Solar Thermal Collectors

Solar Thermal collectors, integral components in the realm of renewable energy, are specialized devices meticulously engineered to capture and harness the abundant energy emitted by the sun. Their primary function revolves around the absorption of solar radiation, a process pivotal to transforming sunlight into either heat or electricity, depending on the collector’s design and intended application.

These ingenious devices exhibit a rich diversity, existing in various forms, each carefully tailored to address specific energy needs and employing distinct conversion methods. The versatility of solar collectors arises from their adaptability to diverse environments and energy requirements.

Moreover, the application-specific adaptations of solar collectors extend to air-based and water-based systems. Air-based collectors, including transpired and non-transpired types, harness solar energy to heat air for space heating or industrial processes. Water-based collectors, such as solar water heaters, utilize sunlight to heat water directly, catering to domestic or industrial hot water requirements.

In essence, solar collectors epitomize the fusion of technological innovation and environmental consciousness. Their varied forms and functions underscore their crucial role in the transition towards cleaner, more sustainable energy sources, offering a multitude of solutions to diverse energy needs across residential, commercial, and industrial landscapes. As advancements persist in materials, design, and efficiency, the trajectory of solar collectors continues to shape a greener and more energy-efficient future.

Solar collector types

Air-based (transpired and non-transpired types)

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

 

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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

 

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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

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 water 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 troughs, parabolic dish systems, and central tower receiver systems.

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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.

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