Energy Secretary Steven Chu addressed the community of Harvard University on Thursday for a commencement speech humorously calling himself a nerd.

The year before, Bill Gates, the mega-billionaire philanthropist and computer nerd stood here. Today, you have me. I am not a billionaire, but at least I am a nerd, Chu, the Nobel prize winner said today as laughs grew.

He also said he was grateful for receiving an honorary degree from Harvard, saying his mom will now be satisfied.

Chu, who was picked as the head of the Department of Energy by President Barack Obama this year, talked about climate change and said it is the right time to help steer America and the world towards a path of sustainable energy.

At the same time he invited graduating Harvard students to contribute to a more sustainable energy future bringing tech solutions, better policy options and integrate sustainability in their business as work in their professional fields.

Chu won the Nobel Prize for Physics in 1997. Prior to his appointment as Energy Secretary in January, he was director of DOE's Lawrence Berkeley National Lab, and professor of Physics and Molecular and Cell Biology at the University of California.