Mother Earth News Blogs > Homesteading and Livestock

Homesteading and Livestock

Self-reliance and sustainability in the 21st century.

My Off-Grid Solar-Powered Air Conditioner

air conditioner

I always thought “air conditioning” and “off the grid” didn’t belong in the same sentence, unless it was suggesting that you COULDN’T have air conditioning off the grid. But like so many things in my life I have discovered that foundations can shift and reality can be altered.

Since moving to our off-grid home 13 years ago we have suffered through heat waves. I am not one of those people who like the heat. I love winter. I love being cold. In the winter I can just keep adding layers until I am warm. I find heat inescapable and debilitating. Of course you can’t grow food in the winter, so summer seems like a pretty essential season. But that doesn’t mean I have to like it.

I suppose if I lived in a city and had an air conditioned house, and office, and car, and didn’t have to grow food during droughts, I’d probably love summer too. But summer just wears me out. Early on in a heat wave I can still function, but after a few days I start dragging more and more. First I lose my appetite, which isn’t a good thing because I’m still burning calories working in the garden. Heat waves are usually accompanied by a drought so watering the gardening becomes a full time job. I’m in the garden by 6 a.m. but I usually can’t work much past 11 a.m. and so I have to wait until after dinner to finish up.

I think what wears me down the most is not sleeping. I end up sleeping on the couch on the main floor, which is usually cooler than my second floor bedroom, but it’s never a restful sleep. So after a few days of not eating properly and not sleeping, I feel like a dirt bag.

As I’ve described before, we have a solar domestic hot water heater that produces more than enough hot water for us at this time of year, especially since we often swim in a local lake during a heat wave, and we aren’t particularly anxious to have hot showers or baths. We also have the diversion load dumping excess electricity into a second hot water tank. So a few days into a heat wave when we are making lots of hot water and not using much, it gets scalding hot. And since these two hot water tanks are in our bedroom, they help to heat up the room just a bit more to make it really uncomfortable for sleeping. Yes, I know, what am I doing with hot water tanks in my bedroom?

Turns out when they built the house in 1888 they hadn’t considered solar domestic hot water heating. Well, they hadn’t actually even considered inside plumbing, so the only way I could configure the system was to put the tanks in the bedroom. Michelle has written blog posts about what she thinks of them. It ain’t pretty, but it works.

So this summer I said “enough!”  I bought a 5,000 BTU “Haier” window air conditioner. And it’s working great! It’s helping to make this heat wave, which is unbelievably brutal and relentless and unending, seem tolerable. I’m not eating enough and I’m spending way too much time in that relentless heat trying to grow food, but at least I’m sleeping. I have a refuge.  

I keep kidding Michelle that we need to start eating dinner in our bedroom.

I did not approach this purchase lightly. I realize that the HFCFCs or whatever the chemical that replaced CFCs is better, but not perfect. But it was $100 and it’s making a world of difference. It draws about 500 Watts of power. When the sun is out my solar panels are making over 1,500 Watts, so it’s using about 1/3 of my output. So I’m running all my other loads, including the water pump, which is going full time, and still have enough to run the air conditioner. I am not using the “dump” or “diversion” hot water heater very much, so our water is just very hot, rather than scalding.

Now Bill Kemp’s off-grid house has been air conditioned for a few years but Bill built an insanely efficient house, so I just assumed I was scuppered with one built in 1888. Bill recommended this unit to me and when he heard how well it was working he went out and got one. Here’s a quote from an email he just sent me.

“I was looking at how they managed to get so much cooling with so little energy. A very simple design takes the water removed from the air and pumps it over the condenser radiator (the hot part that blows the heat outside). The water dripping over it cools the unit as the fan blows the heat away. Same process as how the human body cools itself. Funny that no one thought of this until recently???”

This is what I love about knowing Bill. He buys stuff and takes it apart to see how it works. His wife Lorraine calls it “MacGyvering” stuff. But then when he figures out how it works he can describe it with analogies that I understand.. i.e. the air conditioner works just like you sweating. Now that I can get.

When we first started using it Michelle commented that it couldn’t be dehumidifying the air because it didn’t drip water out the back like all of the other AC units we’ve seen in action.

So the heat wave continues and I am getting a reasonable amount of sleep. My grass is brown. Any plant that doesn’t produce food is in crisis and is not getting any water. Trees are dying. Toronto, which usually gets 74 mm of rain in July, has had 4 mm. My gardens are crying out for rain. All I can give them is well water from the house and drip-irrigated water from the dug well in the vegetable garden. But all my food crops are doing OK. You can tell that at a certain point a lot of activity in plants shuts down when it gets too hot. They just can’t function properly. I’m hoping for a bumper crop of “tropical” sweet potatoes and peppers and all my heat loving plants. There has to be some upside to these summers.

And thanks to my “off grid, solar powered, pretty environmentally friendly and efficient air conditioner,” my personal “feeling like a ‘dirt-bag’ factor” has been remarkably reduced. And all off-grid! Who’d have thunk it! What next? Maybe an electric car I charge off the system! The skies are the limit now!

Photo by Cam Mather. 

For more information about Cam Mather or his books please visit or 

3/3/2015 2:20:44 AM

here's a vid about solar powered air conditioners

9/11/2014 10:33:29 AM

Is there any way I can cool a car in the summer, enough that I can leave my pets safely?

5/23/2014 7:14:19 AM

All window units use condensate water produced from the evaporator to cool the condenser. It's not at all a new idea.

2/24/2014 3:10:36 PM

I do the same with my house unit in the summer. I set up a mister ($30 at Home Depot) to spray water on our coils in the heat of the day. I plumbed a connection from our yard sprinkler system and programmed it to come on from 11am to 6pm. You can feel the temperature of the air coming out of the vents drop quite a bit when the water comes on. Really helps suck the heat out of the coils. I see about a $5 difference in the water bill per month but save a lot more than that in electricity by the increased efficiency. Another thing I did to help was to build a shade over the AC unit with some Solar Screen material ($70 including lumber). I put it up at the roof line so there's no interference with the hot air coming out of the top. The biggest drop I got in electric bill though was tinting the windows on the house. Used SolarGard Silver 20 (80% heat block). Cost was about $1,000 for the whole house but it dropped our electric bill by about $50/mo. Payback is every 1.8 years. Did that 5 years ago so we're about $1,000 ahead now. Even our rooms that face North got quite a bit cooler. We're in North Texas and never get any sun on North windows in the summer but it cut the reflected light/heat by a bunch. This was a much bigger savings than the neighbor that that got new vinyl windows last year for $8,000! We took 2 other steps to cut our electric bill. Both were pretty cheap and easy. We put in a small, Energy Star window unit ($200) like the one in the article in our bedroom. That way we could run it at night and not have to cool the rest of the house. We also put in ridge vents and doubled the number and size of the soffit vents to increase ventilation in the attic ($85 and we did the labor). Our attic is rarely more than a couple of degrees warmer than it is outside now. With all of these simple improvements, we have cut our electric usage in about half of where it was 5 years ago. The biggest factors being the window unit, we got an 8,000 BTU unit that draws 514 watts, and the window tint. The sun is pretty brutal here in North Texas but we were able to get 5 months last year where our electric bill was around $50. Max for the year was in August at $200. A lot of our neighbors hit $450-$500! We do have gas water heater and furnace but we also have 2 teen-agers still at home. We keep the thermostat on the big unit at 75° and the bedroom at 70°. You don't have to do it all at once. Just pick a project each season and by this time next year you will be seeing quite a difference.

brad morton
4/1/2013 4:54:20 AM

Can you give an idea what kind of solar power system you have? In otherwords, how many solar panels and what size do you have? How many batteries do you have? I want to do this badly but am fearful that I will spend thousands of dollars just to keep my off grid man shack cool in the Tennessee heat.

3/24/2013 3:00:56 PM

Well, if its drawing 500w at 120v, then its going to need roughly 4.16 amps, so at 12v bank, 45ah to be your looking at what? 275ah total? Thats my math but im not sure, I knoe it could be less but I round up if my formulas r correct

janice sanchez-arteaga
8/6/2012 12:06:22 AM

swamp coolers which have been used in the dessert work the same way. I also saw something cute at a disney park where you have a block of ice and blow a fan across it. Pretty much all in the same concept!

matt carey
7/31/2012 5:09:17 PM

Hi Cam, Why are your hot water storage tanks giving off so much heat to your bedroom? Insulate like crazy. Its seems counter productive to use an air conditioner in a room that has two tanks of hot water bleeding heat into the room.

7/21/2012 2:50:06 PM

Why not use excess hot water to run the A/C? This must be possible since heat runs a refrigerator on those 3-way units in RVs.

maddy who
7/20/2012 10:38:24 PM

I think this is the brand/model that I read about on Amazon. People were totally freaked out that the water was staying in the unit. A lot of them returned them thinking they were defective. There probably was mention of how it works in the instructions, but of course, nobody reads anything anymore!

ben hurst
5/27/2012 6:30:45 PM

so what about running the a/c at night? What size battery bank would need to keep the a/c going for 6 hours or so?

mike edwards
5/11/2012 6:37:51 PM

I liked your article very much, but the thing that got me most was the fact that you heat hot water. You heat cold water. In a water heater