One large solar panel, or several small ones?

[amwbox]

In researching solar panels for a near future van conversion, I've noticed a couple of things. The cheapest watts/dollar solar panels seems to be the large ones in the neighborhood of 300 watts, and that the more panels the more complex the wiring and mounting needs be.

So, I'm wondering what the disadvantages are of using a single, large solar panel instead of several smaller ones within the same general footprint. Is the larger panel more or less efficient? Does the fact that the larger panel runs at a higher voltage convey any advantages in terms of lower light charging, or whatever else? Would running the smaller panels in series negate this, or would the series connections result in more or less efficiency? So on and so forth.

It seems like just mounting a single panel, with fewer holes drilled, fewer wires, and a lower price per watt is the way to go. Unless there is some key piece of information I'm missing?

Thanks in advance. Long time lurker. Nice to meet everyone.

 

[RogueRV2]

for many reasons, you'll probably end up getting 2 or 3 hundred watts, a couple of golf cart/deep cycle batteries and PWM charge controller as this combination is the least expensive and works good on top of vans and motorhomes. Unless ordered in quantity, 4 or more, the large panels under $1/watt are expensive to ship (freight only) and are 20 volts and higher in voltage, while panels 120 watts and under are often sent via UPS or USPS. The Renology 100 watt is a good value and popular as it performs well and shipping is included in the $159 price.

 

[Optimistic Paranoid]

Panels are made up of individual cells wired together in series - parallel. That is, a number of cells are wired together in series to get the voltage the designer wants. This is called a "string". A number of strings are then wired together in parallel to get the amperage the designer wants.

The top of motor homes are usually full of junk like air conditioners, roof vents, antennas, etc. They often cause a shadow to fall on solar panels. If a shadow falls on a single cell, it doesn't just kill the output of that cell, it kills the output of the whole string that cell is part of.

As a practical matter, it's not only easier to mount multiple smaller panels in between all the junk on the roof, it also usually means there are more strings than you get in a single large panel. More strings USUALLY means more output under shadowy conditions. If the shadows affect 2 out if 6 strings, they kill a third of your output. If the shadows affect 2 out of 12 strings, or 2 out of 18 strings, well, I'm sure you can do the math.

Regards
John

 

[Willy]

I'd go the route of more smaller panels cuz, if one bites it, you can still have power from the remaining one(s). Yup, quite often these panels come with a multi-year 'guarantee', but that don't help ya if you've got a buncha food frozen, now thawing rapidly, and are in the middle of nowhere with a hooped panel. ..Willy.

 

[akrvbob]

There is no one right answer for everybody! There are numerous considerations that make the choice different for all of us depending on our considerations and they have been laid out very well for you!

I wouldn't let panel failure be part of the consideration because they are extremely reliable, I've never known anyone that had one fail except one guy that had hail the size of a baseball destroy his.

On the other hand, I've known numerous people with controllers that failed. You can buy a cheap panel and a cheap controller and then keep a second one on hand to replace it. Because cheap ones only cost $30, why not carry a spare?

Large panels are cheaper but because they are high voltage they will require a much more expensive controller. You probably won't keep a spare on hand and will hate to buy a new one.

I prefer to buy higher quality so I have both in my system:

One 55 watt panel
Two 140 watt panels
One 240 watt panel

I also have 3 solar controllers and three seperate banks of a pair of golf carts.
Bob

 

[amwbox]

Thanks for the replies.

I've got a completely bare van roof, nothing to cause a shadow, so the only shading I have to worry about is from buildings and trees or whatever else that is around me.

As for the cost of a controller, the models I'd been considering are
this

and

this

PWM and MPPT respectively.

Theory goes that since I'll be spending my time in the Pacific Northwest, where it rains half the year, I'll be better off overbuilding the PV system because of vastly reduced power production in the rainy season, in conjunction with a link to the alternator. Having a surplus in the summer is something I can cope with, I guess.

As to price...I'm seeing 250 watt panels for $239. A couple of those would be 500 watts for $478...as opposed to 300 watts for $450 from the 3 Renogy 100 watt panels. Plus shipping of course, for the larger panels, which I understand is expensive. But still. Its also an extra 200 watts and one less panel.

Assuming shadows and reliability aren't massive concerns in my case, is there some kind of electrical/engineering issue I'm missing when it comes to larger or smaller panels? Because if there is, I'm happy to install more smaller panels and take the lesser wattage. But 500-600 watts seems pretty desirable to me.

And, if anyone has any experience with solar in the PNW (or similarly soggy climates), you're input would be really helpful. Am I overestimating how much the weather is going to degrade my solar performance? Is 500 watts (to charge under 500 AH of battery bank) overkill, even considering the rain cloud that hovers over my corner of the world and dumps about half the time?

 

[66788]

I'd go with the TriStar 45 because it's a proven workhorse. I have reservations about Renology as they are a Chinese company and my experience with Chinese products is less than satisfactory. Even if the TriStar was in fact made in China (I don't know) it would be made to US specifications.

Additionally, the TriStar has user adjustable set points and can be used as a load diverter.

66788

 

[LeeRevell]

Just be sure to check the physical size of the bigger panels, to make sure you can fit them up on the roof.

 

[freenez2]

I've used the Tristar 45 for the last 16 months with no problems.

Kyocera 36 volt 245 watt solar panel
2 Sun Xtender 6 volt 224 ah AGMs

 

[wagoneer]

I am using a large 240 panel in a rack on my hightop with 2 big 6 volt agm's and a morningstar 15 mppt controller, all is well. paid 150 for the panel 100 for the batteries and 200 for the controller and 70 for the monitor device. 520 total.

 

[Willy]

I'm up here in the PNW, B.C. being my stomping grounds, and I got by last winter with abt. 180W and a PWM controller. My Waeco CF-50 was kept in the cab of my truck, so needed that much less power, but will be adding another 100W to my setup.. which should be plenty.

A lot, re. solar, is dependent on what you plan on powering. My needs might very well be considerably different from yours, requiring less/more solar. ..Willy.

 

[RogueRV2]

If one is in the Pacific Northwest, especially along the coast, go for it! There is nearly or zero sun for weeks and months. Insolation numbers for NW Montana during the winter go as low as 1-2 hours. In Seattle, WA, the same period is 1 hour or less. Expect 1/3 insolation when overcast. You are wise to consider your solar needs for your primary stomping grounds. If affordable, I'd add another panel to bring to bring my array up from 270 to 370 watts to charge two 6 volt golf cart batteries rated at 210AH. During the summer with 7 hours sun, 200 watts is plenty. During the winter, with only 2 hours of insolation, I expect that 270 watts will be barely enough to run a light bulb and a laptop for 4 to 8 hours. During the winter it is easy to flash freeze just about anything, so a frig is not necessary. If I were in Seattle or along the PNW coast with only 1 hour of insolation during Dec,. Jan., and Feb., it would only run a light bulb and a laptop for 1 to 4 hours and no refrigerator. You should also have a generator to charge the batteries as there are weeks with zero sun. A generator takes up space, weight, but most important, lots of money.

400 watts for your location is like 100 watts in AZ during the winter. I'd stuff at least 400 watts up there and plan for 600 watts if I could afford that. You may then avoid the cost of a generator! So go for it. If you plan carefully and use monocrytaline (smaller area/watt) verses polycrystalline (larger size/watt) and use fewer and larger panels, you'll get the most watts on the roof that you can. In your case, paying the freight on three 200 watts panels, or two 300 watt panels could be smart thing to do. It should be no more expensive to ship one panel than it costs to ship 4 panels. You pay the same. Get the 4 panels and sell the extra locally, or sell it to a friend, or stuff that up on top too! But before buying the high voltage large panels, also consider the cost of a MTTP charge controller. Consider the total cost of the system you have in mind and compare it with a 600 watts and a 12vdc 45amp PWM charge controller, a 500 watt 12 volt system with a 30 amp PWM charge controller, or 400 watts 12vdc with a 25 amp CC, or a starter system using 200 watts and a larger 30amp PWM CC, and a 300 to 600 watt array at 24 volts and a 20 amp 12/24 MTTP CC system. Mix and match various systems you can imagine and crunch the numbers. Here's a quality MTTP for $208:

http://www.ecodirect.com/Morningsta...2-24-Volt-p/morningstar-sunsaver-mppt-15l.htm


From my reading you'll get on average 10 to 15% more power out of a MTTP CC, and up to 30% when temps are extremely cold and the batteries are very low. Given the price of solar panels, if you have the room, buy more panels to get that extra 15% more power. Because of the short distance, the savings in wire is insignificant.

 

[akrvbob]

I think you have a very good plan!

Larger and higher voltage panels are actually more effecient so if the minor strikes against them are resolved, and they are in your case) they are technically a better choice than small panels.

I'd say 500 watts is the minimum for the PNW in winter and you would be better off with a third 250 watt panel if you can get it on the roof.

Kyocera makes a 315 watt panel and if you can't get three of the 250s up there, I'd get two of the 315s. They will fit across the van but they will stick out a little. I have a friend who put two of them crossways for this very reason--to have enough power in the rain.
Bob
Bob

 

[amwbox]

Wow thanks, everyone, this is just the sort of info I was looking for. Last place I went for help brushed me off and called me an idiot for not simply running a generator all the time. Which is obviously impractical for urban camping. Much better crew around here. It sounds like its just a matter of sticking as much PV surface area as possible up there, regardless of panel size. Just have to bear in mind the more expensive controller.

Honestly, if I could simply cover the top of the vehicle in panels from end to end, I would, but I have to leave some space towards the rear for a vent. Also have to leaves some gaps to avoid creating what would amount to a sail, lol. Right now I'm investigating some roof racks with rails along the sides. Some of them seem to be a bit wider than the roof of the van, so the dimensions of the roof rack between the rails will determine the size of the panels. Plus, the rack might help conceal their profile, as well as the profile of the vent. (I'd remove a crossbar or two to suit the vent). Right now, I agree that a couple of large 300+ watt panels seems like the best option. I suppose its possible I could also offset the vent from center and get another panel in beside it...but then I'm looking at potential shading issues.

 

[akrvbob]

No problem with two Kyocera 315 panels and a vent. Here is a pic of my friend installing his 2 315s. We did at the summer RTR in the Coconino NF in 2013. He had a full size basket type ladder rack on a Dodge Maxi van so it was a long van. The vent was behind the panels.:

 

[RogueRV2]

that's the way to go...

 

[amwbox]

Ya, that looks very close to what I'll probably end up with. Was talking to the guys at Vantech, they say the dimension between the rails on this rack is 71 inches:

So the Kyocera 325 watt panels (64.5") can easily be made to fit in between the rails, perhaps even elevated a couple inches to hide behind the rails without causing shading issues. This should leave enough room to put the vent as far rear as possible, which would put it above the bed where I want it anyways.

 

[wagoneer]

WOW whatta rack. Major problem with bubbletop's are mounting such a rack. How much are those?? thanks, i could get in trouble with a rack like that (good trouble)

 

[amwbox]

Spendy. Calling around different dealers it looks to be $1200 new. There is a steel version that is half as much, but its too narrow. I'll just haunt craigslist until I find one cheap. Or investigate building my own. I know a guy with aluminum welding stuff. At $1200 its actually more than my entire budget for the power system lol.

 

[akrvbob]

This is the rack my friend has on his van, $405 is an exceptional price for such a good rack!

http://www.globalindustrial.com/p/m...-accessories/old-ford-dodge-extended-van-rack

But if I remember right it was too narrow for the 315s to fit in-between so he used aluminum angle to mount them on top of the rack. He didn't care about stealth so the panels being visible wasn't important. The 250s are probably narrower so you may want to see if they will fit.

Bob