Duke Energy Corp. provides the most solar-generated watts per customer of any utility in the southeast United States, an environmental group found, with the region projected to have 15,000 MW of that capacity by 2021.

The company will continue to lead the southeast in the coming years on solar, the Southern Alliance for Clean Energy, or SACE, said in a Feb. 27 report. While the nonprofit recognized some of Duke's peers for their work, SACE also called out three electric organizations for not doing enough on solar.

"The Southeast has tremendous solar potential ... and has been experiencing near exponential solar growth for the last five years," SACE wrote in its assessment. The region currently has 6,000 MW of sun-powered generation, with SACE forecasting 9,000 MW of new solar coming online over the next four years.

Much of that development will be attributed to utility-scale projects and existing contracts, the report said. Despite high customer interest, SACE cautioned, less growth is predicted in the residential and commercial sectors. And in 2021, the group said, less than 3% of companies' retail sales will be tied to solar, a percentage it described as "considerably below levels that could trigger changes in grid operation practices."

In 2017, Duke subsidiaries Duke Energy Progress LLC and Duke Energy Carolinas LLC used solar to source a combined 1,591 watts per customer, or W/C, a metric created by SACE to provide what it described as "an equitable, unbiased comparison of various-sized utilities throughout the southeast."

Georgia Power Co., a Southern Co. subsidiary, followed the two Duke utilities, having a 364 W/C rating. Those three power companies are well above the 2017 southeast average of 208 W/C, SACE's rankings of utility systems with more than 500,000 customers.

While Alabama Power Co., another Southern unit, is currently at the bottom of the ranking with 7 W/C of solar sourcing, SACE projects that by 2021, the company will rise to 279 W/C.

The second-to-last place company in 2017, Santee Cooper, provides only 14 W/C. The state-owned utility, legally known as the South Carolina Public Service Authority, will drop to last in 2021, adding just 20 more W/C.

SACE's 'sunblockers'

Santee Cooper, along with the Tennessee Valley Authority and Seminole Electric Cooperative Inc., are the bottom three companies in SACE's 2021 projections, with the environmental group classifying them as "sunblockers" for "sticking with outdated plans with low levels of solar."

"These utilities operate in a public policy vacuum," SACE wrote in its report, "and the slow pace of solar reflects outdated thinking with the utilities' management."

SACE said the Tennessee Valley Authority, or TVA, is exhibiting "monopolistic behavior" and "restricting solar choice" in its service territory. "In contrast to other utilities, TVA's commitment to renewable energy is waning," it said.

The government-owned company faced similar claims at a recent board meeting, during which dozens of citizens criticized everything from TVA's energy mix to executives' private aircraft.

President and CEO Bill Johnson made a point to emphasize the agency's $8 billion commitment to renewable energy over the next 20 years, including "testing the market" for 200 MW of solar. TVA has also started soliciting public comment to update its integrated resource plan.

"TVA is not 'anti-renewable,'" spokesman Jim Hopson wrote in an email to S&P Global Market Intelligence. He said the company has nearly 500 MW of solar under contract, with capacity being added to existing facilities and new ones being built.

The difference between TVA and investor-owned utilities like Duke Energy, Hopson explained, is the former's federal mandate to supply power at the lowest feasible cost. "While renewable energy has come down in price considerably over the past ten years, it is often not the lowest cost alternative," he wrote, adding that solar is intermittent and that TVA wants around-the-clock reliability.

Santee Cooper spokeswoman Mollie Gore said in an email that while the utility is not planning to add significant generation of any kind for the foreseeable future, it has enough capacity to last through the mid-2030s if growth projections hold.

Gore added that Santee Cooper has more than 100 MW of solar online or under contract and it was the first utility to put solar power on the South Carolina grid, among other accomplishments.

SACE says the abandonment of the V.C. Summer nuclear plant expansion "has created an opportunity" for project owners Santee Cooper and South Carolina Electric & Gas Co., a SCANA Corp. subsidiary, "to substantially increase solar power resources."

A spokesman for Seminole Electric did not respond to requests for comment.

Seminole Electric, a nonprofit cooperative serving 1.7 million Floridians, has applied to construct two separate combined-cycle units with a total capacity of 1,623 MW. State regulators meet in March to hear Seminole's case for that gas-fired generation.