Energetic and economic optimisation of a novel hybrid pv-thermal system for domestic combined heating and power

Techno-economic performance calculations have been performed for a hybrid photovoltaic-thermal (PVT) collector design, featuring a novel polycarbonate flat-box absorberexchanger configuration, integrated into a solar combined heat and power (S-CHP) system for the simultaneous provision of domestic hot water (DHW), space heating and power. The demands for electricity (including for lighting, cooling, and other home appliances), DHW and space heating from a singlefamily house located in two different climates, Zaragoza (Spain) and London (UK), were estimated and considered together with the local climate conditions in the S-CHP system performance analysis. The S-CHP system model used in this analysis includes the governing equations of the PVT unit, a hot-water storage tank, a water pump and a tank bypass. The capital (investment) cost of the system and the utility (electricity, natural gas) costs are also integrated into the model. The PVT array area and storage tank volume were sized to meet a minimum requirement for thermal energy demand coverage at each geographical location, and a seasonal optimisation of the collector flow-rate was performed to minimise the levelised production cost (LPC) of electrical and thermal energy and the levelised emissions displacement cost (LEDC). The results show that the S-CHP system optimised for Zaragoza with an array of 14 PVT collectors (covering 22 m, with a 3.4-kWe peak electrical power rating) can provide 77% of the total household thermal demand and 145% of its electrical demand, averaged over the four seasons, with the surplus electricity exported to the grid, generating additional income. With the system optimised for London and an array of 17 PVT collectors (covering 26 m, with a 4.1-kWe peak electrical power rating), the system provides 55% and 153% of the household thermal and electrical demands, respectively. INTRODUCTION A hybrid photovoltaic-thermal (PVT) collector is a solar energy collector consisting of a PV module in contact with a thermal absorber that is capable of generating both electrical and thermal outputs from the same collector area. Similarly to conventional PV and solar-thermal systems, PVT systems have the added benefit of moving energy generation closer to the point of use, and hence reducing the demands on the costly energy distribution infrastructure. This makes these systems particularly promising for domestic applications. The most widely studied absorber-exchanger configuration in PVT collectors is that of parallel copper tubes (sheet-andtube) with water or water-glycol mixtures as the heat transfer fluid [1–6], which is also the one used most commonly in commercially-available PVT panels. In this configuration, the amount of heat that can be extracted, and thus the overall efficiency that can be achieved, depends upon the collector fin efficiency and the tube bonding quality [7]. Consequently, several authors have made significant efforts to optimise the design of these collectors by paying attention to these design aspects [4,5], while others have proposed a flat-box structure with square or rectangular channels in order to significantly increase the heat transfer area between the absorber plate and the cooling fluid [1,7–12]. Some of these studies [1,7,12] have considered extruded aluminium alloy as the absorber-exchanger material; while in others [8,10,11], polycarbonate (PC) is proposed in order to lower the cost and weight of the PVT unit. The work presented in this paper focuses on the technoeconomic performance optimisation of a PC flat-box PVT panel for solar combined heat and power (S-CHP) provision in a domestic application. Previous research undertaken by the authors [13] indicated that with this absorber-exchanger configuration, improved heat transfer and higher efficiencies can be achieved. Specifically, 4% higher optical efficiency and about 15% lower heat loss coefficient were estimated, leading also to a 9% reduction in weight and a 21% reduction in investment cost compared to a commercial PVT system based on a copper sheet-and-tube arrangement. METHODOLOGY A quasi-steady state model of the complete solar combined heat and power (S-CHP) system has been developed in the software EES [14] with which to assess the techno-economic performance of the novel absorber-exchanger PVT collector configuration proposed in this research. The model has been used to simulate the system’s performance over a typical week in each season (winter, spring, summer and autumn). From these simulations, important S-CHP system component parameters, specifically: the number of PVT panels, the required volume of the hot-water storage tank, and the PVT collector flow-rate, have been assessed and optimised. 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics