Compare and contrast passive solar collection and active solar collection.

Passive solar energy collection features buildings that are designed, and building materials that are chosen, to maximize direct absorption of sunlight in winter, even as they keep the interior cool in the heat of summer. One passive solar design technique involves installing low, south-facing windows to maximize sunlight capture in the winter (in the Northern Hemisphere, or north-facing windows in the Southern Hemisphere). Overhangs that block light from above can shade these windows in the summer when the sun is high in the sky and when cooling, not heating, is desired. Passive solar techniques also include the use of heat-absorbing construction materials. Often called thermal mass, these materials absorb heat, store it, and release it later. Thermal mass (of straw, brick, concrete, or other materials) most often makes up floors, roofs, and walls, but also can comprise portable blocks. Any of these may be strategically located so that in cold weather the mass receives a great amount of sunlight and can radiate heat in the interior of the building. In warm weather, the mass should be located away from sunlight so that it absorbs warmed air in the interior to cool it. Passive solar design can also involve using vegetation planted in particular locations around a building. By heating buildings in cold weather and cooling them in warm weather, passive solar methods help conserve energy and reduce energy costs.

This approach contrasts with active solar energy collection, which makes use of technological devices to focus, move, or store solar energy. One active method for harnessing solar energy involves using solar panels or flat-plate solar collectors, which are most often installed on rooftops. These panels generally consist of dark-colored, heat-absorbing metal plates mounted in large, flat boxes covered with glass panes. Water, air, or antifreeze solutions are run through tubes that pass through the collectors, transferring heat throughout a building. Heated water can be pumped to tanks designed to store the heat for later use and through pipes designed to release the heat into the building. Such systems have proven especially effective for heating water for residences.