The term passive solar refers to any means of using sunlight for energy without active mechanical systems (as contrasted to active solar). Such technologies convert sunlight into usable heat (water, air, thermal mass), cause air movement for ventilating, or store heat for future use, without the assistance of other energy sources. A solarium on the equator-side of a building is one common example. Passive solar also is used to refer to technology and design principles aimed at reducing summer cooling requirements. Passive cooling is a subset of passive solar technology.
Technologies that use a significant amount of conventional energy to power pumps or fans are classified as active solar technologies. Some passive systems use a small amount of conventional energy to control dampers, shutters, night insulation, and other devices that enhance solar energy collection, storage, and use, and reduce undesirable heat transfer.
Passive solar technologies include direct and indirect solar gain for space heating, solar water heating systems based on the thermosiphon, use of thermal mass and phase-change materials for slowing indoor air temperature swings, solar cookers, the solar chimney for enhancing natural ventilation, and earth sheltering.
More widely, passive solar includes technologies such as the solar furnace and solar forge, but these typically require some external energy for aligning their concentrating mirrors or receivers, and historically they have not proven to be practical or cost effective for widespread use. "Low-grade" energy needs, such as space and water heating, have proven, over time, to be better applications for passive solar energy utilization.
Solar panels are used in passive and active solar hot water systems
Advantages and Comparisons to Active Solar
Passive solar systems have little to no operating costs, often have low maintenance costs, and emit no greenhouse gases in operation. They do, however, need to be optimized to yield the best performance and economics. Energy conservation reduces the size necessary for any renewable or conventional energy system, and greatly enhances the economics, so it must be performed first. Passive solar technologies often yield high solar savings fractions, especially for space heating. When passive solar is combined with active solar technologies or photovoltaics (for example, to power pumps or fans), even higher conventional energy savings can be achieved.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Passive solar."