A Water-Energy-Carbon Nexus Approach for the Optimal Design and Configuration of Green Roofs and Photovoltaic Systems

This paper addresses the coupling between two technologies commonly used on roofs in urban ecosystems: green roofs and photovoltaic panels. The water-energy-carbon nexus is used as a reference framework to generate a multi-objective model in which the energy transition index, carbon balance, and water consumption are proposed as functions to address the nexus. The economic performance of the system is also considered. The utopia-tracking method, based on objective function normalization and sub-setting, is used to generate nexus performance metrics. Factors such as building thermal load and grid interaction are considered, as well as the use of different vegetation species. Since it is a many-objective problem, alternatives to the Pareto front representation are explored to streamline decision-making processes. The results show that, although green roofs can have significant advantages in carbon abatement environments, considering factors such as carbon sequestration and energy consumption reduction, they are not suitable in semi-arid regions with high water consumption sensitivity. On the other hand, photovoltaic panels generate thermal insulation and power. This makes them a better option for implementation in low-income housing.