Small Solar Cabin - Best way to cool 150 sq. ft ???

[OffGridMikey]

Here is my setup:
200W of 12 Volt Solar Panels (2x 100W in Parallel)
PWM Solar Charger($30 one from Renogy that comes with system)
Trojan T-105 Batteries 6V (2x Wired in Series for 12V (Capacity 225 AH @ 20hr, 185 AH @ 5HR)
Cabin is 16' L x 8'W x 7' Tall (128 sq. ft, ~ 900 cubic ft. volume w/ decent insulation) (Only actually need 2000-2500 BTU's to cool this off on hot summer nights)
Cabin is only used for 2-4 days max, so most of the time 90-95% of the year, the batteries see no load and stay constantly charged.

I've had this system in the field at our hunting camp for 2+ years running basic loads (12V LED lighting inside & out, USB Phone Chargers, Marine Radio so if all is on 7.5-12 amps worth of current would be the max, but on average 2-5 amps is the standard consumption) and never had an issues. My cabin is in middle GA so the summers are pretty brutal, and I share this cabin with the owners brother who is hell bent on putting in an Air Conditioner. In fact he bought a Frigidaire 5000 BTU system for $117 bucks at wall mart which this season we ran off a gas powered generator.

I'm wondering what I would need to change in my setup to run this unit for 5 - 8 hrs a night possibly 3-4 nights in a row?
-Knowing that this window unit requires 515W at max cool, and that I only have 200W of charging power without factoring losses, I'm concerned as to what is the best path forward and would like your help in pointing me down a path that is both economical and takes the environment into consideration (Only lived in 2-4 days at at time, only need AC during the summer, solar panels can charge batteries up when we leave)

Should I try to make it work with this AC unit possibly by adding more batteries in parallel, an extra panel or two with a good inverter?
or
Find a better A/C solution on DC that is built around the 2000-2500 BTU needs that wont draw as much current?

I understand the basic math of using the existing A/C unit on DC (550W @120V = 4.58amps so @ 12V your looking at 45.8amps with a inverter @85% efficiency I would be drawing ~54 amps of current) I'm getting nervous about going this route and would appreciate any advice you can give me so I don't re-invent the wheel.

[OffGridMikey]

More Info

FYI - We did try this crappy inverter he bought:
Cobra 800W Continuous - 1600W Peak but it couldn't handle it past medium cool, and don't think it actually started the compressor. The unit would trip out and start beeping as we took the dial up towards maximum cool and no real cold air actually came out of the unit as opposed to running it off a generator.

It would trip out as we moved the dial from low cool to max cool...
Would this be because of starting current of the compressor motor?

How should an inverter be sized to maximize the efficiency? (I've heard that you want one near or just over the max load capacity)

Can any of your recommend a good inverter for <$200 that could handle this load better or more efficiently?

[Sunking]

You cannot use anything you have, nor can you likely afford to run AC. A 5000 BTU Window Shaker from Wallyworld is not efficient and draws around 500 to 600 watts and running 10 hours uses 5 to 6 Kwh which is a small amount from the mean ole electric company but a huge number for solar.

Assuming the cabin has full direct sun from sun rise to sun down with absolutely no shade you are looking at 1500 to 1600 watts of solar panels, way more if you have any shade what so ever, an 80 amp mppt controller for 24 volt system, and a 1500 pound battery. Somewhere around $8,000 to $10,000 worth of stuff depending on your shade issues.

Happy shopping.

[Amy@altE]

I agree with SunKing. For the amount of use the cabin gets, AC with PV is not reasonable. If it was in a dry climate, you could try a swamp cooler, but it would not work at all in GA. A DC ceiling fan would be the best you can do with PV. http://store.nextekpower.com/secondary/fans.html

[OffGridMikey]

Thanks, Any other cooling ideas?

You cannot use anything you have, nor can you likely afford to run AC. A 5000 BTU Window Shaker from Wallyworld is not efficient and draws around 500 to 600 watts and running 10 hours uses 5 to 6 Kwh which is a small amount from the mean ole electric company but a huge number for solar.

Sunking - Thanks for confirming my suspicions,

I failed to mention we have no 'mean ole electric company' onsite as the camp is pretty remote. It would cost $6-8K to run polls, and even though the yearly cost of A/C is insignificant it changes the tax rate on the property significantly (about $3-4K/yr) based on the acreage.... adding AC power lines is not an option any of us want.

I built this system for <$750 and it's done everything for a our cabin we want. (Lights, Fans, Radio, USB Phone charging)... If I could get some sort of cooling for 500-$750 that would knock 10-15F off the outside temp that is really all we are looking for.

Knowing this, is there a cooling solution that can be run off Solar PV & Batteries that would generate 1500-2000 BTU's worth of cooling that you could think of?

[OffGridMikey]

Decapitation

I agree with SunKing. For the amount of use the cabin gets, AC with PV is not reasonable. If it was in a dry climate, you could try a swamp cooler, but it would not work at all in GA. A DC ceiling fan would be the best you can do with PV. http://store.nextekpower.com/secondary/fans.html

Amy thanks for the reply. I already have some pretty cool 12V DC fans that blow air on both sleeping areas. A ceiling fan would decapitate us.... it's only 7' high in the center and 6'5" on the side.

[Amy@altE]

Get shorter friends ; )

Looks like you've done about all you can do without spending a fortune. Mini-split air conditioners are a nice option for off-grid homes, but again, for your situation where it is only used a few days a year, just not worth the investment.

[Sunking]

Sunking - Thanks for confirming my suspicions,

Your welcome and sorry for the bad news.

When I was dumb, young, and full of come one hot summer in Oklahoma our air conditioning went out. We were poor then and it took a month to come up with enough money to replace the compressor. Sleeping at night was miserable in hot humid Tulsa Oklahoma. Well poor people have poor ways and we solved the sleeping problem. We turned off the heater on the WATER BED. Worked so darn good we actually had to add blankets to sleep on top of blankets to insulate our bodies from the bed. Got it just right so all we needed was a sheet to cover us and a ceiling fan was real comfortable.