Are there any monocrystaline panels you CAN'T or SHOULD NOT use for mobile installs?

I'm seeing some 350w Panels available and wondering if there's anything you should avoid when buying panels from craigslist etc.

I'm no expert, but I've considered the same. Many of these are used panels, that have been taken out of service from grid-tie applications. While 350 watts, in one panel, seems nice for the limited roof top space in mobile applications, there are some drawbacks. Most of these panels are higher voltages, like 48 volts. They can be used, but you will need a more expensive charge controller (like from Victron), that can accept the higher voltage input and decrease it down to 12 volts. What I've learned is, that in this process, a lot of energy is lost. So, I would only consider 12 or 24 volt panels, for mobile roof top applications, instead. With the price decline in new panels, with better efficiencies and temperature coefficients, it doesn't make as much sense to buy older panels, with grid-tie voltages, in my opinion.

Additionally, Larger panels from grid-tie applications, may not have as solid of a frame and may not hold up as well to wind forces and shaking, while driving.

Whatever works for You is the answer. But, I disagree about eliminating the higher voltage panels from your selection. The lower voltage panels generally offer lower power output (watts) then the higher voltage panels. Also You may need more lower voltage panels (which increases the complexity, cables and costs compared to the higher voltage panels. There is something to be said about the smaller form factor, weight and ease of installation of some of the lower voltage panels

An inexpensive MPPT controller automatically converts the correct voltage from the solar panel to your battery and most are >95% efficient. An added bonus as opposed to a PWM or no controller at all, is the MPPT can increase the power generated by your solar panels by >20% in some situations. Some low voltage panels (especially the flexible ones) may be easier to mount on the roof, but I've seen the higher voltage panels also used on roofs of vehicles.

If You don't mind solar panels rated at 44volts, Santan Solar has used 250 watt panels (off grid use only) for $50 a piece.

I have 3 x 330 watt solar panels on my 5th wheel and they are great. (canadian solar)
very rugged and the frame is solid.

I was going to use these exact type panels from Craigslist for a ground based emergency solar generator. While I agree that these 300+ watt panels may not be suitable for MOBILE use, i think they CAN be used even with their higher voltages, you just need an MPPT SCC that can convert the higher V to the appropriate parameters for your batteries.

Some of the nice yet affordable MPPT controllers can handle up to 100V of panel input and most of these 300W panels I’ve seen are around 30-50V. You could be safe with 2 panels in series but you should be safe simply in parallel as long as your SCC can handle the amps.

The issue with these roof top panels is that they are designed to be secured to a frame and stationary on a roof. Also, with a LARGE surface area, I doubt they would take the abuse of road vibration and wind while traveling. One of the panels I’m looking at is 4ft x 6ft, which is significantly larger than one 100W panel attached to its own frame.

NickB369 said:

I'm seeing some 350w Panels available and wondering if there's anything you should avoid when buying panels from craigslist etc.

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You should avoid panels that have no label. The reason is that there have been recalls and I had one with some BP panels. I asked the contractor if he had to ship them back to BP but he said all he had to do was send them the labels and certify that he had destroyed them.

You should also be careful of unknown brands that have no reputation for quality.

Recently I bought some used Sunpower panels off of Craigslist from two different vendors and they have worked out great. I visually inspected them and ran a quick voltage check on each. To be clear voltage alone is not what you need but I didn't have the tools to check out amperage under load so that was a small risk that was not an issue. My point is that with the right underwriting skills you can pick up some bargains.

Ampster said:

You should avoid panels that have no label. The reason is that there have been recalls and I had one with some BP panels. I asked the contractor if he had to ship them back to BP but he said all he had to do was send them the labels and certify that he had destroyed them.

You should also be careful of unknown brands that have no reputation for quality.

Recently I bought some used Sunpower panels off of Craigslist from two different vendors and they have worked out great. I visually inspected them and ran a quick voltage check on each. To be clear voltage alone is not what you need but I didn't have the tools to check out amperage under load so that was a small risk that was not an issue. My point is that with the right underwriting skills you can pick up some bargains.

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Interesting. I haven't considered there were recall notices on these panels. Do you know what they're generally for? I can't imagine it would be for anything we couldn't fix, unless it was for defects within the cells themselves. Some of them are really attractively priced.

I've seen some Sunpower panels i'm interested in taking a chance. on. $100 for a 300w panel is really tempting.

Again, though - i wouldn't chance it on a mobile installation.

Larry619 said:

Interesting. I haven't considered there were recall notices on these panels.
Do you know what they're generally for? I can't imagine it would be for anything we couldn't fix, unless it was for defects within the cells themselves.

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This was 5 years ago and they were BP SX270 panels. The solder joints were corroding. I did not notice any degradation but someone told me about the recall and I took a photo of the label and contacted BP. Incidentally I the warranty check I got for 2.7 kW of eight year old panels was enough to buy 3.6kW of Canadian Solar panels.

I've seen some Sunpower panels i'm interested in taking a chance. on. $100 for a 300w panel is really tempting.

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That is what I bought recently for the same price. A lot of those are coming off commercial roofs when they reroof because after 10 years the owners have received all the benefit of the original tax credit. They can have them removed for free and get a big deduction by installing new panels without having to install new standoffs.
The only thing you need to pay attention to is many of them are 96 cell panels with higher specs and you have to do the math on your string calculations to make sure you can fit them into a system. They also had the old connectors so I upgraded them to MC 4 connectors. Finally I wanted to put 4 of mine on Enphase microinverters and you have to use the most expensive IQ7 plus models. The rest fit in a nice series string because my MPPT charge controller could handle a string from 250 to 600 volts.
NOTE: The above comments apply to a roof mount system even though this is the vehicle mount thread. I was responding to comments or questions.

Squawkbox said:

They can be used, but you will need a more expensive charge controller (like from Victron), that can accept the higher voltage input and decrease it down to 12 volts. What I've learned is, that in this process, a lot of energy is lost. So, I would only consider 12 or 24 volt panels, for mobile roof top applications, instead.

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I think there are a few misconceptions here. Any MPPT controller will reduce the voltage of your PV array down to your system voltage. And from what I understand, higher voltage arrays are actually marginally more efficient with MPPT controllers. With the older and cheaper PWM technology you are right, if your panels aren't matched to your system voltage, a lot of power is lost. This is the problem MPPT controllers solve. And these days, MPPT controllers are not that expensive.

With the price decline in new panels, with better efficiencies and temperature coefficients, it doesn't make as much sense to buy older panels, with grid-tie voltages, in my opinion.

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I agree with the first part here, for mobile applications, efficiency and temp coefficient matter more than in some other contexts, so choose panels (new or used) that reflect that.



In terms of ruggedness for mobile applications, some people say the smaller panels are better (better frame to surface area ratio), but then some others have said the build quality of the larger residential panels and the frame thickness is superior to the small panels. This post may be of interest

Victron rates their SCCs as 98% efficient. That'd be a peak efficiency figure but the losses in the buck converter isn't in the order of 'lots'. Renogy states 98% for their Rover li charger (OEM SRNE). IMO even a cheapie would be somewhere north of 80% peak efficiency.