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Fig. 2: Variation of Direct Transmittance for Studied Meteorological Stations.

Figure 2 Variation of Direct Transmittance for Studied Meteorological Stations.

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factor of 3.6. The details about the study area are found in Nwoko. lo and Ogbulezie [21]. 2.2. Model development [he modeling of Hp involves the correlation of monthly mean daily Hp to meteorological data such as extraterrestrial solar radia- tion (Ho) and clearness index under all sky and cloudless sky con- ditions. Wenxian [14] established a linear model for correlating direct transmittance to clearness index while several researchers developed quadratic models using direct transmittance to clearness index [2-3], [9-10], [15]. In order to generate an appropriate model for the study stations in addition to quadratic type model (model ), two models based on the correlation between direct transmit- tance to clearness index: quadratic-exponential model (model 2) and linear-logarithmic (model 3) are proposed for all sky condi- tions and clear sky conditions (kt) in this research in the forms: Where bi represents the empirical coefficients, (H/Ho) is the clear- ness index, (Hb/Ho) represents direct transmittance and Ho repre- senting the extraterrestrial solar radiation on the horizontal surface for all sky condition calculated using the following equations:
factor of 3.6. The details about the study area are found in Nwoko. lo and Ogbulezie [21]. 2.2. Model development [he modeling of Hp involves the correlation of monthly mean daily Hp to meteorological data such as extraterrestrial solar radia- tion (Ho) and clearness index under all sky and cloudless sky con- ditions. Wenxian [14] established a linear model for correlating direct transmittance to clearness index while several researchers developed quadratic models using direct transmittance to clearness index [2-3], [9-10], [15]. In order to generate an appropriate model for the study stations in addition to quadratic type model (model ), two models based on the correlation between direct transmit- tance to clearness index: quadratic-exponential model (model 2) and linear-logarithmic (model 3) are proposed for all sky condi- tions and clear sky conditions (kt) in this research in the forms: Where bi represents the empirical coefficients, (H/Ho) is the clear- ness index, (Hb/Ho) represents direct transmittance and Ho repre- senting the extraterrestrial solar radiation on the horizontal surface for all sky condition calculated using the following equations:
Table 3: Monthly Mean Daily Values of Extraterrestrial Solar Radiation (H,) in Mjm7day"!, Clearness Index (k,) Under All Sky Conditions and Clear Sky Conditions, Observed (Obs) and Predicted (Model 1, 2 And 3) of Direct Normal Irradiance (H,) in Mjm7day! for Owerri The calculated values of the variation of atmospheric parameters such as extraterrestrial solar radiation (Ho), observed and predicted (models) direct normal irradiance (Hp) and clearness index for clear sky and all sky conditions in the six sites are presented in Table 2 -7 and Fig. 2 — 5. Their corresponding regression coeffi- cients fitted and coefficient of determination employing direct transmittance and clearness index for all sky conditions and clear sky conditions are shown in Table 8, while scatter plot illustrating the observed and predicted values of Hp are shown in Fig. 6 — 11. The associated error from the fitted models were evaluated using mean bias error (MBE) and root mean square error (RMSE) in order to determine the performance of the predictive models pre- sented in Table 9 for Port Harcourt, Owerri, Ibadan, Abuja, Mai- duguri and Sokoto.
Table 3: Monthly Mean Daily Values of Extraterrestrial Solar Radiation (H,) in Mjm7day"!, Clearness Index (k,) Under All Sky Conditions and Clear Sky Conditions, Observed (Obs) and Predicted (Model 1, 2 And 3) of Direct Normal Irradiance (H,) in Mjm7day! for Owerri The calculated values of the variation of atmospheric parameters such as extraterrestrial solar radiation (Ho), observed and predicted (models) direct normal irradiance (Hp) and clearness index for clear sky and all sky conditions in the six sites are presented in Table 2 -7 and Fig. 2 — 5. Their corresponding regression coeffi- cients fitted and coefficient of determination employing direct transmittance and clearness index for all sky conditions and clear sky conditions are shown in Table 8, while scatter plot illustrating the observed and predicted values of Hp are shown in Fig. 6 — 11. The associated error from the fitted models were evaluated using mean bias error (MBE) and root mean square error (RMSE) in order to determine the performance of the predictive models pre- sented in Table 9 for Port Harcourt, Owerri, Ibadan, Abuja, Mai- duguri and Sokoto.
Table 5: Monthly Mean Daily Values of Extraterrestrial Solar Radiation (H,) in Mjm7day", Clearness Index (k,) Under All Sky Conditions and Clear Sky Conditions, Observed (Obs) and Predicted (Model 1, 2 and 3) of Direct Normal Irradiance (Hy) in Mjm7day"! for Abuja
Table 5: Monthly Mean Daily Values of Extraterrestrial Solar Radiation (H,) in Mjm7day", Clearness Index (k,) Under All Sky Conditions and Clear Sky Conditions, Observed (Obs) and Predicted (Model 1, 2 and 3) of Direct Normal Irradiance (Hy) in Mjm7day"! for Abuja
Table 6: Monthly Mean Daily Values of Extraterrestrial Solar Radiation (H,) in Mjm7day", Clearness Index (k,) Under All Sky Conditions and Clear Sky Conditions, Observed (Obs) and Predicted (Model 1, 2 and 3) of Direct Normal Irradiance (H») in Mjm*day'! for Maiduguri
Table 6: Monthly Mean Daily Values of Extraterrestrial Solar Radiation (H,) in Mjm7day", Clearness Index (k,) Under All Sky Conditions and Clear Sky Conditions, Observed (Obs) and Predicted (Model 1, 2 and 3) of Direct Normal Irradiance (H») in Mjm*day'! for Maiduguri
Table 7: Monthly Mean Daily Values of Extraterrestrial Solar Radiation (H,) in Mjmday"', Clearness Index (k,) Under All Sky Conditions and Clear Sky Conditions, _ Observed (Obs) and Predicted (Model 1, 2 and 3) of Direct Normal Irradiance (H,) in Mjm*day'! for Sokoto Guar PEs aoa a evel
Table 7: Monthly Mean Daily Values of Extraterrestrial Solar Radiation (H,) in Mjmday"', Clearness Index (k,) Under All Sky Conditions and Clear Sky Conditions, _ Observed (Obs) and Predicted (Model 1, 2 and 3) of Direct Normal Irradiance (H,) in Mjm*day'! for Sokoto Guar PEs aoa a evel
Fig. 3: Variation of Clearness Index under All Sky Conditions for Studied Meteorological Stations.
Fig. 3: Variation of Clearness Index under All Sky Conditions for Studied Meteorological Stations.
Fig. 4: Boxplot Diagram of the Variation of Direct Normal Irradiance for the Studied Meteorological Stations.
Fig. 4: Boxplot Diagram of the Variation of Direct Normal Irradiance for the Studied Meteorological Stations.
Fig. 5: Variation of Clearness Index under Cloudless Sky Conditions for the Studied Meteorological Stations.
Fig. 5: Variation of Clearness Index under Cloudless Sky Conditions for the Studied Meteorological Stations.
Table 8: Statistical Results for the Validation of the of Predicted (Model) Direct Normal Irradiance (DNI) in Terms of their Capability For Estimating The Direct Normal Irradiance Under Various Sky Conditions for Port Harcourt, Owerri, Ibadan, Abuja, Maiduguri and Sokoto
Table 8: Statistical Results for the Validation of the of Predicted (Model) Direct Normal Irradiance (DNI) in Terms of their Capability For Estimating The Direct Normal Irradiance Under Various Sky Conditions for Port Harcourt, Owerri, Ibadan, Abuja, Maiduguri and Sokoto
Fig. 6: Scatter Plots and Box diagrams between observed and predicted (models) direct normal irradiance under all sky condition (model 1, 2, 3) and under cloudless sky condition (model 1, 2, 3) for Port Harcourt
Fig. 6: Scatter Plots and Box diagrams between observed and predicted (models) direct normal irradiance under all sky condition (model 1, 2, 3) and under cloudless sky condition (model 1, 2, 3) for Port Harcourt
Fig. 10: Scatter Plots and Box diagrams between observed and predicted (models) direct normal irradiance under all sky condition (model 1, 2, 3) and under cloudless sky condition (model 1, 2, 3) for Maiduguri
Fig. 10: Scatter Plots and Box diagrams between observed and predicted (models) direct normal irradiance under all sky condition (model 1, 2, 3) and under cloudless sky condition (model 1, 2, 3) for Maiduguri
Fig. 11: Scatter Plots and Box diagrams between observed and predicted (models) direct normal irradiance under all sky condition (model 1, 2, 3) and under cloudless sky con- dition (model 1, 2, 3) for Sokoto.
Fig. 11: Scatter Plots and Box diagrams between observed and predicted (models) direct normal irradiance under all sky condition (model 1, 2, 3) and under cloudless sky con- dition (model 1, 2, 3) for Sokoto.
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