As climate scientists sound the alarm on the effects of rising global temperatures, many of Colorado's electric utilities are shifting their focus to a popular and potentially profitable goal: zero-carbon.
But they're also stuck with one important question: How do they actually get there?
In an effort to start laying the groundwork for a move away from coal and natural gas, United Power, a northern Colorado utility, has recently started testing new storage technology.
One recent sunny afternoon in Longmont, rows of sleek, white rectangles towered above Jerry Marizza's head. As he walked between them, he struggled to find the right words.
"Each one of these boxes, it's kind of a big…"
He paused. A slight hum filled the silence.
"A big refrigerator," he said, settling on the right comparison.
The boxes, in fact, weren't holding any food. Instead, they contained lithium ion batteries made by Tesla.
United Power, where Marizza works as the new energy program coordinator, bought 80 of the batteries in 2015 and, last fall, installed the units off an I-25 frontage road in Longmont. Their first full charge was in December. The installation is designed to store power from cleaner, intermittent sources such as wind and solar.
When full, the batteries can provide electricity to a small portion of the utility's customers, roughly 1,000 homes for about four hours. Their ability to charge at night, when baseload power is cheaper, has already saved the company about $1 million, Marizza said, adding that there's still a lot of trial and error ahead if the company wants to scale it up.
"How do they act on a cold day? How do they act on a hot day?" he said. "Well, the best way instead of reading the brochure that Tesla hands out is to actually have one."
As United Power began testing its batteries this winter, other companies began outlining their goals to ditch carbon.
Last December, Colorado's largest utility, Xcel Energy, announced it would be carbon-free by 2050. That month, northern Colorado's Platte River Power Authority said it would do the same by 2030.
In its plan, Xcel outlined how existing renewable generation and storage technologies alone won't be enough.
Instead, the company is now setting its sights on a "suite" of new technologies including carbon capture and storage, power to gas, seasonal energy storage, advanced nuclear or small modular reactors, deep rock geothermal and "others not yet imagined."
In the company's announcement of the goal in Denver, president and CEO Ben Fowke said he was confident that technology would come.
"Just look at what we've done in the last 10 years," he said. "Today we're investing in large wind and solar projects that are 70, if not 80 percent less expensive than they were a decade ago."
With the help of a new 150-megawatt wind farm in northern Colorado, Platte River Power Authority, which serves Fort Collins, Loveland and Estes Park, projects that it will be able to serve its tens of thousands of customers with about 50 percent zero-carbon sources by next year.
Steve Roalstad, spokesman for Platte River, said the utility's 100 percent goal will heavily rely on better storage technology.
"Battery storage performance really needs to mature and costs need to decline," he said. "We think it's going to continue in this direction."
While utilities like Xcel are betting on big innovations in the next few years, Colorado lawmakers are also trying to speed up the process.
Democratic House Speaker KC Becker is sponsoring a climate action bill that proposes writing zero-carbon goals into state statute.
"This bill will absolutely drive innovation," she said, "and actually grow businesses and I think help the economy as Colorado continues to attract businesses and those businesses help our utilities figure out 'how do we help reduce air pollution? How do we help reduce carbon pollution?'"
One of the more controversial answers to those questions is the early retirement of Colorado's coal plants, which could leave thousands of workers in Pueblo, Craig and other coal-dependent towns without work in the very near future.
Will Toor, director of the Colorado Energy Office, said there's a huge need for laws that help offset the impact of doing away with coal.
One bill under consideration by Rep. Chris Hansen would make it less expensive to pay off the costs of functioning coal plants that are being shut down, he said.
"He has built into that legislation an ability for a portion of those funds to be used directly for economic development and workforce transition in those affected communities," he said. "So I think that's the kind of policy that's really important too to look at going forward."
About one third of Colorado's carbon dioxide emissions come from large electric utilities like Xcel Energy, Platte River and Black Hills. Other large emitters include transportation, oil and gas production and agriculture.