Upgrading Current RV Setup

porch13 · April 2013

I have a small off-grid system on an RV that is basically permanently parked in Happy Jack, AZ. Here is what I have currently:

One - Kyocera KD210GX-LPU 210W panel
Morningstar SunSaver SS-MTTP-L15 15 Amp Charge Controller
Morningstar Remote Meter
Two – Six volt Interstate Golf Cart Batteries (~210ah)
Xantrex ProWatt SW True Sine Wave Inverter

I recently added the Inverter so I can charge laptops, cell phones, etc. so I can work remotely during the summer. I get full sun to the panel all day but I’m still not happy with the number of amp-hours I’m sending to the batteries (according to the meter). I’m worried that I’m not going to be able to get my batteries fully charged with just the single panel. If my calculations are correct, I could use around 90ah on a peak usage day, mostly during the day. Here is what I’m thinking about doing to upgrade:

Add a second Kyocera 210W panel in series to give me 420W of charging power.
Replace 15 Amp charge controller with a Morningstar TriStar 45A MPPT Charge Controller.

With the reading I’ve been doing, it looks like these upgrades will do a much better job of keeping up with my usage and charging my batteries. I’m not worried about “no sun” days, because I can fire up a generator if needed.

So am I on the right track? Is there something that I’m not thinking of or a better option that I should consider?

Thanks for all of your help!

niel · April 2013

Re: Upgrading Current RV Setup

adding more pv is only a plus as it would reduce the time you need to run the generator. with 1 pv now and all loads going into the inverter it will look something like 210w x 52% efficiency = 109.2w. divided by 12v is 9.1a. over 5 hours of full sun this is about 45.5ah or roughly half of your requirements. doubling the pv wattage puts it right at your daily requirements and no room for error. now you can parallel pvs or series pvs. if parallel you will want to match up the voltage up to about 10%, but preferably within 5%. similarly for series where you'd want to match up the current with the same percentages. this means you don't have to go with the same pv if you wish a bit more power than the calculated breakeven point. for example your pv, if i am not mistaken, has a vmp of 26.6v and an imp of 7.9a. that means for paralleling it should be about the 26.6v. if you opt for series then the current should be about 7.9a. you could as an example buy this trina pv with a vmp of 30.4v and an imp of 7.89a,
http://www.solar-electric.com/trina-solar-multicrystalline-240-watt-tsm-240pa05.html
putting this in series is nearly an exact match in current and the higher voltage yields more output current on the mppt controller. this is a gain over what the 2 kc pvs would be even though not by much. you would have 450w stc in pvs with my example. there will be a physical size difference though if that is not a problem for you by about 6 inches longer in length.

i'm not trying to get you to buy bigger if you don't want to, but i'm letting you know you have more options with a given specific example. it just so happens naws has a great price on that particular pv right now too as you should've noticed in the link.

feedhorn · April 2013

Re: Upgrading Current RV Setup

FWIW: I have an RV system with 700 watts of panels and 4 golf cart batteries. With this I just barely get by year around. I use 60 to 120 AH per day. I can get by with the panels lying flat from March to November but need them tilted up during the winter. You definitely need an amp-hour meter to be sure you are recharging your batteries 100% every day.

vtmaps · April 2013

Re: Upgrading Current RV Setup

feedhorn wrote: »

You definitely need an amp-hour meter to be sure you are recharging your batteries 100% every day.

You do not need a amphour meter (battery monitor), although I recommend you get one. What you do need is an hydrometer. Battery monitors need to be calibrated to the battery they are monitoring, and an hydrometer is the way to know if your batteries are charged (whether or not you have a battery monitor) and to calibrate your battery monitor if you have one.

--vtMaps

porch13 · April 2013

Re: Upgrading Current RV Setup

Thanks so much for the input! I have actually found a great price on a Kyocera 215 Watt panel that I'm looking at. The difference from my current panel is that the 215W has higher IMPP by .19A and higher Isc by .2A. So it looks like I could run these two in series. I have chosen the Morningstar charge controller because I love the one I currently have, but would it be better to spend a little more and go with an Outback or Midnite controller? Not sure if this is a religious discussion or if there are real reasons.

niel · April 2013

Re: Upgrading Current RV Setup

that's fine to go with that pv also, but you only gain 5w stc going with it. if you decide you still need more in pv (like winter needs) you could put another pv in series again with the 2 you will have just as long as you match things up again on the current.

porch13 · April 2013

Re: Upgrading Current RV Setup

Hi Niel, Since I'll be running them in series, I'll have a total of 425W, correct?

niel · April 2013

Re: Upgrading Current RV Setup

sorry as i worded that badly. you will have 425w stc. my point was it is only 5w greater than the exact same pv as a replacement would be.

Upgrading Current RV Setup

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