energies Article Power-Generation Optimization Based on Piezoelectric Ceramic Deformation for Energy Harvesting Application with Renewable Energy Hyeonsu Han and Junghyuk Ko *   Citation: Han, H.; Ko, J. Power-Generation Optimization Based on Piezoelectric Ceramic Deformation for Energy Harvesting Application with Renewable Energy. Energies 2021, 14, 2171. https://doi.org/10.3390/ en14082171 Academic Editor: Dong-Wook Seo Received: 18 March 2021 Accepted: 9 April 2021 Published: 13 April 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Laboratory of Advanced Multi-Scale Manufacturing, Department of Mechanical Engineering, Korea Maritime and Ocean University, Busan 49112, Korea; gustn0211bye@g.kmou.ac.kr * Correspondence: jko@kmou.ac.kr; Tel.: +82-514104292 Abstract: Along with the increase in renewable energy, research on energy harvesting combined with piezoelectric energy is being conducted. However, it is difficult to predict the power generation of combined harvesting because there is no data on the power generation by a single piezoelectric material. Before predicting the corresponding power generation and efficiency, it is necessary to quantify the power generation by a single piezoelectric material alone. In this study, the generated power is measured based on three parameters (size of the piezoelectric ceramic, depth of compres- sion, and speed of compression) that contribute to the deformation of a single PZT (Lead zirconate titanate)-based piezoelectric element. The generated power was analyzed by comparing with the corresponding parameters. The analysis results are as follows: (i) considering the difference between the size of the piezoelectric ceramic and the generated power, 20 mm was the most efficient piezo- electric ceramic size, (ii) considering the case of piezoelectric ceramics sized 14 mm, the generated power continued to increase with the increase in the compression depth of the piezoelectric ceramic, and (iii) For piezoelectric ceramics of all diameters, the longer the depth of deformation, the shorter the frequency, and depending on the depth of deformation, there is a specific frequency at which the charging power is maximum. Based on the findings of this study, PZT-based elements can be applied to cases that receive indirect force, including vibration energy and wave energy. In addition, the power generation of a PZT-based element can be predicted, and efficient conditions can be set for maximum power generation. Keywords: renewable energy; energy harvesting; piezoelectric ceramic; PZT; power generation 1. Introduction Renewable energy refers to the energy collected from resources such as the sun and ocean, which is naturally replenished over time and provides energy mainly for applications such as electricity generation and heat production [1,2]. Of late, due to concerns regarding environmental issues such as climate change and global warming, research on renewable energy harvesting systems is being actively pursued along with the increase in renewable energy development. Among these renewable energies, wave power generation is an ocean energy that primarily utilizes the vibration energy of waves. As wave power generation has relatively lower regional restrictions than power generation based on seawater temperature difference or tidal streams, it has high potential for development [3,4]. Moreover, its power density is 10 times higher than that of the other renewable energies and it can be easily predicted based on the weather forecast; hence, energy harvesting is easy. However, mooring wave power plants in the ocean for large-scale energy harvesting is economically disadvantageous because they are vulnerable to corrosion, and the associated installation cost increases [5,6]. In this study, a piezoelectric energy harvesting system is used to improve the efficiency of Energies 2021, 14, 2171. https://doi.org/10.3390/en14082171 https://www.mdpi.com/journal/energies