Pocobor.

AC vs DC: Edison’s Revenge

Bracket from 1883 Tournament of Genius.

The Original Feud
Though Thomas Edison is remembered as one of the most prolific, influential, and successful inventors in history, he actually lost one of his biggest professional battles.  He spent a large portion of his life wrapped up in a struggle over the future of electricity.  He advocated the use of DC (direct current) power and bitterly opposed champions of AC (alternating current) power such as Nikola Tesla and George Westinghouse.  The “War of Currents” was heated enough that Edison became involved in the development of the electric chair, despite his opposition to capital punishment, to demonstrate what he saw as the dangers of AC power.  He also publicly executed a number of animals via electrocution to prove his point.

In the end, Edison lost; today virtually any wall outlet in the world provides AC power.  However, I think the pendulum may be swinging back and I’m going to float the argument that DC power will enjoy much more widespread use in the next hundred years than in the past hundred.

AC vs. DC Power
It’s actually not quite accurate to imply that DC power has not been used since AC won the power generation and transmission war.  However, it is illustrative to look at the two types of power and their advantages and disadvantages.

DC power uses unidirectional flow of electric charge and is produced by batteries, solar cells, and dynamo-type electric generators.  Generally speaking, it is more difficult to transmit over long distances than AC power without significant energy loss (although high voltage direct current – HVDC – can be used for efficient transmission in certain settings).  Since the adoption of AC power for the electrical grid, the chief use of DC has been in battery-powered applications.

AC power, on the other hand, uses bidirectional flow of electric charge and offers significant advantages over DC for highly efficient power transmission.  Because the power grid is AC, most of the devices in our lives that plug into the wall are designed and optimized for an AC power source (although many of the devices internally convert the power to DC for use).

Centralization vs. Localization
The power grid approach, that has dominated since Edison’s time, uses a combination of large, centralized power plants with a network of transmission and distribution lines to send the power where it needs to go.  AC power is the logical choice in a power grid, because of power transmission advantages. Historically, the economics of power plant design have made a distributed, localized model infeasible.  However, things are now changing.

The Coming Sea Change
Renewable energy generation via technologies such as solar, wind, and hydropower looks to be the way of the future (initially in combination with fossil fuels and eventually exclusively).  In particular, technologies such as solar have a few interesting characteristics: (1) they output DC power and (2) they lend themselves well to a distributed model.  For instance, it’s easy to put solar panels on every roof in a city so that all the buildings are generating power, whereas it doesn’t make sense to have a coal power plant in every home.  In a situation like this, power transmission is not much of an issue since the power is being used in the same place it is being generated.  That being the case, there is no need to convert to AC, send to the wall outlet, and then convert back to DC for use.

Bottom Line
The reason that the today’s electric grid uses AC power (efficient transmission) will matter less and less in a future world where power generation takes place in a more distributed fashion.  Imagine a 12/24VDC world, instead of the 120/240VAC world of today (this brings up a number of questions and issues in its own right, which probably deserve their own post, but we’ll set those aside for now).  The opportunities to both redesign existing appliances and devices and also to create new products that fully take advantage of the new power paradigm are staggering.  So I throw out a challenge to the designers of the world: look around and start thinking about optimizing electrical products for low voltage, DC power – and make Edison proud.

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