Renewable energy has the potential not only to complement but possibly replace fossil energy. A main focus is clean solar energy which has attracted significant attentions from both academics as well as policy makers owing to its sustainability compared to other types of renewable energy sources. Until now, solar thermal and photovoltaic systems are the two main methods for harvesting solar energy due to their great potential integration with hybrid systems for constant power generation. However, the drop in electrical conversion efficiency with an increase in the temperature of the solar cell is the current major challenge in using photovoltaic modules. To this end, there is a great need to control the temperature in order to enhance the efficiency of the solar cell. This includes the use of the waste heat generated from the photovoltaic for other thermal operations.
To this effect, University of Manchester-based researchers: Chukwuma Ogbonnaya (PhD candidate), Professor Ali Turan and Dr. Chamil Abeykoon developed a novel thermophotovoltaic module by exploring the thermodynamics of solar cells photovoltaic generation. This was fundamentally based on integrating the solar, electrical and thermal exergies of a photovoltaic module. The main objective was to better understand the influence of the variations in temperature and solar radiation on the operation of photovoltaic devices. The work is currently published in the journal, Solar Energy.
For accurate modeling of photovoltaic power generation, a computer iterative code-based model was utilized taking into consideration the transcendental equation created by the photovoltaic output voltage. Therefore, the code-based model which allows user manipulation was effectively used to implement a thermophotovoltaic model by integrating the solar, electrical and thermal exergies of the photovoltaic module. Next, the proposed model was implemented in MATLAB and parametric studies conducted to determine the effects of the changes in temperature and solar radiation on the electrical and thermal exergy flow patterns during power generation. Notably, the proposed thermophotovoltaic model was based on several assumptions.
The research team pointed out that heat is an essential parameter for power generation in photovoltaic systems. Therefore, electricity can only be generated exponentially when the temperature of the solar cell exceeds a critical temperature of 223.5K, as observed in most solar cells. However, beyond a critical value, very high temperatures degrade the open-circuit voltage thus leading to low photovoltaic conversion efficiency. Unlike block-based modeling, code-based modeling used programmable codes which allowed user definitions manipulation thus enhancing the ease of system integration and implementation.
The results generated by the proposed thermophotovoltaic model agreed well with the established photovoltaic physics and thermodynamics. For instance, the photovoltaic performance of the 45 W photovoltaic module used could improve by 51% if the waste heat generated is used for other thermal operations. Additionally, the code-based model approach would allow incorporation of more functional parameters and conditions that will improve results’ accuracy.
In summary, a thermophotovoltaic model based on the integration of solar, electrical and thermal exergies of photovoltaic modules is developed. In general, the approach proposed by the University of Manchester scientists would be useful for engineers in designing experiments for the quantification of thermal and electrical outputs of photovoltaic modules at varying temperatures and solar radiation. This would facilitate heat recovery measures for the optimization of both photovoltaic and photovoltaic-thermal systems.
Ogbonnaya, C., Turan, A., & Abeykoon, C. (2019). Numerical integration of solar, electrical and thermal exergies of photovoltaic module: A novel thermophotovoltaic model. Solar Energy, 185, 298-306.Go To Solar Energy