Abstract
A complementary methodology to the teaching of photovoltaic systems is proposed where students can develop a complete project if they were immersed in the industry. The complementary strategy incorporates activities usually not taught which are delivered via web-classroom to develop and reinforce the abilities needed to face the industry once they are graduated. A project-based learning strategy is used to reinforce the teaching on sizing, planning, modeling, installations with international standards, the start-up of a photovoltaic system with a monitoring system. Students carry out a financial investment analysis rarely taught, such as the calculation of the payback period, the internal rate of return and the net present value are made to ensure the project viability. Planning-dimensioning usually is taught analyzing the electrical bill to determine the required sizing capacity without considering the building installed capacity. A three-dimensional dimensioning using the geographic location of a possible installation is proposed to provide better information in terms of losses due to shading or obstacles that may affect an installation. Furthermore, it is proposed to perform an analysis of mechanical stresses on the mounting rail system under natural phenomena such as hurricanes. This type of analysis is not usually taught in classes and it is important since an investment can be lost due to natural phenomena as has already occurred in some solar plants. The proposed activities are aimed to develop self-directed learning skills motivating to do research leading to problem-solving and meaningful activities to work autonomously in a natural and real-life situation. This approach allows the teacher and students to ponder deeply about worthy subjects and issues. Five questions were formulated to verify student satisfaction; the 30 surveyed students have a very positive view of this complementary utilized strategy.
Introduction
Motivation
Educational labor must be reinforced in all possible ways to improve the knowledge of theoretical concepts and provide the needed training to the students for facing the real world industry. Renewable energy systems are used more gradually due to the drop in their cost, especially of photovoltaic systems (PV) which recently has become one of the most popular options. 1 Therefore, increasing demands for well-trained and experienced personnel are needed. Educators should use modern didactic facilities and different teaching strategies such as laboratory hands-on, project-based learning, modeling approach, and cooperative-learning among others.
On the other hand, when a student joins the university, he acquires knowledge that can be implemented in other subjects throughout his career. As shown in Figure 1, a freshman electrical engineer acquires CAD tools, a sophomore gets knowledge of fundamentals electronics and mechanical design, and a junior already performs electrical installations under international standards considering safety. If all these tools can be complemented in the teaching of photovoltaic systems under a scheme of a real project similar to the one that can be faced in the industry once graduates, the student would have the necessary abilities and competencies to carry out a project without problems.
Learning process of an engineer.
Literature review
Commonly, some topics in any curricula are based on the understanding of the PV and IV curves, and obtaining the maximum power point; hence, some educators are motivated to use mathematical modeling such as Vimalari and Kamaraj 2 and Tortoreli et al. 3 Some prefer the design and development of equipment to accompany courses and deeply understand the characteristic curves of the solar panels4,5 but only are focused on the solar panel.
Teaching solar panels should be complemented with real installation of photovoltaic systems when they are available in laboratories. Frankovic et al. 6 describes the installation of a grid-connected photovoltaic power plant with the technique of “hands-on” about fully functional photovoltaic power plant. Even though the wind was considered on the installation, just a wind protection system was provided for the PV plant for a 10 m/s without performing an analysis. Al-Najideen and Alrwashdeh 7 propose to design a 56.7 kW grid-connected as a solar photovoltaic power plant to cover the electricity demand at the Engineering Faculty at Mu’tah University.
Sophisticated software is used by educators to implement modeling/simulation teaching strategy to consider the planning/design of many projects. Sharma and Chandel 8 and Soualmia and Chenni 9 study the performance of a grid tie solar photovoltaic plant installed aided with PVSYST software, and Belu 10 presents how the uses of HOMER software package can be a valuable tool for renewable energy education to design and analyze renewable energy systems. A project-based learning using rubrics in the teaching of Photovoltaic is used by Martinez et al. 11 in which Simulink simulation is done for project planning but the obtained simulation was not validated with real measurements. Recently, three-dimensional (3D) planning is also considered; Robledo et al. 12 create software which allows evaluating the energy losses induced by complex 3D scenes on PV generators. Yaghi et al. 13 discuss the potential of implementing solar panels at the Lebanese International University conducted using HelioScope simulation tool. Najibhamisu et al. 14 evaluate 10 simulation software with their main features and developers of these tools to highlight researchers to identify the suitable software for research analyses. None of these tackles the behavior of the racking systems during natural phenomena; the mounting rails have not been analyzed mechanically on how they would behave during natural phenomena such as tornadoes, or hurricanes destroying an investment in minutes like it happened in Sanchez and Willingham 15 and Godoy. 16 In these studies, the mounting rail system dimensioned is not considered, taking into account the actual installed capacity or the physical conditions of the installation, which sometimes leads to not adequate assembly system; thus, there is no certainty in the cost of the accessories and equipment that are also required in the installation such is the case of the screws, electrical protections, and electrical wiring.
Main contributions
This paper presents a methodology that is complementary to the curricula incorporated into the teaching of solar systems where students can develop a complete project under the strategy project-based learning. In particular, the paper focuses on aspects that are not considered in the teaching of photovoltaic systems, such as 3D dimensioning that includes geolocation to include the mounting system design also on 3D, allowing to take into account the real conditions of an installation. The design of a mounting system with specialized software allows a mechanical analysis to study how it would behave under natural phenomena such as hurricanes. This proposed complementary strategy allows better detailing on the total investment cost with great detail, since 3D sizing obtains exactly the required accessories. Moreover, other complementary activities are also included, such as the validation of grid-tie system modeling versus measurements usually not done in the teaching; furthermore, investment recovery analysis is considered.
Paper organization
The rest of the article is structured as follows: the next section discusses the implementation of the proposed strategy, followed by the student satisfaction and findings, and finally, we conclude this work and introduce the future work.
Complementary proposed methodology
Typical teaching content of photovoltaic systems is to illustrate the theory of the sun movements, the photovoltaic effect, composition of cells and solar panels, PV and IV curves, photovoltaic arrays, sizing and configurations of interconnected and/or standalone systems, modeling, but without actually comparing them with real measurements. Some curricula economic viability is included, without having a certainty of the actual recovery time of the project, nor performing mechanical analysis of mounting rails. Therefore, the complementary proposed teaching strategy is shown in Figure 2, which consists of a series of steps that the student can follow linearly or in parallel for integral learning.
Complementary proposed methodology.
Dimensioning is usually done with the analysis of energy consumption based on the electric bill, but often the place where it will be installed is not known, and there is no idea if there is enough area for the installation or if it is affected by shades, selecting an inadequate inverter, where micro-inverters or optimizers could be a better option. Thus, incorporating a 3D dimensioning using geographic location provides better information and much more professional proposal when management/presenting a project. Similarly for the mounting rails, sometimes those prefabricated in the market do not match to the place where the installation will take place; so a 3D design would also provide greater certainty and consequently the required material for the installation including accessories, and in addition, it enables to calculate the distance to consider the amount and size of electrical cable required. Furthermore, using specialized software like SolidWorks, stimulates winds and could give certainty under natural phenomena such as hurricanes.
In many occasions, the students declare that modeling is only equations and simulations in sophisticated software such as the case of Simulink, PSIM, and others. Thus, cognitively do not dimension their real application until they really apply it in some project or installation in the industry; for this reason in the modeling part, measurements of real monitoring systems already installed are compared with the modeling.
Students should contact primary producers-sellers of photovoltaic equipment to obtain a quotation, leading to the economy for the project regarding its optimal cost and investment recovery time appropriated taking into account the calculation of net present value and the internal rate of return. In addition, students must do presentations acting as presenting an executive project demonstrating the project viability.
Finally, they must carry out a real installation, start-up, and measurements to verify its correct operation. With this complementary teaching strategy, they will domain a procedure of how a project would be carried out in the industry obtaining the competencies required by the business sectors.
3D simulation designs using geolocation
There are many programs performing photovoltaic system modeling to facilitate the task to designers such as Pvsyst, Homer; for instance Helioscope, Sketchup, PVSOL use geolocation between other. All these tools help with the selection of components necessary in the preparation for a project estimating total power generation per day, month and year, including shadows analysis, and some other losses that may occur in the system and thereby take them into account in the design.
Figure 3(a), created by students, illustrates the sizing of a medium-scale photovoltaic system using Sketchup and Google Maps to optimize the largest possible number of panels that will be placed on the building surface. The task is not only to obtain the number of solar panels according to its capacity in Watts and the selection of the inverter to be installed, but also the students must obtain the amount of electrical material and determine the PV arrays for the MPPTs connections of the inverters. They must take into account shadows that may affect, being aware of the best way to perform maintenance; in which, assignments are provided via classroom for the 3D training shown in Figure 3(b) and it is evaluated by an evaluation rubric (Figure 4).
Classroom platform for 3D geographic PV design with its evaluation rubric. (a) Design 3D geographic PV system. (b) Classroom platform for 3D mounting system and mechaninal analyses.
Evaluation rubric for 3D geographic PV system design.
Racking design using 3D SolidWorks
The purpose of this task is to obtain the complete material needed for installation regarding the type of aluminum mounting rails that it would be used with the necessary screws and accessories. Students must design it in 3D according to the place where the installation will be carried out; the aim is to obtain the appropriate one, with lower cost than those found in the market; so they should research online prices of the existing ones. Furthermore, when designing the rack in SolidWorks, the accessories are also minimized since the material to be used can be accurately calculated. Moreover, this software can simulate the weakest parts of the mounting rack, verifying that it can support both weight and winds caused by hurricanes.
The students can design and validate mounting rails capable of withstanding gusts of moderate to hurricane winds with the help of SolidWorks software. The wind load can be calculated by means of the formula of Uniform Construction Code (UBC) Wind ToolBox, 17 which takes into consideration the wind speed, height, exposure, burst response factor, a coefficient of pressure or drag, wind stagnation pressure and the importance factor of the installation. An application example is the structure shown in Figure 5(a) and (b) in which a study of a category 3 hurricane was made spreading the pressure over the entire rails, Figure 5(b) illustrates that does not suffer considerable deformation due to the pressure.
Analysis of uniformly distributed loads on mounting structure. (a) Mechanical loads uniformly distributed. (b) Mechanical stress on mounting rails.
Figure 6(a) shows the activities to be carried out by students; these activities and their evaluation rubric are depicted in Figure 6(b) with the necessary tasks to consider the learning and perform a detailed mechanical analysis on the weakest points of the mounting system.
Analyses of 3D mechanical mounting rails. (a) Classroom platform for 3D mounting system and mechanical analyses. (b) Evaluation rubric for mechanical analyses.
Simulink modeling of 3 kWp PV system
Since this stage students have the knowledge of theory about solar cells, Simulink is a great ally to teach how a complete PV system performs. Some solar panel models have already included in Simulink as a toolbox ready to be used, so it can be utilized during theory and application lessons to show students the effects on the grid and how a parameter affects the energy generation. Here the student must perform simulations of a grid tie photovoltaic system, find a real system already installed with monitoring and compare their simulations with this system.
This activity is carried out because several recollected comments about the incognita that mathematical models are only equations, and although intuitively it represents a real system, there is always uncertainty if no real application is taught; when doing this activity the student changes the paradigm in his teaching. Figure 7(a) shows the simulation made in Simulink as an example of a 3 kW PV system (Mathworks, 2018), the input variables such as solar radiation and temperature are obtained from meteorological stations and are used in modeling. 18
Simulink activity answering modeling. (a) Simulink modelling a 3kW PV system. (b) Generated power of PV system.
The simulations are compared with a real monitoring system. An inverter with WIFI Data Logging Stick is used to get the measurements variables of the PV system; in this case, Figure 7(b) illustrates power coming from the photovoltaic array versus time in an horizon of 24 h with the highest irradiation around of 14 h generating 2.8 kW, dotted line corresponds to the simulations, while continuous line corresponds to the measured system. This activity seems simple, but from the point of view of a student, doing an activity like this provides a better understanding about the importance of modeling.
Figure 8 illustrates the activities on classroom and the evaluation rubric where the student must understand the mathematical model of the solar panel to obtain the PV and IV curves, and then model a grid-tie system and obtain the generation curves as shown in Figure 7(b).
Evaluation classroom for Simulink activity. (a) Classroom activities. (b) Evaluation rubric for Simulink activities.
Cost recovery of investment
The task here for the student is to get formal quotations for the entire project and get the total investment for the project as detailed as possible: the cost of the inverters, solar panels, solar cable, and accessories; also considering savings that will be obtained and how it would be amortized economically considering maintenance, and financing in order to determine if the project is viable.
Figure 9 depicts the activities provided to the students via classroom platform together with the evaluation rubric. These activities consider a measure of payback period providing the years needed for the system to pay itself off. This calculation is not enough for some projects due to the devaluation of money through time and some other economic aspects. For these reasons, the basic economics feature is included in the student’s activities with the calculations of net present value and internal rate of return for the investment for better calculation of the payback period calculated with Microsoft Excel or with some financial calculators tools.
Evaluation classroom for project cost. (a) Classroom activities for payback of investment. (b) Evaluation rubric for cost-recovery of investment.
Installation of a real PV system
Figure 10(a) illustrates the installation of a 3.6 kWp photovoltaic system. In this activity, students select the personal safety equipment performing relevant safety procedures in the installation, following the installation under an electrical diagram and regulations. Adequate electrical wiring, ducts, electrical protections and racking should be fixed using expansion bolt. Then they start making measurements and tests of the equipment for proper functioning; they must even perform the installation and configuration of the monitoring system as evaluated in Figure 10(b).
Installing a PV system activity. (a) Installing a PV system. (b) Evaluation rubric to install a PV system.
Evaluation and findings
The effects of the proposed activities are presented and discussed. First, student satisfaction is analyzed. Then, a comparison is made of the total scores obtained reviewing their rubrics.
Student satisfaction survey
The survey was designed to measure learning experience and capability to successfully complete a project (Figure 11). Thirty students over a total of 40 answered voluntarily the survey on a scale ranging from 0 to 10, where 10 is the highest indicating total satisfaction; the survey was conducted after the end-semester. The students indicate that they feel satisfied with the strategy used, feeling confidence even with themselves to create their own business. The two most significant negative responses were towards the difficulty of learning Simulink.
Answers of question 1 to 5.
Figure 11 shows that for question 1, 58% of the students are 100% sure that they can estimate the real cost of a project, and 25% even if they are not completely sure, they can perform this activity without problems, while a few students do not have confidence themselves. It is clear that the 3D sizing provides the minimum detail of everything needed for the installation including losses due to shadows, temperature, and soiling.
Although answers for question 2 can be considered good in the sense that more than 42% of the students evaluated this question above 9, obviously most of them answered the fact that performing the modeling and comparing it with real measurements provide them with a powerful tool in the analysis of photovoltaic systems. This activity is not as excellent as 3D modeling and still represents a challenge in teaching since 50% of students do not feel having the potential to develop this activity.
The majority of respondents (75%) feel that with the skills and abilities required in the industry (Figure 11, question 3), they acquired this competence to develop any activity related to photovoltaic systems; however, other skills such as the ability to adapt different work situations, personal attitudes, and leadership were not analyzed, among others.
It is interesting that most of them feel motivated and able to start a business in this area just due to the fact of being able to carry out a successful project with these tools, although the results are satisfactory as shown on question 4, in future, it is proposed to introduce activities of resilience, the ability to solve problems under stress and managerial skills.
Overall, the student reviews were positive and they showed satisfaction with the complementary strategy. Most of them also mentioned that they would definitely recommend this course for the following generations.
Findings and students’ feedback
The students demonstrated more interest in the course attending the activities focused to solve a real possible installation. Verifying their designs through simulations and practical activities also improved students’ knowledge retention. As a result, the students’ activities were evaluated through the presented rubrics (Figure 12). It is found that 3D simulations using geolocation were made without problems, this is due 3D dimensioning that simplifies the design process of the photovoltaic solar installation; likewise it occurs with the mounting system design. However, when carrying out the mechanical analysis, it was difficult for them implementing the forces on the weakest part, but this is due to the lack of software training and the knowledge about how wind will impact on the mounting rails, rather than to the study itself. Similarly, it occurs with modeling; the lack of training in the use of this software complicates this activity and its total understanding; in fact, it is observed in the survey that this activity is the most complicated to them.
Evaluation of rubrics.
Conclusions
The simulation with geolocation was developed without major difficulties. In the section of mechanical resistance of the mounting rail system; the difficulty was basically for the students who were not familiar with the hurricane scales and how it impacts on the mounting system. The modeling activity with Simulink was harder to understand due to the detailed level of the PV system; however, the activity with the greatest enthusiasm was the installation of the solar panels arguing that the course had both theoretical and practical part. The teaching method presented can be developed in any training or research center, with great potential to develop abilities for the participants. On the other hand, the survey revealed that the participants had a very positive view of this complementary teaching strategy used in the course and were interested in the use of 3D simulation tools. The feedback regarding the novelty of the proposal and their effect on their learning showed that their developed skills will be beneficial in their later career since they manifest the self-confidence to succeed in this kind of projects. While, Simulink were not equally rated, the general reviews were overall positive, and students were satisfied with their learning experience. Some other activities are planned as future works such as creating tutorial videos by students and teachers following the presented method and uploading it on a website to implement a collaborative learning session for the frequently asked questions, comments to teachers or students or live chat.
Footnotes
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) disclosed receipt of the following financial support for the research, authorship and/or publication of this article: This research was funded by PRODEP-SEP Mexico.
