Solar Collector

A solar collector is an object that is used to collect energy from the sun, which it does by absorbing solar radiation and converting it into heat or electricity. The material type and coating on a solar collector are used to maximize solar energy absorption.

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Solar collector types

Air based (transpired and non-transpired types)

Dark perforated absorber captures solar energy. The fan then draws in air through collectors of small holes and canopies. Later, air is collected in a cavity between the solar collector and building wall. The air is distributed through the building. The air has an improved quality at low cost. The duct should be located near south wall as part of the building envelope. Aluminum louvers (shading devices) are also used as solar thermal collectors.

Water based

These collectors absorb the sun's radiation through a heat transfer liquid. The radiation is converted into useable heat energy by pumping the heat transfer liquid through a heat exchanger that transfers the energy to the water heater system.

Non concentrating like solar ponds (solar radiation is absorbed and trapped on the bottom of the pond. temperature inversion due to density of salt water), flat plate and evacuated
Concentrating like Trough, Dish and power tower

Domestic types

Flat plate unglazed & Plastic Absorber collectors

Low cost
Low temperature (0-10c rise)
Rugged
Lightweight
Seasonal pool heating
Poor performance in cold or windy weather

Flat plate glazed

Simple construction
Insulation and glazing prevent heat loss
High temperature operation (0-50c rise)
Selective surface improves performance
Moderate cost
Heavy and bulky
Easier to integrated

Evacuated tube collector

Very good at reaching high temperature (10-150c rise)
No convection heat loss
Difficult to integrate into roof
Suitable for cold climates
Fragile
Cost more money than flat plate

Domestic solar water heating system (DSWH)

Passive: use gravity and tendency for water to naturally circulate as it is heated through the system without a pump. They are generally more reliable and easy to maintain.

Batch heater: these are the simplest solar hot water systems. Their simple design consists of a tank of water within a glass covered insulated enclosure carefully aimed at the sun.
Thermosyphone features: Natural circulation of water, Flat plate collector, Collector placed below the storage tank, Hot water is taken from the top of the tank

Active: active systems use electric pumps, valves and controllers to
circulate waters or other heat transfer fluids through the collectors.
Active types are two direct and indirect models

The energy density of flat plate and evacuated tube systems limits the temperature rise to 150c. For more temperature applications, need to increase incident energy density by focusing solar radiation onto a smaller area which is used in solar concentration systems such as parabolic trough, parabolic dish systems and central tower receiver systems.

Solar district heating systems

The surface to volume ratio of a central storage tank is much better than that for distributed storage systems. So the storage losses are much lower and even permit seasonal heat storage. Solar district heating is also an option if room heating is to be covered by solar energy. Nevertheless, there are higher piping losses with a central tank.