Final Report Summary - PV/HP GENERATION (A Micro-generation System Using PV/heat-pipe Roof Modules)
This project aims to investigate energy performance of hybrid photovoltaic/thermal (PV/T) panel-based heat pump systems. R134a refrigerant was employed to cool the PV modules. With the low evaporating temperature, it was expected to achieve better cooling effect and better electrical performance of the PV modules than using air and water working fluids. The heat extracted from the PV modules was released later at the condenser for building heating and domestic hot water supply after the Rankine refrigeration cycle. Two types of PV/T panel, flat plate (FP) panel and glass vacuum tube (GVT) panel, were proposed for energy performance comparison. Numerical simulation and experimental testing of the hybrid systems have been carried out in this study. It can be concluded as follows.
Numerical simulation showed that: Under an average radiation of 500 W/m2, the GVT PV/T panel has an average thermal efficiency of 0. 775, 73. 4 % higher than that of the FP PV/T panel of 0. 447; The GVT PV/T panel has an average electrical efficiency of 0. 089, slightly higher than that of the FP PV/T panel of 0. 088; The GVT PV/T heat pump system has an average COP of 5. 6, 9. 8 % higher than that of the FP PV/T heat pump system of 5. 1; In the area of low latitude with higher solar radiation, the thermal efficiency and COP tended to be higher but the electrical efficiency tended to be lower.
The experimental study on the GVT PV/T heat pump system showed that: The COP of the heat pump system increased with the increasing radiation. The COP was not as high as expected due to the low capacity compressor, selected to match the small size and low capacity of PV panel limited indoors. The PV power output and electrical efficiency also increased with the increasing radiation. The electrical efficiency of PV panel in the heat pump system was improved by up to 1. 9 %, compared with that without cooling, based on the reference efficiency of 3. 9 % for amorphous silicon PV modules; The COP of the heat pump system decreased with the increasing condenser water supply temperature. The condenser water supply temperature had little effect on the PV power output and electrical efficiency; The COP of the heat pump system decreased with the increasing condenser water flow rate; The condenser water flow rate had little effect on the PV power output and electrical efficiency; The maximum COP could reach up to 6. 7, with an average value of 3. 8 responding to a radiation of 500 W/m2 and a condensing temperature of 35 ?; Under the same condition, the simulation result of an average COP was 4. 9, 29 % higher than the testing result.
The experimental study on the FP PV/T heat pump system using PV tiles showed that: The COP of the FP PV/T heat pump system had the same changing trend with various radiation, condenser supply water temperature and condenser water flow as that of the GVT PV/T heat pump system; At a radiation lower than 400 W/m2, electrical efficiency appeared to be the same for PV tiles with and without cooling. As the radiation continued to increase, the electrical efficiency with PV cooling became higher than that without PV cooling; At a radiation lower than ~600 W/m2 (cross point 593 W/m2), the COP of FP PV/T heat pump system was higher than that of GVT PV/T heat pump system due to the heat absorption of PV panel from ambient warm air. However, as radiation increased to be higher than ~600 W/m2, the COP of GVT PV/T heat pump system became higher than that of FP PV/T heat pump system.
Economic and environmental analysis has been carried out for the GVT PV/T heat pump system. The results showed that the novel heat pump system, for a traditional residential building of 200 m2 in London area, provided an annual running cost saving by ? 852. 03 compared with traditional domestic gas boiler operation. The simple pay-back time was 7. 6 years. The annual CO2 emission could also be reduced by 707. 8 kg/a.
Numerical simulation showed that: Under an average radiation of 500 W/m2, the GVT PV/T panel has an average thermal efficiency of 0. 775, 73. 4 % higher than that of the FP PV/T panel of 0. 447; The GVT PV/T panel has an average electrical efficiency of 0. 089, slightly higher than that of the FP PV/T panel of 0. 088; The GVT PV/T heat pump system has an average COP of 5. 6, 9. 8 % higher than that of the FP PV/T heat pump system of 5. 1; In the area of low latitude with higher solar radiation, the thermal efficiency and COP tended to be higher but the electrical efficiency tended to be lower.
The experimental study on the GVT PV/T heat pump system showed that: The COP of the heat pump system increased with the increasing radiation. The COP was not as high as expected due to the low capacity compressor, selected to match the small size and low capacity of PV panel limited indoors. The PV power output and electrical efficiency also increased with the increasing radiation. The electrical efficiency of PV panel in the heat pump system was improved by up to 1. 9 %, compared with that without cooling, based on the reference efficiency of 3. 9 % for amorphous silicon PV modules; The COP of the heat pump system decreased with the increasing condenser water supply temperature. The condenser water supply temperature had little effect on the PV power output and electrical efficiency; The COP of the heat pump system decreased with the increasing condenser water flow rate; The condenser water flow rate had little effect on the PV power output and electrical efficiency; The maximum COP could reach up to 6. 7, with an average value of 3. 8 responding to a radiation of 500 W/m2 and a condensing temperature of 35 ?; Under the same condition, the simulation result of an average COP was 4. 9, 29 % higher than the testing result.
The experimental study on the FP PV/T heat pump system using PV tiles showed that: The COP of the FP PV/T heat pump system had the same changing trend with various radiation, condenser supply water temperature and condenser water flow as that of the GVT PV/T heat pump system; At a radiation lower than 400 W/m2, electrical efficiency appeared to be the same for PV tiles with and without cooling. As the radiation continued to increase, the electrical efficiency with PV cooling became higher than that without PV cooling; At a radiation lower than ~600 W/m2 (cross point 593 W/m2), the COP of FP PV/T heat pump system was higher than that of GVT PV/T heat pump system due to the heat absorption of PV panel from ambient warm air. However, as radiation increased to be higher than ~600 W/m2, the COP of GVT PV/T heat pump system became higher than that of FP PV/T heat pump system.
Economic and environmental analysis has been carried out for the GVT PV/T heat pump system. The results showed that the novel heat pump system, for a traditional residential building of 200 m2 in London area, provided an annual running cost saving by ? 852. 03 compared with traditional domestic gas boiler operation. The simple pay-back time was 7. 6 years. The annual CO2 emission could also be reduced by 707. 8 kg/a.