Energy and economic optimization of pv hybrid systems to supply buildings hvac demandbattery modeling and control strategies

Resumen

The main objective of this research is to assess the potential of PV hybrid systems to supply the electrical consumption in the Heating, Cooling and Air-Conditioning (HVAC) systems of buildings. The hypothesis of this thesis suggests that a PV hybrid system is capable of supplying the necessary energy to maintain the comfort conditions inside a building, while this system is technically and economically profitable from the point of view of the consumer. In order to fulfil the proposed objective and contrast the hypothesis, a Battery Energy Storage System (BESS) has been coupled to a PV system already existing in the prototype of the nearly zero-energy building, so-called ‘Magic Box’ at the Instituto de Energía Solar - Universidad Politécnica de Madrid. Likewise, two heat pumps to maintain the comfort conditions inside the house, sensors of temperature, relative humidity and concentration of CO2, have been installed. In the PV hybrid system, control algorithms have been implemented, which are capable of managing the power generated by the PV system, the charge and discharge battery power, and the imported and exported electricity grid, in such a way that the electrical consumption of the heat pumps is always supplied. By means of these algorithms, two control strategies have been implemented (optimizing the PV self-consumption and peak-shaving) and two modes of operation (the battery supplies all loads, or the battery only supplies the HVAC specific load). With the data collected after an extensive measurement programme, a model was developed that reproduces the control strategies implemented in the PV hybrid system, with an error lower than 10%. This model served as the basis for the development of a simulation software tool that allows one to evaluate — for various case studies — the main parameters of the system (PV generation, power exchange with the BESS, power exchange with the utility grid and the battery state of charge). This tool, called PVbat also implements a detailed economic analysis, levelized cost of electricity, payback-time, and various sensitivity analyses (billing saving, self-consumption, self-sufficiency and battery lifetime), which allow one to determine whether the PV hybrid system is profitable or not. By applying this model in two case studies (in Spanish and Ecuadorian scenarios), the starting hypotheses of the thesis have been demonstrated. A third case study also was evaluated (Portuguese scenario), where the economic impact of changing fixed charges in the bill electricity using PV-battery systems was analysed with total electricity consumption in a residential building, suggesting that the peak-shaving control strategy may lead to quite positive economic performance of PV-battery systems especially when the bill structure is based on fixed (power) charges. The thesis is divided into four parts: the first part is the introduction, which details the research problem, the object of research, the hypotheses and the objectives. In the second part, a review of the state of the art of the fields related to this thesis is conducted. The third part presents the methodology used, the experimental stage, the battery control strategies and the validation of the grid-connected PV-battery systems model. The fourth part presents the results of the three case studies, the conclusions of this thesis, the publication of papers and international congresses, and finally, defines future lines of research that may arise from this Thesis.