Solar power as a required part of new construction is starting to catch hold. Last year, we saw South Miami mandate 2.75 kW of solar for every 1000 square feet on new homes. Prior to that it’d been a few cities within California (Lancaster led the way in 2013, with Sebastopol, Santa Monica, and San Francisco) requiring solar with new construction. Now, of course, we live in a time where the whole of the State of California has set a requirement for all new low-rise residential construction to have solar in 2020, and there is much speculation on what that might do to lower installation costs.

On November 27, Watertown, Massachusetts, population ~35,000, voted unanimously to set a requirement that all new commercial construction greater than 10,000 feet, retrofits of sites that are greater than 10,000 feet, and all new residential structures with ten or more units must include solar power.

The Planning Board Report zoning amendments (.pdf) require a solar system equivalent to 50% of the roof area of the building, as well as 90% of uncovered areas of garages. The new zoning requirements did allow for exceptions where the solar ready zone is shaded for more than 50% of daylight hours,

A history of the new solar requirement by Wickedlocal.com, shows that the work on it it started in January of 2016. The legislation was revived in September 2017 after moving slowly, and with the time passing it had to be completely rewritten. And between that rewrite and November 27, there were more iterations before it finally came to a vote that ended unanimously.

NREL suggests that rooftop spaces in the USA could meet 39% of the country’s electricity needs. Of note in this study is that the most recent version significantly increased the potential of rooftop based on increasing technology in the field, specifically noting that it used a 16% efficient module for those calculations. The report noted that if the industry standard moved to 20% efficient solar modules, we’d see that 39% number increased by 25% to just over 48% of the USA’s electricity load.

Also of note in this report is that the data did not include parking lots, building facades and only supposed that 23% of the nation’s buildings could sustain solar power on their rooftops. Recent research suggests that if we could install a 15% efficient solar glass on building facades, that would meet 40% of the nation’s electricity needs on its own.

Recent polling suggests a majority of Americans would support state level mandates requiring solar power with all new homes. Support for a state home solar mandate was strongest among Democrats, at 73%, with 57% of Republicans saying they would support one.