Do solar panels have to be 12 volt - using charge controllers

[ClydesdaleKevin]

Okay electrical gurus...

The time is rapidly approaching to where I'm going to put about 400 watts of solar on the roof, in addition to 2 more golf cart batteries, for a total of 6.

I've been checking out the local craigslist ads, and a lot of folks are selling brand new panels in the 200 watt range for a darn good price.  Apparently when you convert your house to solar, its way cheaper to buy pallets of panels, so these folks end up with 2 or 3 left over panels that they sell on craigslist way cheaper than I can get them elsewhere.

Here is my question...do the panels I put on the roof have to be 12 volt outputs, or does the charge controller take whatever voltage is produced by the panels and bring it down to 12 volts?  The reason I'm asking is that many of the panels I'm seeing put out way more than 12 volts...20-60 volts on some of them. 

Thanks guys!

Kev

[ClydesdaleKevin]

I tried finding this answer on my own in the club resources, but can't seem to get a clear answer.  Hoping Dave and Tim read this, as I'm sure they'll have the right answer.

Kev

[ibdilbert01]

Yes, your are correct Kevin.  A 12v charge controller will drop the voltage to the appropriate voltage to safely charge your batteries.   Be careful when buying china made panels, do your research before buying.   If your not careful, you'll end up with a super duper huge panel that looks great, but functions as nothing more than a wind sail.   

Most high quality panels will put out 20+ volts, taking care of any voltage drop when running cables and still having excessive voltage to work with at the controller.

I have an older model Rogue Power Charge Controller on mine, by far the best charge controller I've ever used, and I've tested a bunch of them.   

http://www.roguepowertech.com/products/mpt3024.htm

You can find a manual on the site, you might want to download it and read it, even if you don't plan on buying the controller, you'll learn a lot on how they work.   

[DonD]

Kev, this article may be helpful??
http://www.modmyrv.com/2009/11/18/rv-solar-energy-system

[ClydesdaleKevin]

Thanks guys!  That was my assumption that a good charge controller would drop the voltage down, but I wanted to make sure before making any purchases.

I try to avoid anything made in China when ever possible...lol!  Some of the panels were USA, some Canada (which were the most affordable I've seen on Craigslist so far), and some were even German I think. 

I'll check out those charge controllers while I'm at it...we'll need a good one to do it right.

Kev

[gadgetman]

The panels you buy all depend on the controller you decide to use. A normal controller would require panels 16 to 19 volts, common for what they call 12 volt panels, most are 17.xx volts.

You can simply wire the panels in parallel to keep adding up the wattage at the same voltage until you reach the max wattage /amps of your controller.

Then there are mppt controllers. These can take panel voltages that vary and up to  its rated max, some as high as 100v, all depends on the controller. Then the controller drops all that to the voltage you need either 12/24/48.

The problem with higher voltage panels is usually their size and the TRUCK shipping required. The largest ups will take is a 140w panel , most panels above that are large.

With mppt controllers you can wire panels in series which add the voltages to get a high voltage for the input. But  when panels are in series and you cover one small section with shade/branch, that series of panels is pretty much dead now.

This doesn't happen when they are in parallel. Your wattage just drops a little. So series doesn't like shade as much as parallel panels do.

Just be sure when you do decide on a controller it large enough to still add panels to as solar is addictive Plan for expansion.

I run 4 130w panels, kryocea ones. y systems will hit 40 amps. I run a normal 4 stage controller but it is made for 2 banks. Morningstar makes it.

If you need help with it all let me know

[ClydesdaleKevin]

Okay...I talked to the guy selling the solar panels.  They are Canadian Solar, model CS6-235PX, brand new with transferable 25 year warranties.  Here are the specs of the units:

STC:                                             NOCT:

Pmax-235w                                  Pmax-170w
Vmp-29.8v                                   Vmp-27.2v
Imp-7.90a                                    Imp-6.27a
Voc-36.9v                                     Voc-33.9v
Isc-8.46a                                      Isc-6.86a

Okay, so here are some more questions.

Anyone ever hear of Canadian Solar, and are they any good?

Their website calls the panels "On Grid" panels, but they are rated with automotive certifications as well, so I'm assuming I can use them on an RV?  Especially if they are mounted in a strong frame with strong roof brackets?

Obviously I'll want to wire them in parellel since I certainly don't want higher voltage than 29.8 volts.  Any other charge controller recommendations to drop this down for use with a 12 volt system?  And do they make RV charge controllers that can handle the power these things put out?

After a LOT of research, I can't find panels even near this power output for as cheap as this guy is selling them...300 bucks a panel, and we are planning on buying two.  That's 470 watts ideal, and 340 watts nominal, which i think will be more than adequate for our usage needs...any comments or suggestions?  Plus he's just a couple of counties over, so we wouldn't have to pay for shipping.

Here is a link to the spec sheet for these things:
http://www.solarvoltpower.net/resources/CS6P-235PX.pdf

Are there any other problems you think I might have associated with these panels before I blow 600 nonrefundable bucks on them?

Dave posted a link for me once about solar, and I can't find it...written by this very well informed but know-it-all kind of guy, with great solar recommendations...any chance you can post that link again Dave?

Thanks guys...any input will be helpful in making this purchase decision.

Thanks again!

Kev

[ClydesdaleKevin]

Okay...most of my questions are answered, and I found the link Dave gave me a while ago...which in my opinion is one of the best and most informative solar articles I've ever read:

http://handybobsolar.wordpress.com/the-rv-battery-charging-puzzle-2/

Kev

[DanD2Soon]

Kev,
Those look to be great panels - Physically about 1/3 larger than the Kyoceras that Gadgetman & I are using with almost identical construction but delivering almost twice the power.  2 of those equal 4 of mine but only use the roof space of 3. 

I haven't shopped controllers for years, so you need reviews from Tim & others whose info is more current than mine, but I'd be looking for nothing less than a 40 amp unit just to handle the 2 panels you're installing - If the budget can stand it, I'd go for a 60 amp just to anticipate 1 more panel. Like Gadgetman said it's addictive.

Good luck - Y'all are gonna love this 'next step' in your RV experience.

[ClydesdaleKevin]

Thanks Dan!  And thanks for your other post about mounting them flat to the roof, which I was leaning towards.  I plan on using 4 inch angle aluminum the whole length of the panels to act as the frame and mount...that will keep 3 inches of air and wiring space under the panels, and distribute the weight of the panels across a greater area of the roof.  I'll use locknuts and rubber washers to soften some of the road vibrations as well.  Where the angle aluminum gets screwed to the roof, I'll simply use putty tape and sealant on all the screws to prevent leaks.

I don't think I'll have a problem at all running the wires down the bathroom vent cap ...thanks for the idea!  That leads right down to the bathroom cabinet, where I already have wires running under a baseboard behind the dinette, right to the compartment under the forward dinette seat, which sits right over the battery compartment, and is where I plan to mount the Morningstar MPPT 45 charge controller, which will easily handle the 3 panels we plan on buying after the weekend.

And alas, we can only fit 3 panels on the roof.  One side to side just forward of the rear AC unit, one front to back right in front of it on the passenger side, between a roof vent and the fridge vent, and one just forward of the front AC unit, which will require removing the CB antenna and relocating it, but that's not a big deal to do.  So the 4 panel idea is definitely out of the equation due to limited roof space for these huge panels, but 705 watts of solar, even flat mounted, should be more than adequate for our needs, especially with the good Morningstar MPPT 45 charge controller maximizing the output, and with good heavy wiring to minimize voltage drop, since these things will sit pretty far from the battery compartment.

So for just over a grand, and that includes the 360 bucks for the controller, we'll have 705 watts of solar...SWEET!  Okay, maybe a bit more than that...2 more batteries at over 100 bucks a pop, the wires which won't be cheap for heavy gauge, the aluminum angle stock, which isn't cheap, and all the hardware.  And the remote panel for the charge controller so I can keep an eye on output without having to stick my head in the dinette compartment.  So I'm estimating about 1600 bucks total, a little over 2 bucks a watt, but that includes everything.

Now the problem is finding the time to go get the panels!  3 day weekend at the Faire coming up, which means I have to build catapults all week late into the night...and then that only leaves me Tuesday to work on any projects.  I'm thinking I could meet the guy selling the panels after work on Monday, get an early start on Tuesday and drive to Jersey to pick up the angle aluminum and all the rest of the hardware, and at least get the panels mounted by end of day on Tuesday, wiring and all.  I'll have to wait for the charge controller to ship, so I can always hook that up the following Monday and Tuesday.

Kev

[gadgetman]

An idea on your wiring, Run a #2 ground from the chassis to the roof and into a junction block with a ground bar for the ground connections from your panels. Then use #10 or #8 from each solar panel through a fuse and down into the coach. This way you have 3 fusses in the box to protect the pos runs down to the controller and to prevent a backfeed problem if there is a panel short since they are is parallel . Now  before the controller install a 3 to 5 gang fuse box so each panel is fused before the controller. This lets you test each panel later if needed by pulling the fuse and checking the panel voltage. The common buss from the fuse block would go to a master battery cut switch (to turn solar off) and then to the controller.

Fuses should be double you solar panel amp rating, 7 amp panel 15 amp fuse.

Have fun, you are going to have a Kick A** system when you are done !!!

[gadgetman]

Hmmmmmmm 720 watts of solar can be  a max of 60 watts !!!!! Sure you want to limit it to 45 amps with that controller ?

720 /12  = 60  even at say 14 volts  720 /14 = 51  Don't throw away the amps you paid for 

[ClydesdaleKevin]

I'm guessing that being flat mounted, unless we are in ideal conditions with the sun right overhead, then I'll probably never see max voltage and output, especially if we are forced to park with the port side of the RV facing the sun.  To starboard, nothing would shade the panels, but to port, if the sun is low in the sky, the vent covers would partially shade the panels.  If parked with the bow of the rig to the sun, the front and rear panel would never be shaded, but the middle panel would if the sun was low enough.  And if parked with the stern to the sun, all three would get shaded by things like the AC units if the sun was low in the sky.

I understand the reason for fuses, and that was my plan when wiring it in.  What is the reason for a master battery cutoff switch?  Are you saying that I should turn the solar off if I'm connected to shore power?  I thought the charge controller would pretty much stem off the voltage when it sensed a charge coming in from the converter.  Do I have to add a switch to cut off the solar when hooked up to shore power?  Not a big deal, just wondering if its necessary.

Kev

[gadgetman]

YOUR PANEL WILL PUT OUT MAX SOMETIMES MORE EVEN FLAT !!!

Mine are 7.8 amp panels 4 of them, I have seen 40 amps rated watts 520.
My panels are made with class A solar cells

[ClydesdaleKevin]

Hmmmmm...

The cheapest place I've found to get the Morningstar is GoGreenSolar.com.  Looks like they have about the lowest prices on anything solar that I've found.

The 45 amp unit is 366 bucks, while the 60 amp unit is a whopping 497 bucks.  Pretty big difference in price.

The remote monitor panel is going to cost me another 70 bucks.

Do you really think its worth the extra 131 bucks for the 60 amp unit? 

Kev

[gadgetman]

Yes Yes Yes, dont skimp on the solar, once its done right its all free and no maintenance. Dont limit your panels by a small controller.


ok you are spending 1600 or so whats another 130.00 to have it right

[ClydesdaleKevin]

You are actually making a lot of sense, Gadgetman, although I don't think the panels are going to put out max output laying flat. 

You are right though...130 bucks isn't going to break the bank, especially since I don't have to frame off the panels completely like I thought I did...which will save me a lot of money in aluminum, which is bloody expensive nowadays!  I'll be saving well over 130 bucks on the mounting system over what I thought I'd have to spend, so I'll take your advice and get the 60 amp unit. 

Another advantage of the 60 amp unit is that, if after using the system I decide we need even more solar power, I still have room on the roof for smaller Kyocera panels, so I could add another panel or two, of smaller wattage, to the system, and the 60 amp unit could handle it.  My 3 big panels are going to max out the 45 amp unit.

Thanks for all your advice!

Kev

[gadgetman]

Ok but one more time    Your panels WILL put out max even flat. 


BTDT that is why I have 2 controllers now and not 1. I made the same assumption with all the reading I did. My panels proved them all wrong ! I bought 4 panels and decreased their rating by 29%, ok this 30 amp controller will handle that. Put 2 up. 7.xx amps each, those hit 30 amps, I didnt trust the controller display so I put my amp clamp on the circuit. Yep they were at 30 amps. Granted to see may amps I had to turn on every load in the RV I could find. The dual batt controller lets me keep the crank batt charged also. I use a 90/10 date  90% to the house 10% to the crank batt.


No big deal I bought another dual controller for the 4th panel. So now I have 2 systems and room to add more panels if I want too. These were morningstar units but not mppt so they were only 130.00 each including the remote display.

[ClydesdaleKevin]

The reason I'm saying I doubt my panels will consistently put out max output laying flat is the location on the roof, and because I don't want to mount them too high.  Unless I park in full sun with the starboard side of the RV facing the sun, I will get some shade across the panels, either from the AC units or the MaxxAire vent rain covers, especially in the winter when the sun is low in the sky.

I see you mounted your panels very high off the rear luggage rack, but we have an AC unit right there so that's not an option for us.  These panels are huge, so getting them low and solid is my goal, but sometimes they'll be partially shaded.  No way to avoid it really.

When we boondock this winter in Arizona it won't be hard to park to starboard, but if we go to state parks and national forests in the summer, as is our plan, we might also end up under tree cover, so we'll get the shade from that as well.

705 watts and smart power consumption should more than compensate for some shade, which is why we decided to go that high in wattage.

Once I have the system all installed, gotta start thinking about replacing the lights we use most in the RV with LEDs...that should help a lot as well.

Kev

[gadgetman]

Yes LED lighting really helps a lot. That and using as many 12v appliances as you can. PC fans come in all noise and cfm levels and draw very little too.

[ClydesdaleKevin]

So the mc4 connectors won't be here until Wednesday, and the charge controller and monitor probably won't be here until Thursday or Friday...so all I can do this Monday and Tuesday is mount the panels on the roof and run the wires, and then install the 2 more golf cart batteries for a total of 6.  I won't have time to complete the system until the following Monday and Tuesday, darnit!

Kev

[ClydesdaleKevin]

So the inept folks at gogreensolar.com STILL haven't shipped out my charge controller and monitor panel, even though they say they ship within 2 business days.  They are giving me excuses like being backed up from the holiday weekend...well, it was just one day!  So I'd understand if it took 3 business days, but now its been 5.  Grrrrrrr....

So, while they do have the best prices, I don't recommend them if you are in a hurry or on a tight time schedule like we are.

Kev

[ClydesdaleKevin]

Just purchased the first LED bulbs...to replace the florescent T8 bulbs over the sink that we use the most, especially when Patti is doing dishes.  We think that fixture has a ballast problem anyway, since its always eating up bulbs.  35 bucks a bulb...yikes!  So 70 bucks to replace the bulbs in one florescent fixture.  I found cheaper T8 LED bulbs, but they only put out 300 lumens as opposed to the 750 lumens a standard florescent T8 bulb puts out.  The 35 dollar versions put out a full 800 lumens each.  I bought an LED fixture as a porch light once for our old Itasca, but didn't think about lumens at the time, and even though it was advertized as super bright, it barely lit the porch at all.  These bulbs will also supposedly work from 8 volts to 30 volts, so I won't have to worry about overloading it during the equalizing stage of battery charging once a month or so.

Anyway, when this set of bulbs gets here, we'll see how it works.  If they work well, we'll buy a second set for the bathroom fixture, the other florescent light we use the most.

Then I'll have to figure out the lumens put out by a standard 1141 bulb...I want to replace as many of the little map light bulbs all around the RV as we can afford, since we use them often, but I want to make sure they put out the same warm yellow light at around the same lumens.

Also want to buy a high lumen white output 1141 LED bulb to replace the porch light bulb, and a high lumen 921 LED bulb for the hood over the stove, since we use that light a lot as well.

Hopefully we can find them on the cheap, because the florescent ones are expensive!

Edit:  Standard 1141 bulbs put out about 150-200 lumens, and we found them from Revolution LED lighting for 8.99 a bulb if you buy a 10 pack, and we happen to have 10 lights including the porch fixture.  Also found 921s from the same company, putting out about 200 lumens, for 9.99 a bulb, and we'd need 5...one for over the stove, and 4 for the fancy light fixture over the dinette.  The 3 frosted vanity light bulbs over the sink in the bathroom are expensive though...25 bucks a bulb for the cheapest I've found.  Before winter, all the incandescent bulbs will get replaced with LEDs...the T8s will eventually get replaced, but at 80 bucks a fixture, it will be more a long term goal, although if the one over the kitchen sink works well, we'll get the ones for the bathroom before winter.

Kev