This article was originally published on Businessweek by Chris Martin, Mark Chediak, and Ken Wells 

There are 3,200 utilities that make up the U.S. electrical grid, the largest machine in the world. These power companies sell $400 billion worth of electricity a year, mostly derived from burning fossil fuels in centralized stations and distributed over 2.7 million miles of power lines. Regulators set rates; utilities get guaranteed returns; investors get sure-thing dividends. It’s a model that hasn’t changed much since Thomas Edison invented the light bulb. And it’s doomed to obsolescence.

That’s the opinion of David Crane, chief executive officer of NRG Energy, a wholesale power company based in Princeton, N.J. What’s afoot is a confluence of green energy and computer technology, deregulation, cheap natural gas, and political pressure that, as Crane starkly frames it, poses “a mortal threat to the existing utility system.” He says that in about the time it has taken cell phones to supplant land lines in most U.S. homes, the grid will become increasingly irrelevant as customers move toward decentralized homegrown green energy. Rooftop solar, in particular, is turning tens of thousands of businesses and households into power producers. Such distributed generation, to use the industry’s term for power produced outside the grid, is certain to grow.

Crane, 54, a Harvard-educated father of five, drives himself to work every day in his electric Tesla Model S. He gave his college-age son an electric Nissan Leaf. He worries about the impact of warming on the earth his grandchildren will inherit. And he seems to relish his role as utility industry gadfly, framing its future in Cassandra-like terms. As Crane sees it, some utilities will get trapped in an economic death spiral as distributed generation eats into their regulated revenue stream and forces them to raise rates, thereby driving more customers off the grid. Some customers, particularly in the sunny West and high-cost Northeast, already realize that “they don’t need the power industry at all,” Crane says.

He’s not alone in his assessment, though. An unusually frank January report by the Edison Electric Institute (EEI), the utilities trade group, warned members that distributed generation and companion factors have essentially put them in the same position as airlines and the telecommunications industry in the late 1970s. “U.S. carriers that were in existence prior to deregulation in 1978 faced bankruptcy,” the report states. “The telecommunication businesses of 1978, meanwhile, are not recognizable today.” Crane prefers another analogy. Like the U.S. Postal Service, he says, “utilities will continue to serve the elderly or the less fortunate, but the rest of the population moves on.” And while his utility brethren may see the grid as “the one true monopoly, I’m working for the day the grid is diminished.”

Anthony Earley Jr., CEO of giant Pacific Gas & Electric, doesn’t share Crane’s timetable for the coming disruption—he thinks it’s further out—but he does agree about the seriousness of the threat. Solar users drain revenue while continuing to use utility transmission lines for backup or to sell their power back to the power company. How can power companies pay for necessary maintenance and upgrades of the grid if that free ride continues? “No less than the stability of the grid is at stake,” he says. So far regulators in Louisiana, Idaho, and California have rejected calls to impose fees or taxes on solar users.

Worldwide revenue from installation of solar power systems will climb to $112 billion a year in 2018, a rise of 44 percent, taking sales away from utilities, according to analysts at Navigant Research, which tracks worldwide clean-energy trends. “Certain regions in California, Arizona, and Hawaii are already feeling the pain,” says Karin Corfee, a managing director of Navigant’s energy practice. “We’ll see a different model emerge.”

After subsidies, solar power is competitive with grid power costs in large parts of those markets. Some areas in the Northeast will reach a similar “grid parity”—where residential solar is equal in cost to power from a utility—within three years; a majority of states could get there in 10 years or less, according to data from a variety of green energy and regulatory sources. A July report by Navigant says that by the end of 2020, solar photovoltaic-produced power will be competitive with retail electricity prices—without subsidies—“in a significant portion of the world.” Green-thinking communities such as San Francisco and Boulder, Colo., are starting to bypass local utility monopolies to buy an increasing portion of power from third-party solar and wind providers. Chicago recently doubled the amount of power it buys from downstate wind farms.