AP This file photo shows wind turbines outside Boulder, Colo.

By 2030, Colorado plans to cut the emission of climate-warming pollution by 50 percent. By 2050, it will be 90 percent.

That means more of the state’s energy will have to come from renewable energy, up to 100 percent by 2040, according to a vision laid out by Gov. Jared Polis.

One big hurdle stands in their way: The system of wires that stretches from power plants to energy users. The grid was never designed to handle the more fluctuating energy renewables provide and energy providers worry that all that new clean energy could test its limits.

“We’re going to need to have a lot of changes in the system to make a very high penetration renewable system work,” said Richard Sedano, president and CEO of the Regulatory Assistance Project, a nonprofit focused on the clean energy transition.

That’s because much of the national grid is old, some of it by more than 100 years, and splintered into local and regional sections that don’t connect. Early morning solar energy generated in New York can’t efficiently move west to coffee machines and laptops in Colorado or California.

One National Renewable Energy Lab study imagines a possible fix: high voltage direct current transmission lines that quickly move renewable energy to parts of the country that need it. Right now, just a few such “express train” lines exist in the country. Permitting constraints and cost are two big limitations. The NREL study estimates it would take $70 billion to build such lines. Ambitious climate legislation like the Green New Deal could direct funding for that kind of project, but Congress has steered clear of that kind of investment.

“Generally we don’t get the kind of direction that will motivate these kinds of big picture developments,” Sedano said. With the energy market in flux, private investors aren’t paying for that kind of large-scale investment yet.

Grace Hood Inside the Energy Systems Integration Facility at Golden-based National Renewable Energy Lab workers test a storage system that would allow some new customers with Holy Cross Energy limit the amount of power they draw from the grid.

That has left any grid improvements to states, cities and local energy providers.

In Colorado, about a dozen cities and counties have committed to 100 percent renewable energy and the state’s largest utility, Xcel Energy, plans to generate 100 percent of its electricity from carbon-free sources by 2050. That’s forcing the utility to begin to improve its section of the grid.

Xcel is building a system it calls Advanced Grid, which will allow for more customers to attach solar panels onto their homes and provide power to the utility’s system. It will also allow for the two-way flow of information between customers and the company so that appliances could one day take signals from the grid about when to draw power — saving customers money.

Improving the grid may also open up new opportunities. Drake Bartlett, a senior trading analyst with the company, said Xcel will explore ways to share power with markets outside of Colorado. Right now the power it generates in Colorado remains in the state.

“As we move towards a carbon-free grid, we have ideas of where it’s going to come from, how we’re going to get there,” he said. “But there are other parts of it that we don’t know.”

That uncertainty extends to what grid infrastructure improvements will be needed. Inadequate updates to the country’s electric grid now could cost customers later. Worst case scenario, they could lead to brown or blackouts, according to Juan Torres associate lab director for the Energy Systems Integration Facility at the National Renewable Energy Lab.

Without federal guidance, each state has to find its own way.

“You have to work within the constraints of the culture and what the people in the region, what their appetite is,” said Torres. California, which has a carbon-free goal for 2045, is importing some renewables from out of state. Overseeing future grid improvements will be the job of the California Independent System Operator.

The state has already invested billions in updating transmission lines to allow easier exchange of energy into Nevada and Arizona and facilitated quick regional sales of energy using a system called Western Energy Imbalance Market.

Neil Millar, executive director of infrastructure development at CAISO, said it will take a “broad suite” of solutions to update the grid and make a 100 percent carbon-free future a reality.

“Reinforcing those different corridors, and getting the appropriate market structure in place so that people can make the best use of the assets they do have is really playing an important role,” Millar said.