Heat pump collection pipes could be installed alongside underground electrical wiring so one would only have to dig once to install both systems.

Some of my thoughts about heat pumps.

Heat pump collection pipes could be installed alongside underground electrical wiring so one would only have to dig once to install both systems. One trench could serve for both the underground wiring and the "ground to heat pump" collection pipes. One could think about heat pump possibilities when installing underground wiring.

Beyond the ground is the idea of heat transfer from moving water; such as seawater in a video I saw about Denmark.

I would guess moving water is even more efficient than the ground since the ground is insulating so heat transfer from the ground is slower. Moving water always brings new warm water to the system for heat transfer.

I think most heat pumps, in homes and small buildings of USA, are air to air systems. These systems bring moving air to the system for heat transfer. Similar to water, it's moving, but during winter, air can be much colder than most bodies of water so the heating is less efficient.

Still air to air systems are less expensive to install than ground pipe, or water based systems so that's why they are more common. Here's one more thought.

As more of Bellingham installs heat pumps, people are likely to opt for air conditioning since it's easy to include with a heat pump system. This might mean more load on the electrical grid, during summer months in Bellingham, as more people will have air conditioning that didn't have it before.

For summer air conditioning, solar is a good fit as during sunny hot days, solar is producing power closer to the times when air conditioning is needed.

I like just contemplating about things in my mind though, admittedly, I'm not an expert at anything.