The Department expects a "nonlinear" surge in solar expansion once the key threshold is reached, "paving the way for rapid, large-scale adoption of solar electricity across the US", with solar providing 27pc of the country's power by the middle of the century. If so, solar may prove to be the bigger story than shale in the end."This could take off very fast and catch a lot of people by surprise. The oil and gas industry is starting to smell that renewables are really dangerous for them," said Mr Leggett.
Like all solar survivors, he has emotion invested in his dream, and the prospect of vindication is sweet. What is new is that big global banks are starting to agree. Earlier this year UBS published a report on the "unsubsidised solar revolution", arguing that every rooftop in Italy, Spain and even Germany should have a solar cover based purely on hard economics.
"We believe the solar sector is at an inflection point," says Vishal Shah from Deutsche Bank. "It has passed the tipping point for grid parity in 10 major markets worldwide."
Deutsche Bank said the dramatic fall in the price of solar panels to between $0.60 and $0.70 per watt - lower than thought possible five years ago - has already rendered solar power competitive "without subsidies" in Japan, South Korea, Australia, Italy, Greece, Spain, Israel, South Africa, Chile, Southern California, Hawai and Chile - in some cases because electricity prices are ruinous. (Italy's solar is not efficient but electricity retails at $0.38 per kilowatt hour, compared with $0.15 in Germany and the UK).
These regions could be joined within three years by Thailand, Mexico, Argentina, Turkey and India, among others. Mr Shah said emerging markets are likely to embrace solar over the next decade for hard-headed commercial reasons, without the need for government subsidies. "Solar is now cheaper compared with diesel-based electricity generation in many markets such as India and Africa," he said.
