Replacing gas heating with solar thermal is even cheaper and doesn’t. Electric heat pumps are viable when electricity is cheap or demand is low and you want AC, the more they drive up electric costs the more alternatives become viable.
Net effect you tend to see them in areas where there’s a surplus of winter electricity which also tends to be places with minimal demand for heating like Virginia rather than Mane. 46% in South Carolina, 42% in North Carolina, 30% in Virginia etc: https://www.statista.com/statistics/1327164/share-of-househo...
Solar thermal heating is not going to produce much energy in the winter when there's fewer hours of sunlight and more hours of cloud coverage - which just so happens to coincide with places that would need heating during the winter. Solar thermal performance is worse with diffuse light (read: overcast days) than PV solar, in fact that's a big part of why it was largely abandoned in the 2000s.
The main advantage of solar thermal is it’s really cheap so you can just scale collection to cover winter heating. That’s why adoption is so high in China even relatively far north. As to the US, the cost savings just isn’t that appealing for most people. It’s frankly ugly, complicated, and has minimal payoff at current prices.* Passive solar design can have significant benefits while looking much nicer. But if you’re increasing the cost of electricity or gas then suddenly it’s looking significantly more attractive.
* Except of course when people want to heat a pool, that takes crazy amounts of energy.
“Israel became the world leader in the use of solar energy per capita with 85% of households using solar thermal systems (3% of the primary national energy consumption)” https://en.wikipedia.org/wiki/Solar_water_heating
As per your link, solar thermal water heating is very variable depending on geography:
> The amount of heat delivered by a solar water heating system depends primarily on the amount of heat delivered by the sun at a particular place (insolation). In the tropics insolation can be relatively high, e.g. 7 kWh/m2 per day, versus e.g., 3.2 kWh/m2 per day in temperate areas.
Because of this, many solar thermal systems are supplemented by convention heaters.
> In winter, the percentage of your hot water heated by the sun drops to as low as 10-20%—as you might expect with short days and weak sun in December. That’s why practically every solar water installed in the US will be connected to a backup conventional water heater to ensure that your hot water needs continue to be met even in January.
