(TNS) — The Upper Midwest’s electricity grid will require big investments over the next decade and beyond as power producers increasingly shift from coal to wind and solar energy.

That’s the word from a study released Thursday by the region’s major electricity providers, which while laying out transmission issues doesn’t offer specifics on costs or new power lines.

But if past is prologue, spending would likely be counted in the billions of dollars and costs would filter down to ratepayers. Such investments would be critical to maintaining power reliability as coal plants — with their ability to provide constant power — give way to variable sources of energy, according to the study.

“We thought of this (study) very much as a first step,” said Michael Lamb, senior vice president of transmission for Xcel Energy, Minnesota’s largest electric utility. “We thought of it as foundational and educational.”

Minneapolis-based Xcel, Maple Grove-based Great River Energy and eight other Upper Midwest electricity providers produced the new report dubbed “CapX2050 Transmission Vision.” That moniker connotes a sequel to Capx2020, a multiyear, $2 billion regional transmission project.

CapX2020 entailed the construction of 800 miles of new high-voltage transmission lines mostly in Minnesota, but also in the eastern Dakotas and western Wisconsin. The build-out from 2004 through 2017 was aimed at reinforcing the regional grid, including integrating a plethora of new wind farms.

“The CapX2020 projects did exactly what they were supposed to do and more,” said Priti Patel, chief technology officer at Great River, Minnesota’s second-largest electricity producer and supplier to 28 retail power co-ops.

However, utilities and clean energy groups say many CapX2020 projects are already near capacity.

Currently, Minnesota gets around 20% of its electricity from wind and just over 1% from solar. But those numbers are expected to surge as utilities pursue aggressive carbon reduction goals to 2050, partly through early retirements of the grid’s historic bedrock — coal plants.

“It’s a massive change for the grid,” Lamb said.

The grid’s main nodes are “dispatchable” and “non-dispatchable” power generators, with the latter on the rise. Coal, gas and nuclear power plants can be dispatched at will and provide continuous power. Wind and solar farms by their nature can’t.

By storing electricity, grid batteries can help renewable power plants effectively become partly dispatchable. But cost-effective batteries for long-term storage are potentially years away.

“Dispatchable resources support the electric grid in ways that dispatchable resources presently cannot and therefore some dispatchable resources will be necessary,” the CapX2050 study said.

Fossil-fuel and nuclear power plants provide support to the grid — regulating voltage and frequency, for instance — that is important for electricity reliability and ultimately quality. According to the report, as coal plants are closed, investments in new technology will be necessary to maintain such services.

“We need to do more than replace the energy those traditional power resources provide,” Patel said.

More money will be needed for more transmission lines, too, and not only because wind and solar farms are geographically dispersed. As coal-fired plants close, more transmission will be needed to ship excess renewable power from one point on the grid to another point that needs it, the study concluded.

What comes next after the CapX2050 study isn’t clear. The CapX2020 project involved years of discussion. And as with Capx2020, projects springing from CapX2050 would require state regulatory approval.

Still, “it’s our responsibility to make sure that any transmission upgrades needed to facilitate a low-carbon future be understood now,” Patel said.

Other electricity providers involved in the CapX2050 study include: Duluth-based Minnesota Power; Fergus Falls-based Otter Tail Power; Rochester-based Southern Minnesota Municipal Power Agency; LaCrosse-based Dairyland Power; and Sioux Falls-based Missouri River Energy Services.

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