To meet peak-load demand, generators must be turned on during the daytime and turned off in the evening. This cycle is repeated every day for every city around the world. In addition, excess power must be generated in case of emergencies such as a generator failure. If not sold, this excess power is a total loss. Long-distance power transmission lines have solved the problem of wasted power.
Utilities routinely buy and sell power among themselves.
If a utility can buy cheaper power and not have to turn on a generator, a real win-win situation is created. The buyer wins with cheaper power and the seller wins by being able to sell its excess power for profit. The last 25 years have seen the growth of extensive interconnected power grids. This includes the countries of the former Soviet Union, Europe, Scandinavia, Mexico and the eastern and western United States. More than 50 nations have interconnections across their borders.