Yup. We have an underground well house. It’s amazing how stable the temp is down there.
The goal was to not pay for heating a small building to house the pressure tanks and water softener. I got the idea from working in underground defense facilities where I noticed it never got cold enough to freeze down there in the winter, nor did it get hot in the summer.
And because it’s merely moving heat around, such systems are in effect more than 100% efficient. Makes solar look better, much better, in remote areas.
I have a relative who showed me his monthly electric bill (spooky big old house, much more Boonies than this one is) has under eight bucks. “Photovoltaics?” He explained that their generating capacity is limited to 70% of their prior average use. And being a (D) he groused that the power company buys at wholesale and sells at retail, which makes perfect sense.
Also, the property tax eval issue is different here, the jump in value from adding, say, 90K worth of cells, doesn’t occur until the property changes hands. Of course, he’s in his 80s, but still, much better. And regarding the 70% limit and wholesale vs retail, remaining on the grid (I believe that’s required) obviates the need for a sturdy outbuilding to house the battery storage for the nighttime hours, as well as the additional homeowner’s insurance that would entail.