## 5 Conclusions  
In this work, a passive method for agricultural products drying was evaluated. The method was based on the solar chimney effect. Experimental results revealed that the highest the drying tube, the most effective the drying was as the air flow was enhanced. Other factors, such as the material and color of the tube, also had a major role but were not as crucial as the tube's height. The drying performance of each tube seems to be also influenced by weather conditions. As occurs by the results, during days with low wind velocities, the difference between the drying rate of Tube 4 compared to the rest of the tubes was higher. The advantage of the method was that the drying time was similar to some solar drying methods, with the advantage of products not being exposed directly to solar radiation, which in some cases affects the quality of the final product. The proposed method can be proven as a reliable solution for drying agricultural products in off-grid regions as the energy consumption for its operation is limited or close to zero. It can also be used as an energy conservation method as part of a hybrid drying system, which operates with artificial ventilation when the weather conditions are favorable. The efficiency of the examined system, in terms of drying rate, seems to be close to solar drying applications (direct or indirect systems). However, the fact that the operation of the system (temperature and air flow) depends on weather conditions makes its operation less stable compared to other solar drying applications where the air flow is performed via artificial systems. In terms of economic viability, a long P.B period is required in the case of bananas, while in the case of potatoes is closer to other applications regarding small-scale applications. The prices of fresh and dried products have a strong effect on the P.B period. Commercial-scale systems have a shorter P.B period than small-scale systems, but a more detailed analysis is required. In the current work, the basic parameters of the system were investigated, such as the air flow inside the drying tubes and the moisture removal of the samples. The performance of the proposed system as a fully developed drying system can be further investigated by examining extensively the characteristics of the drying products. In addition, to check the possibility of extending such an installation on a commercial scale, the use of tubes with larger diameters should be examined (larger drying surface), and the operation using a sophisticated automatic systems that will control the operation of the system (windows opening) when the weather conditions are leading the highest drying rates. **Supplementary Materials:** The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app122211784/s1](https://www.mdpi.com/article/10.3390/app122211784/s1)]([https://www.mdpi.com/article/10.3390/app122211784/s1](https://www.mdpi.com/article/10.3390/app122211784/s1)), Figure S1: Mean weight loss of the potato samples for the first 24 h of drying for the Drying Tubes (DT) and Drying Box (DB); Figure S2: Mean weight loss of the banana samples for the first 24 h of drying for the Drying Tubes (DT) and Drying Box (DB). **Author Contributions:** Conceptualization, V.K.F., Z.D.K. and T.A.K. ; methodology, V.K.F., A.A.L. and S.D.K. ; investigation, V.K.F., A.A.L. and Z.D.K. ; data curation, V.K.F., Z.D.K., A.A.L. and S.D.K. ; writing--original draft preparation, V.K.F. and S.D.K. ; writing--review and editing, V.K.F., S.D.K. and A.G.M. ; visualization, V.K.F. and S.D.K. ; supervision, T.A.K. All authors have read and agreed to the published version of the manuscript. **Funding:** This research has been co-financed by the European Regional Development Fund of the European Union and Greek national funds through the Operational Program Competitiveness, Entrepreneurship and Innovation, under the call RESEARCH-CREATE-INNOVATE (project code: T1 EDK-00100). **Institutional Review Board Statement:** Not applicable.