Recommended PV setup for weekend usage in DYI conversion Sprinter RV?

corbury · April 2016

Hi - I'm new here and I am trying to figure out what kind of PV setup I need (can afford) for my daily driver sprinter van - that also doubles as a weekend camper.

My planned usage needs are:
- Lighting (2-3 LEDs) ? Ah for 2 hours/day (max)
- Espar heater which uses 1 Amp/hour for night time for 8-10 hours/day (max)
- Small water pump (for backdoor shower/small sink) ? Ah for 0.3 hours/day (max)
- Inverter for charging phone and laptop for ? Ah for 1-2 hours/day (max)
- Dometic CF-025DC - which is pretty small - 30 Ah/day?

My current house battery is a new full river DC-115-12:

Nominal Voltage: 12V
Amp Hour Capacity @ 20 hr rate: 115 a/h
Reserve Capacity @ 25 amp discharge rate: 200 mins
BCI Group Size: 31

I am currently charging house battery it off of the sprinter alternator via this charger.

PV System Questions
I am limited on my rooftop real estate because my van has the factory rear ac (which is huge) AND I would like to put a thule box up there as well.

I would like to do this cost effectively - and I understand that my battery is not super large - but I'm realistic about my needs. Worst case is I am sleeping for 2 nights at a backcountry ski location and I need the heater for 20 hours.

Here is what I *think* I need (but I really have no clue):
1. Battery monitor - I have been looking at the victron BMV-700.
2. MPPT charger - recommendations? there seem to be a million out there - victron???
3. Solar panel(s) - monocrystaline - 40" - x1 or x2 100w panels renogy???
4. inverter? Xantrex prowatt 2000W ??? Do I really need something this big?

Ok - so you add all this up and it gets expensive - but maybe that's the way it is. Is there a better option here? - is there a cheaper AND better option here? Am I missing something?

Thanks,

Clyde

westbranch · April 2016

OK a few numbers ...2000W = 12V and ~ 166A you will need to calculate the wire size for the Peak surge , probably 3000 or 4000W... ie it's going to be very large, look at using a smallere inverter
you need to have about 14A name plate Amps to get a decent charge back into that battery, if you don't kill it in one or 2 days.... ie about 2 of those panels, you need to put back ~ 110% of what you use per day
You could use a PWM MidNite Brat or the MidNite KID MPPT...
Drop the AC. You will need a seriously large battery to use it... consider fans.
consider using golf Cart batteries @ 6V, way more storage capacity...

hth

corbury · April 2016

Hi - thanks for the feedback - I will look in to these options.

On the inverter - I agree - I'm not running a microwave or anything like that - maybe a 1000W - or even a 300W inverter?

On the AC - I hardly ever run the rear factory AC (while driving) - and it's absolutely not in the mix to be run when not driving. I only mentioned the rear AC because it takes up a bunch of the roof real estate - thus limiting the number of panels. One scenario I am considering is mounting the panels on a roof rack bars - over the ac unit. but that makes the whole roof combo even larger. I will have to test it out.

Thanks again,

C

BB. · April 2016

What is the battery bank? A single 12 volt @ 115 AH battery bank would, at best, reliably supply:

115 AH * 1/5 hour discharge rate = 23 Amps
23 amps * 12 volts * 0.85 AC inverter eff = 235 Watts AC max continuous

And even that is a pretty high current--Probably good for minutes or 1 hour at a time. You would be much better with 1/8 to 1/20 discharge rate for long term average discharge rate.

So--A good inverter for a smaller 12 VDC system would be this MorningStar 300 Watt TSW inverter or similar.

It is possible to have a much larger inverter with AGM or LiFePO4 batteries--But even then, would 3 kWatts for 15 minutes (to dead battery bank) be very useful.

You need to review your loads and battery bank sizing... You probably would be much happier with 6 volt at ~200-220 AH "golf cart" batteries. Either two in series (12 volt at 200 AH) or four in series/parallel (12 volt @ 400 AH) for the loads you have listed.

Of course, this means more solar panels for charging (i.e., the system grow$).

Could you remove the read A/C system and then have more/easier space for mounting panels?

-Bill

Recommended PV setup for weekend usage in DYI conversion Sprinter RV?

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