Choosing your solar panels

[Hondalee]

I am planning to add solar to my bus, and I am wondering why no one installs the larger panels? I have 235 watt 24v panels and mppt charge controller.
What would make this a bad idea?

[Bumps]

Sounds good to me. If the panels fit on your roof and meet your technical requirements, I'd go for it. MPPT is the way to go on the CC. Have fun with it! \ken

PS. If I had to do it all over again, I would go with a 24 volt configuration. I opted for a 12 volt system with more individual panels to address the shading challenges we sometimes run into. In hindsight, shading has not been as big a problem as I thought it was going to be when I was putting our system together.

[Just For Fun]

Originally Posted by Bumps

Sounds good to me. If the panels fit on your roof and meet your technical requirements, I'd go for it. MPPT is the way to go on the CC. Have fun with it! \ken

PS. If I had to do it all over again, I would go with a 24 volt configuration. I opted for a 12 volt system with more individual panels to address the shading challenges we sometimes run into. In hindsight, shading has not been as big a problem as I thought it was going to be when I was putting our system together.

X 2!! I'd go with the larger panels as long as the roof real estate is available without hampering roof access for cleaning, repairs, etc.

[Reed Cundiff]

If you have an MPPT then it is an excellent idea. There has been a lot of discussion of advantages/disadvantages to higher voltages at Solar Panel Talk, Northern Arizona Wind and Sun etc. As one commentator noted "...The advantage of higher voltages is smaller wire size - easier to install and saves a few bucks. The advantages of low voltage panels is not having to deal with high voltage. 12 V is pretty safe stuff, a string of 240V is a different matter.

You also use a smaller and less expensive MPPT.

I believe that 235 W panels are just at 30 V. The MPPT will work this out. We have 6 x 235 W panels. Would have gone with 6 x 300 W or larger but son had 4 pallets of 235 W panels.
Reed and Elaine

[JFNM]

Originally Posted by Hondalee

I am planning to add solar to my bus, and I am wondering why no one installs the larger panels? I have 235 watt 24v panels and mppt charge controller. What would make this a bad idea?

Many people do! I've been running two 327 watt "high voltage" panels on my rig for a couple years now. I keep eyeing the 435 watt panels with the idea of adding one to the existing.

Other than what has already been mentioned, I can find no down side. The upsides are pretty significant, in my opinion. Oh, I think some people have a VERY small amount of space on their roof so the big panels (physical size) may simply not be an option.

[racertom]

We have 3 245 watt panels to a combiner box on top, #4 (could have used #6) down to an Outback 80 controller to 4 6 volt batteries. Works better than I expected. Have the ability to tilt but have not needed to. I believe my system could support 2 more batteries but I do not have the room.

Do some searching and you will find diagrams of similar systems by others that have done it before. I used those as a base and modified to my requirements. Northern Wind and Solar then suggested a couple of improvements. Bought from them as they were priced right, had everything in stock and were willing to ship a small quantity of large panels.

[Hondalee]

Thanks for the response, you confirm my thoughts on this matter. I just didn't see any advantage to the 12v panels except cheap charge controler and you loose that with the more expensive 12v panels.
Racertom you described just what I plan on doing but with the outback 60 because I couldn't see how I could ever have enough panels to need the 80.

[Reed Cundiff]

Only advantage to 12 V panels is simplicity of 12 V panel to 12 V battery suite to 12 V DC system within RV. Most installers stick with 12 V systems because that is all they know and since most folks are comfortable with 12 V, there is no reason to learn more. Anything beyond takes a bit more sophistication and knowledge to fabricate.

A lot of discussion about this at Northern Arizona Wind and Sun, Solar Panel Talk etc. Or you can go through perhaps a thousand pages at the Cruiser Forum
Reed and Elaine

[BatteryPro]

Originally Posted by Reed Cundiff

Only advantage to 12 V panels is ...

There is one more advantage: conversion efficiency. Using high voltage PV modules results in less PV power being converted. The higher the voltage differential (Vmp vs battery), the greater the loss, up to 9% of total power.

For most people, I would say it's acceptable to waste power using high voltage because it can be offset simply by installing more total power. Besides, most low voltage PV power systems suffer high losses from wire that's too small.

Larry

(Reed, guess I had nothing better to do today than through out some pretty useless info!)

[Reed Cundiff]

Larry

You correct as normal. We have 48 V (nominal) battery suite so the differential of Vmp versus battery is not that great. I believe more people will be going to higher voltage battery suites in the future. Most RV shops know 12 V DC and 120 V AC and that is it.

Reed and Elaine (getting things fixed up for 3 month trip to Mexico - we choose to drive no more than 5 to 6 hours in Mexico. The roads are good and generally divided four-lane toll roads

[Reed Cundiff]

The 48 V nominal battery suite goes through Magnum 4 kW PSWI and through a Mean Well 48 V to 12 V converter. If we ever get around to putting in split-level AC, then we may run 48 V wiring to the split-level(s).
Reed and Elaine

[jharrell]

From my understanding many higher voltage panels are not mobile rated and will void warranty if used in a mobile application, where as the 12v panels are smaller and more have a mobile rating and warranty. Any truth to this?

Looking at the Magnum PT-100 charge controller to integrate with Magnum hybrid inverter and battery monitor. Will use battery monitor for SOC charging and pretty much handle anything I would throw at it, although expensive and somewhat overkill for a small system.

[Timon]

Mobile rated? I've never seen any mobile rating either yea or nea for any panel including the most commonly used ones. Please post any panels that actually show a mobile rating in any of their specification sheets.

I'm not sure I agree that high voltage panels result in less power being converted. I've generally found that high voltage to low voltage is highly efficient compared to lower voltage conversions systems.

[jharrell]

Originally Posted by Timon

Mobile rated? I've never seen any mobile rating either yea or nea for any panel including the most commonly used ones. Please post any panels that actually show a mobile rating in any of their specification sheets.

I'm not sure I agree that high voltage panels result in less power being converted. I've generally found that high voltage to low voltage is highly efficient compared to lower voltage conversions systems.

I just heard about this trying to figure out why places like AMsolar don't sell panels over 150 watts.

I think mobile rated panels would be the ones that don't have mobile exclusions in their warranties which it seems many of the high voltage residential ones do.

Here is a quick example doing a google search on a Sanyo panel, I see similar exclusions in other warranties as well:

"6. Limited Warranty Exclusions.

e. Marine, recreation vehicle, or mobile installations of any kind. Multi-axis tracking systems are not considered mobile installations. "

http://www.panasonic.com/business/pe...d_Warranty.pdf