INNOVATIVE TECHNIQUES FOR PHOTOVOLTAIC PANELS MODELING AND MONITORING

Abstract

In the last years, the photovoltaic (PV) energy market has had an extremely rapid expansion and this brought to the request of effective devices and tools for the estimation of the electrical power produced by PV plants. Nevertheless, often the estimation of energy production coming from PV plants is not a simple task. Indeed, it depends both on weather and environmental factors (e.g. temperature, irradiance, sky conditions, etc...) usually estimated through statistical data and on the goodness of the PV model utilized for the Current-Voltage I-V outputs prediction under real operating conditions (temperature and irradiance). Moreover, during the panel lifetime, the PV panel model should be continuously updated to take into account the ageing of the panel itself. In this PhD thesis, both the PV panel modeling problem, and its adjustment during the PV panel lifetime, are addressed. In the first part of this work, an accurate I-V tracer based on microcomputer assisted DC-DC converter used as electronic load is described. The equipment proposed here is much more complex and accurate than others proposed in literature or available in the market. It is able to trace PV panels with a maximum power up to 300 watt with a very high accuracy, moreover, since it is controlled by means of a powerful control unit, complex algorithms can be executed. Among these, very important are those, developed by the researchers of our Institute, for the identification of the five parameters of the "one-diode" model of a PV panel. Furthermore, since the proposed system is able to collect voltage and current values both in the input and in the output of the DC-DC converter, it can be used for the development of the control algorithms of the DC-DC converters themselves as well. Among these, those for the tracking of the maximum power point (MPPT) are certainly the most important ones. Both PV panels characterization and DC-DC converter control algorithms verification, are topics about maximization of the power a PV panel can deliver, but, in the real world, this is not the only issue to take into the account. Ageing of the PV panel can limit the overall return of investment (ROI) for a PV panel much more than its power delivery maximization. In the second part of this PhD thesis work, it is described an innovative technique that allows to monitor the PV panel ageing in real time, continuously, and online, that is while the panel is working without the need to disconnect it from the load. The task is accomplished simply collecting its working conditions, that is the values of the voltage and of the current set by the MPPT algorithm. The value of the irradiance is not necessary. This innovative technique has been described in the work “A novel technique for online monitoring of photovoltaic devices degradation”, recently published by Elsevier in the journal "Solar Energy". The technique introduced in this work to monitor PV panel ageing, and therefore useful to predict the most suitable moment to change the PV panels of a plant, is indeed useful also in other applications where an updated PV panel model is required. Two of them are described in this work: fast model based MPPT algorithms, and irradiance measurement by means of real, and therefore subject to ageing, PV panel.