Multi-objective optimization of solar energy systems for electricity and hot water generation in collective residential buildings considering the power-to-heat concept

Abstract

An extremely important question concerning the planning and installation of solar systems in residential buildings is how to optimally size solar photovoltaic (PV) systems and solar water heating systems. This question is challenging especially if there is an interest to explore the excess PV generation to produce of portion of the thermal load and assist the solar water heating system under the so-called power-to-heat concept. A tri-objective optimization process is introduced to find the best size of solar PV panels, thermal collectors and storage capacity for a Moroccan collective residential building. Modelling and optimization investigations rely on high-resolution time step over a one year operation, considering pertinent life-cycle objective functions which are the Levelized Cost of Electricity (LCOE), Levelized Cost of Heat (LCOH) and the Renewable Energy Penetration (REP). The collective residential building is located in Fez, Morocco. Instantaneous variations of PV power generation, thermal collector efficiencies, water temperature in the storage tank, auxiliary power and power imports from the grid are determined at each time step. The developed numerical tool can be used in other buildings categories and in other locations revealing a huge interest in improving the feasibility and competitiveness of solar energy systems in buildings. For total annual electric and thermal loads of 96.31 MWh/year and 32.88 MWhth/year, respectively, the optimum design consisted on 25 kWp PV capacity, 18 m2 of thermal collectors and 1.8 m3 of thermal storage. The corresponding LCOE, LOCH and REP are determined to be 17.8 c$/kWh, 3.5 c$/kWh and 45.8%, respectively. The self-sufficiency ratio, self-consumption ratio and solar thermal fraction for the final optimum design are 30.6%, 69.7% and 90.1%, respectively.