Solar panel help

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Solar panel help

Postby Richard Grotto » Tue Sep 15, 2020 10:58 pm

I am still kinds confused, I have a micro camper, I have the Maxxfan, two cell phones possibly an iPad and two LED small exterior lights running off the battery at night.
I want a solar panel to charge it back up to full charge for the next nights power consumption. I am not gonna use much other than that. I am not sure what size panel to buy, I like the portability of the soft side and extremely light panels but I want to know if a 60W would do the duty of do I need to go with a 100W?
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Re: Solar panel help

Postby lfhoward » Wed Sep 16, 2020 4:50 am

Hello,
You’d have to know something about your power consumption during the day. Make a list of what you run, how many amps those devices draw, and how long they are typically on for. That will give you an idea of how many amp hours you will need to replace.

As you’re doing that, some devices may have power consumption listed in watts. Here is the conversion.
Watts = Amps * Volts OR. Amps = Watts / Volts

A 100 watt panel will not necessarily give you that many watts most of the time due to shade from trees and clouds and the angle of the sun. I have a 140 watt panel that at most makes 7 amps through my solar controller at 12 volts. That’s technically only 84 watts. And most of the time it’s less.

But one hour at 7 amps can replace 1 amp of power drawn over 7 hours... so got to know how much power you need to put back during the day.
My off-road camper build on an M116A3 military chassis:
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Tow vehicle: 2008 Jeep Liberty with a 4 inch lift.
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Re: Solar panel help

Postby saltydawg » Wed Sep 16, 2020 6:40 am

Also the flexible panels also have a much shorter life span, if you constantly moving and flexing them or they sit in the sun all the time they will only last a year or two.

Get the "heavy" framed panels. the breif case style works well. Then you can, even when in the shade put the panels in the sun with a longer wire. If you go to long with the wire Make sure you get a mppt charger. Up to 20 feet or so the standard and much cheap pwm style will work.

As was said total up your loads and report back
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Re: Solar panel help

Postby tony.latham » Wed Sep 16, 2020 9:57 am

I have the Maxxfan, two cell phones possibly an iPad and two LED small exterior lights running off the battery at night.


The big question is how long will you run the fan? I don't recall what the Maxxfan draws but it's probably about 1 amp/hour on low. I know they draw less than a Fantastic.

My iPhone battery has a 2.6 amp battery. By nightfall, it may be down to about 50%. I think iPads push about 8 amps. The draw from LEDs is so low they are hard to measure.

We use about 8 amps per night, mostly from my CPAP. My 100-watt panel has the battery juiced up by ten or eleven depending on cloud cover. Noon at the latest. (You'll get about 80% - 90% of what the panel is rated for when pointed directly at the sun.)

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Re: Solar panel help

Postby Richard Grotto » Wed Sep 16, 2020 10:16 am

saltydawg wrote:Also the flexible panels also have a much shorter life span, if you constantly moving and flexing them or they sit in the sun all the time they will only last a year or two.

Get the "heavy" framed panels. the breif case style works well. Then you can, even when in the shade put the panels in the sun with a longer wire. If you go to long with the wire Make sure you get a mppt charger. Up to 20 feet or so the standard and much cheap pwm style will work.

As was said total up your loads and report back


Good info , I though they may have a shorter life span, thanks for confirming it.

I am also looking at a hard shell briefcase style.
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Re: Solar panel help

Postby tony.latham » Wed Sep 16, 2020 10:57 am

I though they may have a shorter life span, thanks for confirming it.


It depends. Most flexibles use PET plastic. They are famous for failing in three to four years. Junk is junk and that's where the flexibles get that reputation from.

ETFE panels are a much higher quality. Mine's made by Renogy. Their flexibles have the same guarantee as the their glass panels.

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ETFE is used in some roofing applications.

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Re: Solar panel help

Postby saltydawg » Wed Sep 16, 2020 11:45 am

Tony I see you have the panel directly on the roof. Has you seen any of the pics from where Rv'ers had them on the roof. The heat cooks the rubber roofing to the point where they start turning brown. I saw one guy who went up with a laser thermo and was getting 190 degrees on the panel with it flat on his roof, and it was partially cloudy.

Look at the pics in the below link
https://amsolar.com/solar-panels-for-rv ... ble-panels
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Re: Solar panel help

Postby RJ Howell » Wed Sep 16, 2020 1:35 pm

Richard, I approach this as..

first: Do a power audit. 'Know what you'll be using for a 24hr period. Even without a meter it's fairly easy as in just learning what the wattage of everything you'll use (and the time you will use it) and writing it down.

Then: Decide where and how you will camp. This you probably already know so even simpler. I you stay 3-4 days in a place... how much sun will you get each day? Where I live I can only plan on an average of 3-4hrs of solar gain.

Now: You know how much wattage you use, and how much sun you can expect, sizing the panel is fairly straight forward. Usually factor for your average sunlight. Example: If I get 4hrs average sun and I require 20amps replaced, I need a 75w panel. 20amps/4 = 5amps x 12.5v = 62.6w x 20% deficiency = 75watts If I used the 3 hrs, then a 100watt panel.

For me... I no longer carry a solar panel. All my charging is done by a DC/DC charger while I drive. My battery is sized to run for 2.5 days (3 max) and I recharge in less than 3hrs of driving (if I actually went that low). Typically we stay put for only a couple days and move on. As of late (this year) we've only stay a couple days 3 times.. mainly over-nighting at places. The DC/DC is the ticket for us!

Oh and do please by a good battery. You don't wish to go all this and the battery can't do the deed. That small a battery, LiFePO4 should be affordable.
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Re: Solar panel help

Postby featherliteCT1 » Wed Sep 16, 2020 5:10 pm

Tom&Shelly previously posted:

"our MaxxFan +. Turns out there are 10 speeds:
0.05 A,
0.15 A,
0.2 A,
0.3 A,
0.5 A,
0.7 A,
1.0 A,
1.35 A,
1.8 A, and a whopping
2.65 A"

viewtopic.php?f=30&t=70092&p=1227602#p1227602
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Re: Solar panel help

Postby tony.latham » Wed Sep 16, 2020 5:46 pm

saltydawg wrote:Tony I see you have the panel directly on the roof. Has you seen any of the pics from where Rv'ers had them on the roof. The heat cooks the rubber roofing to the point where they start turning brown. I saw one guy who went up with a laser thermo and was getting 190 degrees on the panel with it flat on his roof, and it was partially cloudy.

Look at the pics in the below link
https://amsolar.com/solar-panels-for-rv ... ble-panels
I have seen at least one of those.

Renogy says it’s fine to mount these directly to a surface. They give the name of a product they recommend for bonding. Min is screwed down.

I’ve checked the roof with my palm on hot days with the sun at noon. I find little difference between the two surfaces. I’ll guess ten degrees.

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Re: Solar panel help

Postby saltydawg » Wed Sep 16, 2020 7:13 pm

My plan was to mount a 100 watt flex panel on my roof, then have a briefcase one to put out in the sun if I was in the shade. Then I started reading about failures and temp issues, and being the fact that my roof surface will be fiberglass skin epoxied to foam I started to worry about the temp breaking down the epoxy. People have come up with all sorts of ways to get a standoff distance for an air gap. The best I have seen is using corrugated plastic panels.

As much as I still want to just put a 100 watt flex panel on my roof I am not. I am going to make a frame that clamps down on the the frame of a glass panel.This does two things, one keeps a panel on the roof, two when I want to move it out to sun my panel is stored on the roof and providing power while there. So no need for storage, no need for a permanent mounted panel, and I only have to buy 1 panel.

People are free to make their decision on their own, but like using foam and fiberglass panels so I never have to deal with rot. I wont use a flex panel so I dont have to deal with failing, cooking my roof etc etc.

more things for people to read to help with their decision

https://www.gonewiththewynns.com/flexib ... ues-review
https://www.technomadia.com/2014/11/zep ... r-install/
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Re: Solar panel help

Postby bdosborn » Wed Sep 16, 2020 8:49 pm

I have a mixture of solid and flexible panels. The flexible panels haven't overheated and my filon roof is fine. The output has been what I'd expect for a flat panel ~60% of rated output. I wouldn't leave them out in the weather all the time, as Tony said, most of them aren't as UV stable as you'd hope. My trailer is in the garage when I'm not camping so the flexible panels are in good shape.
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