The largest solar power plant of its type in the world isn’t producing as much energy as planned.

One of the reasons is as basic as it gets: The sun isn’t shining as much as expected.

The Ivanpah Solar Electric Generating System opened in February, with operators saying it would produce enough electricity to power a city of 140,000 people.

Figures from the California Energy Commission show the plant is producing about half of its expected annual output for 2014.

The commission said in a statement that clouds, jet contrails and weather have had a greater impact on power production than anticipated.

Jeff Holland of NRG Energy Inc. says the company is confident long-term generation projections will meet expectations.

The plant is backed by $1.6 billion in federal loan guarantees.