Large metal letters spelling out the school’s name are seen at the entrance of Dunbar High School. (Michael S. Williamson/The Washington Post)

In 2013, then-Mayor Vincent C. Gray cut the ribbon on a brand new Dunbar High School, from where he had graduated in 1959. The old school, housed in a dark, windowless high-rise building in Truxton Circle since the 1970s, had long been deemed unsuitable learning grounds.

And now, nearly two years after the new building opened, Dunbar ranks as the “greenest” school in the world, according to the U.S. Green Building Council’s designation system, which ranks buildings based on environmental sustainability.

The U.S. Green Building Council wrote on its Web site that the 280,000-square-foot high school achieved LEED Platinum certified — the highest level certification possible. And, with a score of 91 out of 110 points, it tops all other schools in the world under the council’s Schools-New Construction rating system.

“This masterpiece of a green learning environment encompasses a photovoltaic array that generates enough energy on a sunny summer day to power all classroom lights for eight hours,” the U.S. Green Building Council wrote. “Additionally, deep below the surface of the school’s athletic fields is Washington, DC’s largest ground-source heat pump, with wells reaching down 460 feet. Two 20,000 gallon cisterns and low-flow systems help to conserve more than 1.4 million gallons of potable water each year.”

Founded in 1870, Dunbar was the country’s first public high school for black students and has graduated many prominent community leaders and professionals, including Gray and D.C. Del. Eleanor Holmes Norton. But in recent decades, the school has struggled. In 2012, only about six in 10 students graduated on time and fewer than 0ne-third of students were proficient in reading and math.

In 2014, the school posted bigger gains on D.C.’s standardized tests than any other city school, although that still meant only 41 percent of the school’s 10th graders passed the reading portion of the test.