Yet between these two ends of the spectrum is the hugely important — if less photogenic — commercial rooftop solar market, encompassing factories, malls, churches and hotels.

Non-residential solar has lost momentum in the US compared with other segments, going from the largest sector only a few years ago to the smallest in the first quarter of 2014.

Partly this shift is due to growth in other sectors; much of the incredible financial innovation in the US solar industry over the past year or so has happened in the residential rooftop sector.