• Energy Research

Δημοσίευση σε επιστημονικό περιοδικό Summarization: An analog-digital photovoltaic (PV) array simulator is considered. The analog section is designed on the basis of an equivalent solar cell model while the digital section is constructed realizing the mathematical representation of the array. Fast time responses achieved by the analog section make this part suitable for the study of transient phenomena associated with the interconnected operation of PVs and the utility grid. Its digital counterpart is more appropriate for long-term experimental investigations due to its inherent accuracy and reliability. The combined hybrid simulator offers a versatile and flexible piece of apparatus capable of simulating the performance of any PV array under a variety of operating conditions. The device can be constructed with low-cost components in a compact arrangement offering transportability and ease of operation. Experimental results derived from a laboratory constructed prototype match closely the theoretically computed characteristics. Παρουσιάστηκε στο: Energy Conversion, IEEE Transactions on

Summarization: Particle Swarm Optimization (PSO) is an optimization algorithm considered to be highly efficient for the solution of complicated problems. This paper presents the application of this method for the design optimization of photovoltaic grid-connected systems (PVGCSs). The purpose of the proposed methodology is to locate the optimal number of system devices and the optimal values of the PV module installation details, such that the total net economic benefit achieved during the system operational lifetime period is maximized. The optimization's decision variables are the optimal number of the PV modules, the PV modules optimal tilt angle, the optimal placement of the PV modules within the available installation area and the optimal distribution of the PV modules among the DC/AC converters. The objective function of the proposed optimization process is the lifetime system's total net profit which is calculated according to the method of the Net Present Value (NPV). The methodology's resulting system structures are economically evaluated through the methods of the discounted payback time and the Internal Rate of Return (IRR). The PSO algorithm is compared to the application of Genetic Algorithms (GAs) in terms of efficiency for the current problem. Παρουσιάστηκε στο: Renewable Energy

Δημοσίευση σε επιστημονικό περιοδικό Summarization: A methodology is proposed for the effective integration of photovoltaic (PV) devices into the electric utility distribution network operations. The dispersed PV generator is viewed as an active device used to improve system stability by appropriately modulating the power conditioning unit's output power. Disturbances on the utility system can be damped out by injecting this power into the grid in such a way so that the net effect is a cancellation of undesirable oscillations. The approach is implemented by monitoring the oscillating power and generating control signals which shape accordingly the interface unit's output power. Successful implementation of the scheme relies heavily on the speed and flexibility with which the electronic inverter moves power from the primary source/storage facility to the utility lines. Simulation studies, using the proposed control approach, indicate that application of these policies may result in reduced load following requirements for conventional power generating units, increase the value and acceptability of new energy technologies, and improve power quality and stability of the interconnected system. Παρουσιάστηκε στο: Energy Conversion, IEEE Transactions on

The market for photovoltaic is rapidly expanding and there are some large utility PV power plants, thousands of residential systems, and tens of thousands of remote power systems in use. Even if photovoltaic is a technology that has already demonstrated its effectiveness and holds great promise in electrical generation, the costs are still too high to guarantee a commercial competitivity. This paper presents the performance results of a 15 kWp photovoltaic power plant installed on the roof of a high school in central Italy. The system consists of 220 modules for a total of 22 arrays, which are connected to inverters to allow conventional appliances to be powered by photovoltaic electricity. The PV plant is remotely controlled and data on sun radiation, ambient temperature, modules temperature and power production are continuously acquired by a PC. The measured power plant performances during the year are presented in this paper.Copyright © 2003 by ASME

In this paper, a study on the mismatch effect due to the use of different photovoltaic (PV) modules classes in large-scale solar parks is presented. For this purpose, a new model for simulating current-voltage and power-voltage characteristics is introduced. The model is then applied for calculating mismatch losses in a number of case studies for a PV plant built in Bari, southern Italy. First, in order to test the effectiveness of the model, this is applied to homogeneous strings and field showing that the mismatch losses are zero. Subsequently, the use of inhomogeneous strings (i.e. made of modules belonging to different power classes) is investigated. Finally, the behaviour of 1MWp homogeneous and inhomogeneous PV fields is investigated, again with a focus on the mismatch effect. The operational conditions have been introduced starting from the definition of European efficiency. The use of standard test conditions can in fact lead to gross approximations because mismatch losses depend, as well as, on PV module characteristics, electrical connections and electrical architecture, also on the location of the PV system. The results presented in this work can be used both by PV system designers for carrying out yield calculations, and by operation and maintenance personnel for substituting modules during operation without compromising the productivity of the plant.

The paper presents long term performance analysis of a photovoltaic system with monocrystalline silicon PV cells, operated at the Faculty of Electrical Engineering at the Wroclaw University of Science and Technology. As part of the analysis a simulation of photovoltaic system with similar technical parameters was done and compared to the real installation. The results of this research include characteristics of average value of generated power and energy, insolation, module temperature and outside temperature.

Summarization: The power-voltage characteristic of photovoltaic (PV) arrays operating under partial-shading conditions exhibits multiple local maximum power points (MPPs). In this paper, a new method to track the global MPP is presented, which is based on controlling a dc/dc converter connected at the PV array output, such that it behaves as a constant input-power load. The proposed method has the advantage that it can be applied in either stand-alone or grid-connected PV systems comprising PV arrays with unknown electrical characteristics and does not require knowledge about the PV modules configuration within the PV array. The experimental results verify that the proposed global MPP method guarantees convergence to the global MPP under any partial-shading conditions. Compared with past-proposed methods, the global MPP tracking process is accomplished after far fewer PV array power perturbation steps. Presented on: IEEE Journal of Photovoltaics

In this paper, we focus on studying the efficiency promoting of power generation in the application of a domestic large-scale Photovoltaic System (PV). There are three categories of construction for photovoltaic system. One is set up the PV module at the housetop, another one is set up the PV module as building-integrated Photovoltaics (BIPV), last one is set up the PV module within up to two applications which is call building-applied Photovoltaics (BAPV). We made the analysis for the three constructions, and found out that increasing the economic efficiency of Photovoltaic System must lie with stature of the PV construction. Especially, the PV system is set up on the housetop. There are only two to three hours in high efficiency generation during the whole shining day. It is a great energy loss to solar system. Authors try to make the highest economic efficiency solution for PV system.