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Using mini split AC as energy storage/dump load

apctjb

Solar Enthusiast
Joined
Jun 16, 2020
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In the summer months my off grid system (5.5kw PV; 32kwhr battery, 6kw inverter) has the capacity to produce more energy than my system consumes. On most days my batteries are fully charged by 11am and my PV MPPT charger (2- Growatt 3000 LVM) will start limiting energy harvest for the remainder of the day.

To increase energy harvest I have been experimenting with running my mini split AC's during the day to utilize the excess power my array can produce. On the graph below you can see AC's coming on in the morning and off in the evening. (Load (red line) is 2x what is shown on graph as there are 2 inverters). The second graph is without running the AC's to illustrate the difference in energy harvest.

But here's the rub, I don't really need the AC's on during the summer as this is a second home and I am not there much in the summer, so one could argue that the extra energy harvested is going to waste anyway. Running the AC's keeps humidity levels in the house lower, and minimizes daily temperature fluctuations (inside gets hot during the summer, really hot at times). The downside is it puts extra load on the inverters and more hours of operation on the mini split. (I have no idea if running inverters or mini splits more hours a year materially shortens their useful lifetime, or not)

So curious to hear what others think about running AC's as a method to increase energy harvest and the tradeoffs of running AC's more time than they really need to run.

One last comment; these new inverter based mini splits are pretty amazing. Soft start, variable power levels, programable, and Wi-Fi enabled so I can control them with an app on my phone 2000 miles away. Never thought I would would have AC's running on a simple off grid solar system...

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i like your graph same as mine 3kw with only 12kwhr but 300AH useable bat walmart everstsart 29dc MAXX 24 pcs of them and producing 12kw max that ive seen....
question have you use a DIVERTER they call? i have my bulk at 55 and float at 54.6..i bought another inver 60AMP makeskyblue or something just so i can add 2000kw of solar panel to get 5kw so my growatt spf 3000 lvm ES wont be working too much ill let the other inverter work more
 
Right now I use my outback fm80 that triggers my water heater when battery reaches float. I’d really like to trigger my air conditioning when the water heater is no longer using power if the battery is still in float. I just don’t know how to implement that.
It would also kinda bother me to run an air conditioner when it doesn’t need to be on, although if it was keeping the house I live in cooler then it wouldn’t be wasted
 
That’s great!

The only downside I can see, you have already identified, is more runtime on the AC and inverters.

I am thinking of doing the same thing. Around here (Texas) the inside of cars can get to 130F+. There is some advantage to keeping temps and humidity down in the cabin.

Nice to see it working so well.
 
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In the summer months my off grid system (5.5kw PV; 32kwhr battery, 6kw inverter) has the capacity to produce more energy than my system consumes. On most days my batteries are fully charged by 11am and my PV MPPT charger (2- Growatt 3000 LVM) will start limiting energy harvest for the remainder of the day.

To increase energy harvest I have been experimenting with running my mini split AC's during the day to utilize the excess power my array can produce. On the graph below you can see AC's coming on in the morning and off in the evening. (Load (red line) is 2x what is shown on graph as there are 2 inverters). The second graph is without running the AC's to illustrate the difference in energy harvest.

But here's the rub, I don't really need the AC's on during the summer as this is a second home and I am not there much in the summer, so one could argue that the extra energy harvested is going to waste anyway. Running the AC's keeps humidity levels in the house lower, and minimizes daily temperature fluctuations (inside gets hot during the summer, really hot at times). The downside is it puts extra load on the inverters and more hours of operation on the mini split. (I have no idea if running inverters or mini splits more hours a year materially shortens their useful lifetime, or not)

If you were living there you would have it on every day, no? An A/C system should be designed for continuous use. Of course, quality is not always equal. YMMV. If it were me, I would harvest the energy and let it do what it was installed to do.

So curious to hear what others think about running AC's as a method to increase energy harvest and the tradeoffs of running AC's more time than they really need to run.

One last comment; these new inverter based mini splits are pretty amazing. Soft start, variable power levels, programable, and Wi-Fi enabled so I can control them with an app on my phone 2000 miles away. Never thought I would would have AC's running on a simple off grid solar system...

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Nice graphs.
 
Like you, we have mini splits, and they are in addition to our hydronic heating system. My understanding is that it is advantageous to run them at the slowest possible speed, on a nearly continuous basis. There are many, many devices that actually suffer from non-use. Turning them on and off causing thermal cycling that affects solder joints, etc.

I'd use the mini splits in the manner you are considering.
 
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