Soon solar will be the cheapest power everywhere

Solar is already the cheapest available power across large swathes of the tropics, writes Chris Goodall - its cost down 99.7% since the early 70s. Soon it will be the cheapest electricity everywhere, providing clean, secure, affordable energy for all.
Towards the end of last year, Shell CEO Ben van Beurden made a little-noticed remark. He said that solar would become the "dominant backbone" of the world's energy system.

He didn't give a date for his prediction, or indeed define what 'dominant' means, but he accepted that the sun will eventually provide the cheapest energy source across almost all of the world.
This is what my new book, The Switch, is about. Just how long will it take to wean the world off fossil fuels using just the forces of the free market rather than quixotic governments? What technologies will we need to complement the intermittent power of the sun?
In some ways, van Beurden's thought is an obvious one. The light and heat coming from the sun provides a continuous stream of about 90,000 terawatts of energy to the planet. (Don't worry about the unit of measurement. The important thing is that this number is six thousand times the requirements of the entire world).