AC DC Power Supply

While we talking about storing energy. The law of conservation of energy states energy cannot be created or destroyed only changed in form. So what you are considering is changing kinetic energy to potential energy. With regards to electricity that would be electrons.

AC current and voltage changes their polarity 50 times a second (for 50Hz system). When connected to an AC supply, the energy storage device charges during positive half cycle and discharges during the negative half ...

AC is easier to manage and convert to higher or lower voltage using transformer which are normally very high efficiency machines. Nevertheless DC systems show at least a couple of advantages respect to AC:
1) There are not reactive losses (capacitive and inductive) which affect in particular the long distribution lines and this permits, if necessary, the energy distribution using underground cables. This would be impossible with AC because of the capacitive losses. This is the principle ...

HVDC means High Voltage Direct Current and it enables controllable exchange of Active Electrical Power between two stations since the two stations in case of their being connected over HVDC link. As any electrical engineer would know, flow of power between two ends of a transmission line would comprise two components one of which would be Active Power measured in Watts (W) or kilo Watts (kW) or Mega Watts (MW) etc, and the other component wou ...