Solar power has become big business, with $131 billion invested in 2018, up from just $11.2 billion in 2004 but down from $171 billion in 2017 as unit costs fell. New installed capacity grew from 1.1GW in 2004 to about 107GW in 2018, a steady rise as solar begins to compete with fossil fuels on cost and to be built in nearly every country. This is a book for the solar workers of the future, a business book for those without a business or economics background and those simply curious about major shifts happening in the world energy economy. Key financial, economic and technical concepts are interspersed with the history of the first decade of cheap solar power, and the author's experience of being part of a successful startup in the clean energy sector.