Electron Capital Partners founder Jos Shaver told investors he’s stepping down as chief investment officer and managing partner of the $3 billion hedge fund firm for health reasons.

“Though I am stepping back from the day-to-day management of the portfolio and firm, I will remain an active presence at Electron,” Shaver said Friday in a letter to clients.

Ran Zhou, a partner and portfolio manager, will take on Shaver’s role leading the firm, which focuses on the global energy transition away from fossil fuels. Zhou has worked at New York-based Electron since 2005.

Shaver, who hasn’t redeemed any money from Electron, will remain on the board and investment committee and serve as a senior adviser, according to the letter.

Electron’s hedge fund lost 10% this year through September as shares of clean energy companies and utilities fell. The fund has returned 10% on an annualized basis since its 2005 inception.