Solar Energy: Promising, With Challenges

 "A provocative recent essay in Nature Energy by two solar analysts, Varun Sivaram and Shayle Kann, argues that solar still has some hard economic obstacles to overcome before it can become a major energy source and provide (let's say) one-third of our power. Overcoming these hurdles could mean the difference between solar leveling off as a niche technology and solar taking over the world."

How cheap does solar power need to get before it takes over the world?