Even so, DC distribution has, at least in principle, always had a lot going for it. Even now, at a sufficiently high voltage, it is cheaper than AC for transmitting large blocks of power over long distances. Not having to support three phases, as AC does, DC distribution requires fewer conductors. Meanwhile, the conductors themselves can be made thinner, because they do not suffer from the so-called “skin effect”—the tendency of an alternating current to flow mostly near the surface of a conductor, reducing its effective cross-sectional area and increasing its resistance in the process.
Direct current also uses transmission cables more efficiently. For instance, the power delivered by an AC line is defined by the root mean square (ie, 71%) of its peak voltage. A DC line, by contrast, can be made to operate continuously at its peak value. A high-voltage DC system can therefore carry 40% more power for a given current. Alternatively, it can use a thinner-gauge—and therefore cheaper—wire to carry the same current. But it is when electricity has to be transported underground or underwater that DC truly reigns supreme. Unlike a cable hanging in the air, the live conductor in a buried or submerged cable has to be surrounded by a layer of insulation and then clad in a metal sheath. This makes it not only a means of transporting electricity, but also a huge coaxial capacitor. When an alternating current is applied to this capacitor, an additional current must flow continuously through the cable to keep the capacitor fully charged. The result is extra energy losses caused by the electrical and magnetic fields generated, as well as by the heat produced in the process. This capacitance effect limits the amount of power AC cables can carry, and the distance over which they can operate.
) But I did state my self clearly that it could be wrong. As for the figures according to wiki the combined Hydro and Nuclear power is actually under 17% (2010 figures).