It's ultimately heating the atmosphere above them. I heard this planed had some trouble with thermal balance recently, things were getting too hot.

In seriousness, heating streets with abundant solar energy harvested nearby would be reasonable. But sunshine in winter months is not as intense, and you'd have to build, as usual, a huge battery to keep the energy for the night. (When this is solved, more problems would get solved along the way than just de-snowing streets.)