With solar garden developers chafing at the slow pace of Xcel Energy's approval process, a state-appointed engineer this week released a blistering report on the big utility's handling of one particular Minnesota solar project.

The findings on that one project could apply to many other Minnesota solar garden proposals, according to both solar developers and Xcel.

The independent engineer, working under the aegis of the Minnesota Public Utilities Commission (PUC), among other things criticized Xcel's cost estimates and engineering standards for a proposed community solar garden near Becker, which is being developed by SunShare, one of the largest solar garden builders in Minnesota.

The findings are emblematic of solar garden developers' broader concerns over the process of hooking up to Xcel's grid. "The whole program has been one delay after another," said David Amster-Olszewski, SunShare's CEO. "The success or failure of renewable energy is dependent on connecting to the electrical grid.

Xcel acknowledged its "process has not been perfect," in a filing this week with the PUC. "We acknowledge at the outset that the [independent engineer] is very critical of the company's interconnection approval and design processes," Xcel wrote. "We take that criticism seriously."

But the company disagreed with a number of the independent engineer's conclusions, saying they should be reconsidered by the full Public Utilities Commission.

Since December 2014, Minneapolis-based Xcel has been reviewing around 1,000 applications from solar garden developers, and 150 megawatts of projects are in design and construction, Xcel said. But just one very small project — less than 1 megawatt — is online. Another 622 megawatts of projects are under study. A megawatt is one million watts of power.

"At the end of the day, Minnesota will have one of the largest community solar garden programs in the country," said Laura McCarten, regional vice president of state affairs.

Getting there is the hard part.

In August, the PUC, which has a limited staff, asked the Minnesota Department of Commerce to hire independent engineers to review complaints from solar garden developers about connecting with Xcel's system. Four engineers were hired, and the first of their reports came out this week.

The report notes that Xcel itself acknowledged it had used faulty computer modeling in assessing the Becker plant's connection to its electrical grid. "Xcel has provided inaccurate site data, inaccurate computer models, and has had to rerun those same models multiple times, delaying SunShare's Becker interconnection completions," the engineer's report said.

The independent engineer disapproved of the high variability of Xcel's cost estimates for connecting SunShare's Becker site to its grid, essentially setting a cost estimate ceiling on the utility.

Xcel, in its appeal, said the independent engineer's "characterization of our [cost] estimates is unfair."

SunShare had also complained that the documentation of cost estimates provided by Xcel was of poor quality.

The engineer called SunShare's assertion "credible," adding "it is expected that any corporation of Xcel's stature produce and provide accurate and complete documentation."

SunShare has about 25 solar gardens planned for the state, which together would generate 100 megawatts of power. Each solar garden generates up to 5 megawatts of energy for local residential and commercial users. The Becker solar garden, for instance, would serve about 700 area customers.

Mike Hughlett • 612-673-7003