Air Conditioner & Solar - RV-Dreams Community Forum

thebearII · RV-Dreams Family Member

Air Conditioner & Solar

RVDude · RV-Dreams Family Member

Here's the math... You decide.

I'll convert everything to watts as that way we don't have to deal with X amps @ 12v vs Y amps at 120v issues. Or whether it's volts AC or volts DC.

A 13,500 - 15,000 BTU A/C will require about 15amp at 120v. I would suspect that in your intended mode of operation the AC will run flat out during the 4-5 hour operation window. Hence, the 15amp load will be constant for the entire let's say 4 hour operation window.

Amps * volts = watts (in general) so 15 * 120 = 1800watts * 4 hours = 7200watts-hrs (or 7.2kw-hrs.) to run the A/C for 4 hours.

A typical solar panel (like Howard installed) provides about 100w ea. and let's assume 6 hours of good sunshine a day, so that's 600 watt-hr per panel and you'd need 7200/600 = 12 panels (given a perfect world) just to recharge that battery bank.

This is all assuming a perfect world. Inverters are only 80%-95% efficient (meaning they will use more wattage than they are delivering). Hence, when on inverted AC - drawing from the battery bank - you'll be drawing more than 7,200 watt-hr more like 7200/~80% = ~8,000 - 9,000 watt-hrs.

The charger is itself only 80% efficient or so and this means that to recharge will require more input watts than you get in charging output. So you'll need to 9,000/~80% = ~11,000 watt-hrs to recharge. (BTW, Now we are up to 19 panels).

The solar panels are probably not going to give you full rated output for all 6 sunshine hours unless you have them tilted and tracking the sun. Add even more panels for poor sunshine.

Well, I think you get the picture. Can it be done, certainly. How much roof space you got on top of your rig? And all the above just for 4 hours of A/C operation!

Remember, the microwave may take about 10amps at 120v (1,200 watts) but it'll only be running for a few minutes, not hours. A TV takes only a hundred watts or so it can run for hours.

Load and amount of time the load is used are the two parameters to consider.

-- Edited by RVDude at 00:22, 2008-05-10

skidrowe · RV-Dreams Community Member

The RVDude is right. I occaisionally run into the same requirement, that is, to run the air conditioning for a few hours. When I do, I use the generator to power my air conditioning and simultaneously recharge my batteries. I can run the air conditioning and battery charger for about .35 gallons (of gasoline) per hour. So, for about 1.5 gallons I'm done for the day. Of course, when I'm faced with this situation, I know it's time to drive northward or into the mountains where air conditioning is unneeded! BTW, I have a Yamaha 3000 generator and a Xantrex Truecharge 40+ charger.

thebearII · RV-Dreams Family Member

Thanks RV Dude & Skidrowe...

Guess I'll just have to wait for more efficient solar systems or the fuel cell generator "they" keep promising us.

Now my head really hurts from reading all of RV Dude's calculations.

As the third grader asked once of his teacher "Can I go home now my brain is full"......

RVDude · RV-Dreams Family Member

thebearII wrote:
...or the fuel cell generator "they" keep promising us.

You can't go home yet, we gotta talk about the fuel cell! I too am eagerly awaiting that device. Actually, things are getting closer. Here's a tiny camp-sized fuel cell model already in production and not excessively ridiculously priced.

OK, my class dismissed. We can all report directly to Doc Speedy's class of having class, don't pass go, collect your $200 and hand it over to your DW, and don't collect any brews or remotes.

thebearII · RV-Dreams Family Member

Oops---- Unfortunately Millennium Cell fired all of it's executives yeaterday and ceased operations until the board of directors can find financing.

This is the second fuel cell development company that has closed their doors. I have a feeling the technology just isn't there yet, otherwise investors would be flooding these companies with lots of dollars.

It always worries me when I look at a company website and I see the executives all wore suits and ties for their company photos. Most start up companies are so busy the executives rarely have time to stop and get dressed up for photos.

Sushidog · RV-Dreams Family Member

I know I'm resurrecting an old thread, but here's a possible solution to the old solar ac problem - a new high efficiency variable speed DC mini-split AC: www.hotspotenergy.com/DC-air-conditioner/

I'm actually thinking about adding their medium solar system ( www.hotspotenergy.com/DC-air-conditioner/DC-AC-Complete-Systems.phpt ) my future FT TT to add about 15 hrs/day of solar to make boondocking more comfortable in warmer/cooler weather. My main question: Is there enough unshaded roof space to for the 1,500 watts of solar required? Another, more surmountable problem is finding a TT that has the extra 1,000 lbs of load capacity required for such a system.

It looks like one can get suitable 255 watt panels that are 65" x 39" www.wholesalesolar.com/products.folder/module-folder/Astronergy/CHSM6610P-255.html . If mounted with the long axis of the panel parallel to the long axis of the TT then you could fit 2 side-by-side (assuming there is no roof protrusions to get in the way. Since 6 panels are required, you would need 195" (16' 4") of unobstructed/unshaded roof space. I think there might be enough roof space on a 30ft TT to accomplish this. I would mount the outside compressor unit on the tongue, running the refrigerant hoses under the camper and attach them to a bedroom wall (perhaps the rear bedroom wall on a front bedroom TT.) A 12k BTU AC won't be sufficient to cool even a well insulated TT on the hottest summer days, say for year round camping at Quartzsite, The Slabs or similar venues, but it may be sufficient in the high desert, like on the BLM land north of Flagstaff. Of course if one is trying to cool just the bedroom at bedtime (when it's cooler anyway) then one may be able to camp in the southern desert year round. As a side benefit, that many solar panels covering the roof (with an inch or two of insulating air space underneath) will provide some shade to the camper too, converting at least some of the sunlight that falls on the roof to electricity rather than heat.

This system is also a heat pump providing efficient supplemental heat while boondocking, extending propane life too on those cool evenings when a little heat would be nice. Since I plan on spending most of my time in low cost monthly RV parks (with amenities) I can see the biggest advantage would be to have supplemental AC while traveling, overnighting at Walmart, truck stops, rest areas, etc. en route to monthly stops (as well as the occasional boondocking sojourn.) One could even turn the AC on a couple hours before stopping for the night to pre-cool the camper, giving the same benefit of a cooled-off MH in a lowly TT.

The price is a little high now (around $6k with installation) but if you're planning on installing a smaller solar system anyway, and the high efficiency mini-split AC is used to replace a second roof mounted AC (and the $500 it would cost is taken off the $1,800 cost of the mini-split model) it makes the upgrade a little more affordable. Plus there's the advantage of having that much solar (possibly even with a grid tie in) lowering one's electric bill at FHU RV parks, (which according to Mr. Obama will soon "necessarily skyrocket") saving money even when not boondocking. And I'm not even considering the 30% second home solar tax credit (coincidentally the $1,800 tax credit on a $6k system is exactly what the solar AC unit costs, making it effectively free) currently available from Uncle Sugar.

Comments? Am I crazy, or crazy like a fox?

Chip

-- Edited by Sushidog on Thursday 24th of July 2014 07:38:47 AM

BiggarView · RV-Dreams Family Member

This subject is of interest to me, so I will follow even if Terry or Gene thinks it should be in its own thread.

My first thoughts were to ask if you have a genny already or will have one and then how much would it cost to run it to provide the power needed to do the same thing. There certainly are pros and cons to a solar install and the same for a highly efficient AC (if this proves to be the case in your example) The biggest con is the upfront cost of the system vs the low cost(relatively) of the fuel and maintenance of the genny. Eventually the genny costs should outstrip the solar(depending on the usage) so it seems to come down to a cost/benefit analysis.

Next, 6 panels even at 255 watts each covers a lot of real estate.

Your estimate for weight seems about right, so your concern in this area is valid. Might have to upgrade the trailer suspension components and tires to handle the extra weight.... more $$$$.

Earlier in the thread, analysis of solar output used the figure of 6hrs per day of solar charging might be a bit optimistic (he does say in ideal conditions, however most things I have read on this subject use 5hrs/day as a more realistic estimate.

Somebody in this forum, I forget who, has a stand alone solar array that he carries in/on his truck and sets up at his site... No room on the trailer roof? maybe this is an option for you.

Just my thoughts, always good to read new things on this subject and your link is intriguing to this neophyte solar wannabe.

Brian

-- Edited by BiggarView on Monday 1st of February 2016 09:28:59 PM

Terry and Jo · RV-Dreams Family Member

It would have been better as a separate thread, but since some of the earlier posts still have some relevance, I didn't say anything to Chip about that.

If enough interest continues with Chip's ideas, I may just move the whole thread to the "Boondocking, Solar, and Related Things" category instead of leaving it here. Another advantage to Brian's comments about a generator vs solar, the weight of the genny could be in the truck, instead of being in the trailer.

As for the RV Dreams participant with a separate array of solar (off the trailer), I think Brian is thinking of Bigboomer. Here are some pictures of his setup that he gave as a link in another forum thread.

BigBoomer's Solar System

Terry

Sushidog · RV-Dreams Family Member

Thanks for the reply guys,

Yes, I'm planning on a generator for supplemental power. I'll ditch the little 1,200/1,600 watt generator I currently have that runs the 5,000 BTU AC on my Aliner in favor of a Honda for FT use. If I don't go with a solar AC setup then I'll go with a Honda EU3000. If I go with solar I will get a Honda EU2000 for recharging only.

I can see situations when running a genny would not be welcome, as when dry camping in a Walmart parking lot, rest area or in a CG without hookups that prohibits generator (or generators running at night.)

As far as ROI you must also factor the cost of generator fuel to run your ac - about 3-4 gallons/15hr day depending on how often the AC cycles (what the solar setup is capable of replacing) or about $12/day add to that generator maintenance and repairs, say $15/day. That means that each day I use it I would save $15, so assuming 60 days of use/year = $900/yr add the electric savings when hooked-up (I'm guessing about $40-$50/mo.) So in 1 year $450 elec savings + $900/yr = $1,350/yr. So $4,200 (after $1800 tax credit)/$1,350 = 3.1 yr payback (not considering the $1,000 price difference between a 3,000 watt and a 2,000 watt genny. Even if it takes twice as long, the solar gives added versatility that just might make it worthwhile.

Chip

Sushidog · RV-Dreams Family Member

Another thing to consider is installing one of these high-efficiency mini-split AC units without solar charging. I could use 4 - 12v deep cycle batteries instead of 8 6v batteries to achieve the same 48v dc required, but instead of integrating it with solar, get a Progressive Dynamics PD92080V converter charger and a EU2000 generator to recharge this smaller, 4 battery bank which will run the AC like is used in their small "day" system uses. Since this AC draws so little current (<500 watts running and a max of 960 watts at start-up) I could easily recharge the battery bank with a 1,600 watt EU2000 Honda. A $200 Progressive Dynamics 80 amp converter charger would be a perfect match for this little generator and would recharge the batteries while the AC is running. As a side benefit I would have lots of 12 power available for other things when not running the AC and not be subject to such a huge weight penalty.

To get the 30% solar credit I would have to install at least one solar panel, so I'd probably just get the minimal $4k solar system (saving $1,200) dropping the actual cost to less than $4k with installation! The payback would be quicker, the initial costs lower and I could always add more solar panels and batteries later. I could still run the AC 4-5 hours in the evening to cool off the trailer without running the genny, saving fuel, wear abnd tear on the genny, etc.

Chip

WendysPhotos · RV-Dreams Family Member

We were just going to build one of these for hot days. Since it can be run by 1 little window solar panel. We figure we will have a couple of jugs stuffed in the freezer for it. Since a full refrigerator/freezer is more efficient anyways. I had one for my horse trailer and it worked well to keep temps down. Not the awesomest way, but it helped. I used ice jugs from my cooler that I froze ahead of time. It would not probably work for extended use, but if you were boondocking and on a couple of days the temps spiked it would help.

https://www.youtube.com/watch?v=HxSLbpAwibg This is a youtube video that shows how to make a bucket air conditioner out of a 5 gallon bucket and a small fan hooked to a little car window solar power charger. There are several others along this line too.

Wendy

BiggarView · RV-Dreams Family Member

Gonna have to go read up on the 30% tax credit... to see how we can take maximum advantage. Hopefully it will still be in effect when we go FT. confuse I wonder if a system useful and deployable on a 5er could be set up at home(S&B) then ported over to a 5er.

Brian

waltben · RV-Dreams Family Member

RVDude wrote:
Here's the math... You decide.

I'll convert everything to watts as that way we don't have to deal with X amps @ 12v vs Y amps at 120v issues. Or whether it's volts AC or volts DC.

A 13,500 - 15,000 BTU A/C will require about 15amp at 120v. I would suspect that in your intended mode of operation the AC will run flat out during the 4-5 hour operation window. Hence, the 15amp load will be constant for the entire let's say 4 hour operation window.

Amps * volts = watts (in general) so 15 * 120 = 1800watts * 4 hours = 7200watts-hrs (or 7.2kw-hrs.) to run the A/C for 4 hours.

A typical solar panel (like Howard installed) provides about 100w ea. and let's assume 6 hours of good sunshine a day, so that's 600 watt-hr per panel and you'd need 7200/600 = 12 panels (given a perfect world) just to recharge that battery bank.

This is all assuming a perfect world. Inverters are only 80%-95% efficient (meaning they will use more wattage than they are delivering). Hence, when on inverted AC - drawing from the battery bank - you'll be drawing more than 7,200 watt-hr more like 7200/~80% = ~8,000 - 9,000 watt-hrs.

The charger is itself only 80% efficient or so and this means that to recharge will require more input watts than you get in charging output. So you'll need to 9,000/~80% = ~11,000 watt-hrs to recharge. (BTW, Now we are up to 19 panels).

The solar panels are probably not going to give you full rated output for all 6 sunshine hours unless you have them tilted and tracking the sun. Add even more panels for poor sunshine.

Well, I think you get the picture. Can it be done, certainly. How much roof space you got on top of your rig? And all the above just for 4 hours of A/C operation!

Remember, the microwave may take about 10amps at 120v (1,200 watts) but it'll only be running for a few minutes, not hours. A TV takes only a hundred watts or so it can run for hours.

Load and amount of time the load is used are the two parameters to consider.

-- Edited by RVDude at 00:22, 2008-05-10

Everything's good except your statement of 15 amps for an AC is only at start up. I've measured my 15k btu unit with a Kill-A-Watt and it pulled 14 amps for the first 30 seconds or so and rapidly dropped to about 8 - 9 amps while running on a 82 degree day with 70 percent humidity. This was measuring at the power to the 5er after subtracting phantom loads monitored before turning on the AC. With my four T-105s fully charged and 3kw inverter, I could run the AC for a half hour plus (not that I'd ever want to!). Given enough battery bank, one could run their AC for a few hours, but certainly wouldn't recharge them all that quickly. It's the starting up load that kept me from running the Monty's AC from a single Yamaha 2400 when I'd done that for years with our old TT & 13k btu AC.

Sushidog · RV-Dreams Family Member

WendysPhotos wrote:
We were just going to build one of these for hot days. Since it can be run by 1 little window solar panel. We figure we will have a couple of jugs stuffed in the freezer for it. Since a full refrigerator/freezer is more efficient anyways. I had one for my horse trailer and it worked well to keep temps down. Not the awesomest way, but it helped. I used ice jugs from my cooler that I froze ahead of time. It would not probably work for extended use, but if you were boondocking and on a couple of days the temps spiked it would help.

https://www.youtube.com/watch?v=HxSLbpAwibg This is a youtube video that shows how to make a bucket air conditioner out of a 5 gallon bucket and a small fan hooked to a little car window solar power charger. There are several others along this line too.

Wendy

That's funny. I'm sure it would work for a couple hours, sort of like a swamp cooler with a little thermal assist, but what do you do after your ice melts? That ice can't have many BTUs (only 144 BTU/lb to melt ice according to the literature) to last very long.

If someone were to camp a lot in dry deserts, then this is another viable option: http://www.turbokool.com/ It only draws 4.6 amps at 12v = 55 watts - 1/10th the power draw of even the $1,800 high-efficiency heat pump. It won't provide heat in cold weather like the heat-pump does, though for only $643 it's not bad for cooling 20-25 degrees in dry weather, if you have enough water on board to keep it working, (typically over 10 gallons/day) - that's a lot of water hauling. In Louisiana where I live, where the relative humidity ranges from between 50% and 90% it would prove useless except to grow mold and other fungi. Now if you wanted to raise mushrooms....

One might be tempted to try to use one for supplemental cooling in dry climes, say in addition to a high-efficiency AC, stretching its effectiveness. Though this particular AC only removes 1/4 gallon of water per hour. I've done some calculations and a swamp cooler of this size should use about 1/2 gallon of water an hour - no wonder they don't mention the water consumption rate in their literature. So what happens to the extra 1/4 gallon/hr that the swamp cooler adds to the air when the AC cools it off? I'm sure the air would quickly become saturated with water and the efficiency of the unit would drop to the amount the AC could remove. In short, in a closed system with an AC, you would be cool for a few hours until the air got saturated with water and the dew point reached, then it would either rain inside or all your walls, counter tops, etc would be moist with water! I'm afraid you must choose either one or the other, not both.

Chip

Sushidog · RV-Dreams Family Member

waltben wrote:
RVDude wrote:
Here's the math... You decide.

I'll convert everything to watts as that way we don't have to deal with X amps @ 12v vs Y amps at 120v issues. Or whether it's volts AC or volts DC.

A 13,500 - 15,000 BTU A/C will require about 15amp at 120v. I would suspect that in your intended mode of operation the AC will run flat out during the 4-5 hour operation window. Hence, the 15amp load will be constant for the entire let's say 4 hour operation window.

Amps * volts = watts (in general) so 15 * 120 = 1800watts * 4 hours = 7200watts-hrs (or 7.2kw-hrs.) to run the A/C for 4 hours.

A typical solar panel (like Howard installed) provides about 100w ea. and let's assume 6 hours of good sunshine a day, so that's 600 watt-hr per panel and you'd need 7200/600 = 12 panels (given a perfect world) just to recharge that battery bank.

This is all assuming a perfect world. Inverters are only 80%-95% efficient (meaning they will use more wattage than they are delivering). Hence, when on inverted AC - drawing from the battery bank - you'll be drawing more than 7,200 watt-hr more like 7200/~80% = ~8,000 - 9,000 watt-hrs.

The charger is itself only 80% efficient or so and this means that to recharge will require more input watts than you get in charging output. So you'll need to 9,000/~80% = ~11,000 watt-hrs to recharge. (BTW, Now we are up to 19 panels).

The solar panels are probably not going to give you full rated output for all 6 sunshine hours unless you have them tilted and tracking the sun. Add even more panels for poor sunshine.

Well, I think you get the picture. Can it be done, certainly. How much roof space you got on top of your rig? And all the above just for 4 hours of A/C operation!

Remember, the microwave may take about 10amps at 120v (1,200 watts) but it'll only be running for a few minutes, not hours. A TV takes only a hundred watts or so it can run for hours.

Load and amount of time the load is used are the two parameters to consider.

-- Edited by RVDude at 00:22, 2008-05-10
Everything's good except your statement of 15 amps for an AC is only at start up. I've measured my 15k btu unit with a Kill-A-Watt and it pulled 14 amps for the first 30 seconds or so and rapidly dropped to about 8 - 9 amps while running on a 82 degree day with 70 percent humidity. This was measuring at the power to the 5er after subtracting phantom loads monitored before turning on the AC. With my four T-105s fully charged and 3kw inverter, I could run the AC for a half hour plus (not that I'd ever want to!). Given enough battery bank, one could run their AC for a few hours, but certainly wouldn't recharge them all that quickly. It's the starting up load that kept me from running the Monty's AC from a single Yamaha 2400 when I'd done that for years with our old TT & 13k btu AC.

You are correct. It would be difficult to do with a typical RV roof mounted AC. 9 amps x 120v = 1080 running watts. The high efficiency 48v DC AC (actually a heat pump) I posted only draws 500 watts to make 12,000 BTUs of cooling ((60 watts on start-up) plus being DC you don't suffer the 15-20% power loss due to inverter inefficiency. This means that it is uses half the power of a conventional AC to make the same amount of cooling. The advantage of powering off of a battery bank is that it can give that start-up surge for a few seconds without seriously depleting the batteries or requiring extra battery capacity just for start-up. If 4-150 ah 12v Trojans are hooked up in series to provide the 48 volts and the DC powered AC draws 500 watts at 48 volts = about 10.5 amps. Now you only have about 75 amp hours available because you normally don't want to deplete your battery bank over 1/2 (except in emergencies). So if we have 75 ah/10.5 amps = over 7 hours of air conditioner run time. If we're willing to go down to 40% of battery charge occasionally, then we're looking at 8 1/2 hours of AC run time before recharging. Now it's unlikely that the AC would run continuously for 8+ hrs and not reduce its BTU output because as your room cools off less output is needed to maintain a constant temperature. Note: this type of AC doesn't cycle on and off, but ramps up and down BTU output (and power consumption) altering compressor speed as needed, reducing power surges for start-ups. This means that real world battery draw would be less (and runtime more) than one might think (depending on you insulation and the area you want to cool - in my case, just the bedroom for sleeping.

Chip

-- Edited by Sushidog on Thursday 24th of July 2014 03:26:19 PM

-- Edited by Sushidog on Thursday 24th of July 2014 03:34:41 PM

Sushidog · RV-Dreams Family Member

biggaRView wrote:
Gonna have to go read up on the 30% tax credit... to see how we can take maximum advantage. Hopefully it will still be in effect when we go FT. I wonder if a system useful and deployable on a 5er could be set up at home(S&B) then ported over to a 5er.
Brian

BiggaRView, the current solar tax rebate is set to expire in 2016 unless renewed or replaced with another rebate. I understand that your RV is considered a second home and is elligible under the current program. I may be out of luck though, as I'm not planning to go FT till 2017. But I still might not be ready to buy my solar/boondocking equiptment till 2020 when more funds are available.

Chip

Terry and Jo · RV-Dreams Family Member

Therein lies the problem with regards to reviving an old thread. This thread was started way back in 2008, and technology may very well have improved since then. I imagine that RV Dude's numbers were correct in 2008. If one doesn't look at the date that the posting was made, one can easily get wrong information. When an old thread is revived, so many people suddenly believe that everything in that thread is recent.

So, as a FYI for everyone, please try to post only on current threads and don't revive old ones. If one want to "link back" to an old thread in one's new thread, that is fine, but kindly inform everyone that the link is to an old thread and that some information at that link may be outdated.

Terry