That makes the question of reliability more urgent than ever. Because wind and sunlight are fickle, utilities have used dirtier backup sources like coal and natural gas. If we want to eventually get all our energy—or a large majority of it—from renewable sources, something has to change. As Gates told the The Atlantic in November, “We need an energy miracle.” Gates is investing billions of dollars in schemes that sound like they’re out of an Isaac Asimov novel: batteries the size of swimming pools to store renewable power, technologies that use sunlight to produce liquid fuel.

But over the past couple of years, researchers have come across another potential solution, one that seems almost too simple. The wind is usually blowing somewhere, and the sun is usually shining somewhere. If we could just connect the whole country to a special grid that would let utilities tap into those resources anytime, wouldn’t that get rid of—or at least lessen—the reliability problem?

The most recent high-profile paper making this argument was published in January by researchers at the National Oceanic and Atmospheric Administration and the University of Colorado at Boulder. Christopher Clack and colleagues built a model to predict the long-term costs of putting all kinds of energy into the electrical system. When they imposed a constraint on their model—it couldn’t use coal—they found that the cheapest option involved a grid of transmission lines that could carry solar and wind energy from almost any part of the country to anywhere else. Other technologies—perhaps Gates’s imagined miracle—would still be required to get rid of carbon-emitting fuels altogether, but the new grid would get us quite far, reducing emissions from power plants by up to 80 percent within 15 years.

This conclusion, Clack said, appeared to surprise some energy researchers. Sending wind or solar energy long distances inevitably involves the loss of some power during transmission, and the alternating-current, or AC, lines that connect most of the U.S. are less efficient for long-distance transmission than direct-current, or DC, lines. The paper’s hypothetical grid would use DC instead of AC. Until recently, big investments in high-voltage DC lines have been rare, in part due to the cost of the technology required at substations to make the power usable. But the model found that if you built a nationwide grid, economies of scale would emerge. In short, the benefits of having long, efficient lines outweigh the cost of power conversion. “People assumed that storage was the key or that nuclear was the key—and now I think there’s more of a recognition that you can actually get quite a long way today,” Clack said, just by changing how renewable energy moves around.

This hypothetical grid recalls the interstate highway system championed by President Dwight D. Eisenhower in the 1950s. Back then, the U.S. was connected haphazardly with narrow roads built by state and local governments. Eisenhower predicted that cars would soon become ubiquitous, so he signed a law authorizing funds for an ambitious expansion of the nation’s highways—an approach that turned out to be prescient. Clack’s vision seems similar. So why don’t we invest in a new grid for power transmission, like Eisenhower did for car travel?