The company expected to be the first in the United States to operate a small nuclear reactor is facing setbacks that have caused supporters to question whether the novel technology will ever realize its potential as a tool to combat climate change.

This month, NuScale Power, an Oregon-based nuclear company, learned its first customer needed to push back the timeline for when it plans to operate the first reactor from 2026 to 2029. The entire plant of 12 individual 60-megawatt reactors won’t be completed until 2030, a slip from an expected 2027 time frame.