The solar thermal system on the rooftop of the Kelly Cullen Community in San Francisco pre-heats the building’s hot water system and helps minimize the use and operation cost of gas. (Photo courtesy Gelfand Partners Architects)

The solar thermal system on the rooftop of the Kelly Cullen Community in San Francisco pre-heats the building’s hot water system and helps minimize the use and operation cost of gas. (Photo courtesy Gelfand Partners Architects)

The solar thermal system on the rooftop of the Kelly Cullen Community in San Francisco pre-heats the building’s hot water system and helps minimize the use and operation cost of gas. (Photo courtesy Gelfand Partners Architects)