Renewable sources of electricity overtook coal last year to become the largest source of installed capacity in the world, according to the International Energy Agency.

A recent graph is spectacular showing how the cost of solar energy has come down while the volume deployed has gone up. In 1975 a silicon solar energy module cost over $50 per watt, while now it is less than $1 per watt. The milliwatts installed have risen from 1 to 115,000 ! Since 2000 the deployment of solar has doubled seven times.