Tiny House, Tiny Living, The Tiny Life.

Air Conditioning On Solar Power

Today I wanted to share some info about air conditioning on a solar panel system.  Charlotte’s heat really came full force this week.  I know for many their climate doesn’t get as humid as it does here, for us here, AC is pretty key.  Without AC I can’t really sleep, even with a fan and my house being passive cooled.  While the humidity is still pretty comfortable, it’s HOT and the humidity is coming.  It has been in the high 80’s and low 90’s outside, which made my house in the mid 90’s inside.

I thought I’d do a post today because I’ve been able to run some real world experiments with my tiny house, the AC and solar.  I haven’t seen any real world into practice reports on this stuff, so I figured it would be helpful for you all.

I have yet to hook up my mini split system because it has taken me a long time to find a HVAC installer that would install my mini split, the reason being they all want to sell you the equipment if they are going to install it.  This was an unknown factor to me when I ordered my unit, but these are the bumps in the road you experience when you live The Tiny Life.


For heating and cooling I opted for the Fujitsu 9RLS2 which is a 9,000 btu unit with a seer rating of 27.  To give you an idea, older systems have a SEER of around 8 to 10, modern systems that are labeled highly efficient have a rating of 15 or so, but most today are around 12-13.  This is very important because me being on solar, my system simply couldn’t handle the less efficient systems.  Read about my tiny house solar panel system by clicking here.  The SEER rating is simply a function of BTUs (British Thermal Units) to Watts.  The higher the number, the better.

The other big reason I choose this unit versus a window unit was that my air handler is wall mounted, out of the way and above eye level.  This does a few things:  keeps my limited square footage clear of stuff, it keeps my windows looking nice because I don’t have a window unit blighting a good design, and keeping it above eye level also makes you forget about it because as humans we don’t often look up.

el_pac_08e9_unit_picWhile I’m trying to get an installer lined up I’m using a Portable Air Conditioner which has worked pretty well.  The downside to it is it takes up a lot of space and it’s not as efficient; it has a SEER rating of 12, which makes my mini split system 225% more efficient than this.

I decided to “stress test” my system by turning the Portable AC unit on high and setting the thermostat to 60 degrees and see how long it was going to take for my batteries of my solar panel system to bottom out (50% discharge).  The charge controller on my system automatically turns off the power to my house if the power in that batteries discharges down to 50%, this allows me to not damage the batteries by discharging too deep.

batter tiny house discharge

As you can see by the chart above, keeping discharge at 50% or above gives me a little shy of 2,000 cycles or 5.4 years.  I plan to add another set of four batteries to the system pretty soon, which will give me a good capacity and keep my discharge rate much higher than 50% (though I don’t often get that low)  In about 5 years we should start seeing some really interesting battery technologies hit market, so I plan to hop on that as soon as my batteries begin to fade.

My stress test turned out pretty good.  With the much less efficient portable air conditioner I ran it solid for 3 days starting with a very warm house.  At the end of the three days I was very close to hitting 50%, but it didn’t ever dip below.  I decided that the test went on long enough to be pretty happy, so I decided to stop.  I typically turn off the AC when I’m gone.

The past few days have been a bit trickier because since my system was so low from the stress test, I needed it to build back up, but we have had a series of cloudy days.   I’ve had plenty of power to run the AC over night, but it’s lower than I’d like.  To give you an idea, on a normal sunny day I make about 8,000 watts, on a cloudy day I get between 2,000 and 4,000 watts when the clouds are very thick with no gaps.

The really great thing is when it’s hottest, during the day, I can make lots of power.  This allows me to run the AC full blast and I can make enough power to run the AC and still be dumping 1000 watts into the batteries.  Compare this to heating, you most often need the heat at night the most, which is when the sun isn’t out, so its a major drain on your batteries.  To compound the issue of heating, heaters are often more energy intensive than cooling.

The other night I tried an experiment.  I got my house very cold and turned off the AC at midnight (when I usually go to bed).  Outside it was pretty cool, about 65 degrees and about 45% humidity, so not bad.  I left all the windows closed to see how much my body heat would heat up the house and because in the summer, opening the windows doesn’t help even if it is cooler outside because the humidity increase the “feels like” temperature.

As it turns out in just three hours my body heat warmed the loft of my tiny house up to the point that 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 that I’m one that when I fall asleep, I stay asleep all night, even if I get warm, so the fact that I was woken up goes to show how uncomfortable I must have been, because it takes a lot.

I had prepared for this and all I did was crank open my sky light (the highest point in my house) and the loft end window and 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 some of my real world experiences with the tiny house, AC and solar.  I know I had always been frustrated by not enough stories on this stuff, so hopefully I can help others.

Some key resources for those wanting more technical stuff


  1. Good stuff. Thanks!

    Where are you located? I’d be happy to help with installation of new system, but may be too far away…

  2. Thanks for doing this.
    So few with tiny houses go for independent energy. The AC is the first thing you give up because of the enormous cost. My 500 watt design would never make it. I’m hoping to supplement that with a generator when it’s so bad I can’t stand it. (Only about two weeks a year it’s that hot/humid in Ohio.)

    A quick search puts the Fujitsu at ~$1500 on the smallest model.
    9000 btu is still overkill for me, but the efficiency is hard to beat.

    • You must be a glutton for punishment! I live in southeastern ohio and I LOATHE heat and humidity! I certainly suffer from humidity issues tons more days than 14 or so….

      • No, I just do a LOT of things to keep the house cool without running the AC.

        Opening the windows at night goes a long way to help.
        The ceiling fans help too. 🙂

  3. Hey Ryan,
    Have you tried advertising for an installer on a goods and services website, in Australia we use Gumtree. That’s how I found a local guy who worked for a bigger company but did mine on a weekend. If the local companies have declined to fit it for a reasonable price you need not feel guilty. Just be sure he has the vacuum pump and gauges and that he is willing to come back if you have any issues.

  4. Hi Ryan,
    I too have learned this the hard way regarding if you don’t buy it from them they don’t want the jobs. But I have just told several of them to stuff it! I am not paying 2x for a unit for them to make extra money! Don’t want the job? Fine! As a previous posted stated, have you checked into local job walls or ads or craigslist?
    Thats how I found mine. and I got a rheem tankless hot water unit for the new house for $998 on sale at Home Depot that would have easily cost me more than 2x that much from a local plumbing contractor. I know I know, its how they make their living, but I like most of us have a super tight budget..
    New small house is moving right along, slower than I would like but we should be painting by the beginning of next week and hopefully moving in 2 weeks.
    Thanks for all your great info! Without you I would never have jumped into this the way I have!!

  5. Would give anything for a bit of heat and humidity. Over here in the UK (up north) it’s still like winter!

  6. Great information, especially about the SEER numbers– thanks! Have you checked YouTube for installation videos for a mini-split? We found some really good ones, and the mini-split wasn’t hard to install at all– even for relative beginners with only basic carpentry skills.

  7. Installation yourself isn’t that difficult. Assuming it came pre-charged, you don’t even need to pull a vacuum (the air in the lines and indoor unit will be <5% by mass). The only tools you'll need (other than for mounting the units) is a pipe cutter and a 45-degree flare tool (both together <$50).

  8. Thanks, Ryan, for the great information. I’ve become totally intolerant of temps above 80ª, and hope that I don’t need this, but I’m glad I know where to reference if I do. It’s been heating up here in the PNW in recent years, too.

  9. Have you tried shades, curtains, leaving windows open at night and not sleeping in the loft?

  10. Ryan,
    I’ll chime in here on the topic, because I have used mini split air conditioners (some with heat pump capabilities for the winter) for the 9 years that I lived in Mexico in the state of Sonora. I’ve lived in the desert, both along the sea of cortez and the high sierra madres (which are hotter than you would think they should be in the summer before the monsoons arrive).

    Our first home in Mexico was just a tad over 400sq ft.. It was a size / design common throughout Mexico, often refered to as Infonovit houses (Infonovit is a gov’t burrowing program to help home buyers…obviously most poor families purchase the tiny 2 bedroom casitas.. hence the name). They are made of narrow concrete blocks with concrete floors, concrete ceilings and single pane windows. Yes, without mini splits.. they bake in the summer. It’s brutal.. That first home required two mini splits… One for the two bedrooms.. One for the common areas (kitchen/dining/living).

    We found we could place them in Dehumidify mode and it conserved energy and the house became comfortable… We also found with the air dry in the home, that 80degF felt very comfortable indoors.

    I have used several brands, York (way too loud), Japando (good when new, but it’s performance seemed to deteriote after about a year.. even with good servicing) and Mirage. Mirage was so good, that we purchased several different units over the years.. In Mexico, that brand enjoys good distribution, so repair/replacement is quite easy and affordable. The prices of mini-splits in Mexico is about half the cost of those in the USA.

    Couple of other lessons learned… Don’t install the compressor unit in a direct wind stream… If you have a prevailing wind, try to orient the unit so that it does not take that wind directly (obviously on the sea of cortez, the offshore winds were strong… even miles from the sea where we lived). Another help is to build a small roof shade over the compressor unit. Don’t let the compressor take direct sunlight. Just a roof is sufficient, you don’t need to enclose it (in fact you shouldn’t).

    Awnings to keep hot sunlight off of your windows and front door during the hottest part of the days helps immensely… Windows and doors are poorly insulated in relation to the walls.

    Granted, my conditions were a bit more extreme with regards to heat.. maybe a little less with regards to humidity.. (I’d have to check, but I’m pretty sure Charlotte, NC gets more humidity than Guaymas, Sonora).

    When someone installs your minisplit… They have to evacuate the system thoroughly…. achieving a negative pressure (just like you would with automotive AC systems).. before charging with the refrigerant.

    One thing to get used to with a mini-split… a factor that contributes to it’s higher seer value… is that there is no air-makeup…you are always recycling the same interior air… When weather permits, you’ll want to shut it down and open a few windows with a fan running to change your air out.

    Sometimes the condensate drain can slow down as it accumulates mud… this will result in the interior portion of the unit spitting a little moisture… Don’t put anything directly in front of it that can’t handle an occasional spritz… It’s an item that you have to keep up on if things get a little dusty in your area.

    We now live in Arizona (still in the Sonora Desert), just north of the border. We and are blessed that our pueblo styled town home (about 1200 sq ft) stays cool enough without AC so far.. Good enclosed pations, front and back.. as well as a few mesquite trees on the south facing side probably helps as well. Previous owners installed a heat pump on this home, so that will be a new experience for us when we fire that up in a few weeks.

  11. Hey Ryan,

    This article is very usefull, if you do not mind can you take a wattage reading on your portable ac while it is running? I have looked online and it seems like the numbers vary wildly on how much energy HVAC systems use. We know what the manufacturers SAY it should be but it helps to have a physical example. Another question that I have is do you do your laundry in-house? Washing does not use much energy but drying can be very energy intensive. If you would I was hoping you could get me a wattage reading on your dryer too.


    • Mine uses 600 watts, its a soleus air portable unit, don’t know the model number.

  12. I can run my 8000 BTU A/C unit on the few days it is really needed and cool down the 136sq ft rather quickly by use of bamboo shades which are rolled down to cover all southern exposure windows. The need for greater battery capacity is greatly lowered.

  13. Ryan,
    Sorry to hear you’re having a hard time getting your A/C setup. I too have trouble sleeping in the month or two that it just stays a little too warm at night, but mold is the bigger issue I’m after with an A/C unit as cooling the air also allows one to remove moisture from the air when it condenses (like on a glass of ice water in the summer) on the cold coils of the air conditioner.

    I’ll be setting up my little home, alittlelivin.blogspot.com, off the grid. I plan to use this unit for air conditioning, http://www.hotspotenergy.com/DC-air-conditioner/, mainly for dehumidifying as I live in the temperate rainforest mountains of WNC and mold becomes a serious problem in the late summer.

    AC=Alternating Current Electricity
    A/C= Air Conditioner

    Pretty much all refrigerant compressors (for A/C, fridges, freezers, etc) use DC (direct current) electricity pumps. If you have an AC (alternating current, which is the standard in most houses and appliances) air conditioner unit, you will be converting the AC electricity into DC to turn the compressor pump, which is the component in an A/C system that uses the most power. Converting power from AC to DC or DC to AC always loses power, at best you’ll lose 10%. If you’re off the grid producing DC solar power, you’ll have lost 10% or more through your inverter to get AC power out, then lose another 10% or more changing that AC back to DC for the air conditioner compressor.

    I think the unit I linked above is in a similar price range ($1800) to high efficiency AC A/C units out there. It has a cooling EER rating of 18.61. EER (energy efficiency rating) is slightly different than a SEER rating (seasonal energy efficieny rating) in that a SEER rating takes into account the use of the unit for heating and cooling purposes. Modern A/C units can heat buy running the compressor pump in reverse.

    Unfortunately the Hot Spot Energy A/C unit runs off of 48VDC rather than the common 12VDC of most battery banks and DC solar appliances. To remedy this I’ll be using a DC to DC voltage converter to step up my 12VDC to 48VDC. There is much less loss of efficiency when staying with DC or AC and only changing the voltage.

    Check out the http://home.howstuffworks.com/ac.htm How Stuff Works write-up for air conditioners.

    • What a great find Keenan ! I’m a strong advocate of DC appliances wherever possible just for that reason. I built a 12v PC and lowered my AC need, so I can use a much smaller inverter. Just a refrigerator is planned for it’s use.

      The A/C will have to be run on generator or on the grid.

  14. Hi everyone.
    Just thought I’d describe my experience with my two person tiny house with AC on tiny solar.
    Location: The Kimberley, far NW of Australia. Subtropical. Hot and humid summers (25-40 C) Warm winters (15-30 C)
    AC supplied to only the studio/office space measuring 18m2
    Bedroom and open plan living area have large fine mesh wall panels to allow for sea breeze. Low power consumption Aerotron ceiling fans to these. Amazing fans.

    Tiny Solar Power system:
    12v 1000W PV array, roof mounted.
    Twin 45A Morningstar PWM regulators.
    12v 1000W Latronics DC-AC Pure sine wave inverter (can surge to 3000w for 5 sec)
    12v 560ah sonnenschien gel battery bank

    Major power loads:
    Chest freezer 190kwh/year
    Small refrigerator. 240kwh/year

    Mitsubishi heavy industries 2kw split AC unit. Average power consumption 350w. Max power draw 750w only for v short time.
    This is the smallest and most efficient available in Australia at the moment. We only use it during daylight hours so the energy is never really taxing the batteries.
    Prior to installing AC we installed an extra 400w of panels to compensate.
    $900 unit model number SRK20ZMXA
    A lifesaver in this extra hot El Niño year!
    DIY install.

  15. nice – Very nice idea… Solar with AC… i like it

  16. Any update. Did you ever get minisplit installed? Btw you can do the job yourself. Just rent the tools.

  17. I have a 74 m2 (796 aq ft) flat in Spain which I’ve refurbished to a pretty high energy efficiency standard. All the walls are well insulated, the windows are of very high quality, awnings and blinds (operated automatically by a home automation system) keep the sun and heat out as much as possible, and a heat recovery ventilation system (for summer, it should more accurately be called a heat removal ventilation system, since it cools in incoming air) avoids the need to open windows (and let in heat) to ventilate the house. At night I open the windows to allow the house to cool.

    All this is enough to prevent the house ever going over 30 degrees even on very hot days, but not enough to keep the temperature stable at 25-27 degrees, which for me would be sufficient. In hot weather (max temp 34-39C) it can gain 0.5-1 degree of heat per day, until it stabilises at 28-30 degrees, depending on the weather.

    The combination of A/C and solar panels flashed into my mind the other day and I started researching it, but it seems that for my needs all the A/C units are overpowered. If I could take just 1-2 degreess of heat out of the house during the day with the A/C, it would give me the temperature I need. Would it therefore not be better to have a very low-powered A/C unit that uses solar power exclusively, running throughout the hours of daylight, rather than a high-powered unit running for a few hours and requiring supplementary power from the grid? Most A/C units are designed to cool down a space relatively quickly, because owners switch them on when they’re too hot, and then switch them off when they’re cool enough. I would like a low-power setup that runs automatically throughout the day and delivers the temperature I want when I get home, so it wouldn’t matter if it pulled heat out of the house very slowly.

    I’m not 100% of my calculations, but an efficient A/C unit running for 12 hours at between 200-500w would probably be enough for this small temperature adjustment. Since the flat is in a block of 10, the roof space available for my panels would be limited (perhaps 4 m2 on the south side). At peak output that would give me perhaps 800-1000w, given 2x250w panels.

    My ideal setup would therefore be:
    – An A/C unit capable of running at very low (and variable?) power, using only the output from solar panels
    – The option to use grid power and higher output for exceptional circumstances (e.g. having lots of people over in the house)
    – Control via home automation

    I suspect such a beast doesn’t exist. Am I right?

  18. Panasonic have some a/c units that appear to run on less than 200 watts, after start up, when on a low setting. I am considering one of them for some background heating at home in the UK during the autumn & spring when the solar panels should be producing enough to power it and multiply the wattage by just over 4 times.

  19. We are located in Nashville, Tn. We haven’t tried any installation any solar power installation but seems quite interesting. We will do it as a test and will let you know, thanks for sharing.

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