How to Run Air Conditioning On Solar Power
When I was first planning to move into my tiny house, considering the possibility of running a solar powered air conditioner and cooling system weighed heavily on my mind. After all, living in a humid state, I’ll tell you, I’m one who can’t tolerate the heat. This is especially true, coming from New Hampshire—I’m a cold weather guy and here in North Carolina, it gets hot! An AC unit is critical, even if you’re running on solar power.
Well, Charlotte’s heat really came full force this week. I know for many their climate doesn’t get as humid as it does here, so there are other options besides running a house air conditioner. Unfortunately, here, it’s necessary. Without AC I can’t really sleep, even using a fan to passively cool the house.
Right now, the humidity is still tolerable, but it’s HOT and the humidity is coming soon. It has been in the high 80’s and low 90’s outside, which made my house in the mid 90’s inside.
So, what are the tiny house air conditioner solutions? How do you cool off your tiny house (even off the grid) and beat the heat?
Deciding to Buy a Solar Powered Air Conditioner
I thought I’d do a post today because I’ve been able to run a few real-world experiments with my tiny house and solar powered AC. I haven’t seen any experienced reporting on the topic of running air conditioning on solar power, so I figured it would be helpful for you all to hear what I did.
When it comes to cooling a tiny house, there are three areas to look at: isolation, such as shade, seals and insulation; ventilation, such as fans and setting open windows for cross-winds; and artificial cooling. Many tiny homes, by their portable nature, don’t have basements, where you can retreat if you need to cool off. Since heat rises and your entire home is above the ground, you need alternative methods to cool down.
Desert-dwellers may be able to rely on swamp coolers and evaporation-based cooling systems Here in the humid part of the world, these setups never work because our air is already humid. It’s impossible to cool humidity with MORE humidity.
Isolation, using shade and insulation to your advantage, is important if you live in off the grid. You can keep your house fairly cool by simply, closing off your space, especially in the heat of the day. This is why I decided to park my tiny house under the trees for shade and run my solar panels in the wide-open field. While these methods help and should be employed, of course, chances are you’ll still need to rely on a solar powered air conditioner system to get through the hottest days.
After doing my research on what unit would work best with my solar panel set up and power levels. I ordered my unit before I found an installer. I have yet to hook up my mini split air conditioning system (see the update below where I talk about life on solar with my mini split) because it has taken me a long time to find a HVAC installer who would install my mini split AC. As I discovered after buying my mini split unit, most installers insist they need to sell you the air conditioning equipment if they are going to install it. Obviously, this was an unknown factor to me when I ordered my house air conditioning unit…but these are the bumps in the road you experience when you live The Tiny Life.
How Much Power Does an Air Conditioner Use?
For heating and cooling, I opted for the Fujitsu 9RLS2 which is a 9,000 BTU Ductless Mini Split Air Conditioner Heat Pump System with a SEER (Seasonal Energy Efficiency Ratio) rating of 27. To give you an idea, older, less efficient mini split air conditioning systems have a SEER rating of around 8 to 10. Modern air conditioning systems, labeled highly efficient may have a rating of 15 or so, but most today are around 12-13.
The SEER rating was very important because my tiny house solar panel system simply couldn’t handle the less efficient cooling systems. The SEER rating is determined by BTUs (British Thermal Units) to Watts. The higher the number, the better.
The other big reason I choose this particular mini split air conditioning unit versus a standard window air conditioner was aesthetics. My air handler is wall mounted, out of the way and above eye level. This has a few advantages. First, it keeps my limited square footage clear of clutter. Secondly, it keeps my windows looking nice because there’s no window unit blighting a good design. Lastly, keeping it above eye level also helps you forget about it because as humans we don’t often look up.
While I’m working on getting an HVAC installer lined up to put in my Fujitsu Air Conditioning System, I’m using a portable air conditioner, which has worked pretty well. The downside to using a portable AC unit is it takes up a lot of space and it’s not as efficient. The portable AC unit I’m using has a SEER rating of 12, which means my new mini split system will be 225% more efficient once it’s installed.
Stress Testing My Portable AC Unit and Solar Panel Power System
I decided to “stress test” my solar panel system by turning the portable AC unit on high and setting the thermostat to 60 degrees. I wanted to see how long it would take for my solar panel system batteries to bottom out (50% discharge). The charge controller on my solar panel system automatically turns off the power to my house if the batteries power discharges down to 50%. This automatic shut off on the solar panel system prevents damage to the batteries by discharging too deep.
As you see by the chart above, keeping battery discharge at 50% or above gives me a little shy of 2,000 cycles or 5.4 years for the life of my batteries. I plan to add another set of four batteries to the solar panel system pretty soon, which will give me improved capacity and keep my discharge rate much higher than 50% (though I don’t often get that low). In about 5 more years we should start seeing really interesting battery technologies hit the market. This should coincide with the life of my current batteries, so I plan to hop on these new technologies as soon as my batteries begin to fade.
My solar panel battery stress test was an interesting experiment. I ran the less efficient, portable air conditioner for three days solid, starting with a very warm house. At the end of the three days, I was very close to hitting 50% on my battery reserve, but it didn’t ever dip below that threshold. I decided, after three days, the test had gone on long enough to get an accurate reading and I stopped the test. I typically turn off the AC whenever I’m gone.
Following the test, the past few days were a bit trickier because since my solar panel battery system was so low, I needed it to build back up. Unfortunately, we had a series of cloudy days, making it tough to get more energy. While I’ve had plenty of power to run the AC overnight, the battery reserve is lower than I’d like. To give you an idea: on a normal sunny day my solar panel power system makes about 8,000 Watts, but on a cloudy day (when the clouds are very thick with no gaps) I get between 2,000 and 4,000 Watts.
The Advantage of Solar Powered Air Conditioning
When it’s hottest and the sun is shining the brightest, I can make lots of power! This allows me to run the AC full blast to keep my house nice and cool. Even with the air conditioner on high my solar panel system still makes enough power to add 2,000 Watts into the batteries. Compare this to heating, where you often need the heat the most at night when the sun isn’t out. This results in a major drain on your batteries. Compounding the issue of running heating off solar panel energy, heaters are more energy intensive than cooling and air conditioning units.
The other night I decided to conduct another experiment. I got my house very cold by running the AC unit. Then, I turned off the cool air at midnight (when I usually go to bed). Outside it was about 65 degrees and about 45% humidity–so not bad. I left all the windows closed to see how much my body heat would warm up the house. In the summer, opening the windows doesn’t often doesn’t help anyway, even if it is cooler outside because the humidity increases the “feels like” temperature.
As it turns out in just three hours my body heat warmed up the loft of my tiny house to the point I woke up from being so uncomfortable from the heat! Around 3:30 am I woke up and it was very hot in my loft. I checked the time and was surprised how little time it took. I should note when I fall asleep, I usually stay asleep all night, even if I get warm. The fact I woke up from the heat, shows how uncomfortable it was in my loft because it takes a lot!
Fortunately, I had prepared for this and all I did was crank open my skylight (the highest point in my house) and the loft end window. I switched on a fan to draw in cool air. Within 5 minutes the whole place dropped about 5 degrees and I was back asleep.
So that has been my real-world experiences with the tiny house, AC units and solar panel power systems. I know I had always been frustrated by not enough stories and real-life examples of AC and cooling issues, so hopefully my story will help others.