http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2008/03/01/HO1AV6S5K.DTLThe pre-Columbian ancestors of today's Indians used it. So did the ancient Romans, the medieval Arabs and many other preindustrial peoples around the world.
It's still widely used in less-developed countries, and it is increasingly popular in well-developed countries as energy shortages loom.
"It" is passive solar technology, a building technique used to gather and store free heat from sunlight during the day to use for heating buildings at night. It has been in use since ancient times because it's easy to design and to incorporate into new or existing buildings, inexpensive to install, durable and as reliable as the sun itself.
Passive solar technology came into use when early builders noticed that dense building materials, such as stone and brick, remained warm for hours after being heated by the sun. By facing a stone or brick wall toward the sun (south or southwest), the builders could capture and store the sun's heat in the wall during the day. At night, the warm wall would help heat the building.
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