The man who knows more about doubling rates than anyone else in the world
(he accurately predicted computers winning at chess and the Internet,
including the correct dates),

Ray Kurzweil, interviewed by Lauren Feeney on PBS:

One of my primary theses is that information technologies grow
exponentially in capability and power and bandwidth and so on. If you
buy an iPhone today, it’s twice as good as two years ago for half that
cost. That is happening with solar energy — it is doubling every two
years. And it didn’t start two years ago, it started 20 years ago. Every
two years we have twice as much solar energy in the world.

Think about how fast the Internet has grown in the 21st century.
That’s what he’s talking about: from unknown to TV news anchors
to facilitating multiple revolutions in weeks. He continues:

Today, solar is still more expensive than fossil fuels, and in most
situations it still needs subsidies or special circumstances, but the
costs are coming down rapidly — we are only a few years away from
parity. And then it’s going to keep coming down, and people will be
gravitating towards solar, even if they don’t care at all about the
environment, because of the economics.

So right now it’s at half a percent of the world’s energy. People tend
to dismiss technologies when they are half a percent of the solution. But
doubling every two years means it’s only eight more doublings before
it meets a hundred percent of the world’s energy needs. So that’s
16 years. We will increase our use of electricity during that period,
so add another couple of doublings: In 20 years we’ll be meeting all
of our energy needs with solar, based on this trend which has already
been under way for 20 years.

People say we’re running out of energy. That’s only true if we stick
with these old 19th century technologies. We are awash in energy from
the sunlight.

So why bother with burning forests for energy?

-jsq