So Swing....Is -5 or -10C your Winter norm, or your "extreme " like it is here for me?? I ask since NONE of the DC units are specifically Cold-Climate?? As you indicate, sure the standard units operate that cold, but their COP will be gradually dwindling towards 1.0 / resistance heating (You indicate you don't have enough AC power for THAT though)
Edit: A giant flipside would be a Mitsubishi or any other properly designed Cold Climate unit will be running resistance pan and compressor sump heaters at those temps.
Maybe leading you to Inverter/Battery -> Mitsubishi Cold Climate if power efficiency is your goal?? Although installed / warranted cost for Mitsubishi can be 5-10x others...
You haven't mentioned COST so not sure if that is a parameter for you.
-5 or -10C is rare in these days but happens at least once a winter. Typically more like 0 to 10C
I have been working with mini-splits which still provide a reasonable COP in those temperatures and typically keep working until -15C. The Hotspot also works until -15C I have read, but I would like to know either the COP or the heating output at -7C. Because -7 is tested for a lot of heatpumps and minisplits.
But probably it isn't available for these DC minisplits.
Anyway, maybe I get some useful data from Hotspot or Deye.
I am willing to offer a bit of COP in low temps for the overal idea of the house to work. But if the numbers are bad and the units are noisy, then we are just making life hard for ourselves.
There is AC power available from the grid, it would just be about using the lowest entry connection to the grid that is available. That saves some money, but more importantly is welcomed a lot in this day and age because of all the grid congestion that we have.
So I am looking at it from a wider perspective, and this would be great for holiday homes and tiny houses.
In that sense I'm doing this project also a bit as a study.
Basically I am trying to sell the idea of a 48v DC (holiday) home, with battery and solar, and the tiniest grid connection. Which works for these small houses with most of the tech in one area (short cables for the power hungry stuff)
If there seem to be too many obstacles, the second best plan is the complete opposite. Completely hooked onto the grid, everything AC, possibly even without solar, and just use the cheapest hourly prices in the day.
Both options work great for a home that is usually rented out in the times that energy is more available and cheaper.
When it comes to cost, at this point I think there won't be much difference in cost of importing a Hotspot minisplit than to just install a regular good mini-split and an inverter. It could be that something like the Deye 48v minisplit or some other comes around much lower than the Hotspot, for the whole thing to become cheaper.