The green bubble is an economic theory that the world is facing an over-investment in renewable energy and that the current levels of debts in many clean technology companies are unsustainable.
According to Alexis Madrigal, author of "Powering the Dream: The History and Promise of Green Technology", a large number of windmills and solar heaters already existed in the early 20th century.
[4] From the early 21st century, there has been a large development and investment in renewable energy industry such as hydroelectricity, wind power, solar thermal, and geothermal.
[5] The bubble made a drastic fluctuation in stock prices of companies with respect to green technology; for instance, the stock price of World Water & Solar technologies Inc., which deals with solar powered water pumps, once experienced a steep rise from 5 cents to $2.50 in 2007, subsequently facing a decline to 29 cents after the Great Recession.
[needs update] Juliet Eilperin's Wired article "Why the Clean Tech Boom Went Bust"[2] provided some evidence regarding the fact that the green technology sector was not growing as fast as the market expected.