Solar Panel question- more or fewer panel

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Solar Panel question- more or fewer panel

Postby lrrowe » Tue Mar 15, 2016 9:06 pm

Here is a question for you solar panel gurus.
I have found the solar panels I want to order and I have narrowed it down to two options.

Option 1- install four 140 watt panels measuring approximately 58" x 27" each. This allows for two panels side by side across the 6ft width two rolls long at about 116" long (total). Total watts is about 560 watts. And they would be in phases of 2 at a time.

Option 2 - install six 80 watt panels, 2 across the top times three rows long for a total of about 100 in long. Total watts is 480.

Dollars per watt is about the same.

My thoughts:
The wattage difference is close enough to be considered apples and apples comparison.
I like the smaller 80 watt units because should a failure occur, it is less costly to replace a smaller panel, wattage wise.
I do not believe the more connections required for the smaller units is not that big of a deal versus the larger and fewer 140 watt panels.

So my question is along the path of whether I should be concerned over the quantity of the panels and just go for the best cost for space used?
Bob

First Post on Purchase of Trailer: http://www.tnttt.com/viewtopic.php?f=42&t=60722
Hot water infloor and radiator heating project:[url]http://www.tnttt.com/posting.php?mode=reply&f=54&t=62327[/

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Re: Solar Panel question- more or fewer panel

Postby GuitarPhotog » Tue Mar 15, 2016 9:10 pm

I'm not a fan of mounting the panels on the trailer, simply because it requires you to park the trailer in the full sun, and you lose the flexibility to move the panels as the sun moves.

That said, I would go with fewer panels because the most common point of failure with electrical devices is connections and connectors. The fewer connections, the more reliable the system can be.

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Re: Solar Panel question- more or fewer panel

Postby lrrowe » Wed Mar 16, 2016 8:36 am

Thanks....
I had thought of that and was going to have some panels for portable use. Maybe one 140 watt unit or two 80 watt unit.
And your comment about connections being the weak link also leans me towards the larger and therefore fewer panels.
Bob

First Post on Purchase of Trailer: http://www.tnttt.com/viewtopic.php?f=42&t=60722
Hot water infloor and radiator heating project:[url]http://www.tnttt.com/posting.php?mode=reply&f=54&t=62327[/

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Re: Solar Panel question- more or fewer panel

Postby MtnDon » Wed Mar 16, 2016 9:55 am

More panels, fewer connections.

I don't mean to throw a curve at you but there is one more thing to consider. I don't recall this ever being mentioned specifically here in part I believe because most solar setups on small trailers seldom involve more than 2 panels. When connecting PV panels in parallel, an overcurrent device should be used in each + line from each panel. This is usually done by using a combiner box with fuses or breakers. If the panels were being used connected to a house the NEC makes that mandatory. When the multiple parallel connections occur on a trailer I am not sure what rules there are.

However, the problem is not just that the rule book says so. There is a chance with three and more parallel connected panels that a short circuit is one panel or one panels wiring could cause all the current from the parallel connected panels to be greater than the wiring can safely handle. That could start a fire. So each + panel output should pass through a fuse / breaker before the current of each is combined and sent along to the charge controller. Here's a c-box designed for RV's. But it doesn't seem to have room for fuses, or it's not obvious to me. There may be others as well. The need for fuses was why I went with two larger panels than three smaller ones.
Our 6x12 deep vee nose cargo trailer camper conversion... viewtopic.php?f=42&t=58336

We have a small off grid cabin we built ourselves in the NM mountains; small PV solar system; 624 watts PV, Outback CC & inverter/charger ... http://countryplans.com/smf/index.php?topic=2335.0
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Re: Solar Panel question- more or fewer panel

Postby OverTheTopCargoTrailer » Tue Mar 29, 2016 12:33 am

I would chime in, but don't know to much about solar, so I'm waiting to see your design. I would think smaller panels as it would be harder for them to fly off & they are lower volts.

Cheers Ottct
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Re: Solar Panel question- more or fewer panel

Postby Trevor57 » Tue Mar 29, 2016 5:26 pm

Voltage has absolutely nothing to do with size of the panels, and for that matter neither should panels flying off.
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Re: Solar Panel question- more or fewer panel

Postby OverTheTopCargoTrailer » Thu Mar 31, 2016 10:03 pm

Trevor57 wrote:Voltage has absolutely nothing to do with size of the panels, and for that matter neither should panels flying off.


WOW, thanks for the info. Could you post a link to some 250 watt panels that are around 18 volts ?

Cheers ottct.
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