Beg to differ… vertical drilling and horizontal drilling share almost nothing in common. Vertical wells are cheap, the cost is in getting the rig to the site. I assume Dig is developing something more mobile to reduce these costs. Horizontal drilling costs are drive by existing infrastructure.

TENs are very promising for green field developments or in areas that are undergoing major street renovations (sewer or water line replacements). Agree wholeheartedly that individual/vertical GSHP is very promising as widespread solution.