Thermoeconomic optimization and performance analysis of solar combined heating and power systems: A comparative study

Abstract

Although solar energy is one of the most abundantly available and inexhaustible forms of clean renewable energy, its use suffers from economic barriers mainly linked to its intermittence. This article aims at comparing to a conventional reference system (national grid and gas boiler) four different solar combined heating and power systems, namely photovoltaic panels with solar-assisted heat pump, national grid and solar thermal panels, photovoltaic and solar thermal panels together and photovoltaic thermal hybrid solar collector. The study is carried out for an individual house of 120 m2 located in Chambery, France. The optimal designs (number of solar panels and electrical and thermal storage capacities) are determined for each case using genetic algorithm based on a thermoeconomic indicator, i.e. the total unit product cost. Furthermore, the solutions are compared against one another and with the reference case, using the following additional indicators: solar self-production, solar self-consumption, energy produced by solar panels, energy requirement from grid and fuel savings. Implementation of unit solar panel-driven systems without storage shows the lowest unit product costs, with a positive solar contribution, especially for solar-assisted heat pump with photovoltaic panels (-41% than the reference). Further, a wise increase of the solar system sizes allows to improve the solar self-production (by up to 30%) and fuel saving indexes (by up to 3230.3 kWh/y), at the expense of the solar self-consumption, while maintaining unit production costs lower than the reference system (0.1836€/kWh). Despite of their intermittence, solar thermal collectors, with grid-driven electric boiler as backup, are proving to be an economical competitor to the reference gas boilers (with 11% lower unit product costs). However, photovoltaic systems suffer from low economic competitiveness compared to the high efficiency and low cost French national grid (by −36%), which could be compensated when coupled with heat pump to satisfy heating demand.