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Cycle 7 (2018 Deadline)
Impact of rooftop PV system integration on Tunisian electrical distribution network
PI: Ilhem Slama-Belkhodja (ilhem.slamabelkhodja@enit.utm.tn), Ecole Nationale d'Ingénieurs de Tunis ( ENIT)
U.S. Partner: Jonghyun Park, Missouri University of Science and Technology
Dates: November 2018 - October 2021
Project Overview:
This project aims to study rooftop photovoltaic (PV) system integration effects on Tunisian electrical distribution network (EDN). The solar photovoltaic energy has been promoted for residential (policies subsidies for encouragement, special pricing, etc.) for several years in Tunisia, where electrical energy consumption in residential sector is important: more than 30% of the total electrical energy consumption. In particular, the project will use the Power Hardware-in-the-Loop (PHIL) approach to investigate some solutions considered as promising to cope with voltage and frequency variations due to PV system integrations in the EDN, considering Tunisian conditions. Special solutions will be distributed to storage systems, as several private Tunisian companies are interested in self consumption with local storage and micro grids as concepts. This project will generate a dataset in the field of PV residential load profiles, which will serve as the basis for establishing Tunisian computer models. These models will run in real-time while using a hardware test setup to validate a holistic PV-battery energy storage inverter. The control will be applied across a Tunisian EDN under different loading scenarios and with varying penetrations of PV-only and PV-energy storage units combined. The expected PHIL-based testbed will allow researchers and manufacturers to safely evaluate energy technologies performance and reliability, autonomous devices and their control parameters and their interaction with Tunisian EDN.
The global aim of the proposed project is to assist national policy makers and the main institutions responsible for the development of renewable energies in Tunisia to evaluate Tunisian PV rooftop capacity. The project will take into account the current grid infrastructure, protection plan, and peak demand. The resulting analysis could be used to adopt more appropriate strategies to secure sustainable distribution in the future. As the PHIL-based target platform will be flexible and scalable, it can contribute to high-impact studies beyond the activities included in the project. For example, it can provide private investors or manufacturers of energy technologies with an experimental platform for first evaluation of their new products. The project will engage, motivate, and train Tunisian students preparing them for the workforce in the interdisciplinary area of energy, power, and control through the development of various science activities. This research will contribute to the development objective “Inclusive Private Sector Employment Increased,” which is one of the objectives identified in the Government of Tunisia’s proposed 2016-2020 Strategic Development Plan.
Final Summary of Project Activities
This project brought together numerous facets of research, modeling, training, technical design, and commercialization to develop its MICROGRID platform (MGP), a platform with state-of-the-art equipment and operation according to emerging concepts that involve researchers from several disciplines. It is a testbed environment to identify and develop Tunisia’s electrical grid using modern components and concepts under complex scenarios. The details of the technical work, investigations, results and impact will be grouped in a technical public report available on the project website and on http://www.lse-qehna.tn/.
On the production side, the team worked to determine the IV characteristic of PV arrays under partially shaded conditions. The team was able to develop and accurate model to predict the output of a real PV array under complex operating conditions. These I-V curves can form a database and the comparison of an measured IV curve and those of the database can be used to determine the partial shadow condition and detect possible failures caused by soiling or the existence of an obstacle on the PV cells such as leaves or neighboring buildings. The model was tested on existing PV installations and case studies were done to minimize the impact of mismatching.
The team also researched energy storage technologies and developed an electro-thermal model that allows to follow the evolution of the battery states (voltage, current, internal temperature). The model, combined with a series of tests resulted in a battery energy storage system as a potential solution to mitigate impact of rooftop PV on distribution network. Further testing is ongoing to understand its efficiency and effectiveness.
From a consumption angle, the team designed and generated a “Home Appliances Electrical Signature Database” (HAESD) that provides users with data related to the electrical and harmonic behavior of different types of appliances. This database can be used to build data-driven model of home load behavior in microgrid energy management context. HAESD Database implementation and generation aimed at offering a platform including Hardware from National Instruments (data acquisition system, current and voltage sensors) and software namely LabVIEW, that can be used to acquire one or more periods of voltage and current that supply a given appliance and then to determine all its electrical and harmonic characteristics and signatures according to IEEE 1459-2010. This database is planned to interface with the existing grid. Tunisian grid data will be provided after MOU signature and the impact of grid faults will be investigated, particularly those due to rooftop PV. The home energy management system is under development based on MGP data with the participation of industrial Partners
The above work has been conducted with active engagement of both the private sector and government stakeholders. The team has met frequently regarding Tunisian standards and Tunisia’s strategic plan for integration of electric cars. The government is also interested in the creation of a common research services unit called the MICRPGRID Platform (USCR-MGP). It is a unit approved by the PI's supervising ministry that will allow them to evaluate their skills and the MGP developed within the framework of funded MOU, therefore allowing the team to raise funds to finance the maintenance of the platform and associated.
Private sector engagement has been consistent and diverse. The team met with the Tunisian Company of Electricity and Gas (STEG) which aims to develop an experimental platform for the training of its own technical staff and sought the project’s expertise. Similarly, companies like GAMCO Energy are interested in the team’s skills because they want to develop their business to sell microgrids and customized solutions for African market and Lightency.io which aims to develop customized EMS (Energy Management Systems), integrating the specific constraints of Tunisian, African, and European markets. This interest is being finalized by an MOU.
The PI reports that the project needs deeper experimental tests to be performed on MGP for parameter and operations mode identification since the existing platform has limited documentation. These tests and the MGP model will be established to investigate EMS and microgrid collective self-consumption in Tunisia.
Beyond the commercial and societal aspects of the project, the team updated a number of course modules and has attracted students to work in the field with the possibility to perform investigations in the field with experimental validation. For example, a Thesis Agreement was signed with the STEG, which financing for theses on power quality improvement devices.
Publications
M. Jebali Ben Ghorbal, S. Moussa, J. Arbi Ziani, and I. Slama-Belkhodja, A comparison study of two DC microgrid controls for a fast and stable DC bus voltage, Mathematics and Computers in Simulation, vol. 184, pp. 210–224, Jun. 2021, https://doi: 10.1016/j.matcom.2020.02.008.
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