The 100 percent fever has hit Colorado. From Aspen to Longmont to the state Capitol, the goal of powering Colorado with 100 percent renewable energy is taking hold.

Critics have questioned the economic and technical viability of such an aim. A study released in December by the Independence Institute, a libertarian think tank, put the cost of replacing Colorado’s coal-fired and natural gas-fired generation, which accounted for 55 percent of the state’s electricity in 2016, at $44.8 billion.

Still, two Democratic gubernatorial candidates — Jared Polis and Mike Johnston — have included it in their campaign platforms. State Sen. Matt Jones, a Boulder Democrat, is sponsoring the “Cheaper Cleaner Power Act,” which sets a target of 100 percent renewable power for the state by 2035.

Boulder, Pueblo, Lafayette, Aspen, Nederland, Breckenridge and Summit County are all part of the movement. On Jan. 9, the Longmont City Council adopted a target of 100 percent by 2030.

Colorado isn’t alone. Hawaii has already adopted the standard, California may follow this year, and more than 50 cities around the country have embraced the goal. The 100 percenters contend moving to all renewable energy will not only be cleaner and address climate change, it will also be cheaper.

But would it be?

“It is a pretty big promise to make,” said Amy Oliver Cooke, director of the Independence Institute’s Energy and Environmental Policy Center. “If you want to go there, go with yours eyes wide open. It is going to be expensive.”

In addition to replacing generation, the electrical grid would have to be overhauled to accommodate renewable energy, which is variable with the sun and the winds, and creates more rapid electricity flows across the grid, according a National Renewable Energy Laboratory (NREL) study.

Jones said that since aging plants and lines will have to be replaced anyway, it makes sense to transition to clean energy. “We are going to have to invest in something, and this can be an economic benefit to the state,” he said.

The price of key technologies — wind, solar and battery storage — are quickly falling. Wind costs are a third of what they were 10 years ago, and in just the last year, lithium-ion battery prices dropped 24 percent and solar costs dropped 30 percent.

In December, Xcel Energy, the state’s largest electricity provider, received bids for new wind, solar and storage projects that were among the lowest ever offered.

“We are in a technology revolution in energy, akin to the change from the horse and buggy to internal-combustion engine car,” said Jones. “In 2004, we adopted a 10 percent renewable energy standard, and Xcel said they couldn’t do that.”

Xcel now gets 30 percent of its power from renewable generation and has a proposal to boost that to 55 percent by 2025.

“We may not have a clear path forward today, but we didn’t have a clear path forward in 2004,” Jones said.

There is a consensus among energy researchers and utility operators that high levels of renewable energy can be put on the electric gird. NREL did a study looking at 80 percent renewable energy for the country by 2050. Moving beyond that is the big question.

In the Independence Institute study, the price tag rises steeply in the final years as more battery storage — the least developed and most expensive technology — is added. “The grid can effectively manage relatively high levels of renewables as long as it has something to balance it out,” said Dustin Meyer, an analyst with Energy Ventures Analysis, a Washington, D.C., consulting firm that did the study.

When all fossil-fuel plants shut, Energy Ventures sees the balancing done with batteries.

An analysis by Stanford University researcher Mark Jacobson concluded it would be possible to power the entire American economy with cheap renewable energy by 2050.

Polis has cited, or mis-cited, Jacobson’s work saying going to 100 percent would create 49,000 construction jobs and 21,000 operations jobs in Colorado, while saving consumers 10 percent on energy costs. But Jacobson’s calculations are for converting everything — electricity, heating, transportation, industry — to renewable energy, while most 100-percent plans are just focusing on electricity.

A group of researchers argue that Jacobson’s models were flawed and that as you approach 100 percent, renewables become more expensive and vulnerable to weather fluctuations.

Jacobson responded that the critics willfully mischaracterized his work and were carrying water for the nuclear industry. “We are saying this is technically possible,” Jacobson said in a podcast last year. “Whether it is a good idea or not is a political issue.”

While energy researchers battle over their models, the on-the-ground experience of Aspen, the third community in the nation to reach the 100 percent goal, is instructive.

Getting to 80 percent was relatively easy, the next 20 percent was hard, said David Hornbacher, the city’s director of utilities and environmental initiatives.

Aspen ended up meeting the goal through a power agreement with a new hydro project in Ridgway, Colo., about 90 miles from Aspen, and investing in a wind farm in Nebraska 200 miles away.

“Aspen took flak from renewable-energy advocates for not building their own,” said Elizabeth Doris, who manages an NREL program advising state and local governments, including Aspen. Local solutions were too expensive, Hornbacher said.

“Some of the challenges of the last percentage is trying to make the resource match your load characteristic,” Hornbacher said. For Aspen, the challenge was making sure it had lots of electricity for the Christmas holidays.

Still, there is growing interest across the country in trying to reach the target for reasons of environment, health, economics development or self-sufficiency, Doris said. “It almost gets to a very American ideal, what do you want for your community? Why do you want to do this?”

Mark Jaffe, a former Denver Post reporter, writes on Colorado environment and energy issues.

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