The issue with heat pumps is that most of the ones currently being installed in South East of the US don't work well below +20F let alone 0F or -20F. Most of them are being installed with an electrical resistive backup heat, which is incredibly inefficient.
The problem is when a cold spell like Christmas 2022, with temperatures down towards 0F. All the heat pump users switch to resistive backup heat and it overloads the electric grid and we get rolling blackouts.
In my opinion, heat pumps are amazingly efficient at moderate cold temps, but they really need propane or wood heat backup for the really cold temperatures instead of resistive heaters.
That 100% efficient figure is correct - you get one Watt of heat for one Watt of electricity. It's just that heat pumps can deliver 3 or 4 Watts of heat for each Watt of electricity (usually quoted at around 300% or 400% efficiency!). Compared to that, resistance heaters aren't as efficient.
The explanation that made the most intuitive sense to me is that it takes less energy to move heat from one place to another (air at 273 Kelvin to air at 300 Kelvin, like a heat pump does) than it does to create heat from nothing (like a resistor does). That's why the heat pumps can get deliver more heat to you from the same amount of electricity.
The best natural gas power plants are 64% efficient. A modern furnace is around 95%. Sure electric restive heat is 100% efficient in your house, but the whole system us much worse.
Of course electric can come from many sources, if your is renewable at the time resistive is good. However you might also be using some old 1920s coal generator that is 10% efficient (these still exist, but are only used in the worst emergencies)
Natural gas (not sure about wood; in most areas it’s abundant) is about 1/3 of the cost of electricity in America, so it’s economically less efficient.
Resistive heat is 100% efficient, but heat pumps can operate at greater then 100% efficiency. That's because a heat pump doesn't actually generate heat, but just moves it around. Even when it's cold outside, there's still a lot of heat energy in the air, which can be moved inside to warm your home.
Due to the increased efficiency, heat pumps are better then electric resistive heat (when temperatures outside are within the heat pump's operating range, that is). This is regardless of the method of power generation.
Electricity offers resistive heating, and heat pumps. Heat pumps are much more efficient than resistive heating.
Otherwise, you have chemical fuel which burns, and a bit of electricity to pump it around (either by forced air or water pumps).
In terms of electrical input, resistive heating is the worst of the lot, even if it can be sourced in a carbon neutral way (unlike nat gas or fuel oil).
In the US, anyway, when people say electric resistance heat is inefficient they are comparing it to natural gas heat. It's the same story in water heaters; if you install a HPWH you are betting on not needing to resort to resistance heat because if you do that too much, you probably should've installed a cheaper gas unit instead. (I'm a happy HPWH owner weighing the timing of adding a heat pump for central heat.)
Since heat pumps are moving heat around rather than actually producing it, they can be effectively better than 100% efficient so it's not so much that resistive heat is inefficient, but that it's less efficient than a heat pump.
When I researched this year on replacing my A/C / Propane Furnace system with a heat pump, I found that companies didn't seem to want to advertise what temperatures their heat pumps can operate effectively at. If I look at some marketing materials from Google it seems companies like Carrier and Trane are only willing to talk about their heat pumps working in low temperatures if it's regarding their top-of-the-line (very expensive) variable speed compressor units. No one talks about what temps the mid range units can handle, and I'm guessing it's because they don't work well below 20F.
I am just saying what the typical install is in the South East US. The heat pumps installed may produce some heat at 5F but they can't keep the temperature to the set value, so there are resistive elements (Aux heat) to make up the shortfall.
It's pretty common for people with heat pumps to have Aux Heat kick in during cold spells, which cause power grid overload issues.
I realize you can insulate a house well enough and have a good enough heat pump to avoid backup heat, but 5F or 0F days are rare enough that the codes do not enforce this.
My heat pump is advertised to operate as low as -13F. One thing to note is the efficiency of heat pumps is not optimal when they are operating close to their extremes.
Where I live, most people had electric baseboard heating before they installed their heat pump, so 99% of the time they are using less electricity and on those really cold days, they are using as much as they did before getting a heat pump, so we know our grid can handle that. The grid in the US is weak because Americans have traditionally depended more on fossil fuels or wood for heating.
I disagree with the cold part. It is easier to dress to stay warm in a cold place than to dress to stay cool in a hot place. Both adults and kids bike in Scandinavia in the winter.
Feels like there is a business case for people willing to pay to reduce trip times for trans continental flights.
The problem is that the greenhouse gas impact will be higher for a supersonic trip compared to a subsonic one. This is on top of the issue that we don't really have a good low carbon alternative for longer range air travel (batteries don't have anywhere near enough specific energy). The best option we have is synthetic jet fuel produced from green electricity. Producing jet fuel that way is many times more expensive than fossil fuel jet fuel.
You can take precautions to avoid the oxidation. This is already done reliably on airplanes and in overhead power distribution, where aluminum wire is the standard.
Which is relatively expensive and error prone, compared to copper connections.
For service connections and large scale power distribution where trained professionals are already required and lack of maintenance is already a fire hazard, it isn't a problem.
For small branch circuits where work is often done by random Joe's and where any sort of preventative maintenance is few and far between, it is a failed experiment.
Assuming copper prices continue to outpace aluminum prices, eventually copper will be the expensive option vs. aluminum (done right). Not sure if the error prone aspect could be remedied though.
Compared to electrician labor? It would have to be price at silver prices to matter; most likely.
Either way, home and commercial construction is likely to crater (already starting in many areas) due to cost of $$ going up, so that should help tamp down demand quite a bit.
There are also a new aluminum alloys (aa-8000) with better mechanical properties. The biggest issue is that that the trades/DIYers need to learn new processes. Treating aluminum wiring like copper wiring is a disaster. Also need to overcome the stigma from the aluminum experiment 50 years ago.
It makes a ton of sense to switch to aluminum in housing though. For the same current capability the wire is significantly cheaper, lighter, and stronger.
On a personal level, this reminds me of a concept called normalization of deviance. [1]
Every time we do something which we know may be risky, but we do not have a catastrophic result, we further reduce the perceived risk that the catastrophic result will occur to us.
Lithium Ion batteries degrade very little with low C mid range charge cycles. The time/temperature/SoC degredation is greater. Hence why you don't want to leave a battery sitting at 100%.
The problem is when a cold spell like Christmas 2022, with temperatures down towards 0F. All the heat pump users switch to resistive backup heat and it overloads the electric grid and we get rolling blackouts.
In my opinion, heat pumps are amazingly efficient at moderate cold temps, but they really need propane or wood heat backup for the really cold temperatures instead of resistive heaters.