At the start of the 20th century, inventors Thomas Alva Edison and Nikola Teslaclashed in the "war of the currents". To highlight the dangers of his rival's system, Edison even electrocuted an elephant. The animal died in vain; it was Tesla's system and not Edison's that took off. But today, helped by technological advances and the need to conserve energy, Edison may finally get his revenge.
The American inventor, who made the incandescent light bulb viable for the mass market, also built the world's first electrical distribution system, in New York, using "direct current" electricity. DC's disadvantage was that it couldn't carry power beyond a few blocks. His Serbian-born rival Tesla, who at one stage worked with Edison, figured out how to send "alternating current" through transformers to enable it to step up the voltage for transmission over longer distances.
Edison was a fiercely competitive businessman. Besides staging electrocutions of animals to discredit Tesla's competing system, he proposed AC be used to power the first execution byelectric chair. But his system was less scalable, and it was to prove one of the worst investments made by financier J Pierpont Morgan. New York's dominant banker installed it in his Madison Avenue home in the late 19th century, only to find it hard to control. It singed his carpets and tapestries.
So from the late 1800s, AC became the accepted form to carry electricity in mains systems. For most of the last century, the power that has reached the sockets in our homes and businesses is alternating current.
Now DC is making a comeback, becoming a promising money-spinner in renewable or high-security energy projects. From data centers to long-distance power lines and backup power supplies, direct current is proving useful in thousands of projects worldwide.
"Everyone says it's going to take at least 50 years," says Peter Asmus, a senior analyst at Boulder, Colorado-based Pike Research, a market research and consulting firm in global clean technology. But "the role of DC will increase, and AC will decrease." The main factor driving demand is the need to conserve energy and produce more of it from renewable sources. Alternating current is generated by rotating engines, but renewable sources such as wind and solar produce DC power. To use it, because of the way our buildings are wired, we first convert it to AC.
Another thing that's happened since Edison's time is the advent of the semiconductor. Semiconductors need DC power, and are increasingly found in household appliances. These have to convert the AC supply back to DC, which is a waste of energy and generates heat. In the early years of industrialization this wasn't an issue, but today it's important, especially in the huge and fast-growing business of cloud computing.
How would Edison see all this? He might even have foreseen it. "I'd put my money on the sun and solar energy," he reportedly told his associates Henry Ford and Harvey Firestone in the 1930s. "What a source of power! I hope we don't have to wait until oil and coal run out before we tackle that."