(Bloomberg) -- An unexplained “avian incident” triggered a fire at one of California’s biggest solar farms, affecting 1,200 acres and knocking out 84% of the California Valley Solar Ranch’s generating capacity.

The June 5 incident didn’t damage solar panels at the 250-megawatt power plant, but distribution poles and cables need to be replaced, according a regulatory filing Wednesday from owner Clearway Energy Inc.

About 40 megawatts of the San Luis Obispo County facility are in operation, and it’s expected to return to full service by July 1. Clearway expects the incident to cost $8 million to $9 million this year, after estimated insurance recovery.

The California Valley project was built by SunPower Corp. and was funded in part with a $1.24 billion loan guarantee from the U.S. Energy Department. It was completed in 2013 and sells power to PG&E Corp.

A Clearway spokeswoman didn’t immediately respond to inquiries.

--With assistance from Brian Eckhouse.

To contact the reporter on this story: Millicent Dent in New York at mdent13@bloomberg.net

To contact the editors responsible for this story: Lynn Doan at ldoan6@bloomberg.net, Will Wade, Carlos Caminada

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