Visitor Center at Great Sand Dunes National Park. The intense Colorado sun heats the Trombe Wall behind the lower two pains of those windows. That heat then warms the whole wall which then gives off heat on the inside side of the wall and heats the building. Notice that the wiindows are set back so that the low in the sky winter sun will heat the wall but the high in the sky summer sun will not strike it and therefore not heat it!!!