Measurement and study of Solar Radiation over Bangladesh

Measurement and study of Solar Radiation over Bangladesh (Source : Renewable Energy Research Center under Dhaka University )

Study on global and diffuse radiation of Bangladesh:

Study on solar radiation is important for utilization of photovoltaic and thermal systems over the country. Global and diffuse radiation are being measured in Dhaka and very few other locations. However Bangladesh Meteorological Department is measuring sunshine duration, cloud cover, rainfall and other meteorological parameters in different parts of the country. In RERC, measurement of global and diffuse radiation is going on from beginning of 2003. Earlier, some measurements have been done during 1987-1989 and 1992.

Calibration:

Te pyranometers used for this purpose have been calibrated with a Kipp & Zonen (with calibration certificate) pyranometer. Total hourly global radiation have been measured with an Epply pyranometer and reference pyranometer simultaneously with 2 hand held Solrad data loggers placing the pyranometers in the same condition. Finally pyranometer constants was readjusted for accurate measurement.

Correction:

The measured raw data need some corrections to determine exact radiation falling on horizontal ground. This includes 2 types of correction which are associated with diffuse radiation measurement when shadow ring is used to obstruct the direct part of the radiation.

1) While measuring the diffuse and global radiation a part of diffuse radiation is obstructed by surrounding buildings and trees. This part of diffuse radiation should be found out and be added to the measured diffuse as well as global radiation. The obstacles not more than 5^o were neglected since the radiation coming at an angle less or equal to 5^o have no effect on sensor. The radiation was considered to be isotropic.

The percentage of area covered is 4.7%, therefore diffuse radiation is to be increased by 4.7%. This increased diffuse part is to be added to the measured global radiation.

2) There is another correction for shadow ring which itself obstructs a part of diffuse radiation. According to Drummond’s method the correction factor was found to be 1.07 which should be multiplied to the measured diffuse radiation.

Measured daily averaged global radiation (H) of different stations with correction for obstruction of diffuse radiation

Month	Dhaka	Dhaka	Dhaka	Kolkata	Kolkata *	Joydebpur	Joydebpur	Joydebpur	Bandar ban
Month	RERC	RERC	BCSIR	IMD	IMD	BRRI	BRRI	BRRI	BCSIR
	87-89	2003	Aug99-Apr02	57-78	92-95	87-89	75-89	99-01	May01-Apr02
Jan	4.29	3.25	3.71	4.22	3.65	3.97	3.88	3.69	3.66
Feb	4.86	4.41	4.08	5.03	4.17	4.63	4.68	4.13	4.67
Mar	5.53	4.93	4.82	5.79	5.46	5.32	5.46	5.28	5.18
Apr	5.23	5.68	5.22	6.32	5.89	5.83	5.75	5.30	6.01
May	5.67	5.70	4.24	6.53	6.24	5.53	5.45	4.62	5.72
Jun	5.13	3.95	3.92	4.97	4.69	4.63	4.76	4.26	4.15
Jul	3.87	4.97	4.21	4.64	4.21	4.31	4.36	3.97	4.33
Aug	3.92	4.74	3.73	4.47	4.27	4.48	4.61	4.05	3.75
Sep	4.5	3.77	3.51	4.48	4.29	4.12	4.17	3.71	5.05
Oct	4.61	3.51	3.87	4.56	4.22	4.60	4.45	3.88	3.94
Nov	4.22	4.11	3.91	4.38	3.64	3.98	4.18	4.03	3.14
Dec	3.89	3.4 **	3.49	4.1	3.49	3.80	3.97	3.44	3.25
Yearly Total	1695	1594	1482	1809	1682	1679	1694	1532	1608

*Estimated correction for obstruction of diffuse radiation by 2%

** H_d was estimated for the correction of H of Dec 2002.

Sunshine duration of 2003 for Dhaka

Month	Sunshine duration (Hr)
Jan	5.23
Feb	7.39
Mar	7.16
Apr	8.03
May	7.39
Jun	2.07
Jul	5.03
Aug	5.71
Sep	3.67
Oct	4.83
Nov	8.29
Dec

Determination of correlation coefficients for global and diffuse radiation:

These corrected global and diffuse radiation were used to determine correlation coefficient constants for Dhaka from which global and diffuse radiation of other places can be estimated.

For global radiation estimation from sunshine duration, following Angstrom correlation has been used.

H/Ho=a + b(n/N’)

To include the seasonal effect, the fit was taken for 2 periods, March to September and October to February. The values of a and b as well as correlation coefficients and error have been given below. This a and b can be used to estimate global radiation values all over Bangladesh where sunshine duration is available. This sunshine duration can be measured or estimated from cloud cover or rainfall.

Station	Period	a	b	r	sd
Dhaka	Mar-Sep	0.281	0.383	0.985	0.049
Dhaka	Oct-Feb	0.241	0.419	0.982	0.018

For diffuse radiation prediction, H_d/H=c+d(H/H_o) correlation was used. To determine c and d, global and diffuse radiation of RERC from January to November 2003 have been used. The year was divided into 2 periods Apr-Aug and Sep-Mar for seasonal variation. The other correlation using sunshine duration was also tried but the correlation coefficient was poor. Therefore the values of c and d given below were finally selected to determine diffuse radiation all over Bangladesh. H of places other than Dhaka can be estimated from sunshine duration using correlation for determination of global radiation.

Station	Period	c	d	r	sd
Dhaka	Apr-Aug	0.978	-0.869	-0.905	0.077
Dhaka	Sep-Mar	1.347	-1.657	-0.967	0.110

The following two tables are of global and diffuse radiation of different locations of Bangladesh and Kolkata. All the measured global data have been corrected for obstructed duffuse part and diffuse data was corrected for both obstruction by surrounding obstacles as well as shadowband. Estimated and available measured global radiation data have been presented for three locations of Bangladesh namely Dhaka, Joydebpur and Bandarban. For global radiation, a clear decrease in radiation is observed for recent years which is also true for kolkata and Joydebpur. This may be due to increase in cloud cover which is shown in the graph. For December, H of Dec 2002 was used and for H_dwas predicted using correlation, then necessary correction of H was made.

Evaluated Global radiation (H) of different stations

Month	Dhaka	Dhaka
Month	Evaluated	Evaluated
	79-89	93-03
Jan	4.03	3.55
Feb	4.78	4.31
Mar	5.33	5.21
Apr	5.71	5.61
May	5.71	5.29
Jun	4.8	4.66
Jul	4.41	4.48
Aug	4.82	4.50
Sep	4.41	4.24
Oct	4.61	4.13
Nov	4.27	3.90
Dec	3.92	3.59
YearlyTotal	1728	1626

Measured and evaluated Diffuse radiation (Hd) of different stations with correction

Month	Dhaka	Dhaka	Dhaka	Dhaka	Chittagong	Rajshahi	Kolkata
Month	RERC	Evaluated	RERC	Evaluated	Evaluated	Evaluated	IMD Measured
	87-89	79-89	2003	93-03	92-01	92-01	57-78
Jan	1.20	1.44	1.78	1.78	1.56	1.71	1.50
Feb	1.56	1.66	1.88	2.00	1.86	1.89	1.74
Mar	1.98	2.02	2.42	2.24	2.21	2.15	2.16
Apr	3.21	2.89	2.70	2.88	2.89	2.88	2.66
May	3.30	3.14	3.29	2.97	2.97	3.00	3.09
Jun	2.34	2.97	2.67	2.86	2.87	2.94	3.20
Jul	2.87	2.97	2.89	2.80	2.79	2.83	3.17
Aug	2.50	2.78	2.72	2.75	2.74	2.77	2.92
Sep	2.35	2.47	3.07	2.66	2.60	2.62	2.60
Oct	2.00	1.85	2.05	2.23	2.14	2.10	2.03
Nov	1.03	1.45	1.64	1.76	1.69	1.70	1.54
Dec	1.23	1.33	1.69*	1.59	1.44	1.52	1.33
Yearly Total	778	820	876	867	844	855	850

* Hd of Dec 2002 has been estimated

Hourly global radiation fraction (r_G = H_h/H) for Dhaka

Month	Clock time
	5:30	6:30	7:30	8:30	9:30	10:30	11:30	12:30	13:30	14:30	15:30	16:30	17:30	18:30

Jan			0.024	0.063	0.103	0.135	0.154	0.157	0.142	0.112	0.074	0.034
Feb			0.027	0.063	0.099	0.129	0.147	0.151	0.139	0.113	0.079	0.042	0.009
Mar		0.008	0.036	0.069	0.101	0.126	0.141	0.143	0.131	0.108	0.078	0.045	0.015
Apr		0.018	0.046	0.075	0.103	0.124	0.136	0.135	0.124	0.102	0.074	0.045	0.018
May	0.003	0.025	0.051	0.078	0.102	0.121	0.131	0.130	0.119	0.099	0.073	0.046	0.021
Jun	0.004	0.025	0.050	0.076	0.100	0.118	0.128	0.128	0.118	0.099	0.075	0.049	0.025	0.004
Jul	0.005	0.022	0.047	0.074	0.099	0.118	0.129	0.129	0.120	0.101	0.077	0.051	0.026	0.007
Aug		0.019	0.046	0.074	0.101	0.121	0.133	0.133	0.123	0.102	0.076	0.048	0.021
Sep		0.017	0.046	0.078	0.107	0.129	0.140	0.138	0.124	0.100	0.070	0.039	0.011
Oct		0.014	0.046	0.081	0.114	0.137	0.148	0.144	0.126	0.097	0.063	0.029	0.000
Nov		0.006	0.041	0.080	0.116	0.143	0.155	0.151	0.130	0.098	0.059	0.022
Dec			0.031	0.071	0.111	0.142	0.158	0.157	0.137	0.105	0.064	0.024

Hourly diffuse radiation fraction (r_D = H_D/H) for Dhaka

Month	Clock Time
	5:30	6:30	7:30	8:30	9:30	10:30	11:30	12:30	13:30	14:30	15:30	16:30	17:30	18:30
Jan			0.041	0.079	0.105	0.122	0.132	0.133	0.125	0.111	0.087	0.052	0.006
Feb		0.000	0.044	0.079	0.102	0.117	0.125	0.128	0.121	0.110	0.090	0.060	0.020
Mar		0.016	0.054	0.083	0.102	0.113	0.119	0.120	0.115	0.105	0.089	0.062	0.027
Apr		0.031	0.063	0.086	0.101	0.109	0.114	0.113	0.109	0.100	0.086	0.062	0.029
May	0.004	0.038	0.067	0.087	0.099	0.105	0.109	0.109	0.104	0.097	0.084	0.063	0.033
Jun	0.006	0.032	0.057	0.080	0.098	0.111	0.118	0.118	0.111	0.098	0.079	0.056	0.031	0.005
Jul	0.007	0.029	0.055	0.078	0.097	0.111	0.118	0.119	0.112	0.099	0.081	0.058	0.033	0.010
Aug		0.026	0.054	0.079	0.100	0.114	0.122	0.122	0.115	0.101	0.081	0.056	0.028
Sep		0.023	0.055	0.083	0.105	0.121	0.128	0.127	0.118	0.101	0.077	0.048	0.016
Oct		0.019	0.055	0.087	0.112	0.128	0.136	0.133	0.121	0.099	0.071	0.037
Nov		0.016	0.059	0.091	0.112	0.125	0.132	0.129	0.119	0.102	0.075	0.038
Dec		0.000	0.048	0.085	0.110	0.126	0.135	0.134	0.124	0.107	0.080	0.041

Direct

Normal

Irradiance (DNI) in kWh/m²of Dhaka

Month	Evaluated 79-89	2003
Jan	4.81	2.63
Feb	5.20	4.16
Mar	4.89	3.60
Apr	3.68	3.96
May	3.27	3.11
Jun	2.41	1.68
Jul	1.86	2.78
Aug	2.73	2.69
Sep	2.79	1.51
Oct	4.75	2.16
Nov	5.03	4.28
Dec	5.06

Month

Clock Time