Residential panels.

Anyone using residential panels at 24v or more?  Tell me about your system.  It appears I do not have enough space or $ for a 12v array.
I know even less about the 24 volt setup than I do about 12v. Any info is helpful.
Thanks, Pat

The so-called 12 volt panels typically put out about 18 volts. Residential panels put out closer to 40 volts. The only real difference will be in the solar controller that you use. Mppt controllers work well with a higher voltage residential style panels. Controllers for lower voltage panels are usually pwm.


Maximum Power Point Tracking, or MPPT is an electronic solar controller that can convert the excess high voltage down to higher currents at a lower voltage. Most of them will output to 12 volt, 24, 48, and other voltages. For RV use you only need to worry about a controller that will provide output for a 12-volt system, and they will pretty well all do that.

After I thought about this a bit, my last answer may have been a little bit too abbreviated to be of value to you. Please forgive me if I now explain things in more detail than is needed.


Just like water only flows downhill, electricity will only go from a higher voltage to a lower one. A battery in an RV is about 12.6 volts when it is charged. Therefore, in order to put Power into that battery, electricity has to go in at a higher voltage than 12.6. This is why even so-called 12 volt panels put out closer to 18 volts. If they only put out 12 volts, they wouldn't be able to push any power into the battery.


The controller is what determines how much charge the battery is able to take. The input to the controller can vary. As mentioned, mppt controllers work well with higher voltage panels as they take the higher voltage and convert it down to a level that the batteries can take. To some extent, it doesn't matter what panel you put on the solar controller as long as it is more than the voltage of the battery itself. As long as the controller has enough voltage to work with, it will determine what to give to the battery. To some extent, The More Voltage you can give the controller, the better job it will do.


On my system, I am using 40-volt panels all wired in parallel. The controller that I bought works well at that voltage. If I had used a different controller, I could have used 24 volt panels. Or, with the controller I have now, I could put two 24v panels in series, and give the controller 48 volts to work with. Within the limits of the controller, it doesn't care how much you give it, as long as it is more than the voltage of the battery it is trying to charge. Controllers work best within their design range. My controller works best at 40 volts, so I bought 40 volt panels.


Does that help, or does that only muddy things up?


Can you give us an idea of what your price Target is? Did you have a look at the pictures of the roof on my 30 foot travel trailer? Those panels are a bit narrower than most residential panels, and they fit well on the roof of my travel trailer.

Thank you for your response Frank. All good info.
To back up a little, I am proposing this system for a 30' C Mh. It looks like I need about 1k watts on the 12v side and 5k on the 120v side. A guestimate but I'm learning. Solarman has helped me with calcs and general info.  Elec space heaters  on the solar? Probably not. May not even need them.  We are planning to spend  time in State Parks on the Nor. Ca, Ore, Wash coast May to Sept. to escape the desert heat of So. Nv. Hookups probably not the rule.  Insolation table indicates 5.6 hours per day of good sun at the Portland Ore. latitude.
I think you spend your time in Az and So Cal with more sun. 

You settled on the 40v controller and panels. Why? How did you make that decision?  How many panels? I know you were willing to overkill the panels. Did you? Battery bank?  In the C, weight will play a part too.  I have not looked at $ per watt in the higher voltage panels.    I followed your progress but was not aware or didn't understand the voltage part.

I'm now thinking 800 to 1000w in panels, a 60 or 80 controller , 6v batteries in series and parallel and a 2500 or 3k inverter. If nothing else the overcab  roof space may become useful.  My imaginary budget failed early on and I am currently hoping for the $3k range. After 37 years in the construction business I understand unreasonable expectations, upgrades and busted budgets.  At some point lesser expectations will meet $.
Again thanks for the info and any other you can provide.
Pat

Pat:


>To back up a little, I am proposing this system for a 30' C Mh. It looks like I need about 1k watts on the 12v side and 5k on the 120v side. A guestimate but I'm learning. Solarman has helped me with calcs and general info.<


1000 watts will give you ample if your usage is like ours.  I can't use all our array generates.


>Elec space heaters  on the solar? Probably not.<


Yeah, not practical.  Heating takes lots of watts. Propane is a much better idea.


>We are planning to spend  time in State Parks on the Nor. Ca, Ore, Wash coast May to Sept. to escape the desert heat of So. Nv. Hookups probably not the rule.  Insolation table indicates 5.6 hours per day of good sun at the Portland Ore. latitude. <


A more likely limiting factor there may be tree cover and clouds.


>You settled on the 40v controller and panels. Why? How did you make that decision?<


It was based solely on the availability of less expensive residential panels that had much better performance than what I could get for the typical RV installation.  Those panels are 72 cell instead of 36, and are therefore higher voltage.  That dictated the controller.


>How many panels? I know you were willing to overkill the panels. Did you?<


Yes, but not as much as I thought.  I no longer consider my install solar heavy.  It is certainly adequate, but not, I think, overboard.  One tends to get used to having almost limitless power, and when it is cloudy for a few days and I have to cut back, I don't like it.   I still bring along  my Honda eu2000i generator, but haven't used it in close to 2 years now.


I bought six 205 watt panels because they would fit on my roof.  I almost bought 7, but I would have had very little room to walk around them if I did that.  I ended up with 1260 watts of panels.  However, as they are flat mounted, their efficiency goes down.  In bright sunlight near midday, I get about half of what they are rated for.


FWIW, the panels I have also use bypass diodes.  If part of a panel gets shaded, it does not stop the rest of the panel from generating what it can.  And, by using 40v panels, I don't have to put any panels in series to give the controller enough voltage to work with.  Again, if one panel is shaded, it only takes that panel out of the equation as nothing else is connected in series with it.


>Battery bank?<


6 golf cart batteries.  We have a high cargo carrying capacity on our Arctic Fox, so they are well within what the unit can carry, and combined weights of truck and trailer are well within what our 1 ton diesel is rated for.


>I'm now thinking 800 to 1000w in panels, a 60 or 80 controller , 6v batteries in series and parallel and a 2500 or 3k inverter.<


Those are figures that solarman is more qualified to comment on than I.  However, I have found that our 80 amp controller is WAY overkill for what our panels can generate.  The best I have been able to do is just over 50 amps in ideal conditions.  A 60 amp would have been more than enough. 


We use a 'cheapie' 2500 watt Sunforce inverter, and it does what we need.  We just take turns using the microwave OR the toaster.


>If nothing else the overcab roof space may become useful.<


Indeed.  I found that the cost of the panels is relatively small compared to the overall installation, which includes an expensive controller, and in my case, shipping.  Whether I put up 4 panels or 6, the percentage change in total cost did not go up that much.  I decided therefore to cover as much of the roof with panels as I could.  I don't regret it one bit.


>My imaginary budget failed early on and I am currently hoping for the $3k range. <


That is about what my install cost me.

Thank you Frank. I appreciate your time to respond and sharing the info with me.  I'm going to call Wholesale Solar in Nor Cal and discuss the res. panels with them. I'll be posting again after that.
I like your use of conduit. Makes sense in many ways.
Good to hear you are not reliant on the genie for energy or charging. Quiet.
Pat

Yeah, the conduit has worked well.  Make sure the junction boxes are also UV resistant!  It appears that some of mine are not, and have discolored badly.  Not that it is an issue, as they are on the roof, and no one sees them anyway, but just an FYI.


I bought my panels from Amersco.  They are a huge company, and I bought Mexican made panels.  Those may escape the Chinese tariffs. 


However, the real magic in getting the panels I did was the rep.  Her name is Rebecca Sanchez and was last with Solarflection about 2 years ago.  38365 Innovation Ct. Unit 1004, Murrieta, California, 92563.  PM me and I'll give you the last phone number that I have for her.  An honorable lady that knew her product line and steered me toward the best panel that she had available.

Haha!  Good thing I didn't post that number!  The dear girl gave me her cell number!


Anyway, the company number is 1-800-942-2424.  Ask for Rebecca Sanchez.  She will be expecting your call. 


After the holidays, that is....

Frank B said:

Yeah, the conduit has worked well.  Make sure the junction boxes are also UV resistant!  It appears that some of mine are not, and have discolored badly.  Not that it is an issue, as they are on the roof, and no one sees them anyway, but just an FYI.

Click to expand...

A quick coat of rattlecan spray paint before you do the installation will stave off UV deterioration.

Thanks, Lou.  If it bothers me enough, I can still mask and paint them. But I don't think it is going to bother me unless they warp or crack.

Frank B said:

Pat:

>I'm now thinking 800 to 1000w in panels, a 60 or 80 controller , 6v batteries in series and parallel and a 2500 or 3k inverter.<


Those are figures that solarman is more qualified to comment on than I.  However, I have found that our 80 amp controller is WAY overkill for what our panels can generate.  The best I have been able to do is just over 50 amps in ideal conditions.  A 60 amp would have been more than enough. 

Click to expand...

LOL.. those are my figures..!  a first run through gave 800 watts of panels and a 60 Amp controller..
I would not recommend a 3000 W inverter though .. the batteries I suggested will only cope with a 1200 to 1500 W at best..

Thanks Solarman. I'm getting there with your help.  I don't remember your suggestion on batteries. 4 or6.
Your thoughts on panels?  I would like to avoid 8 panels even if I can fit them. Plus the $ aspect.

Maybe I should start a new thread on this but here goes. I expect to run a 4000w genie for an hour or so daily am. How much can I expect to charge with that? Some of the output would go for kitchen appliances used short time. Coffee maker, toaster.
Pat

Blues Driver said:

Thanks Solarman. I'm getting there with your help.  I don't remember your suggestion on batteries. 4 or6.
Your thoughts on panels?  I would like to avoid 8 panels even if I can fit them. Plus the $ aspect.

Maybe I should start a new thread on this but here goes. I expect to run a 4000w genie for an hour or so daily am. How much can I expect to charge with that? Some of the output would go for kitchen appliances used short time. Coffee maker, toaster.
Pat

Click to expand...

depends on the available roof area you have.. I would suggest you do the obvious and measure the available space then find panels to fit.. 

ideally you need four 200 w panels.. these below are long but thin.. might be a fit for your roof..

https://www.ebay.com/itm/1-200-Watt-12-Volt-Battery-Charger-Solar-Panel-Off-Grid-RV-Boat-200-watt-total-/263697452462

I know this is ebay, but i have done business with fred before and he is reputable..

the one thing about this source is free shipping... others have low cost panels then charge you ridiculous freight charges..

even though it's a 12 v panel, you can series them all or use 2S2P format.

batteries: as stated in my pm, you need a minimum of four GC2's in a 2S2P bank.

genny time depends on your converter charger and battery state of charge ( SOC ).. could be 1 hr or 4..