Did you have to improve insulation or do the heat pumps provide enough power?
We have added a small solar installation (7kWp) and a battery pack (18kWh). It provides 90% of power needed in the summer and allows for decent peak shaving in the winter, to lower network costs.
Additionally we are Co-owners in a windpower cooperative that provides more than our share of electricity into the network. So we are essentially operating our home on wind and solar, as well as powering the electric car.
Unless there's a particular good reason to it's actually not too bad of an idea (with a hot water radiator loop in the home at least) to keep a fuel burning radiator loop heater around and just valve it off to not interfere on normal days. Especially if the heat pump is air source (which the mentioned swedish one isn't).
It's not that I'm against full electrification, but peak cold spell heating in excess of the heat pump capacity is among the last things we ought to "electrify by force."
We'd have massive summer overcapacity at the point where we can generally afford to "just do that". And chances are that it'd not be a resistive heater but a heat pump freezing a pool worth of water to cap the cold side temperature at just under 0C, or something the like, just because of how grid intensive the correlated load of those resistive heaters is.
It might even be cheaper to use synthetic fuel produced in summer than to 100% electrify that cold spell heating capacity. Carbon capture is expensive but there are options from e.g. domestic waste incinerators, paper making, and generally waste wood/plant matter decomposition, where hydrogen can cheaply be added to produce methane (pipes) or propane/butane (tanker trucks with liquified gas).
For example, evaporating a 40,000 L solution of calcium chloride brine can store 4.6 megawatt-hours(*) of thermal energy and release it in the winter by passing water vapour over the solution to dilute it. This can heat geothermal temperatures from 10°C to 27°C which can be used in in-floor heating.
But the big asterisk is that only 11% of that 4.6 megawatt-hours of that thermal energy being "stored" is held in the enthalpy of dilution, and 89% of that heat is coming from the enthalpy of vaporization, and acquiring water vapour in winter isn't so easy.
One would probably need a source of water and use geothermal heat to raise dry cold air temperature to the needed 10°C, while absorbing water vapour from a (relatively small) tank of water. The net result is more of a thermochemical heat pump rather than a thermochemical battery per se. But the point is that, other than some fans, this is not electrically powered.
Then there is the issue of storing such tanks safely underground, and more problems. Still, there might be some innovative solutions lying in this direction. For example, one can replace this open-loop system with a closed-loop vacuum system to boil water, but at the cost of far more complex and dangerous engineering.
In general, using heavily salted water (not sodium chloride that's quite ineffective) to dehumidify humid cold air during heating and reject heat with a wet interface without having to source potentially scarce water to evaporate, is quite an intriguing alternative to classic fan-laden AC "condenser" coils.
Incidentally, KOH is also interesting as it dehumidifies down to quite low humidity (at least indoor-facing) before it saturates (and precipitates out), and as a side-gig scrubs CO2 that can be precipitated out with CaO/Ca(OH)2 as CaCO3 (limestone).
This can be thermally recovered at around 800~900 C to essentially "boil" the CO2 off.
IMHO a chemically appropriate wet heat exchanger based on (cross flow: easy) or (counter-flow: harer to prevent droplet formation) with just a simple corrugated structured packing should be able to operate more hygienically than a theoretically dry, practically humidity-condensing classic mini-split AC coil. And allow most dust to be washed off fully automatically from normal operation. It'd "just" need a regenerator to dry out excess unwanted humidity, but I'd assume there's a reasonable way to boil off the excess humidity from the "salty water". Maybe the common reverse-osmosis filter materials can resist these chemicals; in that case it'd sound like a question of pressurization energy recovery; or it could be put under vacuum and a small heat pump could transfer the enthalpy of vaporization from the condenser [distilled water plus dissolved gasses, vacuum] (that isn't fully flooded due to presence of dissolved gasses in the feed) to the evaporator [salty water, same vacuum]. If the ratio of dissolved gasses relative to the extracted condensate is small enough, I'd guess a water jet "ejector pump" using that very condensate (after it's cooled down enough to not boil in the ejector) would actually work to provide the vacuum for continuously pumping the dissolved gasses that boil out along the humidity... A small centrifugal pump for that can easily be made completely sealed using magnets to transmit the torque to the impeller and a long life ceramic bearing, at least if there's a long enough pipe down to the pump to build minimum inlet pressure (against cavitation).
Also: For vacuum btw. remember the convenience of using gravity to pull a (nearly) 10m column of water down. Dissolved gasses are likely the dominant complication.
> 100 meter borehole into the ground
Expect to pay $10-20k for the hole but it is common in large parts of the world.
If you go heat pump + heat pump water heater + electric washer and dryer + induction stove + electric car, you might want to upgrade, depending on your situation.
I mean, sure, and a tiny one won't work for a mansion. If you're somewhere that cold, you choose a heat pump that works in that temperature range.
Could be better, could be worse.
Had the house been uninsulated it'd be another story, but such houses are very rare in the Nordics.
I've looked at improving old houses in Australia, and you would usually be better off putting the cash in the bank. (After heat pumps, and sometimes a battery).
Real question: As I understand, good insulation in your home helps two ways: Keep the heat inside in the winter, and keep the cold inside in the summer. Do I have that right? If yes, I understand there are lots of places in Australia with very light winters (or none at all), so they are mostly focused on cooling with A/C. Are you saying that installing significantly better insulation is not economically efficient for many Australia homes?
It's a big place, the north is essentially a cooling year round climate.
Most of the older places have very little insulation, lots of airflow, single pane leaky windows.
Usually the areas you need to fix are air leakage, better windows (double glazing), then in ceiling insulation. In order of impact.
Our construction industry is pretty much broken, and considers double glazing advanced luxury alien technology... So it can cost so much to replace the old windows that you can run heat pumps as much as you like with the interest on the sum.
And without that the improvement from more diy insulation upgrades don't really achieve much in a monetary sense.
On the other side, we have a much better solar and battery uptake, and the cost to install is fair. So a typical house might be a leaky wooden crate, but with enough solar and battery to be comfortable anyway.
But very high levels of insulation may never repay their carbon (and financial) cost when a home is heated with a heat-pump from a very low-carbon grid. It's the next part of my research programme: "understanding first" vs "fabric first".