Active solar technologies are employed to convert solar energy into usable heat, cause air-movement for ventilation or cooling, or store heat for future use. Active solar uses electrical or mechanical equipment, such as pumps and fans, to increase the usable heat in a system. Solar energy collection and utilization systems that do not use external energy, like a solar chimney, are classified as passive solar technologies.
Solar hot water 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, used to orient photovoltaic arrays, may be driven by either passive or active technology.
Solar trackers may be driven by active or passive solar 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.
Solar technology comparison
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 pumps or fans. A computer analysis, using thermodynamics and heat transfer software, can be used to compare the performance of various active and passive solar thermal strategies
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