Electricity doesn’t move easily across the country. And that’s been a particular hurdle for renewable energy, as many of the best and cheapest resources lack transmission connections to population centers.

A new National Renewable Energy Laboratory analysis finds that improving those connections could provide broad benefits that far outweigh the cost — including lower-cost, more reliable and cleaner electricity.

The U.S. electric grid is actually comprised of three mostly separate systems: the Western Interconnection, the Eastern Interconnection, and the Electric Reliability Council of Texas. The east-west seam runs along the eastern edge of the Rocky Mountains, from northwest Montana to southern New Mexico.

Each interconnection operates independently of each other with very little electricity ever passing between them, and that limits the reach of regional renewable electricity sources such as solar from the Southwest and wind power from the Great Plains. Both tend to stay siloed in their region instead of reaching potential customers in other parts of the country.

NREL’s new “Interconnections Seam Study” shows that if utilities, developers and policymakers figured out a way to break down those seams, the investments would more than pay for themselves through efficiencies.

“If you have more transmission, you can use fewer generation resources, and you can use those more efficiently,” said Aaron Bloom, a manager in grid systems analysis for NREL who presented his team’s ambitious vision at a conference last week in Ames, Iowa.

The report proposes four scenarios for moving huge amounts of cheap renewable power across the country. All four rely on building more transmission lines — always a tall hurdle — along with bolstering the existing connections where the Eastern and Western grids connect.

Currently, the interconnections come into contact in seven spots including one in Rapid City, South Dakota, and two more in western Nebraska. The HVDC ties combined have a capacity of only 1,300 megawatts. That’s a tiny fraction of the interconnections’ roughly 1,000 gigawatt combined generating capacity.

Enhancing the connections “has always looked like a good idea, and it looks like an even better idea today because our loads have grown and diversified over the past 90 years,” Bloom said. Meanwhile, the equipment is aging, with much of it around 30 years old. “What makes it all come together is that we have to replace these facilities anyway.”

Upgrading all seven connections and building out a network of large transmission lines to optimize them could easily cost more than $1 trillion, but Bloom’s calculations say the undertaking would pay for itself in 15 years and then keep on paying dividends.

The reason: all of that transmission capacity would allow for the development of the highest-quality and lowest-cost renewable resources, with fewer geographic limitations.

Under any of the four scenarios, coal’s share of generation nationwide between 2024 and 2038 would fall from 260 GW to less than 120 GW. Solar would increase over that period from 64 GW to more than 320 GW, and wind would increase from 94 GW to more than 320 GW. The team picked 2024 as a starting point because utilities plan generation far in advance and many are already committed to generation plans until about that time.

While all four options would bolster renewables, the two plans involving massive transmission lines would get there for a lower cost because they would allow access to very cheap solar and wind power.

Bloom’s study doesn’t specify who might initiate this grand transmission scheme. He said it likely would be the same people who invest in transmission projects now: utilities and merchant transmission developers.

The report also doesn’t address the public resistance that inevitably arises in the course of a massive transmission or pipeline project. Clean Line Energy Partners, a Texas transmission developer, has been working for years to build high-voltage DC lines to move power from Kansas and Iowa to Illinois and Indiana — much shorter routes than those proposed by Bloom. Both routes — known as the Rock Island and the Grain Belt Express — remain mired in proceedings before judges and state regulators.

Bloom remains focused on what he sees as the potential here.

“We have the best wind and solar in the world,” he said.”We need a rebirth in how we think about transmission.”

Correction: The NREL report projected changes in gigawatts of installed capacity under the four scenarios. An earlier version of this story misstated the unit of measurement.