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Use of Solar Energy in Acient Times
The earliest known use of solar energy seems to be the construction of ancient dwellings that were designed to capture the suns heat during the day and release it at night time, thus warming their homes at night. These techniques were used by the Egyptians, Romans and Native Americans.
Roman bath houses went to the extent of orienting the building to gather the maximum amount of heat from the sun as opposed to orienting to the cardinal directions.