FWIW: I'm heating my rad floor system at my crane yard building, with an electric boiler, with electricity I generated this spring, summer, and fall. The utility stores this access, not really, but in effect. I get a credit shown on my billing statement, same difference. I use no power except for a light for a minute or two until heating season starts. I keep the slab at 50 degrees. Electric boilers have no combustion losses, 100% efficient pretty much, and no flue gases to deal with (running a vent stack through the roof, etc.) Same with the home shop and hangar, all electric, all excess generated by yours truly.
I've found for something like a hangar or a shop, using the rad floor to just take the chill off is real easy, and then for when you're doing like something fabric work and you want it that last 10 or 15 degrees warmer, an aux heater (in my case a 4KW wall mounted electric heater, along with a cheap ceiling fan) can easily do so, as you don't have a huge heat sink of an ice cold concrete slab.