Big utilities are learning to live with, and in some cases even love, large-scale renewables. But the spectacular rise of the rooftop PV market signals something altogether more unsettling: the democratisation of power generation and a two-way energy market.

By the standards of the energy business, US rooftop solar has an exciting story to tell: close ties to Silicon Valley’s elite; charismatic young leaders like SolarCity’s Lyndon Rive and Sunrun’s Lynn Jurich; a convenient adversary in the old utility monopolies; and the promise of market disruption and consumer empowerment.

Homeowners’