This SC parallel resonance scheme has been rattling around in my head for decades. This scheme [to ever have a chance of being practical] would be accompanied by the advent of room temperature electrical super conductivity (SC). It is a parallel resonant inductor/capacitor (L/C) superconducting (SC) circuit. The circuit would exhibit an extremely high 'Q' due to essentially zero (I2R) power loss owing to zero circuit resistance. The inductor would have two additional coils that mutually couple to the inductor flux path. One coil would serve to excite or charge and the other would provide AC power output to a load.
A design using 2650 uF in parallel with 2650 µH at 1650 volts would have a resonant frequency of about 60 Hz and store 3600 joules of energy (1 watt-hr).
Electrical energy in a capacitor is found from E=.5cV2 and Charge is found from Q=cV. There is an analogy between electrical and mechanical. Kinetic mechanical energy is found from E=.5mV2 and momentum is found from P=mV. Notice the similarity: Voltage has Velocity analog and Capacitance has Mass analog. Charge has Momentum analog. But according to relativity, velocity has a limit of 'c' where further energy manifests as Beta mass increase Beta=1/sqrt(1-(v/c)2). Following the analogy, what if voltage also becomes relativistic? That might imply that a capacitor would only have to have insulation adequate to prevent insulation break down of the 'relativistic' limiting voltage.
So, if a superconducting relativistic resonant circuit were built, energy could be pumped into it with no limit. As the energy increased to approach relativistic voltage the capacitance would begin to increase by Beta. As this occurred the resonant frequency would drop off due to increasing capacitance.
Does the relativistic analogy exist between voltage and velocity, capacitance and mass? Could such a device be built? If so, it would be kind of neat that the state of charge or internal energy could be monitored by the frequency of resonance. There, I said the idea was wild and crazy.