You know about AC and DC, but have you heard of IAC?
Probably not, since I just made it up to describe how we are increasingly relying on wind and solar power to generate electricity. In the process, it's stored in batteries in the form of DC before passing through inverters to convert to AC and then converted back to DC again to be used by the computer chips that ultimately drive our LEDs, consoles, video projectors, and almost everything else we connect to electrical power. Each of those conversions comes with an energy cost, which is why I believe that we might one day return to a DC grid.
In the meanwhile, we'll continue to use that intermediate step using AC.
The only reason that we use AC today is because 125 years ago when Edison began building and selling DC generators, we didn't know how to change the voltage of DC, so the voltage produced by a DC generator was the voltage that had to be used by the consumer.
And when it comes to distributing electricity, there's a trade-off between safety and economy; the higher the voltage, the more dangerous but the more economical, and the lower the voltage, the safer but the more it costs to distribute. That's because of the relationship between power, voltage, and current. To transmit the same amount of power at low voltage requires bigger conductors, which cost more money.
That problem left the door wide open for George Westinghouse to walk through with his newly purchased patent on the transformer, which allowed him to build and sell AC generators. That, in turn, allowed consumers of electricity to remove their very loud and smelly generators from their property and tie into the electrical grid, which was supplied by very large generators located far from the premises, and that's mostly how it's done today.
I was reminded of this recently when I checked into my hotel in Shanghai and I found a variety of electrical connectors, including USB, which provide low-voltage DC to charge batteries in all of our devices. That's not unusual these days, but if it becomes more commonplace and expands to include higher current DC outlets, it could alleviate some issues having to do with electrical power distribution. For example, with AC, we now have to think about power factor and harmonics, which can cause overloads and overheating of electrical apparatus. Neither of those exists in the DC domain. And low-voltage DC is much safer than the 100VAC to 240VAC that we currently use around the world.
Converting to DC won't happen any time soon and there are no guarantees that it will happen at all. But imagine having universal voltage at the connection point (5VDC?), universal connectors, and universal frequency (0 Hz!). In the meanwhile, watch out for the effects of low power factor and harmonics.