Types of Solar Thermal Collectors
Solar thermal collectors are one the important part of any solar thermal system. Efficiency of any solar thermal system is depends upon how much the collector concentrate and convert solar energy of irradiation into thermal energy. solar thermal collectors are classified according to technique they are using for tracking sun and so we can classified them into three categories: stationary, single axis and two axis tracking solar thermal collectors.
Stationary Solar Thermal Collectors
In stationary solar thermal collectors, there is absence of tracking mechanism and due to this the overall efficiency of this type collectors are very less compare to other collectors it ranges from 1% to 5% of total solar irradiation. we can concentrate solar energy equal up to 5 sun concentration only. Flat plate collectors ( glazed and unglazed) , evacuated tube collectors and compound parabolic collectors falls into this category of solar thermal collectors. we can achieve 40ºc to 90ºc temperature from flat plate collector, 50°c to 160ºc temperature from evacuated tube collectors and in compound parabolic collectors temperature ranges from 70ºc to 220ºc. this types collectors are used where we require less temperature and higher cost effectiveness.
Single-Axis Tracking Solar Thermal Collectors
In single-axis tracking solar thermal collectors, there is tracking mechanism for single axis which track sun at different – different angle during day or for particular time period ( season ) and due to this the overall efficiency of this type collectors are high compare to stationary collectors it ranges from 5% to 10% of total solar irradiation. we can concentrate solar energy equal up to 50 sun concentration. Linear Fresnel reflectors, parabolic trough collectors and cylindrical trough collectors falls into this category of solar thermal collectors. we can achieve 60ºc to 240ºc temperature from Linear Fresnel reflectors, 50°c to 300ºc temperature from parabolic trough or cylindrical trough collectors.this types collectors are mainly used in power generation application or in industry for some chemical reaction processes. Temperature generates by this type collectors can directly used to run turbine by water in power generation so this type collectors are widely used.
Dual-Axis Tracking Solar Thermal Collectors
In double-axis tracking solar thermal collectors, there is tracking mechanism which can track sun according to both axis which can concentrate more solar energy and convert into thermal energy. For double-axis tracking, collector is situated in direction which is parallel to solar irradiation coming from sun for that collector have to move its direction constantly and due to this the overall efficiency of this type collectors are highest compare to all other type collectors. It ranges from 10% to 17% of total solar irradiation. we can concentrate solar energy equal up to 1000 to 1500 sun concentration. Due to this high concentration we can achieve very high temperature from double-axis solar thermal collector. parabolic dish reflectors and Heliostat field collectors falls into this category of solar thermal collectors. we can achieve 100ºc to 500ºc temperature from parabolic dish reflectors and 150°c to 1000ºc temperature from Heliostat field collectors. this types collectors are mainly used in industry where very high temperature needed such like melting and molding processes or in high temperature chemical reactions. Due to high complexity and cost of application is high limits the use of this type concentrators or collectors.