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Old 08-01-2017, 11:46 AM   #1
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Solar ... on roof of tow vehicle?

I've 2016 Bambi, a 16-footer, which has no solar assistance.

We've not done any boondocking, but we will. Looking ahead, I'm considering adding a solar panel.

I am, however, reluctant to mount one on the roof (I know this is commonly done but not my preference).

I could get a free-standing panel and prop it up once we set up camp. I have a slight worry, though, that this bit of value could walk away under the arm of a shady fellow user of the woods while I'm out on a hike.

So, what if I mounted a panel or two on the roof of my Suburban?

I never use the rack that is up there. Seems a potential home for a small solar array.

Has anyone tried this or considered it and decided against?

I've yet to ramp up on solar knowledge, so please bear with me if this seems a crazy question.
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Old 09-10-2017, 11:16 AM   #2
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Sorry you didn't get an answer on this, WhereStream... but not surprised as it's an unusual idea. I did a quick Google search and found several threads on other forums where people discuss the pros and cons in more detail.

I've thought of doing this as well with our vintage rig: I don't want panels on our 1950s trailer roof... but we'll have a vintage roof rack on our tow vehicle car and I thought it might be neat to put thin panels on that, instead... and charge while we're on the road.
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Old 09-10-2017, 11:42 AM   #3
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Interesting idea, and interesting to me as we have a Suburban, too. It seems a portable system (i.e. Zamp) would make more sense. You could leave it with the trailer (charging, and locked to something) if you went on a day trip, and would be less likely to have clearance issues in your garage or a parking ramp. Not sure if want it up there full time on my daily driver. Seems like a tempting target for thieves, although you may be intending to make it a removable rack so it's not a risk.
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Old 09-10-2017, 11:54 AM   #4
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I get nervous thinking of drilling holes in the Bambi to mount panels.

More comfortable with attaching solar panels with stick-em, maybe, but I'd prefer to keep the roof as clean as possible.

I can always get a "suitcase" setup and stand the panels in the sun in the campsight, but I'm intrigued by the idea of using some of real estate on the top of my Suburban. Also, can charge the batteries while cruising down the road, which I could not do with a stand-up panel (but could, of course, if I mounted panels on the trailer).

I'm going to explore this top-of-the-tow idea further when I get closer to my solar dream.
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Old 09-10-2017, 12:11 PM   #5
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I've had a few people recommend I do the same thing, but for how I travel, it's more hassle than it's worth.

My tow vehicle isn't always with my airstream. I may be running to the store, or off driving in a national park without the airstream, etc. Unless you're going to be installing a huge battery bank in the tow rig, the solar panels won't be doing any good when your tow rig isn't connected to the Airstream.

One other thing most people (myself included) don't understand about solar is that this is a trickle charge. With one or two panels, you're not going to be able to go without a generator (especially if you're using an inverter). You just don't get the same amount of juice out of solar panels than you do out of a generator, or even a 15a hookup.

A lot of people tell us "but you could park your tow rig in the sun, get the benefit of solar, and park your RV in the shade." In theory, that sounds awesome, but in our experience boondocking and full-timing for over a year, there are very few sites laid out to accomodate that. Furthermore, since my battery bank is with my Airstream, it makes the most sense for the panels to be with the airstream too. Whether I'm towing, parked, or ditching the airstream for a day or two, the solar panels are still hard at work, charging my batteries, without me having to tilt, run cables, or run any logistics. It's out of sight, out of mind.

It might be a good option for you, but it would prove to be far too inconvenient for us. Have you considered mounting panels on your bambi with VHB tape instead of screwing them in? My current airstream has 600w of solar using VHB tape and Dicor; no screws, and we're very happy with it. We also removed the solar panels off our prevcious Airstream (which also used VHB tape and dicor), and there is zero damage. It amazed us how difficult the brackets were to remove with just tape on them!
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Old 09-10-2017, 01:28 PM   #6
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Hi

One of the most compelling arguments for solar is charging the battery while the trailer is in storage. The panel(s) are mounted on the top of the trailer with "super tape" so there are no holes there. Wires often come in through a pre-existing hole. The net result is a very low risk in mounting them and a pretty good benefit as a result. Indeed, if you store the trailer in the garage the "charge when stored" feature may not be a big deal.

Bob
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Old 09-10-2017, 02:05 PM   #7
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Quote:
Originally Posted by WhereStream View Post
Also, can charge the batteries while cruising down the road, which I could not do with a stand-up panel (but could, of course, if I mounted panels on the trailer).


Don't forget - if you have a seven pin trailer connector, you're getting a charge from your tow vehicle while you're hitched and driving that is greater than the trickle of your rooftop solar.

Some great dialog on the topic. Thanks for asking the question.

Larry
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Old 09-10-2017, 02:53 PM   #8
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I'm curious about this tape.

Sticky enough to hold a panel in the wind? I'm impressed.

Yet you can remove the panel without distress.
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Old 09-10-2017, 06:01 PM   #9
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There are professional installers on the forums that swear by 3-M VHB tape and sealant. Search for posts by 'Lewster'. Highly experienced and trusted solar and electrical installer.
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Old 09-10-2017, 06:30 PM   #10
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I'm curious about this tape.

Sticky enough to hold a panel in the wind? I'm impressed.

Yet you can remove the panel without distress.
Hi

Sticky enough to hold it on in the wind? Yes, most certainly.

Easy to remove? No so much. You pull the panel and put the next one on with a new batch of tape.

Bob
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Old 09-10-2017, 06:31 PM   #11
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Thanks for the long and informative post, explore more.
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Old 09-10-2017, 07:48 PM   #12
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Originally Posted by explore more View Post
With one or two panels, you're not going to be able to go without a generator (especially if you're using an inverter). You just don't get the same amount of juice out of solar panels than you do out of a generator, or even a 15a hookup.
Rule of thumb— assuming you've got enough battery capacity to last more than 24 hours without recharging and without going below 50% charge state while boondocking— then the minimum solar panel capacity, in watts, is the same as the total battery capacity in amp-hours.

If you have two Group 24 batteries, for example, each rated at 80 amp-hours, then you would need at least 160 watts of solar panels— and be parked in direct sun— to reasonably charge your batteries daily without resorting to other power sources.

This rule of thumb takes into account the fact that you can only charge in daylight hours but use the batteries 'round the clock, the fact that the solar panels will not operate at peak efficiency all the time because output is reduced in early morning and late afternoon, and occasionally cloud cover will result in days when you don't get full solar panel output even at noon.

Of course, when it comes to solar panel capacity, more is usually better since then you can charge the batteries even when you have multiple days in a row of reduced panel output. The rule of thumb isn't "watts = amp-hours," it's "watts > amp-hours." How much greater is up to your budget and available mounting space.
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Old 09-10-2017, 07:50 PM   #13
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I could see using the 3m VHB tape for flexible panels where you can conform to the roof, it is very strong.. I couldn't trust it for solid framed panels.

Most charging is done during the day, obviously, but this is usually when you're away on day trips so you'll lose most of the solar panel utility if it's on the tow vehicle.
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Old 09-10-2017, 08:33 PM   #14
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Hi

So using the "stock" solar as an example:

The panels are rated as being 160W (2x80W). Looking at the ever popular owner's manual, it's not very specific about what to expect out of the panels. Random observation in the mid day sun, has never shown more than 10A out of the panels. At the 13.6V charge voltage that would be 136W. That's about 85% so not to bad at high noon.

If you averaged 10A for 8 hours a day, that's doing pretty good. The energy drops off as the sun heads for the horizon. That would give you 80 AH into the batteries. Best guess is that this is a bit optimistic. There's 200AH of battery in the stock system. It will not fully charge a full 50% draw in a normal "solar" day.

Some would suggest that having 48 hours worth of batteries is a good idea. They would also suggest that being able to charge in one day what you will use in two is insurance against a cloudy day or three. By that standard, the stock setup falls even further behind.

That said, just about *any* solar will keep your batteries trickle charged. If you have 1A of parasitic loads, that's not unusual. 24AH per day or 48AH per two days would be the result. A system much smaller than the stock system would be quite able to keep up with this.

Bottom line - there are a range of battery setups you *could* have. Equally there is a range of solar you *could* match them up with. On a small trailer there isn't enough room on the roof for megawatts of panels. There also isn't enough axle capacity for tons of batteries.

Provided you mount them flat, panels don't put up a lot of drag. The wind hits them edge on. Weight wise the decent ones are not all that heavy. Since tape mount is pretty common, if it didn't work, I believe you would hear about it pretty quickly.

Bob
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