatible to me for parallel connection. The controller appears to be unsuitable for series connection.
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Old 07-20-2014, 01:36 PM   #10
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I believe the reason GoPower doesn't allow paralleling the 95 watt panel with the 160 watt panel is the metal frame of the 95 is connected to the positive side & the frame of the 160 connected to negative. If the frames are electrically connected together, that would cause a problem. Of course on a fiberglass trailer they wouldn't have to be, but code, at least for house sized systems, requires grounding the frames of the panels.
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