Highest Voltage with RV Solar Systems

[Shadowcatche]

I have a 180W solar panel that I picked up off of ebay. What I was ignorant of was that this panel was meant for a grid tie system and will put out over 50V which necessitated an MPPT controller, Morningstar. I have been looking for a flexible panel to be able to put out on an extension cord and found a 144W Unisolar panel that puts out 34V that was tear off from some ones roof that I picked up for $67 and found a Steca PMW controller that can handle up to 37V input.
The trailer is set up for wilderness boondocking and conservation was one of my prime goals.

[Wanderman]

Rules of thumb, are all thumbs!

Every solar install is different, whether it's because you have to work specific hardware because of space limitations or you want the system to perform a specific task. There are no absolutes.

My panels are 36V nominal feeding an MPPT controller into 12V nominal batteries.

The first task in ANY new install is to define what you want out of it. For example, if you are only looking to extend you battery capacity you will go one way. If you are looking to be 100% energy self sufficient, you'll go another. For most it's someplace in between.

Figure out how much power you use...conserve!...then decide how much solar you "HAVE" to have to charge a set of batteries that meets your demand without being overdischarged.

When I began to research my system, I made MANY missteps. Thankfully I didn't spend a huge amount of money for something that wouldn't work.

I wrote it all up for the RVnewsletter family. It's a 6(!) part series of articles you can read them here:

WanderMan: A Better Solar Charging Mouse Trap.PART 1

I'm working on new lithium phosphate battery technology now.

Maybe this info will help....

Rich "The Wanderman"

[CapnMorgan]

I went to the ATL RV show yesterday and talked to some battery guys. These AGM's were very impressive, they are used for telecom backup. The form factor would allow for quite a large array. Weight would be a limiting factor. I was wondering if anyone had used a 'non-golf cart' form factor to build a large array.
I am trying to find a spec page for these batteries. Found some similar ones, just not these.

[Shadowcatche]

NorthStar Battery, country of origin appears to be China NorthStar - Extend Battery Life and Save Energy
Lifeline Battery, country or origin is the US
With out looking I would bet you can pick up the same form factor from them. They are EXPENSIVE who ever but they are much less hassle and life expectancy is some what longer if they are taken care of. I pick up my 150 AH Lifeline battery tomorrow (I only need one) and this double the size that the trailer came with. It had a Crown AGM (made in China) that failed, less than one year old.

[BigV]

This got off track a bit.

Most of the MPPT controllers I've looked at are most efficient at 2 x battery voltage. So for an average RV that means 24v panels in parallel. Fortunately those are the best bang for the buck right now.

The controllers are designed to handle higher voltage because many do higher voltage battery banks. One of the most popular is the Morningstar SunSaver MPPT. This controller auto senses a 12 or 24v battery bank. For off-grid applications a higher voltage battery bank is more common.

[Dave Wilburn]

With the current panel pricing, it seems if one isn't too worried about the cost of an MPPT controler, then 24V panels seem like the hot ticket.

My question is, if you want to add more panels to the system later, do they all have to be the same voltage to hook them in parallel? What about hooking two slightly different panels in series? What must one know prior to adding more panels to an existing system?