I mean, one way to look at it is that the energy density of this concrete supercapacitor, when fully charged, is about 4 orders of magnitude smaller than the ch

I mean, one way to look at it is that the energy density of this concrete supercapacitor, when fully charged, is about 4 orders of magnitude smaller than the chemical energy density of wood. So depending on the design, electrical shorts might be something to worry about, but I have a hard time worrying about it as a significant fire hazard when compared to all of the other flammable things you might find in a house.