It's no secret that it is difficult to get an interview with Indian Prime Minister Narendra Modi. When you do get one, questions have to be vetted by the prime minister's office in advance. Even the nation's angriest man cannot ask Modi the tough questions his leadership faces.

The Indian prime minister, like many of his predecessors, has always been more charitable in his interviews to journalists not from India. But he's just met a very different kind of interviewer: David Letterman.

The longtime American talk show host is now helming a documentary series for National Geographic on climate change and solar energy. As part of this, Letterman gets to interview Modi. "I am not nervous but very very excited," in a preview of the upcoming episode.

Modi has gone back and forth on the question of climate change, writing a book about it when he was Gujarat Chief Minister, but later also claiming "climate change is not of our making." He was also seen on a viral clip which showed him going off on a tangent, rambling about ageing and folklore rather than climate change.

This time, he seems to have stayed away from the philosophical path. Letterman's questions appear to have got a more direct response, which seems appropriate considering Modi has made India the spearhead of the International Solar Alliance, an international effort to move to renewable energy.

Is there a way three-hundred to four-hundred million without electricity can go right to solar?

"If the world helps me with technology, helps me with resources, I will be the very first person to switch over to clean energy completely,” 

Here's another excerpt from the Letterman episode, which will air on National Geographic channel on October 30.