Performance Analysis of Hybrid Photovoltaic Thermal and Heat Pump System Using Computational Model
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Date
2020-10
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Addis Ababa University
Abstract
Renewable energy resources such as solar energy have great potential in meeting electrical and thermal energy demand in off-grid areas of developing countries. Working on this breakthrough and well-tried sector changing the lives of millions of people living in off-grid areas. In recent decades, enduring plenty of studies and development works on solar technology, specifically on the hybrid photovoltaic and thermal collector have been given attention. As a part of this global research and development trend, this research integrates photovoltaic, solar collector, and heat pump (PV/T-heat pump) to one system by combining to deliver both electrical and thermal energy simultaneously or thermal energy alone (hot water).
Cooling of photovoltaic panels by water improves the electrical conversion efficiency and produces warm water as a by-product. The photovoltaic thermal system is being used for the co-generation of electrical energy and hot water. In this study, the annual performance of a glazed photovoltaic thermal system (a combination of PV module and solar flat plate collector) with a storage tank was investigated at first by a dynamic computational model. The PV/T model was developed using MATLAB under the actual hot water demand condition for co-generation of electrical energy and hot water, and simulation was conducted for two locations in Ethiopia, Dire Dawa and Addis Ababa.
The computational model determines the electrical energy production and temperature of water at different points and other components of the PV/T system within a given time interval. Also, summaries of monthly and annual incident solar irradiance, electrical energy generation, thermal energy transported to storage, and thermal energy supplied as hot water to end-users are computed, considering the hourly hot water consumption pattern and storage size effect. The simulation, which is conducted for 20 ��2 PV/T system consists of 12 panels with each 1.65 ��2 module areas resulted in the generation of 803 kWh/year thermal energy and 310 kWh/year electrical energy. The annual average electrical efficiency, thermal efficiency, hot water end-use overall efficiency, and co-generation (PV/T) efficiency of the system were 15.4%, 50.4%, 38%, and 65.8%, respectively. Moreover, the maximum hot water temperature was below 50oC; hence, the PV/T system can be used for water preheating and reach about half of the heating load in tropical areas besides electrical energy generation.As the Photovoltaic-thermal system can only be used for preheating water, the warm water can be used as an input to the heat pump water heater to attend required water temperature by the end-user. The electrical energy required by the heat pump water heater will be covered by the electrical energy generated by the PV/T system. It shall be noted that the heat pump uses an average of 1 kW of electricity to generate 3 kW of thermal energy. The hybrid PVT-heat pump system is appropriate and capable to deliver thermal (hot water) and electrical energy to the user either on the domestic or institution scale without an additional alternative source of energy.
The performance of the hybrid PV/T-heat pump system was analyzed and compared in two Ethiopian cities, geographical and environmental representative zones of the highland and lowland regions, namely Addis Ababa and Dire Dawa respectively. The analysis was done on the system COP and outlet hot water temperature in both selected sites considering an illustrative month of the year regarding the solar irradiations availability. Besides, the end-use hourly hot water consumption pattern (variability effect in three dissimilar cases constant, restaurant, and motel) on the system performance was examined.
Eight different heat pump compressor electrical energy consumption scenarios with a constant hourly hot water consumption fraction pattern were analyzed. On those eight different energy consumption patterns cases have been comprehended the effect on the system; COP, hot water temperature delivery value, end-use efficiency, and heat generation capacity of the PV/T-heat pump system.
In those diverse situations, the heat pump system in most of the cases generated above 55℃ annual average hot water temperature, and the system come of an outcome 3 COP were analyzed. Finally, the economic analysis of the system was evaluated. The payback period and the cost of energy were leveled as 16.96 years and 2.16 ETB/kWh, respectively.
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Keywords
Hybrid Photovoltaic Thermal, Computational Model, Heat Pump