The annual letter from the Gates Foundation calls for an "energy miracle" — the creation of a cheap and clean source of energy to get power to the 1.2 billion people on the planet without electricity.
"We need to try lots of crazy-seeming ideas so we can find a few that help us solve the world's energy challenge," Bill Gates writes in the letter, urging today's high school students to take on this task.
We asked people who work on energy issues in the developing world: In your mind, what would an energy miracle be? Are there any downsides?