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Economy of grid-connected photovoltaic systems and comparison of irradiance/electric power predictions vs. experimental results
Full text linkThis thesis is focused on various aspects concerning the Distributed Generation (DG) from Renewable Energy Sources (RES) and in particular from PhotoVoltaics (PV).
The PV generation strongly depends on weather conditions (irradiance and temperature), therefore the solar irradiance forecast is very important for grid-connected PV systems. The PV power injected into the grid is concentrated during sunlight hours, in which the maximum peak load demand occurs and, as a consequence, an impact on the electrical system occurs.
The task of the Transmission System Operator (TSO) is to ensure a constant balance between supply and consumption within the grid. Therefore, the presence of strong fluctuations of the solar radiation requires additional regulatory actions and compensation, through the use of short-term power backup, causing an increase in network costs.
Thus, the solar irradiance forecast is necessary for an accurate evaluation of the PV power from PV systems, for the management of electrical grids in order to minimize the costs of energy imbalance and for the decisions concerning the energy market.
This thesis essentially consists of two parts. In the first part, the profitability of investments in the rooftop grid-connected PV systems subjected to incentive and the grid-parity analysis in the two main European PV markets (Italy and Germany) are presented. In the second part, in order to minimize the costs of energy imbalance in the Italian electricity market, the comparison of irradiance and electric power predictions with respect to the experimental results of grid-connected PV systems is presented
Il Generatore Fotovoaltaico: Mismatch e Risultati della simulazione con le configurazioni di ombratura considerate
No full textEconomic analysis of investment in the rooftop photovoltaic systems: A long-term research in the two main markets
No full textNowadays, due to incentive policies, the PhotoVoltaic (PV) installations become an economically attractive investment. The different policies aim to reduce the PV installation costs, consequently to the deployment of the market. In recent years, a progressive price decrease of components for PV installations has occurred, according their learning curve: every doubling of the volume implies approximately a cost reduction of -20%. In order to reduce the burden of the incentive rate on the national budget, maintaining the economic margin of the investment attractive for investors, a progressive tariff decline has also taken place. This paper provides a technical-economic analysis of investments in PV systems installed on the rooftop, considering incentive policies, and applies it to some significant case studies in the Countries, in which PV market is the most prosperous (Germany and Italy). The analysis puts into evidence the past and current economic margins of the PV investments since 2006 to 2012. Four case studies from 3 kWp to 1 MWp are examined in detail. The profitability indexes in terms of net present value and internal rate of return, evaluated throughout incentive duration of 20 years, become very interesting above all in Italy (higher than 100% of the installation cost and higher than 10%, respectively) since 2009, when an abrupt decrement in installation cost occurred. In Italy the best profit margins occur for large-size PV plants and are poorly counterbalanced by the decline of the feed-in tariff up to 2012, when a new framework has given a knock to the investments, whereas in Germany the best margins happen for medium-size PV plants and are well adjusted by the feed-in tariff. However, it is predictable that a cut in German feed-in tariff will take place, because the profit margins have been higher in last year than in the previous year
Data Pre-Processing and Representation for Energy Calculations in Net Metering Conditions
No full textThe different representations of the input data for energy system studies need to be conducted to the same time step for the purpose of carrying out power system calculations. Availability of data with different time steps, or even provided with irregular timing, needs a pre-processing phase to unify the representation within the same time step. This paper describes a dedicated pre-processing tool that accepts input data with different characteristics and provides a regular representation of the output. A specific application in which the differences between the time steps are relevant is analysed by considering a grid-interfaced system with local generation and local load, carrying out the input/output energy calculations and the assessment of the energy-related economics in net metering conditions
Characterization of solar irradiance profiles for photovoltaic system studies through data rescaling in time and amplitude
No full textThis paper addresses the representation of the data coming from solar irradiance measurements, to be used in evaluations referring to the operation of photovoltaic systems. Starting from the consideration that for different days of the year the sunrise and sunset timings change and the solar irradiance patterns at clear sky conditions occur with different maximum amplitude, a bi-normalization procedure is applied in order to produce comparable normalized patterns for the various days. The normalized patterns are then subject to clustering in order to obtain a meaningful grouping of similar days. Finally, from the clustering results a day-type succession matrix is constructed, whose entries are interpreted as the conditional probability of finding a given day type providing that the type of the preceding day is known. Data used in the analysis are taken from real sites
Accurate measurements of solar irradiance for evaluation of photovoltaic power profiles
No full textThe measurement, as accurate as possible, of solar irradiance is the starting point for the evaluation of photovoltaic (PV) power profiles in an electricity market in which many gigawatts of PV power are connected to the national network. This paper discusses the setup of five meteorological stations in South of Italy and the yearly experimental results of short-term global irradiance on the horizontal plane and on the best tilted plane. The 'broken clouds' phenomenon causes noticeable peaks in the irradiance and thus in the PV power. Its knowledge and prediction can be very useful to the Transmission System Operator for the management of peak generation. The evolution of relative humidity can give important information if the direct measurement of irradiance is missing. Finally, simple models for the irradiance in clear/cloudy sky situations can be used as a first approximation tool to predict the PV power profiles for the electricity marke
Which are the constraints to the photovoltaic grid-parity in the main European markets?
No full textA new concept of Photovoltaic (PV) grid-parity is presented for three typical case studies in Europe by including the distribution-network limits and the fixed costs of the electricity bills. Real cases are described for residential/tertiary sector loads: the PV penetration results, achieved without investments in the distribution upgrading, are presented through the ratio of the admissible PV energy ratio which can be close to 30% of the total consumption for residential users and 45% for tertiary-users. The future approach of distribution limits certainly will increase the electricity bills which have been analysed here in the current situation: in Germany the fixed costs are negligible, whereas in Italy the common loads of apartment-blocks are charged by the cost of the available power. The grid-parity problem is analysed by the net present value which provides the cost effectiveness or not of the PV installation. The results are obtained by the interest rates of 3-6% in Germany and 4-10% in Italy. The grid-parity for dwelling houses and tertiary-sector users is reached in Germany and Central/Southern Italy; it is achieved in Germany for the users in apartment-blocks, while it is unrealistic to be reached in Italy with the current tariff situatio
Weather forecast-based power predictions and experimental results from photovoltaic systems
No full textConsidering the distributed generation from solar energy, the topics of this paper are multiple: firstly, to analyze accurate measurements of solar irradiance from pyranometer and to compare them with 1-3 day weather forecasts by the suitable statistical error parameters. Then, to describe a detailed PhotoVoltaic (PV) conversion model, from the solar irradiance to the AC power profile delivered to the utility grid, and to compare the simulation results with the 15-min mean power measured by the energy-meter of a real grid-connected PV system with megawatt size. The results show that an adequate accuracy can be obtained and that useful information can be provided for fault diagnosis of a portion of a PV array
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