One major expenditure for many of our energy consumption in a household is heating water. The climate here is very agreeable to a passive system and with modification i could see it being used in many places around the united states. The roof top of the building I'm in is very utilitarian (kinda ugly) as most are in Mexico. most of the roofs are flat, providing for a utilitarian space for cleaning dishes, laundry, and other household needs. At the top of the photo are several black water storage tanks that gravity feed the building with hot water. For night time heating they could use a solar water pump to circulate into tubing in the floor if temperatures dropped but they rarely do outside of the mountains, where such a system could really shine. For my offgrid cabin I would like to add this to the system, and create a polycarbonate enclosure to increase the heat and provide some insulation value to prevent a freeze up, doubling as a solar chimney for passive cooling if used like a skylight, taking further advantage of passive lighting indoors. It's probably obvious that because of the climate most buildings are painted light colors like white to keep them habitable during day light hours.