Looking ahead to a carbon-free future, Xcel Energy’s nuclear plants are in the process of moving from full-power baseload production to more flexible operations that can work with the fluctuations in renewable energy production.

“The goal is to keep our renewables running at full power without any curtailment,” said Nate Bibus, project lead of the Flexible Power Operation effort. “It’s what our customers want, it’s what is best for the company, and we’re showing that nuclear energy can integrate well with renewables.”

You see, the company has lots of wind power coming online in the next few years, especially starting in late 2020 – not all that far away. And plenty of solar energy is slated to come online in the future, too.

Considering that future state, Nuclear began meeting with Commercial Operations to see how the two groups could successfully work together in the sometimes-tricky, power marketing world. They recognized that increases in renewable production would eventually result in the need to down-power the company’s baseload nuclear units.

Without that option, spot pricing could force electricity prices down to the point where the company would need to pay to move its electric production onto the grid – actual negative pricing, which some companies have experienced.

The two business units began by joining an industry working group on flexible nuclear operations at the Electric Power Research Institute to gain insights on the issue, he said. They obtained lots of data, considered past research and experience, and began laying out what needed to be done.

“With that information, we performed an internal audit of our plants, looking at how we might be able to move to flexible operations,” Bibus said. “After completing a thorough analysis, we developed a phased approach to begin actual demonstrations late last year.”

In December, a first demonstration was held at Minnesota’s Prairie Island Nuclear Generating Plant in conjunction with Commercial Operations and the Midwest Independent System Operator (MISO). Commercial Operations bids the company’s electric generation into the Midwest electricity market, and MISO helps run that market and control the overall grid.

Both the Monticello and Prairie Island Nuclear Plants held subsequent demonstrations which also proved successful. Each demonstration lasts between six and eight hours, he explained, with the plant moving power levels down, holding at times, then moving back up and holding again.

Both plants showed they could lower power to 75 or 80 percent of full load – meaning the flexibility to add or remove upwards of 280 megawatts of generation.

Prairie Island is now bidding into MISO’s day-ahead market – where power plants agree to power down the next day between specific hours, if needed, to give the operator flexibility in managing the grid, Bibus said.

In a phased approach, the company is now participating in that market no more than three days a week for 12 hours at a time. Eventually, the goal is to have the plants available for flexible operations on a daily basis for longer periods of time. Xcel Energy is now looking much farther in depth on what flex power looks like to make their nuclear power plants as nimble and flexible as a combustion turbine power plant with faster response and lower minimum power levels, he said.

The plants also are looking at moving to much lower levels of output – all the way down to 22 percent of full load at Monticello and 36 percent at Prairie Island. An analysis will be completed by the end of the year to determine what form flexible operations will take in the first quarter of 2020. That analysis will look at equipment, reactor operator roles, training needs and other possible shifts in staffing, Bibus said.

“Moving to flexible operations involves reactor operators changing how they do their work in small ways, and how work is scheduled differently,” he said. “While running at full power in a steady state, operators have some time to take on other tasks, whereas with variable levels, they are obviously busier with power-change requirements.”

Nuclear’s training simulators at both plants are a big help in training operators for these changes and fine-tuning skills, he added.

“Being able to move the plants up and down is exciting,” Bibus said. “And to achieve our carbon-free goals and meet demand, we need to complement wind and solar with the biggest carbon-free resource we have – nuclear power.

“Flexible power allows our generation mix to fluctuate to meet our customer needs around renewable energy,” he added. “This new way of thinking is an innovative example of how the company is transforming to address market pressures and customer expectations. It’s a continuous improvement effort aimed at maximizing renewable and carbon-free energy, while maintaining grid stability.”