Written At 18,000 btu/hr, I'm guessing this is either a window unit or a PTAC.  Typical efficiency for PTACs range from 9.4 to 13 EER.  Let's use 9.4, since it is the least efficient.9.4 EER = 1.28 kW/ton = 0.000106 kW-h/BtuWe are looking at 1 hr (demand) and 18,000 Btu, so the peak energy consumption for the unit at AHRI standard (ANSI/AHRI/CSA 310/380-2014: Standard for Packaged Terminal Air-Conditioners and Heat Pumps (CSA-C744-14)) rating conditions for that unit is:0.000106 *18,000 = 1.9 kW  or for 2, that would be 3.8 kWBut that still doesn't answer the question completely.  AHRI 310/380 assumes an outdoor air condition of 80F (26.7 C).  If the actual temperature you are experiencing is higher than that, the efficiency and capacity will be reduced.  That means it will take more electricity than 3.8 kW to get the units to run and they won't be producing 18,000 btu/hr any more.On top of that, the comment Mr. Lawrence left alludes to the second problem, namely will the sun be shining at peak power when the air conditioner is seeing its greatest load. 

The answer is likely to be "no".  For further information on that see my answer to: When  will the time come when some air-conditioning manufacturer realises  that since air conditioning is most needed when the sun is at its  hottest, the whole unit could be directly powered by the sun?So the answer is "maybe" but depending on the efficiency of the A/C units, you may have some times when there is insufficent power to run 1 or both.Written Here you can convert BTU to Kw in this linkBTU/hr to kilowatts (kW) conversionsince you have two 18000 BTU air conditioners i guess you would need a 12KW system.. but also be aware that when i say a solar panel is of 10W, it means that it only gives 10W at the maximum sunlight.. the power depends on the amount of sunlight , depending on the sunlight, the current changes drastically.Briz Solar Powered Window Air Conditioner Concept We just dissembled and stored away our bedroom window air conditioning unit, a bit of a pain in the behind, but necessary as autumn weather starts letting itself be known in our area.

Wouldn't it be nicer if your air conditioner wasn't an ugly and loud appliance and instead was integrated into the shape of window blinds? Oh, and it would also be solar powered, so no need for power cords! Designers Nari Kim and Pullip Lim envision their air conditioner to operate even while the windows are open: By installing Briz on the windows, which is operated by solar power, fresh air can be supplied as water runs through both tubes beneath the bottom part of the blinds emitting dry mist (fine water particles). The evaporation heat caused by the dry mist cools the hot water that enters the window. This, instead of artificial cold wind, natural fresh air that like the breeze of the forest can be supplied by using this system...[without] worry about the expensive electricity bills because it operates only on solar energy. Sounds a bit like a miniature swamp cooler, but in a smarter, space and energy efficient form. More about this air conditioning concept at Yanko Design.

8,192 posts, read 23,724,630 times 3,040 posts, read 8,930,309 times Originally Posted by Racelady88 115V x 15A = 1725 Watts Due to inrush (starting) current, you will want to go at least 25% bigger. I would recommend one even larger than that, probably something around 3000 Watts, though you could probably get by with 2500 Watts. These are for peak load ratings. how to test an ac unit capacitorSustained load ratings should be around 2000 Watts.hvac package unit reviews Don't forget that with a window type A/C unit, you will need to mount the shell of the unit outside the van for proper venting of the hot exhaust air. ac unit disposal nycThis will most likely need to be out the rear of the vehicle so it doesn't protrude beyond the sides of the vehicle into an adjacent lane.

Also keep in mind that if the inverter is being run off the starting battery that it wouldn't take long for the battery to drain to the point where the vehicle won't start. You will most likely want to be sure that there is a separate battery for the inverter, and that it is isolated from the starting battery so the ability to start the vehicle isn't compromised. You'll also want to be sure that the vehicle's charging system is adequate. Also remember that in order to keep the batteries charged in the vehicle, the engine will need to be run long enough to recharge them. 4,515 posts, read 17,060,880 times Originally Posted by jdavid93225This is what I needed to know. I have a brand new deep cycle RV/Marine battery to push the inverter. The unit is going to take the place of one of the rear windows. He is going to be so excited to have A/C. 3,020 posts, read 20,105,444 times 3,460 posts, read 3,731,105 times 1800 Watts at 12 volts would be 150 Amp draw on the alternator/battery....ouch

I'd look at one of the RV units runner mentioned. They should already be set up to run on 12 volts. A ROOM AIR CONDITIONER WILL ONLY WORK FOR ABOUT 20 MINUTES OR LESS ON BATTERY POWER FROM TWO BATTERIES. A single battery might not even provide the amperage to start the AC after the first couple uses. Boy times have really changed... When I bought my Statpower 1500 I paid almost a $1 a watt all those years ago... If you are really serious about finding the most efficient A/C... you need to look at some of the marine units... start at a place like West Marine... I think they have several offerings in the Master Catalog...Our ultimate goal is to make the Airstream Off-Grid not relying on gas, propane or electrical hookups to meet our needs. During the warmer summer months the Airstream can get pretty warm inside – especially when in full sun! (Aluminum is a VERY good conductor!) With the weather heating up we began to look at different cooling options. Is it feasible to cool our trailer with an electric AC powered by the sun?

What other cooling options are there? Read on for the answers to these questions. The Land Yacht was originally outfitted with a AC-powered roof-top air conditioner. It seemed to function well but it was large, heavy and in my opinion made the exterior look like dump. (Especially after gale-force winds across the Montana plains stole the plastic shroud.) Given these facts plus wanting an off-grid solution I decided to remove the roof top air conditioner. I added a roof vent to the opening where the old AC was installed so if we decided to upgrade to a newer, slimmer, unit we could easily remove the vent and install the new one. Plus the vent adds some nice light and additional ventilation. I originally thought we would forgo an air conditioner altogether…the northwest summers are mild (with only a few short weeks of mildly uncomfortable heat) and the time we would spend in hotter zones would only be during mild winters. I installed two Fantastic-Fans (one in the front and the other in the rear) which can really move some air.

I thought this would suffice… I quickly changed my mind as summer set in! Aluminum is a fairly good conductor of heat and when the Land Yacht is exposed to long periods of hot sun the interior is like an oven. Our dual set of fantastic-fans was no match for the sun radiating through the aluminum! Trying to have a toddler nap in an aluminum can in the sun is not a good idea. With this shift of thinking I began looking into various cooling options… I had seen on the Air-forums people tactfully installing window air conditioners. I liked this option given the Northwest summer climate…we could install / use the air conditioner in hot weather then remove it altogether when not needed. My next question was, “Is there a good DC solar powered off-grid solution?” While there appears to be decent DC powered air conditioner technology it is expensive and I haven’t found a suitable non-permanent window solution. Until I find a fitting and affordable solution I purchased a small 6500btu window unit and I am going to run some tests to see if it would be feasible to power the air conditioner through an inverter with our future solar array.

Update: After doing some math its not feasible to consistently cool the Airstream with our window unit. See the usage data below. We purchased a fairly cheap 6500 btu air conditioner for about $150 from Costco. If I was a little more patient I could have purchased a AC off of craigslist for about $75-$100 but we were going on a road trip and the weather was going to be HOT. I wanted our window air conditioner to be easy to install and easily stored when not in use. The brackets I made to hold the compressor are pretty basic…a piece of wood that that has notches router’d out to fit on the bottom of the window, a little support from the propane tanks via a threaded piece of steel plus a little foam and we are in business. Can’t be more pleased with the setup! When we need the AC we simply throw it in the window, no bulky box on the roof and it does a good job cooling the trailer! The AC uses almost 5amps AC. Convert this to DC Amps and you get 45amps. This means the AC would draw 270ah to run 6hrs per day.

To only run the AC for 6hrs per day you would need over 500 Watts of Solar Panels + 540ah of battery capacity. For our setup this isn’t feasible. In the future when we have more of a permanent setup an electric AC may be feasible with a larger solar setup. Meanwhile here’s our plan to cool the Airstream Off-Grid. When we purchased the Land Yacht it had a large Coleman AC unit on the roof that worked fairly well. But this unit was big, bulky and the plastic shroud that covers it blew off in HIGH Montana’s winds as we drove it across country. So the fact that the AC is big, ugly and to replace the AC shroud would not be cheap ($200+) we decided to remove it. Here is our plan to keep cool during the summers: We installed 2 Fantastic fans (one at the front and one at the rear) in the trailer. These fans can be powered by our solar battery bank and can really move some air which will help us stay cool(er) and comfortable during the warmer months. (We plan to spend our summers in the NW which is very mild during the summers but the Aluminum can get pretty hot.)