Off-Grid A/C questions!

[utherjorge]

Good morning!

I have hypothetical questions about camping. I believe I'm looking to take a pop-up camper and outfit it as a platform rather than add a rooftop tent to my rig(s). I recognize this is heresy, but I respectfully ask that you all stay your torches and pitchforks.

I like the idea of a pop-up camper as I know it can be towed by all three of my rigs, especially with the small size I am thinking of. However, while I see a lot of advice for refurbing a camper, including water, heat, and power, but I see very little that answers my questions about retrofitting A/C....and whether it's really doable. We are camping at Assateague in July this year, among other places, and I'm planning ahead.

Specifically, let's pretend I decide how and where I'll retrofit a small A/C unit into the pop-up. That's great! But is it reasonable to be able to be off grid (there are no power hookups at Assateague's National Park campground for instance) and use A/C in the first place?

 

[DiploStrat]

Short answer is. "probably not."

Guesstimate about 50A DC @ 12v for every hour the air conditioner runs. May be a bit higher by day, lower by night. Call it 10 hours of run and you are looking at around 500Ah.

So:

-- Put 1000w+ on the roof and you have about 50A per hour with good sun. You might well get 8 hours at Assateague in the summer.

-- How would you recharge a 500Ah battery bank?

It ain't easy.

Now, put the mosquitos on a tread mill ...

 

[glennm01]

Actually, 1000+ watt array would produce way more than 50 amps in peak sunlight. And if the a/c unit is being run during the daytime, it wouldn't even touch the battery bank with an array that large. My 5000 BTU unit (plenty for a small camper) pulls about 450 watts with the compressor running, and if we assume it's on 50% of the time, and factoring in the small load even when the compressor is off, you'd need about 250 watts of juice every hour to keep it running. Totally doable, but your big challenge will be figuring out how to fit enough panels on such a small rig so that you can still accommodate your other electrical loads. Maybe you could build a flexible panel array that deploys on the ground.

 

[DiploStrat]

My rule of thumb has always been 5A per 100w of solar. More modern panels may get a bit more, but allowing for clouds, trees, etc., 5A has been a good planning point.

You might, indeed, see a 50% duty cycle, but for planning, you are better off assuming 100%. This past summer, we were looking at 100F+ and our air conditioner, set on 6k BTU, could only make it to around 85F.

Jason probably has the best set up around, but:

-- He is demoing in Oaxaca - near perfect combo of sun and altitude, and, 0 humidity.

-- His camper has the panels arranged to shade the sides, no windows, and a small air conditioner. But, I have to assume that it works, as he is Canadian, and they are not known for heat tolerance!

you tube everlanders - Bing video

www.bing.com

 

[glennm01]

I can only relate my experience surviving this past Southern California summer (i.e. regular highs in the mid to upper 90s and periodic stretches over 100): Zero trouble maintaining the mid to low 70s in my rig, this with 1100 watts of solar, 5k Btu a/c, routinely running the a/c from 11am until midnight most days. Until about 6pm, I found the a/c was basically free, i.e. running entirely off of surplus from the panels. And a 50% duty cycle is being generous. If I'd have to guess, I'd say it was more like 35-40%, and even less after dark. I realize 1100 watts is enormous and probably unrealistic for most, but the whole thing worked so well that I believe one could pull it off even with a few hundred less and maybe a slightly higher temp set point. All of this presumes a decent amount of insulation of course, and lithium batteries (since they charge considerably faster than lead acid). Again, totally doable with the right setup in my experience, but the main challenge for most will be figuring out how to have enough solar capacity onboard.

 

[john61ct]

Without a huge roof, or just overnight stays, off grid aircon requires an inverter genset.

Honda and Yamaha are robust and quiet.

Cheaper units are a roll of the dice.

 

[DiploStrat]

I have about 640w of solar, which translates to the high side of 30A. The world gets really different when you pass 1000w.

 

[john61ct]

Expensive battery bank too.

Best to base everything off the genset

then if you get a lot of solar + storage going, that progressively reduces your runtime hours per month

and even when you think the solar's enough, you still have backup for when you need it

or want to park in a nice shady spot

 

[simple]

Looks like a neat place to go camping.

Regarding staying cool, you will be fighting a poorly insulated enclosure so factor that in as well. I realize on the east coast it's not just about staying cool but also staying dry in the humidity. Fingers crossed the humidity will be low while your there.

This doesn't do much for humidity but is a low tech solution for daytime temps. You might consider pitching a shade structure (big tarp) above your camper to function as a heat shield. Looks like you will be at the coast so you could also pitch your structure so the opening is facing off shore / on shore to funnel wind through it carrying the heat away between the camper and heat shield. You could also run some small solar powered fans at a fraction of the cost of AC.

 

[Peter_n_Margaret]

A few running off grid A/C in Australia.
Typical would be 1200W of solar, 400Ah of lithium and the smallest Mitsubishi Heavy Industry inverter A/C.
The back up power supply is the vehicle alternator. Leave the generator at home
Cheers,
Peter
OKA196 motorhome

 

[sg1]

All that is possible in a large RV. But where would you put 1000 w solar and 500 Ah batteries in a pop up camper? How do you lift a roof with 1000 w solar? Remember the op is thinking about a pop up. In a pop up ac works only with shore power or generator. If you use a generator I hopefully will never camp anywhere near you.
By the way, I agree with DiploStrats rule of the thumb assumption of about 5 A per 100 w. Only in very special conditions (Andean highlands at noon) I got significantly more. Certainly not at East Coast US where the Assateague's National Park is located.

 

[john61ct]

All that is possible in a large RV. But where would you put 1000 w solar and 500 Ah batteries in a pop up camper?

See my post #6

 

[Peter_n_Margaret]

My new build 6m (20ft) bumper to bumper OKA motorhome will have about 1200W of solar and 400Ah of lithium batteries.
If it needed more it could have it.
Cheers,
Peter
OKA196 motorhome