TECHNICAL AND ECONOMIC EVALUATION OF DIFFERENT UTILIZATION OPTIONS BASED ON COMBINED PHOTOVOLTAIC AND SOLAR THERMAL (PVT) SYSTEMS FOR THE RESIDENTIAL SECTOR

Abstract

In this report glazed and unglazed channel tubed PVT collectors are examined and research is conducted to find the most suitable heat application for different household sizes. Also a prototype unglazed channel tubed PVT collector developed within the Nanosol project is experimentally tested and these results have been used to validate the simulation model. The simulations make use of a 1 dimensional thermal model based on the equations of Hottel and Whillier. The glazed and unglazed PVT collectors are optimised for different PV types, tubing materials, dimensions, flow rate and other parameters. The objective of the optimisation procedure is to find the lowest payback period and the highest exergy production. Earlier research has pointed out that the three most promising heat applications for PVT collectors are preheating DHW, preheating water for a heat pump to provide low temperature central heating and a combination of both. The total system makes use of the optimised PVT collectors and this system is optimised for different sizes and capacities of the system components and different control schemes for the operation of the circulation pump. The optimisation is based on reducing the simple payback period. Results show that the lowest simple payback period is for using an unglazed PVT collector applied for preheating DHW for a large household. The optimised simple payback period for this PVT system is 8.4 years and mainly the electric yield is decisive for this result. This optimised system has a collector area of 34.4 m2 and a storage tank volume of 216 L. Another observation is that a small flow rate is often optimal since this leads to higher PVT outlet temperatures resulting in a higher operation time of the circulation pump. Aside from the associated gas savings, a higher operation time also results in more cooling which increases the electrical yield of the PV cells. Using PVT collectors for preheating water in a heat pump is less beneficial and the lowest payback period is achieved by a glazed PVT collector (16.4 years). A combination of both systems led to comparable results to the PVT heat pump system. Still the additional functionality enabling the system to preheat water for DHW reduced the simple payback period slightly to 15.8 years.