Short Answer:

The types of solar collectors are mainly divided into two categories: non-concentrating solar collectors and concentrating solar collectors. Non-concentrating collectors include flat plate collectors, evacuated tube collectors, and air heaters, while concentrating collectors include parabolic trough collectors, parabolic dish collectors, and solar power towers.

Each type of solar collector is designed for a specific temperature range and application. Non-concentrating collectors are suitable for low to medium temperatures like water heating, while concentrating collectors are used for high-temperature applications such as power generation.

Detailed Explanation :

Types of Solar Collectors

Solar collectors are devices used to capture the sun’s radiant energy and convert it into useful heat energy. Based on the method of collecting and concentrating solar radiation, solar collectors are broadly classified into two main types:

Non-Concentrating (Flat Plate Type) Solar Collectors
Concentrating (Focusing) Solar Collectors

Both types serve the same purpose of utilizing solar energy for heating or power generation but differ in their design, working temperature, and efficiency.

Non-Concentrating Solar Collectors

In non-concentrating solar collectors, the area that receives solar radiation and the area that absorbs it are the same. These collectors capture sunlight directly over a large area without focusing it on a smaller region. They are generally used for low to medium temperature applications (up to about 150°C).

The most common types are:

a) Flat Plate Collector (FPC):

The flat plate collector is the most widely used solar collector for domestic and industrial water heating.
It consists of a flat absorber plate, which absorbs solar radiation and converts it into heat.
The plate is coated with a black surface to maximize absorption and minimize reflection.
Tubes are attached to the plate through which the working fluid (usually water or air) flows and absorbs heat.
The collector is enclosed in an insulated casing with a transparent glass cover that allows sunlight in and prevents heat loss (greenhouse effect).

Applications: Used for water heating, space heating, solar cookers, and drying.
Temperature range: 30°C – 100°C.
Advantages: Simple design, low cost, and long lifespan.

b) Evacuated Tube Collector (ETC):

An evacuated tube collector consists of multiple parallel glass tubes, each containing an absorber and a vacuum in between.
The vacuum acts as an insulator, preventing heat loss and improving efficiency, especially in cold climates.
Sunlight passes through the outer transparent glass tube and heats the inner absorber, which transfers the heat to the working fluid.
The tubes can be positioned at an angle to capture maximum solar radiation throughout the day.

Applications: Hot water generation in residential and commercial buildings.
Temperature range: 50°C – 150°C.
Advantages: High efficiency, excellent performance in low sunlight conditions, and low maintenance.

c) Air Collector:

In this type of collector, air is used as the working fluid instead of water.
Air passes through channels or ducts placed below the absorber plate, where it absorbs heat from sunlight.
These collectors are simple and used for space heating or drying agricultural products.

Applications: Solar dryers, building heating, and industrial drying.
Temperature range: 30°C – 100°C.
Advantages: Simple design and no freezing or leakage problems.

Concentrating Solar Collectors

Concentrating solar collectors use mirrors or lenses to focus sunlight from a large area onto a smaller receiver area. This increases the temperature of the working fluid, allowing the system to achieve high temperatures (150°C to 1000°C or more).

They are mainly used for industrial heating and power generation where high-temperature heat is required.

The main types of concentrating solar collectors are:

a) Parabolic Trough Collector:

The parabolic trough collector uses a parabolic-shaped mirror that focuses sunlight onto a receiver tube (absorber) located at the focal line of the mirror.
The receiver tube carries a heat transfer fluid (like synthetic oil or molten salt), which absorbs the concentrated heat.
This high-temperature fluid is then used to produce steam that drives a turbine to generate electricity.

Applications: Solar thermal power plants and industrial heating.
Temperature range: 150°C – 400°C.
Advantages: High efficiency and suitable for large-scale applications.

b) Parabolic Dish Collector:

The parabolic dish collector has a dish-shaped mirror that focuses sunlight onto a small receiver located at the focal point of the dish.
It can achieve very high temperatures due to its precise focusing capability.
The heat is used to drive a Stirling engine or other heat engines directly connected to the receiver.

Applications: Small-scale power generation and high-temperature research.
Temperature range: 500°C – 1000°C.
Advantages: High efficiency and compact design.

c) Solar Power Tower (Heliostat Field Collector):

The solar power tower system consists of a field of heliostats (mirrors) that track the sun and reflect sunlight onto a central receiver mounted on a tall tower.
The concentrated solar energy heats the fluid in the receiver (usually molten salt), which is then used to generate steam for driving turbines.
It can achieve very high temperatures and allows thermal energy storage for continuous operation.

Applications: Large-scale solar thermal power generation.
Temperature range: 500°C – 1200°C.
Advantages: High output and efficient energy storage capabilities.

d) Linear Fresnel Reflector Collector:

Uses long, flat, or slightly curved mirrors arranged in rows to reflect sunlight onto an elevated receiver tube.
It is a cost-effective alternative to parabolic trough systems with slightly lower efficiency.

Applications: Industrial heating and medium-scale power generation.
Temperature range: 150°C – 400°C.
Advantages: Simpler construction and lower installation cost.

Comparison Between Non-Concentrating and Concentrating Collectors

Feature	Non-Concentrating Collectors	Concentrating Collectors
Sunlight Collection	Direct and uniform	Focused using mirrors/lenses
Temperature Range	Low to medium (up to 150°C)	High (up to 1200°C)
Applications	Water heating, drying	Power generation, industrial heating
Efficiency	Moderate	High
Cost	Low	High

Applications of Different Types of Solar Collectors

Flat plate collectors: Domestic water heating, solar cooking.
Evacuated tube collectors: Hot water supply for hospitals and hotels.
Parabolic trough collectors: Solar power plants and process heating.
Solar tower systems: Large-scale power generation.
Air collectors: Agricultural drying and building heating.

Advantages of Using Different Types of Solar Collectors

Utilizes a renewable and free energy source (sunlight).
Reduces greenhouse gas emissions.
Provides energy for a variety of temperature ranges.
Low maintenance and long operational life.
Reduces dependency on fossil fuels.

Conclusion :

The types of solar collectors are classified mainly into non-concentrating and concentrating collectors, depending on how they capture and use sunlight. Non-concentrating types like flat plate and evacuated tube collectors are ideal for low-temperature applications, while concentrating types such as parabolic trough and dish collectors are suitable for high-temperature power generation.

Each type plays a significant role in solar thermal energy utilization and helps promote renewable, sustainable, and clean energy systems for both domestic and industrial applications.