326K (+127 deg F) and 340K (+152 deg F) for their less and more pure samples respectively. And, yes, if it's a superconductor as we understand them, that's the temperature at which it would have zero resistance as well.
It's obviously a hyperbole. But if we once were to use these SCs to transport energy from solar farms in Sahara, it might have to operate in that temperature range.
Five meters down in the desert you're under 25 degrees year round. It's the average that matters for soil temps, not the peaks. You can approximate this by taking the average air temperature and defining the surface as the top five meters. Below the 10 meter mark the day/night cycle influence is pretty much negligible (but that would be more costly).
LK99 isn't necessarily a stand-in for helium cooled superconductors - if all SC were equivalent to any other, YBCO and similar would have been enough to make MRIs significantly cheaper - LN2 is easy and cheap to produce.
