Active solar
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[edit] Definition
Active solar is a term referring to those technologies that can be employed to convert solar energy into usable heat, to cause air-movement for ventilation or cooling, or to store the heat for future use, and which use electrical or mechanical equipment, such as pumps and fans, to facilitate this. Solar energy collection and utilzation systems that do not use external energy are classified as passive solar technologies. A solar chimney is an example of a passive solar technique for enhancing natural ventilation.
Solar water heating systems, except those based on the thermosiphon, use pumps or fans to circulate water, an anti-freeze mixture, or air through solar collectors, and are therefore classified under active solar technology. The solar collectors can be nonconcentrating or 'flat-plate', or of various concentrating designs. Most solar-thermal collectors have fixed mounting, but can have a higher performance if they track the path of the sun through the sky. Solar trackers, sometimes also used to orient photovoltaic arrays, may be driven by either passive or active technology.
Because passive solar systems require no additional energy to operate and therefore have zero operating costs, emit no greenhouse gasses in operation, and can have low maintenance costs, passive solar technologies should be given full consideration.
[edit] Passive and Active solar technologies compared
However, active solar-thermal systems, via small pumps or fans, can have significantly higher solar savings fractions than passive solar technologies due to greatly-enhanced heat transfer and transport. An interesting hybrid approach is to use photovoltaics to power these pumps or fans. A computer analysis, via a program such as F-Chart, can be used to compare the performance of various active and passive solar thermal strategies.
[edit] See also
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