National Exhibition and Seminar (Title : Climate Change Mitigation : Role of Renewables) on Renewable Energy . Dhaka, Bangladesh, 24-25 March, 2008
Focus on Climate Change Mitigation: Role of
Renewable
Daily global radiation tilt factor for Dhaka
H.R Ghosh, S K Khadem, N C Bhowmik and M Hussain
Renewable Energy Research Centre, University of Dhaka, Bangladesh
E-mail: hrghosh@yahoo.com
Solar Radiation Measurement at RERC
• Measurement of Global radiation
– Eppley Precision Pyranometer
• Measurement of Diffuse radiation
– Eppley Precision Pyranometer
– Manually adjusted tracking shadow ring
• Measurement of Tilted surface radiation
– Eppley Precision Pyranometer
– Tilt angles
• 100 for Mar-Sep (Monson)
• 400 for Oct-Feb (Winter)
Other features-
– ICP-CON data acquision card
– One minute interval
Solar radiation on tilted surface
• The total radiation on a tilted surface (HT)
HT=Hb+ Hd+ Hr
– direct or beam solar radiation (Hb),
– sky-diffuse radiation (Hd)
– ground reflected radiation (Hr)
Theoretical study
Tilt factor Rb for beam radiation
Tilt factor Rd for diffuse radiation
Tilt factor Rr for reflected radiation
To estimate monthly average tilt factor Liu and Jordan
proposed the following equation
Estimated tilt factor
Measured and Estimated Tilted surface radiation
Errors
|
|
Measured |
Isotropic model |
An isotropic model |
|
Jan |
4.16 |
4.13 |
4.28 |
|
Feb |
4.26 |
4.19 |
5.66 |
|
Mar |
5.19 |
5.11 |
5.18 |
|
Apr |
4.64 |
4.69 |
5.37 |
|
May |
4.90 |
4.64 |
5.38 |
|
Jun |
4.64 |
4.41 |
4.13 |
|
Jul |
3.84 |
3.74 |
4.33 |
|
Aug |
3.96 |
3.84 |
4.18 |
|
Sep |
3.43 |
3.35 |
3.84 |
|
Oct |
4.09 |
4.05 |
4.06 |
|
Nov |
3.96 |
4.01 |
5.50 |
|
Dec |
4.22 |
4.34 |
4.76 |
|
Error |
rms error |
% of error |
|
Isotropic model |
0.02 |
0.36 |
|
An Isotropic model |
.51 |
11.97 |
Conclusion
• For the months Mar-Sep radiation value increases due to the lower tilt angle than that of common practice
• For May month data is insufficient
• Anisotropic model has shown a large
• discrepancy in winter (Oct-Feb) with the others, more data will help to do a strong comment
