Direct Current (DC)

The DC described here is nothing to do with Washington, but is “Direct Current”. In physics terms it refers to electric current where the flow of charge is always in the same direction.  As opposed to AC (Alternating Current), where the flow of charge changes direction periodically (usually represented via a smooth sine-wave picture).

From a business perspective, the key things to know are that DC is:

  • what’s produced by a solar photovoltaic (PV) panel: an inverter then converts DC output to AC
  • what’s used by modern electronics
  • what’s input and output into a battery
  • used for some high-capacity and long-distance grid connections, as energy losses along the line can be smaller

Whereas AC is:

  • what’s produced by generators which spin (which is all of them other than solar PV)
  • what comes out of the socket in your wall
  • what’s carried by most of the grid (transmission and distribution), other than some very long-distance, high-capacity lines and some undersea cables

So in an electricity system, electric current can be changed multiple times from DC to AC and back (and each time, a little bit of energy is lost).

For example:

  • A solar PV array on someone’s roof produces DC
  • That DC may be directly connected to a battery for storage
  • The solar inverter converts DC from the solar array/battery to AC, which is fed into the grid (or, if they’re off-grid, into the standard home wiring)
  • To power their laptop, it’s converted back to DC by that little box on the charging cable (the one that gets warm)