The main problems with having a huge EM field to power the entire planet (or even just a city) are that: - every piece of conductor of the right length is basic

The main problems with having a huge EM field to power the entire planet (or even just a city) are that: - every piece of conductor of the right length is basically an antenna for the frequency at which the EM field resonates, therefore will generate a voltage across its extremities that can generate wild sparks and cause electric shocks; - an EM field (and pretty much any other field) in the space is proportional to the inverse of the square of the distance from the source, which makes it for a pretty inefficient way of transmitting energy at long distances. The field could be not isotropic, for instance by "focusing" it in one direction, but that defeats the purpose of accessing the energy from everywhere.