Low-Energy Fridays: AC/DC—Not Just a Rock Band
If you’re like me, you have hazy memories from high school physics class about the difference between alternating current (AC) and direct current (DC). But what you may not know about is the century-long battle between AC and DC for control of the electric grid.
When Thomas Edison pioneered the use of electricity as a power source in the 1880s, it exclusively relied on DC current, in which electricity flows through a circuit in a single direction. DC power was relatively simple, but it had its drawbacks. Electric power tends to dissipate as heat as it travels over distances; given the technology of the time, this meant electric generation had to be fairly close to its end user. Edison envisioned smaller power plants located on each city block, but even in such circumstances, users farther away from the power source could experience reliability issues.
Nikola Tesla, the other great electric mind of the late 19th and early 20th centuries, was able to solve this problem. Tesla realized that rapidly alternating the direction of currents would make it easier to increase or decrease voltage and thus retain power over longer distances. (If that wasn’t confusing enough and you’d like to learn more, see this primer).
Whether due to competitive incentives or personal pique, Edison helped launch a public relations campaign against the alternating current idea. To prove that AC was more dangerous than DC, he held a series of demonstrations in which he electrocuted various animals—ranging from dogs to elephants—with high-voltage shocks from AC power. Public authorities were also prevailed upon to use AC power as a means of execution, hence the origin of the electric chair.
Despite this grisly history, AC’s economic advantages soon won out. Modern electricity use remains a hybrid of AC and DC power systems: Most electric-powered household items, from your smartphone to your television, still operate using DC power; by contrast, the electric grid itself uses AC power with transformers to turn power from AC into DC for consumer use.
But DC power may be launching a grid comeback. Technological advances in recent decades have allowed the development of high-voltage direct current (HVDC) transmission lines, which lose only half as much electricity through heat dissipation as AC lines do and require less initial investment, as they don’t need to be equipped to handle alternating current. Potential drawbacks include more outages and less flexibility for integrating into the existing AC grid system.
Europe has a network of HVDC lines, and others are under construction in China. An early attempt at utilizing this technology in the United States is the proposed Grain Belt Express line that would run from Illinois to Kansas. As a so-called merchant line, it would depend on market revenues for profitability rather than recovering costs via captive utility customers. The line has proved controversial, however, losing its federal loan guarantee and facing repeated court challenges.
Whether the advantages of DC-based transmission make it superior to AC is something that can only be determined by experience. We are all better off for the fact that Edison’s attempt to ban AC current was unsuccessful. Similarly, attempts to revive DC transmission should stand or fall based on market merits rather than government whims.