Solar for RV

Thanks

2 12v panels wired in series will give you 24v output.  3 panels wired in series is 36v, and 4 panels wired in series is 48v.

2 12v panels wired in parallel is 12v output.  3 panels wired in parallel is 12v output, and 4 panels wired parallel is still only 12v.  The difference is the amperage increases the more panels you wire in parallel.

Exactly what would be the reason for essentially wasting half of the output of your 24v array by allowing the controller to reduce the output to 12v?

It's one thing if you're stuck with used inexpensive 72v direct-to-grid panels and looking to use them to charge an off-grid 48v battery bank for example (which they were never intended for).  Then the loss may be deemed acceptable due to the cheap per watt cost of the panels.
But it's another thing entirely to intentionally waste your new panel's output by not correctly designing your system for the correct voltage of your battery bank.

Ken (nice name):
I am with James. Wire the panels in series for 24V.
Not only is there no advantage to wiring in parallel, in some lighting conditions it would be a distinct disadvantage.

I am happy to see that you are considering are going for temp sensor. I like them for all systems, but they are even more necessary in an RV situation.

Ken

So which way is better for me go go with?

2 135w panels hooked parallel with the 30a ProStar PMW to charge 12v battery bank

or

2 135w panels hooked series with the BS3024iL MPPT to charge 12v battery bank?

I'm looking to get the most from the system because I think that the 2 135w panels are at their limit to my needs and down the road I might have to add more panels but at the moment money is an issue and looking for a starting point. From what I've read MPPT work best in cold conditions and I won't be using it in the cold. This is just for summer camping 2 days a week.

Thanks, I looked into mppt controllers several years ago.  While they have their uses, they aren't the be-all end-all of PV controllers, and the excessive cost must be weighed against the added benefit.
In this instance, is roughly 4 times the cost for the mppt controller worth it over the non-mppt controller such as the Xantrex C40?  It certainly isn't to me, and you read the original poster stating that he wasn't going to be using the system during the times when an mppt controller would be a benefit, i.e. during the wintertime.  He's using the system during the summertime, so why oversell him what he doesn't really need, particularly when he already told you he's on a budget?

Telling people to buy more expensive hardware than they really need was the downfall of the solar movement in the 1970's.  I see that we haven't really learned much in the intervening 30 years, and it doesn't comfort me that things will necessarily go any better this time around.

Thanks guys for the help.

I think I will go with a PWM style controller and save a few bucks. I will also concider adding another group 27 battery.

My rough estimate of power usage is 40ah to 60 ah per day. I just installed a Trimetric battery monitor that way I will know what my usage will be. We went camping this past weekend and I had a problem with one of my batteries so I didn't get an accurate handle on what we use. With only the fridge running on gas for 2 days it dropped batteries to 60% and running a gen for hours I couldn't get above 65%. Once I swapped out the bad battery for a good one it went to FULL in minutes.

Thanks again.
Ken

I just finished a instal on our horse trailer with liveing quarters. I went a little bigger than your thinking but we camp for weeks at a time and I didn't want to worry about power and I didn't want to listen to a generator. I'll try to post this link to a articule that I think you will find a great help.
Bob
http://docs.google.com/Doc?id=dcr9s9n5_126x8xdwf2&invite=215280009

Sorry I can't take the credit for this vary smart mans article. I can only follow instructions somewhat but I've read this several times and have garnered allot from it.
 I found this article after I purchased two Evergreen 210 watt panels and the Morningstar Trystar 45 control.
 We just got back from 10 days in a national forest in which we had two days of rain and several days we used the heater all night without any need of a generator.
 This system charges in overcast and even rain!
 I know it's a little overkill but I don't go camping with my horses in the middle of nowhere to sit and listen to a generator drone on for hours.
 This has been my first trial as I just got it installed but it seems to be doing everything I want it to do and allot more.
 I want to thank everyone at AltE for there advice and help with this project. Now all I have to do is convert everyone I go riding with.
 PS- The Trystar 45 control doesn't make any noise with these panels.
 THANKS
 Bob Baker

I don’t see why Fred thinks that  Handy Bob’s articles would be “persona non grata around these parts”. There is a lot of good info in them, but it has the danger of being mis-used.

Handy Bob has a disrespect of RV dealers/solar sellers around Quartzsite AZ, not of all people in the solar business. Fred seems to apply a similar disrespect to everyone in the solar business.

Solar systems in RV’s while being similar to residential systems, do have different aspects that you need to consider. And conversely, you cannot apply “what works best for RV’s” to all PV systems.

Golf cart batteries are the entry level batteries of the solar business.  They could even be called the bread and butter of the small system. But for larger systems, they are just training batteries.  There are a lot better batteries out there, particularly for larger stationary systems.

Charging at 14.8 is Trojan’s recommendation; it is not the gospel for every wet cell batteries. Interstate recommends a bulk charge setting of 14.4. 
Note that Handy Bob mentioned a battery temp sensor. While I like them for all installations, they are even more important in RV’s. And, if you are charging above 14.4 volts without one, you are living dangerously. The warmer the ambient conditions, the more important the sensor is. I’ve gotten to the point where I no longer consider them optional.

Wire sizing is important. I generally aim for 3 percent drop or less. It is also important to consider future upsizing of the system. I weigh the cost of going larger now vs. the cost of future rewiring.  But “bigger is not always better”.  #6 and #8 are SMALL wires with a marginal cost difference. Look at the price difference in a 1/0 and a 3/0  before saying bigger is better. Carte blanche oversizing wires can be a huge waste of money.

But the point that I really differ with these gentlemen on, is the value of the MPPT controller.  If you live (or RV) in an area with great solar conditions, you may not see great value in it.  But, where you will see the value of it is in less than optimal conditions. It shows gains in the hours before and after the peak sun period. If you have any type of overcast, marine layer, smoke, smog, dust, etc, that reduces the solar insolation, you can have a boost even during the peak sun hours. 

In my area, I usually see a summertime increase in production that is close to 10%.  Over in the fog belt (closer to the coast) it is closer to 15%.  We never get the 30% boost that the mfgs claim for wintertime, primarily because we don’t have subfreezing, crystal clear winter days. You can count the days below 40 degrees on one hand.  MPPT is not “only useful in winter”.

You do have to try to quantify what this increase is for a particular microclimate, and weigh the value of it. The best way to do that is install one on an existing system with known production and then compare the difference in monthly production.  In my area, it is a no brainer. Yes, it costs more. But it is a lot cheaper than increasing your array by 10%.

False.  For the record, HandyBob clearly states that he believes the majority of players (not just in Quartzsite) in the solar biz (RV or otherwise) are less knowledgeable than they portend to be, and more likely to simply parrot manufacturers dubious claims and figures, and more likely than not to simply push the hardware that will bring them the most revenue. And install it incorrectly or inefficiently.

I simply happen to agree with him.  That isn't "disrespect", its simply a observation of the industry.  Sadly I might add.

LOL!  So lacking a valid argument on the subject and confronted with your distortions of HandyBob's article and distortions of my references to it, you resort to namecalling?  WTF?

Is that what happens also when one of the recipients of your purportedly great solar installations dares to question you on what you're doing (or done) and why?  Call them names and become defensive?  LOL!

As long as we're back on the subject of solar, maybe next time you install solar panels in cloudy, hazy, foggy, or otherwise sun obstructed locations you'll use thin film/amorphous panels which are capable of putting out close to their rated wattage even on cloudy days in ambient light instead of the higher priced panels and mppt controllers you love so much.  Ah, but thin film/amorphous panels and standard controllers using thick wire and "training batteries" (for new solar system owners) aren't near the money maker that all of the latest wiz-bang stuff is, eh?

Apparently, you're the exact kind of individual that HandyBob was referring to.  What a surprise.  Thanks for proving HandyBob's point.

howdy from idaho. mr flinstone would you be so kind to email me at coaltrainhowdy @ gmail.com  thank you