WASHINGTON (Reuters) Even though he is 15th in the line of succession to the U.S. presidency, Energy Secretary Steven Chu still thinks he's a nerd.

And some in Washington wouldn't argue with his assessment.

While many of President Barack Obama's cabinet secretaries zoom around the nation's capital in black sedans, Chu will occasionally pull into Energy Department headquarters on his bike, with his security detail peddling close behind.

In his commencement address at Harvard University on Thursday, the Nobel Prize-winning scientist admitted he may not be as exciting as previous speakers like Microsoft founder Bill Gates and "Harry Potter" author J.K. Rowling.

"Today, you have me. I am not a billionaire, but at least I am a nerd," Chu said at the beginning of his speech.

Chu went on to talk about the threat of climate change and ended his talk with a line that could have been conjured up by an obsessed adult "Star Trek" fan.

"May you prosper and help save our planet," Chu said.

While not the exact works so often spoken by Mr. Spock, it was close enough.

(Reporting by Tom Doggett; Editing by Christian Wiessner)