A MILP approach to supply solar energy from surrounding residential complexes to a university campus

The Instituto Superior Técnico (IST) university has a campus located in the center of Lisbon and its electrical consumption represents a relevant share of the yearly budget. The campus is surrounded by plenty of residential complexes with available roof surface, which can be used to generate energy from solar. The goal of this work is to find the number and type of equipment that IST should install on the roofs of the surrounding buildings to maximize the reduction of yearly energy related costs of both IST and the residents. To this end, photovoltaic (PV) and solar-thermal collectors with thermal storage (ST) technologies are considered for installation on the roofs of four category of buildings having the highest potential capacity of energy generation. Investment costs for this installation are supposed to be charged on the IST only. A design/operation optimization procedure of the system composed by the energy equipment of the users and IST is proposed on the basis of a Mixed Integer Linear Programming (MILP) model of this system, starting from a detailed analysis of the electric and thermal consumption curves of campus and buildings. The model has been run over four days, each representative of one season. Results show that the thermal energy required by the residents are not significant enough to justify any investment in ST. So, a base scenario is first created considering only PV modules with a specific cost of 2 €/kWp. In this case, the optimum results show that it is convenient to cover all the available surfaces with PV modules and IST achieves a yearly saving of 8.671% while each resident’s savings are in a range of 24 to 29%. Finally a sensitivity analysis on the specific cost of PV modules shows the strong decrease of IST’s savings with the increase of this cost, while the residents’ savings remain constants for a unity cost lower than that of the base scenario. For higher costs, the optimum area occupied by PV is lower than the available surfaces, so the savings of residents is lower as well.