Torture test of the Solar A/C

[jimindenver]

I called it that because under normal conditions we are in the mountains where it was only 82F today, not 95F. We would have the trailer vented and would start the A/C as soon as it heated up.

As it was I picked up the trailer at 10:30 AM when it was already in the 80's in side and out. The Max air covers had a lot of heat trapped under them so I couldn't use the vents to get the heat load off of the ceiling. By the time i got the solar hook up and the A/C installed it was 88F. The A/c kept the trailer down to 81 or 82F even though it quickly climbed into the mid 90's. I ran it from 11 am till 5 pm when the shadow from the trailer was getting close to the panels.

Was it a success? I'd say so considering I am using a 5000 BTU A/C in a 25 Ft box sitting in the sun. It didn't have the ability to over power the heat load but coming in out of 95 degree heat to 82 degrees is a noticeable difference. I could have mounted it in the bedroom and pulled the curtain. That would have been a much smaller space to cool down had we really needed it.

Would a 5000 BTU A/C keep a insulated van cool?  The trailer isn't insulated all that well and is close to 200 sq ft. I would believe you would have a better shot in the van.

 

[c_hasbeen]

was it a torture test for you or the AC/Solar? LOL

 

[jimindenver]

The hardest thing was miving the three 50 pound panels around in the heat.

I moved the trailer about 30 minutes after I shut off the little A/C. In that time the temperature inside had climbed to 90F.

 

[akrvbob]

Remind us what you have for solar--if I remember right you have 750 watts laid on the ground. Did you tilt them and track the sun?

What is your battery bank? What were the batteries at when you stopped the AC and what were they at the end of the day?
Bob

 

[jimindenver]

Remind us what you have for solar--if I remember right you have 750 watts laid on the ground. Did you tilt them and track the sun?

What is your battery bank? What were the batteries at when you stopped the AC and what were they at the end of the day?
Bob

Bob

I have three 250w poly panels that in this test were run in series. They were flat about two inches off the ground. I tried to level them up but the drive slopes to the west and they had some negative pitch most of the day. I have been leaving them flat as they will be mounted so that I can get use to that power level. Tracking is addictive but quite the hassle with three panels.

The battery is my dieing 8-D starting battery. It was resting at 12.4v before the test and had 15, maybe 30 minutes on the panels before I started the A/C. The panels held the voltage under load above 13v until 3 pm when peak sun had past. It had dropped to 12.3vby 5 pm but bounced back up to 12.9v when I stopped the test and put a charger on the battery as the panels were about to be in the shade.

The trailer is poorly insulated and in 84f heat it was up to 94f inside without the A/C running. The temp would have easily been over 100f when it was 95f outside so the little A/C was easily holding the temperature down 20 degrees or more of what it could have been. Had I mounted it in the bedroom and pulled the drape it could have easily cooled that space.

These are the panels set up, you can see the A/C in the back lower window.

[img=600x338]http://i78.photobucket.com/albums/j...186e15eac79d9514bc1e28d858.jpg~original[/img]

The A/C in the bunk.

[img=600x338]http://i78.photobucket.com/albums/j...8057fa8387908188c2d7dbfb5d.jpg~original[/img]

 

[akrvbob]

My guess would be that unless you've changed the layout it didn't get very good circulation blowing into the bunk. I'd say it did remarkably well and passed the test with flying colors!

Thanks for telling us about it!
Bob

 

[Oneleggedcowboy]

I have a 5000 but window ac in my slide in camper window and it gets cool enough to cycle on and off. That's plugged in to shore power. I also have a 5000 but window ac in a hole I cut in the living quarters back wall of my gooseneck horse trailer. I is mounted up high at the ceiling level, remember cool air falls. The living quarters are uninsulated steel
The area is about 6x6 with the gooseneck part 6 by 6 but of course only 30 inches tall. It cools nicely even in the sun to a temperature that you can take a nap in the afternoon. That's with a fan bl9wingnon you in addition to the ac. This is also plugged into shore power or the 2500 wstt generator. As for solar power running it I would go with Bob's method of head north and higher elevation where you won't need ac. It would be more scenic to sit outside with fresh air and sunshine too!

 

[amwbox]

Interesting, thanks for posting. A few questions if you don't mind:

Does the charge controller go into sustained absorption mode for the full duration of the high draw from the AC (I'm guessing the AC draws around 600-700 watts)? 

What sort of real world wattage were you getting from the panels flat on the ground like that during the test?

Was the charge controller heating up quite a bit, since its sitting in a hot ambient temperature and running at near capacity for hours on end?

Is it possible to draw down the batteries if the solar system is delivering more wattage than the AC is drawing? 

Are the batteries being worked hard, boiling, or is most of the heavy lifting being done by the charge controller? 

Do the batteries have to be continuously charging/discharging, or does the power just pass through them from the charge controller? 

I'm not sure I properly understand what's happening to a system where the AC is drawing roughly the same amount or less as what is being put back by the panels. For example, with 750 watts of solar, and a 700 watt load, wouldn't that still be 50 watts going into the batteries?

Any insights from anyone would be great.

 

[highdesertranger]

you're inefficiencies will eat up that 50 watts. highdesertranger

 

[ZoNiE]

Interesting, thanks for posting. A few questions if you don't mind:

Does the charge controller go into sustained absorption mode for the full duration of the high draw from the AC (I'm guessing the AC draws around 600-700 watts)? 

What sort of real world wattage were you getting from the panels flat on the ground like that during the test?

Was the charge controller heating up quite a bit, since its sitting in a hot ambient temperature and running at near capacity for hours on end?

Is it possible to draw down the batteries if the solar system is delivering more wattage than the AC is drawing? 

Are the batteries being worked hard, boiling, or is most of the heavy lifting being done by the charge controller? 

Do the batteries have to be continuously charging/discharging, or does the power just pass through them from the charge controller? 

I'm not sure I properly understand what's happening to a system where the AC is drawing roughly the same amount or less as what is being put back by the panels. For example, with 750 watts of solar, and a 700 watt load, wouldn't that still be 50 watts going into the batteries?

Any insights from anyone would be great.

All about the same questions I wanted to ask!!!

I'd bet you would do better with larger battery capacity, but I realize this was using a dying battery so was good use of it.

Can you check the SG of the cells before, during, and after? Curious as to what is going on in the cells too. Bubbling a lot? Lower level afterwards?

 

[jimindenver]

One at a time here.

Bob, I was really pleased with the test on one hand. You are right in that with all of the things working against the little A/C that it did a good job. 81* doesn't sound great until you come in out of 95* heat.

Onelegged

10,000 ft of elevation IS where we go to escape the heat. Even there it gets hot and while I'd rather sit in the shade of a big tree, Honey and the dogs have become somewhat more spoiled.

 

[sushidog]

Thanks for the info. It's good to hear of people proving the naysayers wrong. Off grid solar AC can be done, and you've just proven it!

I'm planning on a little bigger solar system for my future FTing rig, a 30ft, well insulated TT.

I plan on using this super high efficiency 12,000 BTU mini-split AC HSAC-12AC unit: http://www.geinnovations.net/Specifications.html It makes 12,000 BTUs of cooling (and heating) power for about the same energy consumption as a typical 5,000 BTU window shaker. The best part is this native 48v dc appliance only draws 11.5 amps (560 watts), so there's no inverter conversion inefficiency too. It has a variable speed rotary compressor that scales up and down as needed, avoiding the typical start-up power surge by not cycling on and off.

I will be using 8-GC-2 golf cart batteries recharged by a 6-300 watt solar panels (2 banks of 3 panels wired in series), flat mounted about 6 inches off the roof to provide shade (reducing the TTs heat load) while allowing the solar panels to run cooler and more efficiently. The high voltage system will keep the wire size down too. I will use a 48v inverter for my a/c needs, which is a little more efficient than 12v models too. I also plan on having a low-voltage system for my minimal 12v needs, like slide-outs, water pump, LED lights and refrigerator board. This will use 2 Sam's club GC-2s and a single 300 watt dedicated panel. At today's prices (I have already cost out all system components) such a system will cost around $6,500 if I build it myself - including the rather expensive super-efficient (21.43 EER) heat pump. I won't be building this system for another 3+ years, so the price of solar may drop a little by then (allowing me to be able to afford what I really want, 6-Sun Power E20-435 watt high efficiency panels.) http://global.sunpowercorp.com/cs/B...tion/pdf&blobcol=urldata&blobtable=MungoBlobs

Who knows what, if any, solar rebates will be available at that time to make it a little more affordable? But even if they have all ended, I am still willing to pay the price for completely independent off-grid extended boondocking. When I factor in the savings on CG or RV park fees it would still yield less than 2 yr payback - yet have a 20+yr system life (less battery costs). Who knows, if LiFePo-4 batteries drop in price substantially over this time (or at least by the time my first bank of cheap FLAs needs replacing) I'll ideally go with them instead, for a huge weight savings and better system performance overall, if they become affordable.

Chip

 

[sushidog]

Jim, if you can afford it ($655 +$98 shipping) on Amazon and have the available space, Klimair makes a 9,000 BTU mini-split heat pump with an EER of 15, which is over 50% higher than a typical 5,000 BTU window unit. This means it will produce almost twice the cooling while consuming only 600 watts (which is probably less than you are using now). Plus you get the benefits of the true variable speed rotary compressor, avoiding high current starts and stops. http://s3-eu-west-1.amazonaws.com/static.fw1.biz/Templates/32505/myimages/klimaire/ksio.pdf

Chip

 

[jimindenver]

Interesting, thanks for posting. A few questions if you don't mind:

Does the charge controller go into sustained absorption mode for the full duration of the high draw from the AC (I'm guessing the AC draws around 600-700 watts)? 

What sort of real world wattage were you getting from the panels flat on the ground like that during the test?

Was the charge controller heating up quite a bit, since its sitting in a hot ambient temperature and running at near capacity for hours on end?

Is it possible to draw down the batteries if the solar system is delivering more wattage than the AC is drawing? 

Are the batteries being worked hard, boiling, or is most of the heavy lifting being done by the charge controller? 

Do the batteries have to be continuously charging/discharging, or does the power just pass through them from the charge controller? 

I'm not sure I properly understand what's happening to a system where the AC is drawing roughly the same amount or less as what is being put back by the panels. For example, with 750 watts of solar, and a 700 watt load, wouldn't that still be 50 watts going into the batteries?

Any insights from anyone would be great.

When the 8-D is charged up, the controller can stay in float at 45a. This test the 8-D was only at 12.4v and held in the 13's all day until 3 pm. On it's own, it can't even start the little A/C.

Flat the panels can produce in the 660w range pretty easy. They were running a bit lower due to the heat. The panels were off the drive by a few inches for ventilation.

The charge controller got considerably hot by the end of the test. Hot enough that it made me think that in the fall I could run a 400w heater on one end of the trailer and have the controller at the other end.

Generally the A/C takes 450w once the pressure has built up. That's mid 30 amp range on a clamp on meter between the inverter and battery. The system is dropping about 10 amps over that so theoretically the battery is still receiving some charge but not much. Normally our batteries are in float by 9 am or so and we wont need the A/C for a few hours after that.

The only thing the battery has to do when the system is running at peak is absorb the portion of the start surge that the solar system can't handle. After that split second, the battery is doing nothing. Even once peak light has past the battery only has to make up what the solar isn't providing and even with a dieing battery the voltage drop was slow.

The load will accept the power coming from the source with the least resistance and that is the charge controller. The power skates across the terminals just as if the battery wasn't there.  I have actually run a test with a load on a inverter powered by a system. Once it all up and running, I pulled the battery out. The load continued to run as long as the sun shined.

The whole point of building a larger system was to be able to run the A/C directly off the panel and not drain the battery. Even with a forth panel I would be just short of running a 6000 BTU energy efficient unit.

Zonie

The new bank is three 225 Ah Lifeline 8-D AGM's. Should the need come, I can run the A/C off of them. The plan is to cycle them as little as possible to make them last the longest. I've been doing it with the GRP 27 that runs the trailer functions for years now. It's 4 years old and still going strong.

The old 8-D wasn't getting hot as it was only getting a small charge from the leftovers of the solar. 10 amp or less just doesn't push a 8-D around nor will it make it boil. I'm told that my whole system is barely enough to charge ONE of my Lifelines if I got them down to 50%. Literally 40-50a is too slow of a charge, especially for three of them. Believe it or not the manual says I could use 500a per 100 Ah of battery. I have 675 Ah so I could hit them with over 3000a and they would gobble it up. That is their biggest advantage IF you can use it.

As for testing the old one, it goes to the recyclers tomorrow. It's not dead but it can't be hooked up to the AGM's either. It would draw them down as the weaker battery and have to be recharge with a separate set of settings. New it could run our microwave but it wasn't built to last. Still they are an impressive amount of power for the money spent. Even more so when someone posted the 40% off coupon to one of the auto parts stores. That made the 250 Ah just over $120 if you have the room and can vent it.

 

[Oneleggedcowboy]

Wow Jim this is a great thread!!! Impressive what your panels were capable of. Keep on figuring it out, I would love to be able to have AC in a off grid cabin in Ax. Don't have the cabin yet but working on it!

 

[amwbox]

When the 8-D is charged up, the controller can stay in float at 45a. This test the 8-D was only at 12.4v and held in the 13's all day until 3 pm. On it's own, it can't even start the little A/C.

Flat the panels can produce in the 660w range pretty easy. They were running a bit lower due to the heat. The panels were off the drive by a few inches for ventilation.

The charge controller got considerably hot by the end of the test. Hot enough that it made me think that in the fall I could run a 400w heater on one end of the trailer and have the controller at the other end.

Generally the A/C takes 450w once the pressure has built up. That's mid 30 amp range on a clamp on meter between the inverter and battery. The system is dropping about 10 amps over that so theoretically the battery is still receiving some charge but not much. Normally our batteries are in float by 9 am or so and we wont need the A/C for a few hours after that.

The only thing the battery has to do when the system is running at peak is absorb the portion of the start surge that the solar system can't handle. After that split second, the battery is doing nothing. Even once peak light has past the battery only has to make up what the solar isn't providing and even with a dieing battery the voltage drop was slow.

The load will accept the power coming from the source with the least resistance and that is the charge controller. The power skates across the terminals just as if the battery wasn't there.  I have actually run a test with a load on a inverter powered by a system. Once it all up and running, I pulled the battery out. The load continued to run as long as the sun shined.

The whole point of building a larger system was to be able to run the A/C directly off the panel and not drain the battery. Even with a forth panel I would be just short of running a 6000 BTU energy efficient unit.

Awesome info! Thanks so much. 

Well, if you are able to successfully feed an AC unit from a solar controller...then you're living the dream, I'd say! AC powered by the sun is just about the most perfect complementary situation I can think of. Its too bad that the hottest part of the day occurs just about the time the sun is starting to taper off, but still...being able to enjoy AC through the middle of the day without slaughtering batteries sounds like magic to me.

As for the heating of the charge controller, if its passively cooled I'd investigate attaching a PC fan to the heat sink...or maybe aim some of that precious cold air at it. Or maybe look into a liquid cooling loop. The custom PC market is full of liquid cooling gear for electronics right now, might be just the thing, with some  modifications:

 

[sushidog]

If you are only drawing 450 watts to produce 5,000 BTUs your AC has an EER of 11.11, which is much more efficient than the 5,000 btu Maytag in my Aliner which only has an EER of 9.7 and draws 520 watts, after it's been running for a while (of course, it draws about twice this on start-up.)

What brand of AC do you have, for future reference, in case mine ever needs to be replaced?

Chip

 

[jimindenver]

Chip

This is the unit I an using. It took me a year of research and even driving to the stores to see the actual tags on the units to find this one. It is rated at 446w on high. It showed 450w on a kill a watt and the EER is listed at 11.2.

http://www.ajmadison.com/cgi-bin/ajmadison/FFRE0533Q1.html?brand_store=1

I did consider adding start cap but when the system is running and the battery is even partially charged, it starts so easy I have to check the meters to make sure the compressor is running. Until I got the new batteries I figured I would keep the remote handy and switch to fan only when a cloud passed.

 

[sushidog]

Sweet. Thanks, Jim. It's not too pricy either.

I know what you mean about being quiet. My Maytag is very noisy and vibrates quite a bit, but I had an 8,000 btu LG that was so quiet that I could hardly hear when the compressor kicked in. When I first turned it on I let it run about 5 minutes on high and didn't hear the compressor kick in so I thought it was defective. I went to the window to take it out so could return it and get another only to discover ice cold air blowing on my belly!

Chip

 

[jimindenver]

Thanks for the info. It's good to hear of people proving the naysayers wrong. Off grid solar AC can be done, and you've just proven it!

I'm planning on a little bigger solar system for my future FTing rig, a 30ft, well insulated TT.

I plan on using this super high efficiency 12,000 BTU mini-split AC HSAC-12AC unit:  http://www.geinnovations.net/Specifications.html It makes 12,000 BTUs of cooling (and heating) power for about the same energy consumption as a typical 5,000 BTU window shaker. The best part is this native 48v dc appliance only draws 11.5 amps (560 watts), so there's no inverter conversion inefficiency too. It has a variable speed rotary compressor that scales up and down as needed, avoiding the typical start-up power surge by not cycling on and off.

I will be using 8-GC-2 golf cart batteries recharged by a 6-300 watt solar panels (2 banks of 3 panels wired in series), flat mounted about 6 inches off the roof to provide shade (reducing the TTs heat load) while allowing the solar panels to run cooler and more efficiently. The high voltage system will keep the wire size down too. I will use a 48v inverter for my a/c needs, which is a little more efficient than 12v models too. I also plan on having a low-voltage system for my minimal 12v needs, like slide-outs, water pump, LED lights and refrigerator board. This will use 2 Sam's club GC-2s and a single 300 watt dedicated panel. At today's prices (I have already cost out all system components) such a system will cost around $6,500 if I build it myself - including the rather expensive super-efficient (21.43 EER) heat pump.  I won't be building this system for another 3+ years, so the price of solar may drop a little by then (allowing me to be able to afford what I really want, 6-Sun Power E20-435 watt high efficiency panels.) http://global.sunpowercorp.com/cs/B...tion/pdf&blobcol=urldata&blobtable=MungoBlobs




Who knows what, if any, solar rebates will be available at that time to make it a little more affordable? But even if they have all ended, I am still willing to pay the price for completely independent off-grid extended boondocking. When I factor in the savings on CG or RV park fees it would still yield less than 2 yr payback  - yet have a 20+yr system life (less battery costs). Who knows, if LiFePo-4 batteries drop in price substantially over this time (or at least by the time my first bank of cheap FLAs needs replacing) I'll ideally go with them instead, for a huge weight savings and better system performance overall, if they become affordable.  

Chip

Wow!   Nice system.

What will you use as a controller, your VOC will easily reach over 150v.

The 9000 BTU heat pump is impressive, nearly twice the cooling  for only 150w more. Now that the batteries are in the trailer, the pump could sit on the tongue.

Had I known the levels I was going to get to, I would have gone 24v for the inverter bank. I had no idea I was going to run into these batteries back when I bought the inverter.  Should one 8-D prove to be weaker than the others, I'll run it as the trailers bank and the other two for the inverter.

Campground fees? What are those? I'd pay a fee to get into our favorite boondocking areas before I'd stay at a campground for free.

We did spend 16 days in campgrounds the first trip out with this trailer. We had electric but no water sewer. It really wasn't bad when we were alone during the week but on the weekend it was hell. Those are the only fees we have paid in 25 years.

We also tried a free campground on a lake and while it was calmer, those people were generator happy. I decided that all spending the money on solar, a huge bank or the quietest generator just means you will get to listen to someone else run theirs.

The solar system will pay for itself in fees in two or three years. having the ability to go where we want and have all the comforts of home is worth far more to us.

Good luck with your build. I look forward to watching it grow.