New to Solar - Install Questions for my RV

jason_calgary
jason_calgary Registered Users Posts: 2
Hello all. First of all I wanted to say thanks to all who contribute to this wonderful forum - I've been finding it very helpful.

A bit of background to begin. I would like to extend the camping season with my family here in Calgary. Being close to the mountains is great, but it also makes for a shorter camping season (cold evenings / mornings). We normally "dry camp" (i.e. without hookups), and as a result run our forced air furnace during these cooler periods. To compound the issue, we own a hybrid style RV. Basically it has 3 solid walls (sides a back), with the front folding out as a tent. The result is great for a more 'true' camping experience, but lousy for heat retention. Needless to say this is our largest energy draw. We are very cognizant of the electrical use in the trailer. To this end, we never cook in the trailer, preferring to use a Coleman stove outside, under the awning. As a result the water pump is also used quite rarely (I have a 5 gallon jug that I fill and bring to the cooking area). The refrigerator is run off of propane. I've also replaced all the incandescent bulbs with LED's.

In terms of energy use I estimate the following (per day):
Furnace - 5 hours @ 7 Amps = 35 Amp-Hours
Water Pump - 1/2 hour @ 6 Amps = 3 Amp-Hours
Misc. Lights - 2 hours @ 2 Amps = 4 Amp-Hours

My battery bank is 2 6 volt GC's wired in series (approximately 200 Amp-Hour capacity).

Camping for 2 nights is totally possible (and we have done it plenty of times), but I would like to extend our time out (3+ nights), without using a generator.

This is where my journey begins. I have purchased a Trimetric Battery Monitor, and would like to start really quantifying the draw in the trailer. In the design process, I would also like to think about installing solar.

I have room on the trailer's roof for a large residential style panel (65"x40" - Canadian Solar CS6P-235P). It will take up all the room in front of the trailer but I'm hoping it will suffice for my needs. This will be mounted flat on the roof (no tilt). Specs are the following:
235 Watts (24 volt)
Watts (PTC):
215.7 Watts
Max Power Voltage (Vmpp):
29.8 Volts
Max Power Current (Impp):
7.9 Amps
Open Circuit Voltage (Voc):
36.9 Volts
Short Circuit Current (Isc):
8.46 Amps
Max System Voltage:
600 Volts

I have a local supplier here in Calgary for about $1/Watt. If I assume 5 hours of sunlight - that would give me:
8 amps x 5 hours = ~40 Amp-hours

Almost enough to bring my battery bank up to fully charged (I've calculated a draw of ~42 Amp-Hours/Day).

Since its a 24 volt panel I will need a MPPT Charge Controller to "downconvert" to 12 volts (compatible with my battery bank). I was thinking that the Morningstar Sunsaver 15 MPPT would do the trick. The reading that I've done on the forum would suggest the following:
- 235 watt array * 0.77 panel+controller losses * 1/12.5 volts = ~15 amps

Here come the questions:
1) Do the above assumptions seem reasonable?
2) If I'm not totally out to lunch on the above, can you point me to any wiring diagrams / information that might help with the install?
3) I'm also a little confused on what happens when the solar system is installed, and I plug into shore power. How does the charge controller and the in-trailer charger work together? or do they? Pardon my ignorance here, but I don't understand this interaction.

Thanks again for any advice you can offer.
Jason

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: New to Solar - Install Questions for my RV

    Welcome to the forum Jason.

    You know what the rule-of-thumb about solar on RV's is? Put up as much panel as will fit. :D
    Sometimes this means spending the extra $ for monocrystaline panels. Sometimes it means you are stuck with inadequate panel that won't fully recharge the batteries but will just extend their run time.

    In your case you are looking at one 235 Watt panel, which ought to make 15 Amps using an MPPT controller. If you've got no more room on the roof and don't want to add portable panels (which have to be set-up and taken down as needed) you could connect it with a Morningstar MPPT 15 controller. With those panel specs you will have to use an MPPT type to maximize the power on your 12 Volt system. You should have just above the 5% recommended minimum charge rate with that, so it is possible.

    Your solar will have no affect on the shore power connection: it is all DC direct to battery whereas the shore power is AC. It does not matter that both will contribute to battery charging at the same time as they are both regulated charge sources. The time you get in trouble with shore power is when you put in a 'real' inverter and toss (or not) the RV's "converter" and the AC wiring gets mixed up with ground bonds and transfer switches and all that stuff. Happens a lot around here. :D

    I'd say your plan will work and help you out at least a little and reduce generator time.
  • jason_calgary
    jason_calgary Registered Users Posts: 2
    Re: New to Solar - Install Questions for my RV

    Thanks Cariboocoot.

    So the next question is where to get a hold of some good wiring diagrams / plans. Or at least good examples to follow?

    Again, any suggestions would be very helpful.
    Thanks,
    Jason
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: New to Solar - Install Questions for my RV

    Ah, my weak point: wiring diagrams. I've done so much of it I don't even have to think about what I'm doing. But when it comes to explaining ... I hesitate. :p

    Not a complicated thing: one panel, (+) and (-), to input on charge controller. No fuse needed. Output of controller (clarified by niel) to battery, should have fuse. Wire sizing will depend on current and, most important in this case, distance (you want to keep V-drop minimal). Keep controller as close to battery as possible, as those wires will be the lower Voltage/higher current and most susceptible to V-drop.

    Not much more to it in this case.