Dynamic Coupled Thermal - and - Electrical Modelling of Sheet - and - 1 Tube Hybrid Photovoltaic / Thermal ( Pvt ) Collectors 2 3

12 In this paper we present a dynamic model of a hybrid photovoltaic/thermal (PVT) collector with a sheet-and-tube 13 thermal absorber. The model is used in order to evaluate the annual generation of electrical energy along with the 14 provision of domestic hot-water (DHW) from the thermal energy output, by using real climate-data at high 15 temporal resolution. The model considers the effect of a non-uniform temperature distribution on the surface of 16 the solar cell on its electrical power output. An unsteady 3-dimensional numerical model is developed to 17 estimate the performance of such a collector. The model allows key design parameters of the PVT collector to 18 vary so that the influence of each parameter on the system performance can be studied at steady state and at 19 varying operating and atmospheric conditions. A key parameter considered in this paper is the number of glass 20 covers used in the PVT collector. The results show that while the thermal efficiency increases with the additional 21 glazing, the electrical efficiency deteriorates due to the higher temperature of the fluid and increased optical 22 losses, as expected. This paper also shows that the use of a dynamic model and of real climate-data at high 23 resolution is of fundamental importance when evaluating the yearly performance of the system. The results of 24 the dynamic simulation with 1-min input data show that the thermal output of the system is highly dependent on 25 the choice of the control parameters (pump operation, differential thermostat controller, choice of flow rate etc.) 26 in response to the varying weather conditions. The effect of the control parameters on the system’s annual 27 performance can be captured and understood only if a dynamic modelling approach is used. The paper also 28 discusses the use of solar cells with modified optical properties (reduced absorptivity/emissivity) in the infrared 29 spectrum, which would reduce the thermal losses of the PVT collector at the cost of only a small loss in 30 electrical output, providing the electrical performance does not deteriorate when the selective coating is applied. 31 32