How close is St. Petersburg to its clean energy promise? It doesn’t know.

St. Petersburg made history in 2016 when it became the first city in Florida to commit to switching to clean energy, citing the threat rising seas pose to a place surrounded by water on three sides.

By 2019, it had produced a detailed plan with an ambitious goal: Homes, businesses and all other infrastructure within city limits would be completely powered by renewable energy by 2035.

But five years after that plan was adopted, the city doesn’t know whether it’s on track because it doesn’t have data on where its electricity comes from.

Based on limited information officials recently received from Duke Energy,...