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Old 02-08-2013, 01:22 PM   #1
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12v vs 24v solar panels

Hi,
I've been on the verge of starting to buy a solar system for my TT for about a month now. As I read more, I scrap my old plans and have to go back to the drawing board. Our solar ambitions started when we saw the 45w Harbor Freight system. As we looked into it more, we realized that this was not going to be enough.

Our next thought was a 130w 12v panel with a 10amp PWM controller kit that we saw. But if we wanted to expand this we would need to replace the controller. Now, I'm not sure if this would be enough to keep the batteries charged for a typical 7-10 night trip.

Then I thought I read that 24v panels with a MPPT controller was a better way to go. Now I can't find where I read it! The 24v panels are cheaper per watt than the 12v panels but the controllers can be twice or more than the PWM controllers. Was looking at a 220w 24v panel and then the ability to expand up to 440w.

So, first question is which would be the better way to go 12v or 24v? Second question, do the controllers with a digital display give you the same information as a Trimetric 2024 battery monitor?

Thanks! Any advice would be greatly appreciated!
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Old 02-08-2013, 01:37 PM   #2
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Old 02-08-2013, 01:58 PM   #3
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My suggestion would be to go with the 24 volt panels and the MPPT controller. Solar electric power components and solar panels has some good info on their page.
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Old 02-08-2013, 05:25 PM   #4
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there are pluses and minus of both.

12v panels are smaller, look carefully at the size of the panels and the roof area. you may not be able to get a 24v up there. I couldn't fit the larger panel.

24v are cheaper per watt, until a tree branch breaks it. you'll have to replace the whole panel. And you might be able to find 12v panels near the same price. I did.

12v will need a larger wire size to reduce voltage drop. that costs a little more $.

the 12v mppt controller is a bit cheaper than a 24v one. But a 24v mppt controller will be cheaper at the higher amperage ratings. Under 30a output, you'll find the 12's are cheaper.

ultimately the deciding factors are roof real estate and how much power you need. If you're going big time, you'll probably want to go 24v.

I bought the Blue-Sky system with digital remote control, IPN pro. I bought this system as it provided me a MPPT controller, a programmer for the controller, and a battery monitor and status indication. In the long run, a few $ more, but only one display that does it all.
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Old 02-08-2013, 05:43 PM   #5
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Here is another thing to consider when determining whether to go 12 or 24v. If a single panel of either passes into shadow, the output will dramatically drop.

If you only have one 24v, 280w panel in your system, and it is in shadow, you will have very low to no output.

However, dual 12v, 140w panels in parallel will give you the same power and if one panel is in shadow, you will get half power until the shadow passes.

why is this important? remember that you won't know if your camping spot has good sunlight or shade. You also might not know how the sun passes over your site. Unless you camp in the wide open at all times, it's likely your panels will be partially shaded at some time.
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Old 02-08-2013, 05:50 PM   #6
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Old 02-08-2013, 06:21 PM   #7
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80 Amps? Sure, I guess. I paid $30 for my 30A PWM controller. 400W @ just 12V is under 35A. You'd be hard pressed to draw 35A other than dead batteries not hooked up to the charger until noon.

The 24V panels and a MPPT charger will charge your batteries sooner and longer/later than a 12V panel and PWM charger will.

I was in the same boat, pouring over website after website and changing my plans every couple of weeks until I just bought my stuff. If you spend $2000 on parts, its going to take a while to break even. I went with cheaper 12V and PWM stuff and other than still wanting to add another panel, I'll be fine just like it sits.
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Old 02-08-2013, 07:19 PM   #8
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Quote:
Originally Posted by RPAspey View Post
I bought the Blue-Sky system with digital remote control, IPN pro. I bought this system as it provided me a MPPT controller, a programmer for the controller, and a battery monitor and status indication. In the long run, a few $ more, but only one display that does it all.
RPAspey,

Can you post a link to the system that you bought?

I have not been able to find a Blue Sky System that meets your description.

I foresee a challenge ahead for me. I normally run down the Fridge Roof Vent with the Solar Panel wires, but the 8289WS has the Fridge in the slide. I have run down one of the vent pipes and come out the side of the pipe in the underbelly as high up as possible. Then caulk it well to prevent odors. At times the vent pipe will put me closer to the battery location.

Thanks

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Old 02-08-2013, 08:30 PM   #9
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here's the link: http://www.blueskyenergyinc.com/prod...ar_boost_2512i

If I posted it right, that link should be for the controller. The display module is here: http://www.blueskyenergyinc.com/prod.../ipn_proremote

I bought my stuff from solarblvd.com
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Old 02-10-2013, 07:48 AM   #10
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Thanks for your replies everyone!
And thanks RPAspey for bringing up the size thing!! I've been pouring over the volts, amp, charge controller options I haven't really looked at the size of these panels. I had a general idea, but... I hope that I would have looked into that before I hit the order now button. I would have been quite disappointed when a big honk'en 24v panel showed up on my door step. And HEAVY!
And thanks Rod for bringing me back in line with what I really need to do. Drink beer in the mountains! Oh.. and charge a couple batteries during 7 - 10 day outings with no hook ups, a couple times a year.
I think I will go with the 12v panel and a controller that will allow me to expand as necessary.
I hadn't planned on mounting the panel/s on the TT right off the bat. Maybe just make a stand to basically prop them up by the hitch, like I've seen a couple times. Has anyone done this with decent results?
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Old 02-10-2013, 08:56 AM   #11
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the, there was one poster who made an awesome setup for the front of his rig. panels could turn & tilt. I just can't find the original post.
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Old 02-10-2013, 09:03 AM   #12
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I found a pix of that setup, but my apologizes to the original poster as he deserves the credit. What a great idea.

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again, not my idea. Hopefully the person who made this will chime in.
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Old 02-10-2013, 10:08 AM   #13
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That was my original plan, too. On a pole, with a side of pole or top of pole mount. He probably gets great charging results. Better than roof mounted panels.

I was concerned with transporting and moving and damaging the panels, and again, longer setup and breakdown (Which already seems to take way longer than it should). And of course, 100 new holes in a brand new under-warranty roof...

I ended up with cheap and easy Z brackets and panels flat mounted to the roof. Again, I guess simplicity and ease of use were my priorities. And mine are always on, always plugged in, and always charging. I have an extension cord that I made to keep my truck plugged into the trailer (its always had a problem with running down the battery because it sits for weeks and months at a time.) Also, when I take off to go riding, or hiking, its one less thing I worry about walking off...
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Old 02-11-2013, 08:07 AM   #14
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Thanks for the pic. That's kind of what I was thinking. I wish I could see the pivot area in a little more detail.
I had the same thoughts rattling around in my brain. Holes in roof, hauling and set up, panels walking off, etc. I have a feeling that after a couple times I'll be mounting them on the roof. I'm still a little leery about the permanent wiring. The portable wiring seem like it would be a no brainer.

Now back to equipment selection.
I've been looking at this 130w rv kit on unlimited-solar.com for about $350. The problem is, if I decide to add another panel I've already out grown the 10amp controller. Correct?
I may call and see if they will substitute a 20 - 30 amp controller.
I will probably pay more for a kit, but for my first venture into solar it might be best.

Thanks again for your advise guys!
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Old 02-11-2013, 02:00 PM   #15
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130watt is good for minimal draw on batteries such as lights and normal parasitic draws & maybe the inverter for an hour or so while watching a LED tv. depends. with solar, more is better. Remember that shade, clouds, and hot weather will lower their output. Also, two panels means your boondocking trip won't be over if one breaks.

Also note that if you intend to upgrade batteries, that you will need a minimal charge current based on the AHr rating of the batteries. You can get that value will come from the battery Mfg website.

BTW, 2 x 140Watt 12V panels are about $365 at solarblvd.com.
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Old 02-11-2013, 04:11 PM   #16
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130watt is good for minimal draw on batteries such as lights and normal parasitic draws & maybe the inverter for an hour or so while watching a LED tv. depends. with solar, more is better. Remember that shade, clouds, and hot weather will lower their output. Also, two panels means your boondocking trip won't be over if one breaks.

Also note that if you intend to upgrade batteries, that you will need a minimal charge current based on the AHr rating of the batteries. You can get that value will come from the battery Mfg website.

BTW, 2 x 140Watt 12V panels are about $365 at solarblvd.com.
Those look a lot like the DMSOLAR panels I and many others have bought. Link below. Pretty good shipping and they are $320 for a pair of them. Shipped to the house they are around $400.

http://www.amazon.com/145w-Polycryst.../dp/B007VPQP5Q
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Old 02-11-2013, 04:26 PM   #17
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yeh, they are spec the same. and cheaper too!
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