Passive solar technologies harness heat energy absorbed from the sun. Heat flows from warmer materials to cooler materials until there is no temperature difference between them. Passive solar technologies are based on this law and can be used in various applications using the heat flow methods to transfer the heat to the desired activity or space. These activities may be cooking, heating and purifying water, solar lighting, causing air movement for ventilation, and other such passive space heating and cooling techniques for solar architecture without the use of mechanical services.