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Bezrukovs V.P.,Institute of Physical Energetics of Latvia | Bezrukovs V.P.,Ventspils University College | Bezrukovs V.V.,Ventspils University College | Zacepins A.J.,Institute of Physical Energetics of Latvia
Journal of Physics: Conference Series | Year: 2014

Performance evaluation of wind turbines (WT) for different heights of the rotor hub is made based on the wind speed and direction data obtained in 2009-2013 on-shore in the north of Latvia using a LOGGER 9200 Symphonie measurement system mounted on a 60 m mast. Based on the measurement analysis results, wind speed distribution curves have been modelled for heights of up to 200 m using power and logarithmic (log) law approximation methods. The curves for the modelled Weibull's parameters are plotted in dependence on height. The efficiency comparison is made for different WT types taking into account the distribution of the wind energy potential in height in the Latvian territory. The annual electric energy production was calculated for the WTs with different heights of rotor hubs. In the calculations the technical data on the following WT types were used: E-3120 (50 kW, hub height 20.5/30.5/36.5/42.7 m), E-33 (330 kW, hub height 37/44/49/50 m), E-48 (800 kW, hub height 50/60/75 m) and E-82 (2.3 MW, hub height of 78/85/98/108/138 m). © Published under licence by IOP Publishing Ltd.


Bobinaite V.,Lithuanian Energy Institute | Bobinaite V.,Institute of Physical Energetics of Latvia
Renewable and Sustainable Energy Reviews | Year: 2015

Abstract The Baltic States realize the necessity to develop wind electricity sectors. This comes from the Baltic States concern of energy security, competitiveness and sustainable development of energy sectors. The paper deals with the financial aspects of sustainability of wind electricity sector. Namely, it aims at performing a comparative analysis of financial sustainability of companies producing electricity from wind resources in the Baltic States during 2009-2013. The financial statement analysis method is employed and the financial ratio technique is used. Altman, Liss and Tafler bankruptcy forecasting models are used to show both "health" and viability of the companies. 4 groups of financial ratios are computed: financial leverage, profitability, liquidity and assets utilization. Support schemes are recognized as a relevant factor influencing on the financial sustainability. The results of the analysis revealed that financial sustainability of the companies is moderate in the Baltic States. Lithuania and Estonia use high share of debt (80-85%) to finance economic activity, whereas Latvian companies use relatively high share of equity capital (35-40%). This shows that credit risk is available in the companies. Liquidity of the companies decreases. Operational efficiency is higher in Estonia and Lithuania than in Latvia, when profitability indicators are analyzed. During the latter several years efficiencies of assets utilization were similar in the Baltic States. The efficiency of current assets utilization is higher compared to efficiency of non-current assets utilization. Companies in Latvia demonstrate middle but increasing and in Estonia - high but reducing bankruptcy probabilities. Lithuanian case reveals that bankruptcy probability varies from high to low depending on the financial ratios analyzed, however, bankruptcy probability reduces. Companies should make liquidity, solvency, efficient use of assets and profitability management as a part of their corporate management policy framework. © 2015 Elsevier Ltd. All rights reserved.


Sirmelis U.,Institute of Physical Energetics of Latvia | Grigans L.,Institute of Physical Energetics of Latvia
9th International Conference on Electrical and Control Technologies, ECT 2014 | Year: 2014

In this paper the authors present a simple solution for recovery of braking energy in tram systems. The proposed solution is stationary supercapacitor (SC) energy storage system (ESS) where ESS consists only of series connected SC cells without DC/DC power interface converter. For the evaluation of the proposed solution a detailed simulation model is developed and experimentally measured tram power diagrams are used as input data. Simulations for twenty-four hours long tram system operation are performed to assess the energy consumption with and without supercapacitors. © Kaunas University of Technology, 2014.


Lvovs A.,Institute of Physical Energetics of Latvia | Mutule A.,Institute of Physical Energetics of Latvia
Latvian Journal of Physics and Technical Sciences | Year: 2013

The estimation of power supply interruption costs was performed in Latvia in 2012, in the framework of a survey study (the first officially recognized study of interruption costs in Latvia since restoration of Independence in the early 90's). The survey involved ∼ 3000 end users, which are classified as the major electrical energy consumers in the country. As a result, the customer damage functions (CDFs) and the functions of cost deviations depending on the interruption occurrence time have been created. The study is unique not only for Latvia, but also for the whole Baltic region. The information obtained is usable for improving the quality of supply regulation (also known as Performance Based Regulation (PBR)) and for planning and running the power networks.


Priedite I.,Institute of Physical Energetics of Latvia
Engineering for Rural Development | Year: 2014

The paper illustrates economical assessment of the grid-connected onshore micro wind turbines. The calculation is based on onshore wind speed hourly minimum value of 4 m height in Latvia approximated according to each wind turbine tower height. The result shows that increase in annual expenditure on electricity produced by onshore micro wind turbines is more than 264 %.


Arina D.,Latvia University of Agriculture | Orupe A.,Institute of Physical Energetics of Latvia
Environmental and Climate Technologies | Year: 2012

The article presents the results of experimental work in the first waste mechanical Pre-treatment Centre in Latvia Daibe. The goal - to detect the main parameters for sorted waste parts and to compare them with parameters stated for refuse derived fuel (RDF) in a cement plant in Latvia (Cemex). Samples were taken in four fractions-coarse, medium, fine, metal. The parameters - upper, lower heating values, moisture, ash content, S, Cl, metals were determined. Results-coarse fraction has greater potential of the production of the RDF, but reduction of its content of Cl would be necessary.


Purvins A.,European Commission | Papaioannou I.T.,European Commission | Oleinikova I.,Institute of Physical Energetics of Latvia | Tzimas E.,European Commission
Energy | Year: 2012

The present article analyses the effects caused by variable power. The analysis concerns a country-scale electricity system with a relatively high penetration of seasonally variable hydro power plants and wind farms in the total electricity generation in 2030. For this purpose, the Latvian electricity system was chosen as an appropriate case study, as around half of its electricity is already generated from hydro power and numerous wind farm installations are planned for 2030. Results indicate that in such systems high renewable power variations occur between seasons causing a high probability of power deficit in the winter and power surplus in the spring. Based on the results, the wind farms' influence on the power deficit and surplus occurrences are discussed in detail. Wind farm generation decreases the probability of the electricity system being in power deficit, but increases the probability of the system being in power surplus. In the latter situation, the maximum value of power surplus increases since it is enhanced by the wind farm generation. Probability equations to express these changes are provided. © 2012 Elsevier Ltd.


Kroics K.,Institute of Physical Energetics of Latvia
Vide. Tehnologija. Resursi - Environment, Technology, Resources | Year: 2015

Interleaved converters are used in many different conversion systems involving various topologies and are related to different fields of application due its advantages over single-phase converters. Such advantages include reduced current in switching devices and passive elements, reduced output current ripple, and so on. Reductions in size and costs of magnetic components and inductors current ripple can be achieved by an integration of magnetics. In this paper application of 2-phase coupled inductor designed in convenient way by using commercially manufactured coil formers and ferrite cores is analyzed to developed 4-phase interleaved DC-DC converter. Different structures of the coupled inductor for 4 phases is studied. The steady state phase and output current ripple in buck mode of the interleaving magnetic integrated bidirectional DC-DC converter is simulated. The necessary count of inductors for selected topology are manufactured and placed on the PCB board. © Rezekne Higher Education Institution (Rēzeknes Augstskola), Rezekne 2015.


Kroics K.,Institute of Physical Energetics of Latvia
Vide. Tehnologija. Resursi - Environment, Technology, Resources | Year: 2013

This paper represents a design and implementation of a digital control of variable frequency interleaved DC-DC converter using a digital signal processor (DSP). The digital PWM generation, current and voltage sensing, user interface and the new period and pulse width value calculation with DSP STM32F407VGT6 are considered. Typically, the multiphase interleaved DC-DC converters require a current control loop in each phase to avoid imbalanced current between phases. This increases system costs and control complexity. In this paper the converter which operates in discontinuous conduction mode is designed in order to reduce costs and remove the current control loop in each phase. High current ripples associated with this mode operation are then alleviated by interleaving. Pulse width modulation (PWM) is one of the most conventional modulation techniques for switching DC-DC converters. It compares the error signal with the sawtooth wave to generate the control pulse. This paper shows how six PWM signals phase-shifted by 60 degrees can be generated from calculated values. To ensure that the measured values do not contain disturbances and in order to improve the system stability the digital signal is filtered. The analog to digital converter's (ADC) sampling time must not coincide with the power transistor's switching time, therefore the sampling time must be calculated correctly as well. Digital control of the DC-DC converter makes it easy and quickly to configure. It is possible for this device to communicate with other devices in a simple way, to realize data input by using buttons and keyboard, and to display information on LED, LCD displays, etc. © Rēzeknes Augustskola.


Priedite I.,Institute of Physical Energetics of Latvia
ENERGYCON 2014 - IEEE International Energy Conference | Year: 2014

The paper illustrates economical assessment of the grid-connected onshore micro wind turbines. The calculation is based on onshore wind speed hourly minimum value of 4 m height in Latvia approximated according to each wind turbine tower height. Economical assessment of the grid-connected solar cells is studied based on the real solar cells output data of Latvia. Results of performed study show that the use of solar cells 25 years for power generation in Latvia is profitable. © 2014 IEEE.

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