Zahariev, Svetlozar Kirilov. “Validation and Optimisation of Common Clear Sky Models With a Use Case for North-East Bulgaria”. ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA 5, no. 1 (June 9, 2021): 1–12. Accessed October 2, 2025. https://aj.tu-varna.bg/index.php/ajtuv/article/view/224.