It’s not easy to understand why city governments don’t already require that all new commercial buildings need to have solar panels on their roofs. That seems a simple measure that will generate a lot of clean, renewable energy. Ideally, such a measure would apply to all new buildings including residential homes. That’s what Santa Monica in California has decided. In fact, as “the first city in the world”, Santa Monica has gone a step further and requires all new single-family homes built within city limits to be “zero-net energy”. That term refers to buildings that generate as much energy as they consume.