Heat pumps are at the 400% efficiency level so by your numbers they're already ahead. And PV has other advantages. It's easier to install since it doesn't require specific tubing and the panels are much lighter. The energy is useful for other things when you don't need as much hot water. And efficiency goes up in winter because PV is more efficient in the cold whereas efficiency of thermal solar goes down as you need to heat the panel before heating the water. It will depend on your local PV and heat pump costs but thermal solar seems less and less relevant these days.
AIUI, ground source heat pumps get really expensive when the ground is really hard. A reasonable proxy is “do your neighbors have basements?” If the answer is “no”, then it’s probably because digging is more trouble than it’s worth.
Efficiency is still good for air source heat pumps IIRC. They only go down to 100% at well below freezing which is probably not a problem in Hawaii. Ground source only requires a small hole though, of the kind that is done for water. I'm in a granite rich area where basements are very rare but water wells are very common and reasonable cost to drill.
> “do your neighbors have basements?” If the answer is “no”, then it’s probably because digging is more trouble than it’s worth.
Basements are popular in cold climates because footings already need to be dug several feet down to get below the frost line. In warmer areas, basements are uncommon even if digging is easy.
