# Design Limitations of Laboratory Solar Chimney for Engineering Education
## 2 A Brief Overview of the Existing Solutions  
The basics of solar chimney power plants are [3]: Solar radiation heats the air beneath a flat, round, transparent roof that is open all around its circumference. Heating of the air occurs due to the greenhouse effect. The ground beneath the chimney and the roof form a hot air collector. The hollow cylindrical tower is attached to the roof at its center by an airtight seam. The turbines coupled with a generator are mounted at the base of the tower. Lower density hot air rises from the base to the top of the tower, the updraft draws more hot air from the collector, and the surrounding cooler air fills the collector from the circumference. This flow is continuous because of solar radiation. The energy contained in the flow is transformed into kinetic energy via the turbine, which is transformed into electric energy via the generator. The Manzanares prototype has the following dimensions: The height of the chimney is 200 m with a radius of 5 m, while the radius of the roof is 120 m. The roof is fixed from the ground at a height of 10 m. Its output power is 50 kW. A very simplified mathematical model was proposed to analyze the output power of this solar chimney power plant, as presented in detail in [3]. Nevertheless, the model showed that fundamentally, the efficiency of the chimney depends only on the height of the tower. In the years to come, solar chimney power plants were built at several sites where the climate is either tropical or dry and studied excessively within the framework of the Navier-Stokes model of a fluid in motion. There are roughly two \"paths\" to analyze the efficiency of a solar chimney power plant. In simple terms, one is to analyze velocity and the other is to analyze energy. For example, the solar chimney power plant in Tibet has an impressive chimney of 1000 m and a collector radius of 2825 m. It produces an output power between 372 and 829 TJ per year, depending on the solar region [13]. The analysis of the Tibet solar chimney power plant was based on the Pretorius and Kroger airflow model, which accounts for thermal storage [14]. The model had one modification, the flow is compressible, which simulates the velocity of flow more accurately, as shown in [15]. It was concluded that an increase in the collector area and the height of the chimney results in an increase in power output. During the day, the power output gradually decreases as the temperature of the atmosphere increases. Simultaneously, it increases as solar radiation increases. However, at night, the power output is greatly affected by the temperature of the atmosphere. Two solar chimney power plants were built in Iran, one in Kerman with a chimney of 60 m and a collector radius of 40 m that produces approximately 4 kW, and the other three times larger, producing between 175 and 265 MWh per year. Before construction, a study [16] was carried out to simulate the performance of the solar chimney power plant in different regions of Iran. [PERSON] and [PERSON] proposed a flow model in cylindrical coordinates, which relied on the Manzanares prototype as a test case. However, theirs is the more complex model as it accounts for turbulence. On the other hand, the thermodynamic analysis of the Algerian solar chimney was based on the momentum-energy balance theorem proposed by [PERSON] et al. [17] and applied by [PERSON] et al. [18]. The results showed that the output power is determined by the height of the tower, the collector surface, the ambient temperature, and the solar irradiance. An important factor that boosts the system's performance is the collector and turbine efficiency. Furthermore, with increasing tower height and collector surface, the generated power improves. With the 200 m chimney and collector radius of 250 m, the Algerian solar chimney power plant produces between 140 and 200 kW output power. Different geometries have been experimentally studied to investigate the performance of solar chimney power plants.