The Development of an Application to Design a Solar Updraft Tower Power Plant and to Estimate its Power Generation

A solar thermal converter is an alternative device to optimize the generation of electricity. One implementation of it is Solar Updraft Tower (SUT) which has some advantages such as easy installation, zero-emission


INTRODUCTION
The growth of renewable energy utilization becomes increase over the world.
Implementation of clean energy is being a prospective alternative to minimize the use of conventional power plants which has several negative impacts on the environment.Solar energy is one of the renewable energy resources which has a large potency, especially in tropical countries.Currently, the most common solar energy converter used is photovoltaic.This kind of solar converter is widely used due to its easiness in installation and long lifetime.However, the technology of solar converter should be improved to meet sustainable energy and fulfill the electricity consumption.Another potential solar power plant is Solar Updraft Tower (SUT).
SUT harnesses the concept of convection due to heat transfer process gained from solar radiation to create a differential of air density and produce airflow.SUT has several primary components such as a solar collector, a tower or chimney, and a wind turbine coupled with an electricity generator as shown in Figure 1.The airflow is produced when solar radiation reaches the collector.In this condition, the heat is transferred to the air inside the collector and thermal expansion influences the decrease of air density.The operational data was collected from previous study [6] and processed using the proposed application to identify the mechanical power and several output parameters with respect to the variation of inlet tower diameter.

RESEARCH METHOD)
This study follows a research flowchart as shown in Figure 2. Starting with literature study and problem identification, this research discovered the necessary of power generated from SUT calculation to be more feasible and easier.The algorithm is then developed using mathematical equations as described in this section.Subsequently, an interactive interface is developed and linked to the algorithm.Operational data is applied to the application in order to estimate the mechanical power.After the calculation is done, the next steps is data analysis to discuss the result.Lastly, conclusion is gained to point out the findings.
Cp is the specific heat capacity of air obtained from properties table of air at 1 atm.
The mass flow, ṁ, can be calculated using Equation (5).ṁ = ρin .At .Vmax (5) ρin is the density of inlet air obtained from properties table of air at 1 atm.At is the cross section area of the tower.Vmax is the velocity of airflow through the tower without turbine.The solar energy is converted into kinetic and potential energy.The potential energy is represented by pressure drop (ΔP).
In a tower without turbine system, the pressure drop can be written by Equation (6).
g, Ht, and ρout are the gravity acceleration, height of tower, and density of air at outlet tower.Based on the simplification of the system, the mechanical power output of SUT can be calculated using Equation (7).
Equations 1-7 described the fundamental concept of SUT design used in this application.Therefore, the input and output design parameters are referred to as the equations.All parameter is summarized by Table 1.The material of the solar collector is a mica plastic sheet.Mica plastic was used to forward the solar radiation due to its high specific heat.

Figure 3. 3D design of the prototype
In order to make the heat trapped perfectly, the ground of the prototype was covered by a zinc plate.The plate has an area of 1 m 2 and was coated using black paint to reach a better heat absorption.The thermal diffusivity was assumed to be 1.The prototype also using an isolation system to prevent heat losses and unwanted wind that interfere with the SUT system.The prototype computer design is shown in Figure 3.
The prototype used automatic data acquisition to collect data continuously.
Operational data such as temperature and velocity were acquired over the preferred time.The data retrieval time determined due to optimal radiation in a day start from 9 AM to 3.30 PM of Western Indonesia Time.The solar radiation (G) data were obtained from the Meteorological, Climatological, and Geophysical Agency (BMKG) due to the unavailable solar radiation sensor of the prototype.To make an ease for inputting the data, the application has an interactive user interface as shown in Figure 4.The effect of inlet diameter difference will be discussed in this section.Figure 8 shows the mechanical power output generated by SUT.The power output has a parabolic trend that changes over time.It reaches the highest peak value mostly at 12.00 WIB and the lowest at 15.30 WIB.

CONCLUSION
The emphasis of this study is to develop an application to design a solar updraft tower that can be used to estimate the mechanical power output of the system.The application can be implemented in any region regardless of the solar intensity which makes this application is more applicable.From the result, the bigger tower diameter produces a larger capacity of power output.The Subsequently, the hot air flows from the bottom to the top of the tower and drives the wind turbine to produce electricity.The concept of SUT had been proven and validated by Haaf et al[1][2], with a test result of a SUT prototype in Manzanares, Spain.

Figure 1 .
Figure 1.SUT Scheme: 1. Solar collector, 2. Ground, 3. Tower, 4. Wind Turbine SUT had commonly been discussed by previous researchers.Jörg et al conducted a study of commercial SUT design based on theory, practical experience, and economic consideration [3].The study found that the height of the tower increases the thermodynamic efficiency.Ayub et al proposed that a large range of the ratio of the collector and tower diameter is more effective to obtain a better performance [4].The study also recommends the use of glass as the material of solar collector to trap the heat effectively.The previous studies implied that the geometry and material of SUT components influenced the power output.Other studies tried to improve the SUT technology through several novel concepts.Bilgen and Rheault proposed a Sloped Solar Updraft Power Plant (SSUPP) which has a thermal performance slightly higher than the conventional SUT with the optimum slope of collector range from 5°to 7° smaller than the altitude[5].However,

Figure 2 . 3 )
Figure 2. Research flowchart of SUT The power output produced by SUT depends on solar energy (Q̇solar) and system efficiency (ηsystem).The value of solar energy varies over time due to the intensity of solar radiation.The system efficiency is calculated by multiplying the efficiency of the collector, tower, and turbine.However, in this paper, the system is accustomed to neglect the turbine.The formula of power output expressed by Equation (1).
Volume 7, Number 1, May 2022 ISSN 2528-2611, e-ISSN 2528-2700In this paper, experimental data is collected from a previous study[6].The experiment was conducted in Surabaya, Indonesia.Therefore, the condition related to solar radiation depends on the weather at the location.The prototype was scaled to fit with laboratory dimensions.The tower was made of Polyvinyl chloride (PVC) which has smooth wall surfaces that prevent fluid resistance.PVC is also lightweight and flexible.The height of the tower is 2 m with vary inlet diameter of 0.048 m, 0.114 m, and 0.165 m.The frame of the collector was made of Aluminium which has several advantages such as lightweight, strong, and easy to form in any shape.The collector frame was a square-based pyramid with a height of 0.3 m and a base area of 1 m 2 .
There are several features provided in this application such as introduction, start design, and about the author.The introduction contains a brief explanation of the basic theory of SUT, the history of SUT and its concepts, and several studies related to SUT.This feature aims to give the user an overview of SUT and its evolution.Therefore, this application is suitable for all types of user, i.e, those whom not familiar with solar thermal energy conversion.The user is also able to learn more deeply about SUT by review several related studies only by clicking the button.Users can start to design by getting on the start design button.The user should input several data to Volume 7, Number 1, May 2022 ISSN 2528-2611, e-ISSN 2528-2700 obtain the output design.The interface is shown in Figure 5.

Figure 4 .
Figure 4. Application homepage Two kinds of input data should be loaded including geometry parameters and operational data.Geometry parameters contain the length (L) and width (B) of the solar collector base, height of the tower (Ht), inlet (di), and outlet diameter (de) of the tower.The geometry data can be inserted directly into the column on the left side of the interface.The shape of the collector may be different depends on the design, i.e, F Ayub et al [4] used a cone-shaped collector which has a circle-shaped collector base.However, the prototype used in this study has a squarebased pyramid collector.For operational data, the user can insert the data using a static data loader by clicking the browse button.This button will redirect to the user's directory and read-only *.csv file.The data file should

Figure 5 .Figure 6 .Figure 7 .
Figure 5. Features in introduction page After inserting all data, the user can start the calculation by clicking the run button.It will process the calculation and plot the result.There are two plots, e.g, power output and solar radiation versus time, and pressure drop and velocity versus solar radiation.The first plot shows the mechanical power output generated by SUT.

Figure 8 .
Figure 8. Power output and solar radiation VS time Comparing with the power output, solar radiation also has the same trend which the intensity depends on the time.The intensity of solar radiation also strongly depends on the altitude and latitude of the location where the experiment was conducted.From the graph, the power output increases along the increasing inlet diameter.Based on Equation 7, the power output is influenced by the value of pressure difference across the chimney and the velocity of the airflow.Figure 8 represented the relation of pressure drop and velocity of air toward the intensity of solar radiation.The pressure drop and the velocity have a parabolic trend with the highest value