Solar Energy and Solar Collectors

Solar Energy and Its Utilization

• Solar energy is a clean, cheap, and abundantly available renewable energy source.
• Solar energy can be used directly as thermal energy and indirectly using solar photovoltaic cells to convert it to electricity.

Solar Collectors

• Solar collectors are devices that collect solar radiation and transfer the absorbed energy to a fluid.
• The main types of solar collectors are:
  • Non-concentrating (flat plate) collectors
  • Concentrating collectors (parabolic dish, parabolic trough, power tower, and stationary concentrating collectors)
• The important features of a solar collector include:
  • Collector efficiency
  • Concentrating ratio (CR)
  • Temperature range

Types of Solar Collectors

Flat Plate Collectors

• Absorbs both direct and diffuse solar radiation
• Does not require a sun-tracking system
• Simple construction and low maintenance

Evacuated Collectors

• Uses a vacuum-sealed glass or metal tube to minimize heat loss
• Inner tubes contain a heat-absorbing material that converts sunlight into heat

Parabolic Trough Collectors

• Uses a parabolic reflector to focus sunlight onto a receiver
• Can achieve high temperatures and efficiencies

Mirror Strip Collectors

• Uses a series of curved mirrors to focus sunlight onto a receiver
• Can be used for both heating and cooling applications

Solar Energy Storage

• Solar energy storage systems are necessary to match energy generation with load demand
• The main types of solar energy storage systems are:
  • Thermal energy storage
  • Chemical energy storage
  • Electrical energy storage
  • Hydrogen energy storage
  • Electromagnetic energy storage
  • Biological energy storage

Thermal Energy Storage

• Can be achieved through sensible heat storage or latent heat storage
• Sensible heat storage uses the heat capacity of a material to store energy
• Latent heat storage uses the phase change of a material to store energy

Solar Pond

• A solar pond is a large, shallow pond with a salt concentration gradient
• The top layer has a low salt concentration and is at atmospheric temperature
• The bottom layer has a high salt concentration and can reach temperatures of 70-85°C
• The hot brine solution can be used to generate electricity

Solar Water Heater

• A small capacity water heating system using natural circulation
• Suitable for domestic hot water supply
• Consists of a flat plate collector and a water storage tank

Solar Thermal Pump

• Uses solar radiation to generate mechanical power for pumping water
• Suitable for irrigation pumping and has low running and maintenance costs

Solar Cookers

• A device that uses sunlight to cook or heat food
• Can be used for both domestic and industrial applications### Solar Cookers
• Harness energy from the sun and convert it into heat for cooking
• Typically have reflective surfaces (mirrors or panels) that concentrate sunlight onto a cooking area
• Reflective surfaces focus sunlight onto a specific point, increasing intensity
• Cooking area designed to absorb and retain sunlight, using materials with high solar absorption properties (blackened surfaces, dark pots)
• Dark colors absorb more sunlight and convert it into heat, raising the temperature of the cooking area
• Heat is transferred to the cooking vessel or surface, cooking the food

Solar Distillation

• Process of converting saline water into pure water using solar radiation
• Solar device used is called a solar still
• Solar still consists of a shallow blackened basin filled with saline or brackish water to be distilled
• Basin is covered with a sloping transparent roof, allowing sun rays to pass through and be absorbed by the blackened surface
• Water evaporates due to solar heat, rises to the roof, cools, and condenses
• Condensed water is collected by the condensate channel and drained out from the solar still

Solar Thermal Power Plants

• Can use different systems, including:
  • Low temperature solar power plant using flat plate collectors
  • Low temperature solar power plant using solar pond
  • Medium temperature solar power plant using focusing collectors
  • High temperature solar power plant using distributed collector systems (solar farms)

Central Receiver System or Tower Power Plant

• Principle: focus incoming solar radiation to a central receiver or boiler using thousands of plane reflectors (heliostats)
• Mirrors are installed on the ground and oriented to reflect direct beam radiation into the absorber or receiver (boiler)
• Boiler is mounted on a tall tower, allowing it to be in the field of view of all mirrors at all hours of the day
• Beam radiation is absorbed by black pipes, heating the working fluid, which drives a turbine and produces mechanical energy
• Turbine is coupled to an alternator, producing electrical energy