RV Summer project (system sugestions)

derspower

Hi im new here to solar forums and just bought a small RV last month and would like to mont solar panels on the roof for some extended power when i will be with out hook ups for 3 ish days at a time. I am primarily living in this RV yet am frugal with power and mostly use it for lights at night, a water pump when i need it and the stereo which is in the house battery circuit and some charging of phones, laptops, ext.... I know I will use more power in the winter, but can always hook up more to make sure i keep a good charge but want to plan ahead to use more power. 

I am in school training to be an electronics technician and am interning as a wind turbine technician for GE. I am still learning but am figuring out this electronics thing but really just need the practice and more experience to feel that i know what i'm doing . That saidI would like to do this right the first time to save money from costly mistakes so i'm willing to spend a little more up front to do it right and need a little help with some suggestions of what to do.

Right now my plan is to buy 1 100 watt 12v solar panel, mppt charger found one for $100 at 20A, cabe, and hardware, i'm figuring about $240 for all this amazon pricing maybe more. I have already bought 2 15 watt 12v solar panels and then did research and figured i would need more power then that to charge my 95 amp hr battery that is most likely in poor condition based on its history, assumptions of previous owners, and myself who have discharged it way more then I should have knowing how bad it is for the batteries. Iv just been getting a feel for the power im dealing with... Any way iv been thinking about the 100 what in parallel with the two 15 watts that would be connected in series with each other and then to the mppt controler. and here the questions lie.. 

Should i upgrade and get a larger battery or maybe another in parallel with it ? I would need to do some retro fitting for two batteries but for more power in the bank it could be nice. 
 
Should I connect the pannels in a parallel circuit before it hits charge controller? I feel this is best practice but am wondering what happens if you can have two solar circuits going to 1 charge controller. Meaning hook everything strait there.. I ask this because there is already 10' of cabbel on the 15W's  that would be awkward to strip and connect to the more legit solar cabal of the 100 watt. Also should i just pay the 13ish $ to just return the 2 15 w solar panels and save myself the troubles if a 100 would be fine and maybe get a as well 50w to be sure?

All suggestions appreciated!
Thanks! 

Anders,

vtmaps

Welcome to the forum,

derspower said:

Should i upgrade and get a larger battery or maybe another in parallel with it ? 

The first step in designing a system is to determine your loads so that you can figure out the size of the battery you need.
Once that is done, you can figure out what you need to charge a battery of that size.  Avoid parallel batteries... figure out what you need and get a single string of batteries of the size you need.

derspower said:

Any way iv been thinking about the 100 what in parallel with the two 15 watts that would be connected in series with each other and then to the mppt controler.

When you put panels in series, the current through each of them is the same.  Make sure the Imp is the same for all panels you put in series.

Your system is small, and if you use panels with Vmp = about 18 volts, then it would probably be more cost effective to put them in parallel and use a PWM controller. 

derspower said:

Should I connect the pannels in a parallel circuit before it hits charge controller? I feel this is best practice but am wondering what happens if you can have two solar circuits going to 1 charge controller.

When you put panels in parallel, that is called combining them.  The Vmp of each panel (or string of panels) must be the same.  If you combine more than two panels (or strings of panels) you must have a combiner box with circuit breakers.  This is for safety... if one string faults, the combined output of the other strings could backfeed the faulted string and cause a fire.

--vtMaps

oil pan 4

Unfortunately industrialized large scale wind power generation has very little cross over to small scale solar beyond basic electricity.
A $100, 20 amp MPPT charge controller is likely junk.
15 watt panels are almost unless unless you have a lot of them.
Do not connect different panels in series or parallel with each other. Only series like panels. With a 12v system you should not need to series panels.
Ideally you put one set of panels on a charge controller. If you have to mix panels for some reason make sure the panels have the same number of cells in series that way the voltages match or are really close. 
Don't try to parallel a new battery with the old one, the old one will likely suck up more voltage during charging, have higher internal losses.
Its best to stick with one size of panel if you can.
How much power do you plan on using per day?