Imagine you spend about $10,000 for a 3-kW solar photovoltaic (PV) system – the size needed for an average family – and your neighbor to the east adds a second story to his garage.

The addition is designed for offspring who will perhaps never leave home, but it shades your new solar panels. It’s not too bad in summer, but in winter it blocks all but an hour of late morning sun. You would have been better off taking that two-week vacation in Jamaica or Cabo San Lucas.