Depending on actual load profiles connected to grid containing a PV system, losses and power quality disturbances vary during the day due to the power unbalance in the connection node. With the increase in size of PV power plants this problem becomes more important. Different load profiles have different correlation with the daily power generation from the PV system. Therefore, economic and technical impact of different daily load curves on grid connected PV systems should be considered. This paper gives an analysis of aforementioned problems. After the description and comparison between different load profiles and daily load curves, a simulation model is described and different situations of occurring problems are tested and analyzed. Simulations were carried out with real load profiles. Finally, this paper gives an overview of problems and gives few proposes for their solution.

The advancement of LED technology in the last 10 years has completely put other light technologies into the fore-ground. LED has almost entered all spheres of life. When it comes to products that use LED technology, one of the most important issues is lifetime. This paper contains a detailed overview of the research in the field of lifetime testing of LED components and products which have an LED element. Mathematical models for accelerated LED ageing tests are given in this paper. Ageing tests with constant temperature and constant current were analyzed. In this paper a simplified model of the lifetime of LEDs in products is proposed. The results of testing several samples for a product with an LED based technology are given.

Analysis of harmonic propagation in transmission network represents an important factor in exploitation of the power system. These analyses are conducted in time and frequency domains. In a case of a robust power system, analyses are usually conducted in frequency domain and usually carried out in the Three-phase system (TPS), so that all effects of interest in the frequency spectrum are taken in consideration. Transmission line (TL) modeling in TPS and frequency domain, with the usage of Kron Matrix Reduction (KMR), can be found in this paper. The model is created for frequency values between 0.05 (Hz) and 10 (kHz), which represent the frequency spectrum of interest. Mathematical procedure for implementing the KMR can also be found in this paper. Usage of KMR for voltage profile analysis on a TL is shown on a plain example. The proposed model is compared with tested mathematical models from EMTP-RV.

The paper describes a photovoltaic system (PVS) composed of a group of photovoltaic (PV) panels and presents the initial evaluation of power quality (PQ) in the low-power microgrid connected to these PV panels. This PVS is called solar tree and it is built as a research platform at our faculty to conduct teaching and research on renewable energy sources. The solar tree can operate in two modes: on-grid and off-grid (autonomous operation). An off-grid mode was analysed and experiments were carried out in order to determine the maximum power that can be delivered to the load connected to this autonomous photovoltaic system (APVS). Also, the various consumer's responses to a sudden load changes in this APVS were analysed. The experiments were carried out by using modern power quality monitoring devices and PQ of this single-phase APVS with energy storage is examined in terms of compatibility with the relevant international standards.

Phasor estimation is an essential task in power system since the voltage angle and voltage RMS determine the available active power and its flow. This paper proposes fast and simple algorithm for harmonic phasor estimation in a three-phase system. Harmonics are considered the most serious power quality (PQ) problem in the emerging scenario with a growing proportion of power electronic based devices in the power system. The algorithm is based on well-known mathematical transform and recommendations given in relevant IEC and IEEE standards. The presented algorithm can be used to generate input data for Harmonic State Estimation.

Solar cells are the main candidate for the replacement of conventional energy sources, because they can provide almost permanent power at low cost and almost no pollution. In this paper, an organic solar cell with an active layer made of P3HT and PCBM material is considered and the effect of the active layer thickness on the efficiency of photovoltaic conversion. Furthermore, the efficiency of the energy conversion of the organic solar cell and conventional silicon cells was compared. Finally, optimal thicknesses of the active layer and the layer for rejecting minority carriers are chosen.

Many renewable energy sources are not able to provide the demanded electrical energy during the day. This problem is getting more important with the increase of power plants which are based on renewable energy. The proposed method for overcoming the aforementioned problem is the building of hybrid power plants with two or three different energy sources. The most common hybrid power plants are solar-wind power plants, who produce electricity by using the complementary characteristics of solar irradiation and wind speed. The hybrid solar-wind power plants contain a lot of power electronic devices that affect the power quality disturbances. Therefore, an analysis of the dynamic of such power plants is necessary. First part of this paper presents the modeling of hybrid solar-wind power plants. The second part analyzes the impact on power quality of hybrid solar-wind power plant during its daily working cycle.

Renewable energy sources in addition to all the advantages over the non-renewable energy sources have a lot of limitations, where the biggest of them are the price and the inability of constant electricity generation. One way of overcoming the problem of inability of constant electricity generation is to build hybrid power plants with renewable energy sources. This primarily highlights hybrid solar - wind power plants, which produce electricity by using solar radiation and wind energy. Since the hybrid solar - wind power plants consist of a photovoltaic power plant and a wind power plant and are usually constructed as a distributed source, it is necessary that the regulatory frameworks define criteria and actions for the connection of a hybrid solar - wind power plant in the power system. This paper gives a short overview of criteria and actions for the connection of a hybrid solar - wind power plant in the power system according to official documents in Bosnia and Herzegovina.