Effects of the Italian financial crisis on the photovoltaic dissemination in a southern city

The aim of this paper is to estimate how the profitability of grid-connected PV (photovoltaic) systems may vary month by month due to the changes in all parameters involved in the economic evaluation (discount rate, PV electricity selling price, inflation rate, price of PV devices etc.). The effects of these variations were investigated for a district of a city in the South Italy (Palermo). The results of the analysis provided the trend of the actual coverage of the district power demand from June 2010 to August 2012. In particular the load match index, which considers the daily energy demand covered by PV systems, ranged from almost 30% to less than 12%, which is less than the value of 17% of the final energy consumption in 2020 from renewable energy sources that Italy is obliged to ensure by the European Union Directive 2009/28/EC. Finally, a sensitivity analysis related to shading and mismatch factors was carried out. If 10% of the solar energy had been shadowed, the load match index would have reduced of 70%. Similarly, if only 40% of electrical production had been used, the load match index would have lowered to an almost null value in January 2012

An improved photographic method to estimate the shading effect of obstructions

A new photographic method is presented to evaluate the shading effects of obstructions on surfaces exposed to the sun. The method overcomes the difficulties caused by the need to accurately describe the surrounding objects to estimate the shading effects by means of the usual tools that use the spatial reconstruction of obstructions or cylindrical or polar suncharts. The photographs of the surrounding objects are used as the background on which the solar disc is depicted at the various hours of the day. In this way it is easily detectable if the sun is visible from the place where the photographs were taken or if the surrounding obstructions obscure the sun. In spite of the complex mathematical background of the new method, the practical application of the procedure is very simple, and only requires the measurements of three angles for each photograph. The procedure permits to verify the suitability of a generic site for solar exploitation; its main benefit is the simplicity of use and the transparency of the obtained results. This method is particularly useful to evaluate the technical feasibility of small solar systems installed on the buildings of densely urbanised cities. The accuracy of the method was tested by performing an experimental verification in the field. For this purpose, the sun was photographed at different hours of the day. The photographed solar discs and the calculated sun’s positions were compared. The differences between the photographed and calculated sun’s positions corresponded to small time lags that do not exceed few minutes in the worst case. To further investigate the reliability of the proposed method, the impact of image distortion, which always affects all methods that use cameras to get information about the photographed reality, was also examined

A Criterion for Rating the Usability and Accuracy of the One-Diode Models for Photovoltaic Modules

In selecting a mathematical model for simulating physical behaviours, it is important to reach an acceptable compromise between analytical complexity and achievable precision. With the aim of helping researchers and designers working in the area of photovoltaic systems to make a choice among the numerous diode-based models, a criterion for rating both the usability and accuracy of one-diode models is proposed in this paper. A three-level rating scale, which considers the ease of finding the data used by the analytical procedure, the simplicity of the mathematical tools needed to perform calculations and the accuracy achieved in calculating the current and power, is used. The proposed criterion is tested on some one-diode equivalent circuits whose analytical procedures, hypotheses and equations are minutely reviewed along with the operative steps to calculate the model parameters. To assess the achievable accuracy, the current-voltage (I-V) curves at constant solar irradiance and/or cell temperature obtained from the analysed models are compared to the characteristics issued by photovoltaic (PV) panel manufacturers and the differences of current and power are calculated. The results of the study highlight that, even if the five parameter equivalent circuits are suitable tools, different usability atings and accuracies can be observed

Load mismatch of grid-connected photovoltaic systems: Review of the effects and analysis in an urban context

The mismatch between generated and consumed electricity is a relevant topic of the energy and economic assessment of photovoltaic (PV) systems. Due to the load mismatch some amount of PV electricity may be exported to the grid because the electrical demand is temporarily lower than production, whereas a consumption, which is higher than production and/or that does not match the available PV generation, will require to be supplemented by the public grid electricity. The presence of the load mismatch can cause the effect of disadvantageously purchasing electricity from the grid and/or squandering the unexploited PV energy. If only a very small part of the PV generation is used to supply the household appliances, benefits may not compensate disbursements. Moreover, instead of giving a benefit to the community, an amount of surplus electricity generated by a great number of PV systems may represent a significant problem for the grid operators. In this paper the study of the effect of the load mismatch on the energy and economic analysis of the PV potential of a district of a city of the South Italy is presented. The authors propose an appropriate methodology able to explore the architectural morphology of buildings and evaluate both the solar potential of PV systems installed on roofs and the economic aspects involved. The impact on the grid of the electricity generated by large-scale PV systems, which is a worry to the traditional electricity producers and dispatchers, seems to be much less than expected if the economic viability is considered in the assessment of the real penetration of PV systems. The results, which confirmed the importance of the role played by the load mismatch, suggest that only the generation of the PV electricity that is really consumed by the PV producers should be wisely supported by the economic incentives

Review of the energy and economic parameters involved in the effectiveness of grid-connected PV systems installed in multi-storey buildings

The assessment of PV energy in an urban context is extremely complex because many factors have to be considered. Moreover, when the purpose is calculating the realistic amount of the electricity demand of a city that can be covered by the photovoltaic generation, it is necessary to estimate the number of photovoltaic systems whose installation is economically advantageous. Such a topic requires an economic analysis, which is affected by the number of energy and economic parameters involved and the values assigned to them to perform calculations. Some parameters are perfectly known and unvarying, like the paid incentives. Adversely, some parameters, like the efficiency degradation of photovoltaic panels, can only be supposed. Other parameters require some information that is specifically related to each particular photovoltaic system. With the aim of estimating the influence of the manifold energy and economic parameters that characterize how photovoltaic penetration develops in urban areas, a specific study was conducted for a city in the south of Italy. A sensitivity analysis was carried out in order to verify parameters have an irrelevant influence and what are the parameters whose definition can be a crucial element of the energy and economic analysis of photovoltaic systems because dramatically impact on the results. The presented study represents a valuable help for photovoltaic systems designers and energy decision-makers because it permits to evaluate the impact of the deviations of the main parameters on the profitability of photovoltaic systems and the role played by them in the effectiveness of the energy policies implemented to achieve the required shares of electricity demand coverage

UN METODO FOTOGRAFICO PER LA STIMA DELL’EFFETTO OMBREGGIANTE DOVUTO ALLE OSTRUZIONI

Si propone un nuovo metodo che consente di utilizzare l’immagine fotografica di ostacoli ombreggianti per valutarne l’effetto oscurante nei confronti della radiazione solare diretta incidente su di una superficie. Il metodo descritto è simile a quello che prevede l’impiego del diagramma cilindrico dei percorsi solari, calcolati in funzione dell’azimut e dell’altezza solare, e la sovrapposizione su di esso del poligono raffigurante l’oggetto ostruente costruito in base alle coordinate cilindriche dei suoi punti più significativi. La nuova procedura prevede invece la sovrapposizione sulla fotografia del percorso solare opportunamente trasformato secondo le regole della prospettiva. E’ così possibile tracciare direttamente sulla foto la posizione assunta dal sole agli orari richiesti per qualunque giorno dell’anno e località, utilizzando a tale scopo la conoscenza di un numero estremamente limitato di dati, peraltro facilmente reperibili. Le porzioni del percorso intercettate dal contorno degli ostacoli rappresentati nell’immagine fotografica indicano le fasce orarie durante le quali il punto della superficie ricevente risulta ombreggiato. Viceversa i restanti tratti del percorso solare evidenziano la presenza della componente diretta radiazione. Sono presentati, inoltre, i risultati del confronto tra i dati calcolati e quelli sperimentali condotti presso il Dipartimento di Ricerche Energetiche e Ambientali (DREAM) di Palermo.A new, simplified photographic method is proposed to estimate the shading effects of obstructions. In spite of the complex mathematical background of the new tool, its practical application is very simple, and only requires the measurements of three angles for each photograph. The proposed method is particularly useful for overcoming the difficulties caused by the need to accurately describe surrounding objects to estimate shading effects. The new method uses the information contained in a picture and allows one to draw daily solar paths directly on the photograph. The procedure is useful to verify the suitability of a generic site for solar exploitation; its main benefit is the simplicity of use and the transparency of the obtained results. This simple method is also particularly suitable to evaluate the technical feasibility of small solar equipment, which would not require complex software to define the daily solar path

A procedure to calculate the I–V characteristics of thin-film photovoltaic modules using an explicit rational form

Accurate models of the electrical behaviour of photovoltaic modules are effective tools for system design. One or two diode equivalent circuits have been widely used even though some mathematical difficulties were found dealing with implicit equations. In this paper, a new model based on a simple rational function, which does not contain any implicit exponential form, is presented. The model was conceived in order to be used with thin-film photovoltaic modules, whose current–voltage curves are characterised by very smooth shapes. The parameters of the model are evaluated by means of the derivatives of the issued characteristics in the short circuit and open circuit points at standard rating conditions, and assuming that the calculated current–voltage curve contains the rated maximum power point of the simulated panel. The capability of the model to calculate the current–voltage characteristic for values of the solar irradiance and cell temperature far from the standard rating conditions was verified for various thin-film technologies, such as CIS, CIGS, amorphous silicon, tandem and triple-junctions photovoltaic modules. A comparison with the results obtained by another rational model and other two-diode models, which were used to simulate the electrical behaviour of thin-film photovoltaic modules, is also presented

Air quality and relative humidity in commercial aircrafts: an experimental investigation on short-haul domestic flights

Nowadays the achievement of a comfortable environment in aircraft cabins is a factor of paramount importance in air travel business competition; on the other hand, the need of reducing the propulsion fuel cost has driven the airline companies to adopt air handling systems that may reduce the levels of thermal comfort and air quality inside the cabins of commercial airliners. With the aim of contributing to a better knowledge of this matter, this paper reports the results of an experimental study upon the indoor air quality aboard commercial aircrafts for 14 domestic flights less than 1 h and half long. The parameters monitored were temperature, relative humidity and carbon dioxide concentration; the measurements were performed during the whole flight from the take-off to the landing. The relative humidity inside the cabin was also calculated using the rates of outside air and the carbon dioxide as a ventilation tracer; the theoretical results were compared with the measured data. The relationship between relative humidity and carbon dioxide concentration during fights was highlighted in order to define the environmental conditions that may provide acceptable levels of both the air quality and hygrometric comfort to the crew and passengers. The results of calculations confirmed the possibility of improving the hygrometric conditions in aircraft cabins without the need of using humidification systems

A correlation linking the predicted mean vote and the mean thermal vote based on an investigation on the human thermal comfort in short-haul domestic flights

The results of an experimental investigation on the human thermal comfort inside the cabin of some Airbus A319 aircrafts during 14 short-haul domestic flights, linking various Italian cities, are presented and used to define a correlation among the predicted mean vote (PMV), a procedure which is commonly used to assess the thermal comfort in inhabited environments, and the equivalent temperature and mean thermal vote (MTV), which are the parameters suggested by the European Standard EN ISO 14505- 2 for the evaluation of the thermal environment in vehicles. The measurements of the radiant temperature, air temperature and relative humidity during flights were performed. The air temperature varied between 22.2 °C and 26.0 ° C; the relative humidity ranged from 8.7% to 59.2%. The calculated values of the PMV varied from 0.16 to 0.90 and were confirmed by the answers of the passengers. The equivalent temperature was evaluated using the equations of Fanger or on the basis of the values of the skin temperature measured on some volunteers. The correlation linking the thermal sensation scales and zones used by the PMV and the MTV resulted quite accurate because the minimum value of the absolute difference between such environmental indexes equalled 0.0073 and the maximum difference did not exceed the value of 0.0589. Even though the equivalent temperature and the MTV were specifically proposed to evaluate the thermal sensation in vehicles, their use may be effectively extended to the assessment of the thermal comfort in airplanes or other occupied places