Solar radiation on tilted surface.

PPTs

1. Solar radiation on tilted surface- The rate of receipt of solar energy on a given surface on the ground depends on the orientation of the surface with reference to the sun. A full sun tracking surface that always faces the sun receives the maximum possible solar energy at the particular location.

2. Solar radiation on tilted surface- A surface of the same area oriented in any other direction will receive a smaller amount of solar radiation. Measuring instruments give the values of solar radiation falling on horizontal surface. Most of solar collectors or solar radiation collecting devices are tilted at an angle to horizontal, it is therefore necessary to convert data for hourly radiation.

3. Solar radiation measurement- Measurements of solar radiation are important because of the increasing no. of solar heating & cooling applications, and need for accurate solar radiation data . Experimental determination of the energy transferred to a surface by solar radiation required instruments which will measure the heating effect of direct/ beam solar radiation.

4. Solar radiation measuring devices-

5. Pyrheliometer- Measure beam radiations of sun. It uses thermopile for measuring e.m.f difference .

6. Pyrheliometer-

7. Problems of pyrheliometer- Aparture angle Circum solar contributions. Exact tracking of sun.

8. Angstrom pyrheliometer-

9. Angstrom pyrheliometer- It consists of two metal strips s1 & s2 . One of the strips say s1 is focused directly to the sunlight to receive the solar energy. The second strip s2 is covered with sheath M so that it is not focused to the sunlight. Then s1 strip gets heated to high temperature where as s2 is at low temperature .

10. Angstrom pyrheliometer- A thermocouple is connected between the two strips with the galvanometer G . S1 acts as hot junction whereas S2 acts as cold junction. Hence an amount of current flows and thermo e.m.f is generated. A circuit consisting of battery, a voltmeter, a rheostat, a plug key and an ammeter is connected to S2.

11. Abbot silver disk pyrheliometer-

12. Abbot silver disk pyrheliometer- It consists of a silver disk located at the lower end of a tube containing a diaphragm that serves as the  radiation  receiver for a  calorimeter. Radiation falling on the silver disk is periodically intercepted by means of a shutter located in the tube. causing  temperature  fluctuations of the calorimeter that are proportional to the  intensity  of the radiation . The instrument is normally used as a  secondary instrument .

13. Eppley pyrheliometer-

14. Eppley pyrheliometer- This device used for measuring beam radiations. It consists of double walled brass tubes & removable quartz window. The tube is filled with dry air is sealed with crystal window. Temperature compensated bismuth silver thermopile is mounted at one end of brass tube.

15. 2.Pyranometer- Pyranometer can be used to measure both beam radiation & diffuse radiation .

16. 2.Pyranometer- In pyranometer, the radiation from surrounding atmosphere passes through the glass drone & falls on to the black body situated at the center of the instrument. Now the temperature of the body rises after absorbing all the radiation & thus rise of temperature also experienced by the thermopile.

17. 2.Pyranometer- So one side of thermopile will be hot & other side will be cold due to the heat sink. This will create a potential difference between two terminals of thermopiles. Since we know that the temperature difference is related to absorbed by the black body we can say output voltage is linearly & proportional to the radiation .

18. 2.Pyranometer- By using shading ring we can obtain the diffuse radiation Hence we can calculate diffuse and beam radiation by using pyranometer . I total = I B + I D

19. a. Eppley pyranometer- Temperature difference is measured using a thermopile with black & white surface. The sensor has alternate black & white surfaces, making 10-50 thermocouple junctions . The sensor can have concentric rings design or wedges in a circular pattern.

20. b. Yellot solarimeter - Also known as photovoltaic solar cell. In Si solar cells, the light current is a function of incident solar radiation . Their spectral response is not linear.

21. Sunshine recorder-

22. Sunshine recorder- Measures duration of bright sunshine in a day. Sun’s rays focused by a glass sphere to point on a card strip held in a groove in a spherical bowl mounted concentrically with the sphere. Whenever there is a bright sunshine , the image formed is intense enough to burn a spot on the card strip.

23. Sunshine recorder- As the sun moves across sky, image moves along the strip. Thus a burnt space whose length proportional to the duration of sunshine is obtained on the strip.

24. Solar radiation data- Solar radiation data provide information on how much of the sun's energy strikes a location on the earth's surface during a particular time period. Solar radiation data should include following information- Whether they are instantaneous measurement or values integrated over some period of time (Usually hour or day). The time or time period of the measurements .

25. Solar radiation data- Whether measurements are of beam , diffuse or total radiation and the instrument used. The receiving surface orientation (horizontal, may be inclined at a fixed slope or normal) If averaged, the period over which they averaged (Monthly average of daily radiation .