Solar energy collectors

Design of solar energy collectors

1. Submitted To:- Submitted By:- Dr. Sandeep Gupta Kanav S inhmar Er . Shivani Garg M.Tech .(E&EM)(P) Design of Solar Energy Collectors

2. Solar energy Solar energy is radiant light and heat from the Sun that is harnessed using a range of ever-evolving technologies such as solar heating, photovoltaics , solar thermal energy . It is the largest source of energy received on Earth, but its intensity on the earth’s surface is quite low. Solar energy is rapidly becoming the ultimate energy source because of its non- pollluting charcter and its inexhaustible supply .

3. THE SUN Sun is the ultimate source of most of our renewable energy supplies. The sun is an enormous nuclear fusion reactor which converts hydrogen into helium at the rate of 4 million tonnes per second. It radiates energy by virtue of high surface temp, app. 6000°C.

4. SOLAR ENERGY COLLECTOR Solar energy collector is a device which absorbs the incoming solar radiation, converts it into heat, and transfers this heat to a fluid (usually air, water, or oil) flowing through the collector . The solar energy thus collected is carried from the circulating fluid either directly to the hot water or space conditioning equipment, or to a thermal energy storage tank from which can be drawn for use at night and/or cloudy days.

5. Solar collectors are classified as low, medium or high temperature collectors. Low –temperature collectors are used for smaller non-intensive requirements. Medium-temperature collectors are used for heating water or air for industrial and commercial use. High temperature collectors concentrate sunlight using mirrors or lenses and are used for fulfilling heating requirements up to 400ᴼC/20 bar pressure in industries. Temperature range of solar thermal technologies:- Temp. range Low temperature heat <150˚C Medium temperature heat 150-400ᴼC High temperature heat >400ᴼC

6. Types of Solar Collectors Non-Concentrating collectors Concentrating Collectors In these type, the collector area is the same as the absorber area. The whole solar panel absorbs light. Non concentrating solar collectors are generally used for low and medium temperature requirements. Concentrating collectors have a larger interceptor than absorber. Concentrating collectors are used for high temperature requirements.

7. Classification of Solar Collectors

8. Non Concentrating Technology Non concentrating solar thermal collectors are generally used for low and medium energy requirements. Solar water heating is the perfect example of a non – concentrating Common collectors used for solar water heaters are - Flat Plate Collectors and Evacuated Tube Collectors. type of solar thermal application.

9. Flate Plate Collector Flat Plate Collectors -consist of a thin metal box with insulated sides and back, a glass or plastic cover (the glazing) and a dark colour absorber. The glazing allows most of the solar energy into the box whilst preventing the escape of much of the heat gained. The absorber plate is in the box painted with a selective dark colour coating, designed to maximize the amount of solar energy absorbed as heat. Running through the absorber plate are many fine tubes, through which water is pumped. As the water travels through these tubes, it absorbs the heat. This heated water is then gathered in a larger collector pipe to be transported into the hot water system.

10. Components of flat plate collector:- 1. A metallic flat absorber plate 2. Tubes or Channels 3. A transparent toughened glass sheet 4. Fibre glass insulation

11. Evacuated Tube Collector Evacuated tube collectors are more modern and more efficient in design. In evacuated tube systems, this heat loss is reduced by almost totally eliminating conduction and convection heat losses. These can heat water to much higher temperatures and require less area. However, they are also correspondingly more expensive. Instead of an absorber plate, water is pumped though absorber tubes (metal tubes with a selective solar radiation absorbing coating), gaining heat before going into the collector pipe.

12. Concentrating Collector Concentrating collector is a device to collect solar energy with high intensity of solar radiation on the energy-absorbing surface. A concentrating collector is a special form of flat plate collector modified by introducing a reflecting (or refracting) surface ( concentrator) between the solar radiation and the absorber . Here the receiving area of solar radiation is several times greater than the absorber area and the efficiency is high. Mirrors and lenses are used to concentrate sun rays on the absorber. The temperature of working fluid can be raised only up to 500 C. For better performance, the collector is mounted on a tracking equipment to always face the sun with its changing position

13. Schematic of C oncentrating Collector

14. Types of Concentrating Collectors There are different types of concentrating or focusing collector These are as follows : A. Point Focus Technology 1. Fresnel Reflector based dish (ARUN dish) 2. Dual axis tracked paraboloid dish Line Focus Technology 1. Parabolic troughs collectors (PTC) 2. Linear Fresnel Reflector (LFR) Non Focusing Technology 1. Compound Parabolic collectors (CPC)

15. Fresnal Reflector Based Dish Fresnel Reflector Based Dish (ARUN Dish) is made from panels of flat mirrors mounted on a frame such that the incident sunlight is reflected on to a cavity receiver which is specially designed to reduce heat losses. Usually Fresnel Dishes are large and could have an aperture area of 100 m 2 or 160 m. The reflector and the receiver mounted on top are moved to track the Sun such that the reflectors faces the Sun at all times throughout the year. Fresnel Dishes have high efficiencies throughout the year.

16. Schematic Daigram of fresnal Reflector

17. Paraboloid Dish Collector Paraboloid Dish consists of mirrors mounted on a truss structure such that the incident sunlight is reflected on to a cavity receiver which is specially designed to reduce convective and radiation heat losses. The entire array of mirrors and receiver move to track the sun. The reflector and receiver mounted on top are moved to track the sun such that the reflector faces the sun at all times throughout the year. These systems have light structures. Paraboloid Dishes have high efficiencies throughout the year.

18. Schematic Diagram Paraboloid Dish

19. Parabolic Trough Concentrator (PTC) Parabolic Trough Concentrators (PTC) are troughs made from shaped metal and coated with a reflecting material such as highly polished metal (usually aluminium ) or metallised plastic which can withstand sunlight as well as rain and the elements. These surfaces reflect the incident sunlight on to a metallic collector pipe (the receiver) that runs axially along the trough. PTCs can be connected in series on a common axis.

20. SCHEMATIC DIAGRAM FOR PARABOLIC TROUGH

21. Linear Fresnel Reflecting Concentrator Linear Fresnel Reflecting Concentrator (LFRC) is made from multiple strips of straight reflecting material which are mounted on specially designed frames. The mirrors are arranged in a fresnelized manner which reflects the incident sunlight on to a focal line of metallic collector pipe (the receiver) that runs axially above the array of reflectors. The reflector strips are moved such that they always reflect the incident sunlight on to the receiver tube.

22. SCHEMATIC DIAGRAM FOR LINEAR FRESNEL SYSTEM

23. Heliostat field collectors Heliostat field collectors (HFCs) also known as “Power Tower” or “Central Receiver Plant”. In order to avoid the cost and heat losses in transporting a working fluid to a central location, use of sunlight itself as the transfer medium is proposed . In the typical central receiver, the reflector is composed of many smaller mirrors each with its own heliostat to follow the sun. They are nearly flat mirrors that collect and concentrate the solar energy on a tower-mounted receiver located 100 to 1000 meters distant. To maintain the sun’s image on the solar receiver, heliostats tracks the sun throughout the day.

24. SCHEMATIC DIAGRAM FOR HELIOSTAT FIELD COLLECTOR

25. Advantages of HFCs 1. They solar energy is collected optically and transferred to a single receiver point, thus minimizing thermal-energy transport requirements; 2. They typically achieve concentration ratios of 100–1500 and so are highly efficient both in collecting energy and in converting it to electricity; 3. They can conveniently store thermal energy; 4. They are quite large (generally more than 10 MW) and thus benefit from economies of scale.

26. Reference http://epgp.inflibnet.ac.in/view_s.php?category=277