Nwokolo, Samuel, and Julie Ogbulezie. “Estimation of Direct Normal Irradiance under Various Sky Condi-Tions in Data Sparse Tropical Ecological Zones in Nigeria”. International Journal of Advanced Astronomy 5, no. 2 (October 5, 2017): 90–105. Accessed November 24, 2024. https://sciencepubco.com/index.php/IJAA/article/view/8329.