NEW YORK, Oct 5 (Reuters) - Shares of Rivian Automotive Inc fell by more than 20% on Thursday, after the electric vehicle maker unveiled plans to issue $1.5 billion worth of convertible green bonds.

Irvine, California-based Rivian expects the bonds, which will mature in October 2030 and can be converted to either cash or its shares, will help it to "de-risk" the launch of its R2 sports utility vehicle in Georgia, a company spokesperson told Reuters on Wednesday.

It is the second time in less than a year that Rivian is issuing such a green bond, which raises capital from investors seeking to back climate-focused projects. The company had issued a $1.3 billion convertible green bond in March to support the launch of its smaller R2 vehicle family.

Rivian's shares fell 20.5% to as low as $18.83 on the session, and were on course for their biggest daily percentage decline since May 2022. Its shares are now up about 4% year-to-date.

Rivian, which is backed by e-commerce giant Amazon, has been burning through cash to ramp up production and keep up with market leader Tesla (TSLA.O), which has slashed prices. The company beat estimates in the third quarter by producing 16,304 vehicles and delivering 15,564 vehicles to customers. It is on track to deliver 52,000 vehicles this year.

As of Sept. 30, Rivian had about $9.1 billion in cash on its balance sheet, down from $10.2 billion in June. In August, Rivian Chief Executive Robert Scaringe said it had enough money to last it through 2025 as it keeps a lid on costs. (Reporting by Chibuike Oguh in New York; Editing by Lance Tupper, Alexandra Hudson)