Solar power is now the least expensive source of electricity on average in 58 emerging economies around the world, according to Bloomberg New Energy Finance. Why is that important? Many of those countries are part of the developing world, places where, until recently, people have been living in conditions barely more advanced than feudal times.

Energy is what allows human beings to perform deeds that exceed what is possible by using muscle power alone. It builds cities, establishes transportation networks, and creates wealth. Until the advent of the internet, billions of people were blissfully unaware of the modern world. No more. Now that those people know what is possible, they want to share in the blessings of an advanced society — now, not generations in the future.

China is the perfect example. After World War II, it awoke from its own feudal dream and aspired to join the world’s leading nations. To make that happen, it built hundreds of coal-fired electrical generating facilities. Today, the US has less than a dozen cities with more than one million inhabitants. China has 106 and is building more every day.

India is anxious to replicate China’s success. Until recently, it […]