# Design Limitations of Laboratory Solar Chimney for Engineering Education
## 1 Introduction  
A solar chimney power plant is made up of a solar collector, a chimney, and a turbine. It raises the air temperature by absorbing solar irradiation, while the buoyant force drives the movement of the air stream within the system. Due to the optical transparency of the collector, the Greenhouse effect warms the air.  
The principle that warm air rises above cold air has been known since 200 B.C. Without much understanding of the fundamentals governing this principle, it was actively made use of for centuries in greenhouse installations for food cultivation and chimney systems to create updrafts for cooling or heating places of residence. The first recorded machine that resembles the modern form of a solar chimney is [PERSON]'s apparatus for roasting meat [1]. This apparatus, invented around 1500, relied on the circulation of warm air in a chimney to turn a spit via paddles; that is, the kinetic energy of air particles was transformed into the kinetic energy of paddles which roughly equaled the work done by the spit. In the 1900s, various solutions were proposed to transform that kinetic energy into electric [2]. Finally, the first solar chimney power plant was built in 1982 in Manzanares, Spain [3]. The Spanish solar chimney power plant has been used excessively as a study case in numerous studies carried out in the past two decades, mainly in review papers such as [4, 5, 6, 7], since energy production shifted to more green solutions, where solar chimney power plants were presented as important renewable energy sources and a possible green future [8, 9, 10].  
The motivation for this study was to make teachings of the advanced principles of thermodynamics and their practical applications, primarily in power engineering, more comprehensible to the (under)graduates of the Faculty of Electrical Engineering, ComputerScience and Information Technology Osjiek (FERIT Osjiek). Therefore, the objective of the study was to design a cost-effective solar chimney power plant of a geometry limited to the one of a laboratory classroom, with a focus on design limitations.  
The study was carried out in two phases. The first phase included the investigation of the literature, simulation of the solar chimney power plant in the ANSYS environment, and the corresponding thermodynamic analysis. Note that the simulation was based on the Manzanares solar chimney power plant prototype for comparison. The second phase included the determination of the initial parameters in the CAD and CFD software and the design of the mock-up, the investigation of the appropriate turbine, and the construction of the small-scale solar chimney power plant. The results of the first phase presented in this paper are part of the Master's thesis of [PERSON] [11] under the (co)mentorship of the co-authors of the paper. To obtain financial funding, the second phase of the study was conducted as a part of the FERIT pro-Student project. However, pro-Student requires that a mock-up is (50 \(\times\) 50 \(\times\) 50) cm so that one can \"fit on a table\", and funds a project up to EUR 1327.00 [12]. Therefore, in this paper, we present how boundary conditions affect the functionality of the solar chimney power plant and show that a geometrical limit exists where the buoyant force is overcome by boundary physics. The paper is organized as follows: in the second part, the physical background of a solar chimney power plant is described, and a brief overview of existing solutions of smaller geometries is presented; in the next part, an ANSYS analysis of a small-scale solar chimney power plant is compared to the Manzanares mathematical model, followed by construction and analysis of a mock-up; finally, design limitations are discussed.