Symposia & Conferences
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Item Novel slow switching technique for efficient solar energy harnessing for off grid photovoltaic systems(proceedings of the 4th International Research Symposium on Pure and Applied Sciences 2019, Faculty of Science, University of Kelaniya, Sri Lanka, 2019) Piyumal, P. L. A. K.; Ranaweera, A. L. A. K.; Kalingamudali, S. R. D.; Kularatna, N.Electricity consumers in remote areas where the grid connection is not available rely on diesel generators or off grid photovoltaic (P V) systems. These PV systems uses battery banks as backup energy storage. Those battery banks are charged by using a battery charge controller connected to a PV array. Because of the recent advances in solar charge controllers, they can reach maximum of 90% charging efficiency, where 10% will be unutilized. Since the efficiency of conventional solar panels lies around 20-25% which is relatively low as compared to other energy generation methods, it is important to utilize as much energy as possible produced by the solar panels. Also, when driving loads, energy stored in the battery bank again goes through a converter or inverter by wasting considerable amount of useful energy. Hence, the purpose of this study is to minimize the energy loss of the charging process of the battery bank while using the energy produced by the PV array in an effective manner. In previous publications, it was introduced a novel way of using supercapacitors (SCs) in an off grid PV system. When charging an empty capacitor in parallel with a source, 50% of energy is wasted irrespective of the value of total loop resistance. In contrast, by connecting a SC bank in series with a typical solar charge controller, it was shown that the energy loss of the combined system is less than the energy loss of parallelly connected SC bank and the battery bank in their individual systems. Experimentally, it has been shown that a 9% increment in overall charging efficiency of the combined system when a charge controller having 80% of efficiency is used to charge the battery bank in typical off grid PV system. The present study introduces a possible method of utilizing the energy stored in SC bank in an effective manner using an intelligent electronic switching scheme. The proposed method uses a second SC bank along with the existing one along with a smart electronic switching circuitry which is able to switch each SC bank between charging or discharging stages when necessary. When one SC bank is in its charging state, the other SC bank will be in its discharging state through a proper load. After that, when the first SC bank is fully charged or the second SC bank is fully discharged, positions of each SC bank is swapped so that the second SC bank will start its charging process while the first SC bank is now discharging through the load. This way both charging and discharging of SC bank can be done efficiently while charging the battery bank in the system by the same manner.Item Supercapacitor based novel approach for efficient solar energy harnessing(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Piyumal, P. L. A. K.; Ranaweera, A. L. A. K.; Kalingamudali, S. R. D.; Kularatna, N.Finding greener solutions through renewable energy sources to provide energy demand in 21st century is an important task due to the shortage of world energy sources. From many types of renewable energy sources, photovoltaic cell is the most popular device that can be used to harvest solar energy and produce electricity. Currently, efficiency of conventional solar panels lies between 20-25%. In addition, part of energy is lost during the power conversion process in solar power converters. Standalone photovoltaic systems used in houses and other buildings in remote areas employ solar charge controllers to charge their battery banks in order to store energy. Efficiency of these systems relies mostly on the efficiency of in built DC-DC converter of the charge controller. With the advancement of modern semiconductor technologies and electronics, maximum of 90% efficiency can be achieved by a brand new solar charge controller. Usually this value will be decreased with the years of usage. Hence, the purpose of this work is to minimize the energy wasted during charging process of the battery bank of a standalone photovoltaic system. The initial approach was to connect DC-DC converter and battery bank in series with a capacitor charging loop. When an empty capacitor is charged by delivering Q charge using an external source, it can theoretically be shown that 50% of energy will be lost in the charging loop regardless of the resistance of the loop. If a useful resistive load is attached to the capacitor charging loop in series, this wasted energy can be effectively utilized by doing a treasured work while charging the capacitor too. In this work, this basic concept was used by replacing the conventional capacitor from a supercapacitor and attaching the DC-DC converter and the battery bank as the useful resistive load. Thereby, charging both supercapacitor and battery bank has been done. Theoretical analysis of this novel method shows promising outcomes on achieving high charging efficiency. Experimental results show this technique increases the overall charging efficiency of a standalone photovoltaic system by 9% when 80% efficient DC-DC converter is used to charge the battery bank. Therefore, it can be concluded that the overall charging efficiency of a typical standalone photovoltaic system can be enhanced by adding supercapacitor in series. The energy stored in both devices could be used to drive DC or AC loads using necessary electronics.