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Author Topic: Solar panels on tent trailer - Worth it?  (Read 1549 times)

KodiakJack

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Solar panels on tent trailer - Worth it?
« on: April 22, 2018, 10:46:55 PM »
So I just got a 2005 Viking epic tent trailer. It’s a little eight footer. It came with a “condition unknown” 12v battery. I’m playing with the idea of getting a solar panel to top it up during the day, so it got lots of juice at night.

The trailer has an inverted, LED interior lights, 3 way fridge, and furnace.

Our camping style is to abandon the site during the day for adventures abroad, then return for supper, a camp fire then bed. Our only use of the electrical system would be the LED lights at night (for maybe an hour or so if we get chit chatting), and the 120v inverted outlets for charging cell phones, or maybe inflating a mattress or something.

Would this be a good application for solar?  Where does one go to find the best deal on solar panels? Are they worth the hassle?

Here’s one on sale locally. Thoughts on it?
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xvz12

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Re: Solar panels on tent trailer - Worth it?
« Reply #1 on: April 24, 2018, 07:33:13 PM »
Just FYI, Harbor Freight has a 100W system that is very similar for the same price, Twice the bang for the buck.

Isaac-1

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Re: Solar panels on tent trailer - Worth it?
« Reply #2 on: April 24, 2018, 08:30:54 PM »
Smaller solar panels can help maintain the battery while the trailer is not in use, though to power the refrigerators control electronics, run LED lights at night, and charge the battery enough to power the furnace blower fan during cooler nights you will likely need 150 -200 watts worth of solar panels minimum if camping in the spring or fall with shorter days, if not you would still need to run a generator to keep your batteries charged while camping.

Here goes the math

Knowing the exact model of refrigerator and furnace you are using would help give a better estimate, though as a general rule an RV refrigerator will consume 5-8 watts of power for the control electronics, which would run 24 hours per day.  Lets assume on the high side so 8 x 24 = 192 watt per day, lets round that to an even 200 to keep things simple.  Lets assume you have a small Suburban brand NTQ series forced air furnace, which has an amp draw of about 3 amps while running, 3 x 12.8  = 38.4, rounding again gives us 40 watts per hour, assuming running only at night, 8 hours per night, for 30 minutes out of every hour.  40 x 8 x .5 = 160 watts per day.  LED lights should be trivial in comparison, even assume you want it fairly brightly lit, a 60 watt equivalent LED light bulb draws about 9 watts per hour, let say 3 hours per night we are still just under 30 watts per day.  This all brings us a grand total of about 400 watts per day you must replace into your battery.

For mid America average spring / fall lighting levels a fixed mount flat solar panel will generate 4 to 5 hours worth of peak output per day if exposed to open sky.  Shading can reduce this considerably, battery charge losses account for 20-25% of the total solar output.  So working with a single 150 watt solar panel with 4 hours of peak output per day we get 150x4 600 watts per day x .75 for battery charge losses, and we just about break even at 450 watts of available power added to the battery on an average day.  Of course you may want to go larger in case of cloudy weather, wanting to recharge cell phones, run radio, etc. 
2002 Safari Trek 2830

KodiakJack

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Re: Solar panels on tent trailer - Worth it?
« Reply #3 on: April 24, 2018, 09:16:23 PM »
Just FYI, Harbor Freight has a 100W system that is very similar for the same price, Twice the bang for the buck.

I appreciate the heads up, but I’m in Canada, and the nearest harbor freight is 8 hours away, then there’s currency exchange and duty...

Thanks though.
You're free to make your choices, but not free from the choices you make.

KodiakJack

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Re: Solar panels on tent trailer - Worth it?
« Reply #4 on: April 24, 2018, 09:41:49 PM »
Smaller solar panels can help maintain the battery while the trailer is not in use, though to power the refrigerators control electronics, run LED lights at night, and charge the battery enough to power the furnace blower fan during cooler nights you will likely need 150 -200 watts worth of solar panels minimum if camping in the spring or fall with shorter days, if not you would still need to run a generator to keep your batteries charged while camping.

Here goes the math

Knowing the exact model of refrigerator and furnace you are using would help give a better estimate, though as a general rule an RV refrigerator will consume 5-8 watts of power for the control electronics, which would run 24 hours per day.  Lets assume on the high side so 8 x 24 = 192 watt per day, lets round that to an even 200 to keep things simple.  Lets assume you have a small Suburban brand NTQ series forced air furnace, which has an amp draw of about 3 amps while running, 3 x 12.8  = 38.4, rounding again gives us 40 watts per hour, assuming running only at night, 8 hours per night, for 30 minutes out of every hour.  40 x 8 x .5 = 160 watts per day.  LED lights should be trivial in comparison, even assume you want it fairly brightly lit, a 60 watt equivalent LED light bulb draws about 9 watts per hour, let say 3 hours per night we are still just under 30 watts per day.  This all brings us a grand total of about 400 watts per day you must replace into your battery.

For mid America average spring / fall lighting levels a fixed mount flat solar panel will generate 4 to 5 hours worth of peak output per day if exposed to open sky.  Shading can reduce this considerably, battery charge losses account for 20-25% of the total solar output.  So working with a single 150 watt solar panel with 4 hours of peak output per day we get 150x4 600 watts per day x .75 for battery charge losses, and we just about break even at 450 watts of available power added to the battery on an average day.  Of course you may want to go larger in case of cloudy weather, wanting to recharge cell phones, run radio, etc.

Thanks for that.

I’m still getting to know the systems. 

The fridge is a Dometic 2193. When running on propane, according to my interpretation of the manual, the propane system runs continuously without a thermostat, the temperature just being controlled by the flame setting. So I don’t think there’d be any electrical draw from it. It says to make sure both dc and ac power are switched off before using propane to cool.

The lights are just 2 dome lights in the ceiling. The previous owner has replaced the little lights inside with KEDs. They’re about the size of my little finger.

The furnace is kind of a moot point. We’re used to tenting it, so I’m pretty sure we can get by without heat. The only time I’d use it would be when moose hunting, and then we’d have a fleet of generators anyway. But for arguments sake, the furnace is a Suburban NT-12SE. I don’t see anything in the manual that depicts its draw.

So realistically, it would be pretty negligible use I think... I think.
You're free to make your choices, but not free from the choices you make.

KodiakJack

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Re: Solar panels on tent trailer - Worth it?
« Reply #5 on: April 24, 2018, 09:47:43 PM »
A couple other questions about solar in general:

Could a solar system charge a battery “all the way” or just keep it topped up?  If you had a battery that was at say 25%, could a small solar system over the course several days bring the battery back to 100%?
Or would that be bad for the battery?

Would there be any harm in mounting the panel to the top of the trailer more or less permanently? So that it’s keeping the battery topped up year round?
You're free to make your choices, but not free from the choices you make.

HappyWanderer

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Re: Solar panels on tent trailer - Worth it?
« Reply #6 on: April 24, 2018, 09:54:19 PM »
Harbor Freight solar is junk, so you're not missing anything.

With the fridge on propane and LED lights, you should be fine with a 100 watt panel. Amazon is a good source for Renergy panels and controllers. Portable is good, because you can tilt it towards the sun for greater efficiency.

Ditch the inverter for charging electronics: it has a current draw of its own. Charge the phones directly from 12 volts. No reason to convert DC to AC and back to DC for charging.
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KodiakJack

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Re: Solar panels on tent trailer - Worth it?
« Reply #7 on: April 24, 2018, 10:07:45 PM »


Ditch the inverter for charging electronics: it has a current draw of its own. Charge the phones directly from 12 volts. No reason to convert DC to AC and back to DC for charging.


Hmm. That’s a good point, but there’s no “cigarette lighter” type outlets. The only 12v outlet is the funny jack in the overhead light:  http://www.rvforum.net/SMF_forum/index.php/topic,113289.msg1024114.html#msg1024114

Is there a typical solution for this?  Aftermarket 12v “powerbars” so-to-speak? Or outlets I could install?  I’m awfully new to this world. :-/
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HappyWanderer

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Re: Solar panels on tent trailer - Worth it?
« Reply #8 on: April 25, 2018, 07:56:25 AM »
Get one of those multi-outlet accessory cords and cut off the lighter plug. Put a fuse on the end and connect directly to the battery. Instant charging station.
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KodiakJack

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Re: Solar panels on tent trailer - Worth it?
« Reply #9 on: April 25, 2018, 10:22:05 AM »
Get one of those multi-outlet accessory cords and cut off the lighter plug. Put a fuse on the end and connect directly to the battery. Instant charging station.

What size fuse should one install? 10a? 

Could be used for charging phones... maybe a little 12v air pump for blowing up mattresses and beach toys... bicycle pump... fan... whatever.

You're free to make your choices, but not free from the choices you make.

HappyWanderer

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Re: Solar panels on tent trailer - Worth it?
« Reply #10 on: April 26, 2018, 07:21:59 AM »
10 amps sounds right.
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KodiakJack

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Re: Solar panels on tent trailer - Worth it?
« Reply #11 on: April 27, 2018, 06:01:30 AM »
10 amps sounds right.

Went amazoning, and stumbled across this one.  Thoughts?

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Kevin Means

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Re: Solar panels on tent trailer - Worth it?
« Reply #12 on: April 27, 2018, 11:19:28 AM »
Could a solar system charge a battery “all the way” or just keep it topped up?  If you had a battery that was at say 25%, could a small solar system over the course several days bring the battery back to 100%? Or would that be bad for the battery?

Would there be any harm in mounting the panel to the top of the trailer more or less permanently? So that it’s keeping the battery topped up year round?
When boondocking, our solar array is our primary method of recharging our house batteries, so yes... solar can be used to fully recharge batteries. However, our array is fairly large, we're able to tilt our panels toward the sun and we're located in Southern California. Those things have a significant impact on the effectiveness of solar. Our array wouldn't be nearly as effective in Canada. The sun is much lower in the sky, especially in cooler months when RVers rely more on solar power.

A lithium battery would be fine if it were repeatedly discharged to 25% but repeatedly discharging a lead/acid battery anywhere near that far would shorten its life considerably. FWIW, I don't let our battery bank get below 75% and our last set of batteries lasted seven years.

When a lead/acid battery gets deeply discharged, it should be fully recharged as quickly as possible. A solar array may, or may not be able to do that, depending on the size of the array compared to the AH capacity of the battery bank, available sunlight, shading and draw on the system.

If the panel was approved for outdoor use (some smaller panels aren't) it should be fine to mount it on the roof... as long as it was installed correctly.

Kev
2011 Winnebago Tour 42QD
Towing a Jeep Rubicon Unlimited LJ
RVI Brake 2, Minder TM-66 TPMS, 960 watts of solar
(Can't wait to spend more time RVing)
Lakeside, California

KodiakJack

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Re: Solar panels on tent trailer - Worth it?
« Reply #13 on: April 27, 2018, 07:10:24 PM »
Thanks gang!
You're free to make your choices, but not free from the choices you make.

pip

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Re: Solar panels on tent trailer - Worth it?
« Reply #14 on: May 20, 2018, 02:57:12 PM »
I appreciate the heads up, but I’m in Canada, and the nearest harbor freight is 8 hours away, then there’s currency exchange and duty...

Thanks though.

Just throw fly down in that quest, and stash it in the belly.  Problem solved.   ;D

John From Detroit

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Re: Solar panels on tent trailer - Worth it?
« Reply #15 on: May 20, 2018, 03:42:11 PM »
If you have LED lighting, then yes. a solar panel may do well

If the fridge is 3-way.. DO NOT USE THE 12 volt SETTING,, EVER, Pull the 25 amp fuse (HINT the fuse needs to be that big for a reason).

Leave the 3 and 5 amp fuses in place.

Just for accent lighting I use LED's amazing how much light you get with a solar panel not much bigger than a special commerative postage stamp   (Like 1x2 or 2x3 inches)

Newer LED's.. I have two flashlights. COB led's my measurement 3 watts.  Advertised 1200 Lumens. a 100 Watt Lamp is 1200 LUMENS.. That's a whole lot of light for 3 watts of draw  3 watts is 1/4 amp at 12 volts  20% of a 100 amp hour battery would last you .. Several days.
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xvz12

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Re: Solar panels on tent trailer - Worth it?
« Reply #16 on: May 21, 2018, 07:37:50 AM »
Just finished installing 2 100w Renogy solar panels on the roof of our pup yesterday.....give me a few days to test & I'll report back with results.

Rene T

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Re: Solar panels on tent trailer - Worth it?
« Reply #17 on: May 21, 2018, 08:24:17 AM »
One other thing to keep in mind is will your crank up mechanism take the extra weight of the panel. I would find out what the weight is of the panel you're thinking on installing, put something on the roof of equal weight and try to raise the roof.
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KodiakJack

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Re: Solar panels on tent trailer - Worth it?
« Reply #18 on: May 25, 2018, 08:51:07 PM »
Ok folks, I grabbed this tonight. $160CAD for 2 40w panels, 2 controllers, etc. each weighs 15 lbs. so no worries with the weight. Question: if you had a “two of everything” pack like this, would you hook each up to the battery separately? Or combine them through one charge controller?
You're free to make your choices, but not free from the choices you make.

KodiakJack

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Re: Solar panels on tent trailer - Worth it?
« Reply #19 on: May 26, 2018, 10:00:54 AM »
I set the 2 40w panels up and they’re charging well. We’ll try it out next weekend to see if it keeps up. Thanks for your help everyone!
You're free to make your choices, but not free from the choices you make.

Alfa38User

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Re: Solar panels on tent trailer - Worth it?
« Reply #20 on: May 26, 2018, 12:47:43 PM »
Which way did you set it up??
Stu
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Kevin Means

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Re: Solar panels on tent trailer - Worth it?
« Reply #21 on: May 26, 2018, 12:49:58 PM »
Ok folks, I grabbed this tonight. $160CAD for 2 40w panels, 2 controllers, etc. each weighs 15 lbs. so no worries with the weight. Question: if you had a “two of everything” pack like this, would you hook each up to the battery separately? Or combine them through one charge controller?
Welcome to the world of RV solar! I'm glad it's working for you. You should only need one controller, but it has to be rated to handle the output of both panels. Without knowing the specs of your controller, I can't say whether or not it would be adequate. That isn't to say two controllers won't work. In fact, they will, but two controllers cost more, and require additional wiring.

Kev
2011 Winnebago Tour 42QD
Towing a Jeep Rubicon Unlimited LJ
RVI Brake 2, Minder TM-66 TPMS, 960 watts of solar
(Can't wait to spend more time RVing)
Lakeside, California

KodiakJack

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Re: Solar panels on tent trailer - Worth it?
« Reply #22 on: May 26, 2018, 01:56:42 PM »
Which way did you set it up??

2 separate controllers.
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KodiakJack

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Re: Solar panels on tent trailer - Worth it?
« Reply #23 on: May 26, 2018, 02:07:11 PM »
Welcome to the world of RV solar! I'm glad it's working for you. You should only need one controller, but it has to be rated to handle the output of both panels. Without knowing the specs of your controller, I can't say whether or not it would be adequate. That isn't to say two controllers won't work. In fact, they will, but two controllers cost more, and require additional wiring.

Kev

The panels were a two-pack of 40w panels and came with two of everything including controllers.

I thought I was going to have to monkey with wires to make it long enough to reach the battery, so I figured while I was splicing and dicing, I may as well wire them up through just the one controller. (Which does have enough capacity btw). But once I got them assembled, I realized I had more than enough cable to reach as is, so I just hooked them both up separately. I was worried they would “fight” each other... sensing the input from the other unit and cycle off too early. But that doesn’t SEEM to be the case... I’m certainly open to guidance on that.

Voltage while charging climbed to about 14.8 for a while, then it cycled off and came back to about 13.7.
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Kevin Means

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Re: Solar panels on tent trailer - Worth it?
« Reply #24 on: May 26, 2018, 09:18:58 PM »
It sounds like they're working fine. PWM controllers keep the voltage up around 14.4 to 14.8 until the float phase, then the voltage is reduced to about 13.8 to keep them topped off. Happy RVing!

Kev
2011 Winnebago Tour 42QD
Towing a Jeep Rubicon Unlimited LJ
RVI Brake 2, Minder TM-66 TPMS, 960 watts of solar
(Can't wait to spend more time RVing)
Lakeside, California

Ernie n Tara

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Re: Solar panels on tent trailer - Worth it?
« Reply #25 on: May 27, 2018, 07:13:36 AM »
Hi,

I'm not familiar with solar controllers but it would seem that PWM (I presume that means Pulse Width Modulated) would be quite inefficient. That is due to the fact that some percentage of the output will be lost in reducing the average Voltage. For example given 28V from the panel, reducing the charge Voltage to 14 would require shutting the output off 50% of the time (the batteries act as a filter to average the output). What am I missing?

Sorry to get off subject,

Ernie
Ernie 'n Tara

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Kevin Means

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Re: Solar panels on tent trailer - Worth it?
« Reply #26 on: May 27, 2018, 12:02:32 PM »
You're right Ernie, PWM controllers are less efficient than MPPT controllers (by about 30%) but PWM controllers are also significantly less expensive. There are some cheap Chinese MPPT controllers that are close to the same cost, but... well... need I say more?

PWM controllers are well suited for topping off house batteries, like Brad wants to do, because the batteries won't get drawn very far while the RV is in storage. If the batteries were going to be drawn down more, like when camping, an MPPT controller might make more sense, although the size of the array, the depth of discharge and the battery bank's total AH capacity are important considerations.

An MPPT controller's ability to convert excess voltage to amps is a real benefit when trying to pump as many amps as possible back into a more deeply discharged battery bank, however, we have to weigh the cost of the more expensive controller with its abilities. If the batteries don't have much draw on them (like when the RV is in storage) and they don't get drawn down very far, a PWM controller should easily be able to keep an RV's battery bank topped off - without having to convert excess volts to amps.

Additionally, a single 12 volt 100 watt solar panel only puts out about 18 - 21 volts under ideal conditions. Since a PWM controller charges at 14.4 to 14.8 volts in the bulk and absorption phases (which probably won't be a factor while the RV is in storage) there isn't much excess voltage for an MPPT controller to work with, and there's really no need to convert the panel's excess voltage to amps while the batteries are float charging.

Kev
2011 Winnebago Tour 42QD
Towing a Jeep Rubicon Unlimited LJ
RVI Brake 2, Minder TM-66 TPMS, 960 watts of solar
(Can't wait to spend more time RVing)
Lakeside, California