Field Of Renewable Energy Sources Research Articles

Performance enhancement of savonius hydrokinetic turbine using split airfoil blade: A numerical investigation

There is a concerted global effort to advance technology in the field of renewable energy sources due to the escalating energy crisis and escalating environmental pollution. One promising avenue for small-scale power generation is hydrokinetic technology. Among the various hydrokinetic turbines, the Savonius Hydrokinetic Turbine (SHT) stands out due to its specific advantages, but it has faced challenges in terms of performance. To address this, a novel blade design for the SHT has been developed, aiming to enhance its performance. This new turbine is referred to as the Split Airfoil Savonius Hydrokinetic Turbine (SASHT). To evaluate and compare the performance of both the conventional SHT and the newly developed SASHT, a Computational Fluid Dynamics (CFD) analysis has been conducted. This analysis encompasses a range of Tip Speed Ratios (TSR) from 0.7 to 1.2, with an inlet velocity of 0.8 m/s. The results reveal that the SASHT demonstrates a notable improvement, with a maximum Coefficient of Power that is 17% higher than that of the conventional semi-circular bladed SHT. This research offers valuable insights into the flow physics and performance parameters of these hydrokinetic turbines, showcasing the potential for more efficient and sustainable energy generation.

Citation Analysis of Post Graduate Theses Submitted to Department of Renewable Energy Sources in College of Agricultural Engineering and Technology, Dr. Balasaheb Sawant Konkan Krishi Vidyapeeth, Dapoli, Maharashtra

Citation analysis helps to understand the different ways that users look for material. Citation analysis can be used to calculate the obsolescence rate. Finding the rate of obsolescence of publications in the field of renewable energy sources is the aim of this study. Citation analysis is being done on M.Tech. (Agril.Engg.) PG theses that were submitted to the College of Agricultural Engineering and Technology's department of Renewable Energy Sources. The study uses theses that were submitted between 2017 and 2021. There are 14 theses in total, with 707 citations. Analysis is also conducted to determine the Authorship pattern and Types of Information Sources that the researchers mentioned in their theses.

Calculation of the economic and environmental efficiency of introducing advanced technologies in the energy supply of buildings

This article discusses the use of advanced cogeneration technologies at existing combined heat and power plants, regulating the supply of thermal energy in a building using an individual heating point. For Uzbekistan, an urgent problem is the serious study of the use of energysaving technologies, in particular in the heat supply systems, for the efficient use of investments. The achieved effect of reducing specific energy consumption for the production and consumption of thermal energy to the level of world standards will ensure the energy and environmental security of the country, which urgently requires accelerating the implementation of these projects. The search for large and small projects for the technical and technological renewal of production to ensure the competitiveness of products, as well as the means and sources for this should first become the most important task and responsibility of the manager and engineering staff of each heat supply enterprise. The article provides calculations on the basis of which the payback, investment, efficiency of measures in the field of renewable energy sources for electricity and heat supply are determined, as well as the calculation of thermal energy savings when installing an individual heating point.

ГЕНЕТИЧНІ АЛГОРИТМИ В ЗАДАЧАХ ОПТИМІЗАЦІЇ РОБОТИ ФЕС

Solving the tasks of finding the maximum in the field of renewable energy sources. The scientific work is devoted to the application of genetic algorithms to solve the problems of optimizing the efficiency of solar energy in renewable energy sources. The main focus of the work is on finding the maximum parameter values in solar power plants. The relevance of the study is due to the constant growth in the popularity of the use of solar energy and the need to increase its conversion efficiency. The application of genetic algorithms in solving the tasks of finding the maximum in solar energy is an important step in achieving optimal configurations of FES and ensuring the stable functioning of this type of power plants in general. The work includes the analysis of the influence of various parameters on the efficiency of photovoltaic panels and the development of optimal strategies for the use of genetic algorithms to improve their performance. The obtained results open up new opportunities for increasing the competitiveness of FES in the field of renewable energy sources. The genetic algorithm is recognized for its ability to provide quality results and work faster than the selection method. This method is widely used in world practice [6]. Modern algorithms for tasks where the size of the search space is so large that the exact finding of the optimal solution becomes impossible, then in such cases heuristic solutions meet the requirements, have also been studied. One of the goals of the research is the analysis of optimization algorithms and their applicability for solving the optimization tasks of solar energy. Genetic algorithms, although effective, have their limitations - in many cases, they tend to converge to a local optimum (or even an arbitrary point), instead of a global one. This indicates their inability to decide how to maintain high fitness in the short term. Additionally, the complication is related to how to protect evolutionarily formed parts from destructive mutations [7, 9]. In the process of research, the specified limitations were taken into account and mechanisms were developed to reduce their negative impact. The algorithm considered in the work is not only resistant to local minima, but also, due to the internal parallelism expressed in working with individual solutions, rather than whole classes of solutions, provides a relatively fast search for the optimal solution. Research methods basically use the iterative technique of improving results

Unveiling transport properties in rare-earth-substituted nanostructured bismuth telluride for thermoelectric application

Abstract Thermoelectrics is an emerging technology in the field of renewable energy sources, and the exploration of doped materials has opened up new avenues for enhancing their performance. La-doped thermoelectric materials with the composition Bi2−x La x Te3 (x = 0.0, 0.1, 0.2, 0.3, 0.4) were synthesized using the WOWS sol–gel method and sintered at 500 °C for 5 h. X-ray diffraction analysis confirmed a rhombohedral crystal structure with lattice constants of a = b = 4.41(2) Å and c = 29.81(3) Å. Scanning electron microscopy revealed particle-like shapes (0.7–2.5 μm). Fourier transform infrared spectroscopy confirmed the single-phase nature of the samples. DC electrical measurements showed increasing conductivity with temperature. AC electrical analysis demonstrated frequency-dependent behavior with increasing AC conductivity and decreasing loss factor and dielectric constants. Seebeck coefficient measurements exhibited temperature-dependent behavior. Thermal transport properties showed increasing thermal conductivity and volumetric specific heat with temperature, while thermal diffusivity decreased. The composition Bi1.9La0.1Te3 with x = 0.1 doping displayed lower thermal conductivity, higher electrical conductivity, and a higher ZT value, making it more suitable for thermoelectric applications. Furthermore, the sample Bi1.8La0.2Te3 exhibited favorable characteristics for energy storage applications compared to the other samples. These findings provide insights into the potential applications of La-doped bismuth telluride compounds in thermoelectric and energy storage systems.

Product-service system and possibilities of its application in the field of alternative energy

The aim of this article is to study and justify the possibilities of using a product-service system in the field of alternative energy, as well as to develop business-models for introducing relevant innovative developments in the field of renewable energy sources to the world market. Thus, CO₂ emissions are reduced, and the demand for green energy is met. There are few studies in the literature linking the product-service system and renewable energy sources. The originality of this work lies in the correlation of these two concepts. The authors conducted a preliminary analysis of the energy market and developed three business models based on the product-service system applicable in the field of renewable energy: On-Grid, Off-Grid and Hybrid systems. The results of the study show that the proposed business-models are ideal in an environment where traditional electricity tariffs are high or there is no power grid, as well as when it is possible to be a prosumer (consumer and producer of electricity at the same time) at the legislative level. The favorable impact of the product-service system application to renewable energy sources on the environment is substantiated. Also, the purchase of renewable energy by consumers will not require an initial investment. These models consider the demographic, legal, and cultural characteristics of countries and communities. Companies operating with renewable energy can apply these business-models regardless of which country they operate in or what type of renewable energy they provide, which shows the importance of applying alternative business-models for the development of renewable energy.

Design and development of renewable electric vehicle

Electric cars play an important part in the area of renewable energy, both in India and internationally. This is because they help reduce the use of fossil fuels, prevent air pollution, which is very hazardous for human beings, and lower the cost of the vehicle’s purchase upfront. The technique that is being presented is intended to supplant the utilization of non-renewable fuel that is now used in our day-to-day lives. The primary objective of this proposal is to develop a novel concept for a solar-powered three-wheeled vehicle that will solve and address issues relating to environmental pollution and the scarcity of fuel, as well as to monitor a variety of parameters that will result in an increase in the driver’s level of safety. In light of this, various governments as well as other private sectors have expressed an interest in making financial investments in the automotive and automobile industry, in particular in the realm of renewable electric vehicles (REVs) and the most recent advancements in the field of renewable energy sources. In this article, we take a look at a few different systems that are already in use and present an outline of a solar-powered three-wheeler vehicle that integrates a number of different safety measures.

GLOBAL TRENDS IN IMPLEMENTATION OF RENEWABLE ENERGY SOURCES AND FEATURES OF THEIR IMPLEMENTATION DURING THE RECOVERY OF UKRAINE'S ECONOMY

The world trends in the introduction of renewable energy sources (RES) and the peculiarities of their implementation during the recovery of the economy of Ukraine are considered.
 It is shown that the world energy sector is undergoing a fundamental transformation, therefore it is necessary to develop a new energy security paradigm that will ensure reliability and availability while simultaneously reducing emissions, and green energy is an unconditional global trend of the coming decades. It has been determined that diversifying our energy supply by investing in RES is one of the promising ways to protect ourselves from the risks of energy dependence. The state and effectiveness of RES use at the beginning of the third decade of the 21st century is analysed (according to the Renewable Energy Policy Network for the 21st Century and The International Renewable Energy Agency).
 Consolidated energy and climate statistics for 2021 according to the document World Energy & Climate Statistics - Yearbook 2022 (World energy and climate statistics - yearbook 2022) are provided, comparing statistical data of individual countries and Ukraine. The analysis of the effectiveness of the implementation of various types of RES at the level of world markets and Ukraine for the period 2010–2021 and 2020–2021 was evaluated using the average estimated cost of electricity production throughout the life cycle of these power plants (LCOE).
 When considering the European policy in the field of RES and energy efficiency, the schedule of the development of renewable energy in the EU and the characteristics of the REPowerEU plan, developed by the European Commission, are presented, which outlines the course for reducing the consumption of oil and gas in general, as well as the introduction and use of "green" energy sources. A detailed description of the development of renewable energy in Ukraine in 2020-2021, as well as world trends in RES, which will affect the reconstruction of the Ukrainian economy, is provided. The impact of the full-scale war unleashed by Russia against Ukraine on the operation of renewable energy in Ukraine is shown, the main directions of the recovery of our country in the post-war period with the use of RES are highlighted.

Quality Improvement of Operation of The Tracking Photovoltaic Systems

Achievements in the field of Renewable Energy Sources (RES) have revolutionized the traditional and centralized energy model into a modern and decentralized one, utilizing existing energy infrastructure. Photovoltaic modules have become a popular source of emission-free and renewable energy. The prospects for the future of the energy market are promising, thanks to technological advancements in the Renewable Energy Sources industry. The optimal conditions for the operation of a photovoltaic module are a temperature of 25°C, air mass of 1.5, and sunlight intensity of 1000 W/m². Furthermore, industry literature confirms that the most optimal angle of solar radiation incidence, guaranteeing the highest energy yield, is 90 degrees concerning the surface of the photovoltaic module. Such conditions are challenging to achieve in the daily operation of micro photovoltaic installations. Scientific research on RES focuses on creating new photovoltaic cells, optimizing existing installations, and facilitating economic improvements in generator procurement. In this paper, the authors investigate the impact of environmental conditions on the efficiency of photovoltaic cells, paying attention to temperature and the angle of solar radiation incidence.

Quality Improvement of Operation of The Tracking Photovoltaic Systems

Achievements in the field of Renewable Energy Sources (RES) have revolutionized the traditional and centralized energy model into a modern and decentralized one, utilizing existing energy infrastructure. Photovoltaic modules have become a popular source of emission-free and renewable energy. The prospects for the future of the energy market are promising, thanks to technological advancements in the Renewable Energy Sources industry.

Сучасні протиріччя у вітчизняній електроенергетиці

The article is concerned with studying the current state of the domestic electric power industry and the existing and potential contradictions between stakeholders in the process of its restoration and modernization. Based on the studies of world experience, possible changes are indicated, namely: recovery of the energy system on the basis of decentralization; development of mini-power plants; creation of an energy storage system at existing hydroelectric power plants; development of hybrid projects in the field of renewable energy sources (RES) and the introduction of other generating capacities of «green» energy. The need to amend the Draft Concept of the «green» transition of Ukraine until 2050 to increase the share of electric energy from the nuclear energy sector is substantiated. It is noted that the domestic energy sector will undergo significant changes in the coming decade, but positive changes are possible only with the interaction and beneficial cooperation of all business structures, as well as with the support of their activities by individual territorial communities and public organizations. Attention is focused on a significant number of stakeholders in the electric energy market, some of which have counter interests, which will cause conflicts and contradictions. The article also points out that one of the important ones is the contradiction between the need for a radical energy transition to new technologies and the interests of current raw materials and energy monopolies to maintain the status of traditional energy for as long as possible. As a result of the study, it is determined that the current sector of the domestic electric power industry is characterized by a significant number and versatility of contradictions, which are proposed to be classified on the basis of «sphere of manifestation» into the following: economic; social; market-based, and technological. It is proposed to consider the processes of detection and identification of contradictions as an important prerequisite for a solid foundation in order to ensure a stable, consistent and innovative development of the electric power industry sector of the national economy.

REGULATION OF THE EFFICIENCY OF THE ENERGY SECURITY SYSTEM IN THE INDUSTRY OF RENEWABLE ENERGY

This article outlines that for most countries of the world, the practical application of renewable energy sources is one of the most priority directions for developing the national energy industry. The annual increase in the volume of energy resources from various renewable energy sources was also noted. The forthcoming book on the growth of the specified indicator was also noted. The countries of the world that currently occupy leading positions in the practical implementation of renewable energy sources on national markets are outlined, including the European Union, the United States of America, China, and India. The fact that energy policy formation is implemented based on the complete domination of non-traditional energy sources over the usual and established fossil and destructive forms for humanity is noted. The strengths of renewable energy sources that should be taken into account are outlined, among them: internal energy characteristics of the potential, which by their content are necessary to satisfy the needs of humanity. Experience convincingly proves that the most significant development of alternative and renewable energy sources should be expected in those countries that today are energy-dependent on fossil and traditional fuels, supplying them to other countries while having a significant external debt burden. It is this circumstance that stimulates own extraction of energy resources through the use of RES; renewable energy sources are available and have an unlimited term and reserves of their use; the economic and ecological component of replacing fossil and dangerous, high-cost energy resources with more accessible, safe resources of non-traditional origin; optimization of price policy by limiting the cost of hydrocarbon resources and minimizing unforeseen losses; complete greening of the environment through the use of environmentally friendly technologies and the use of innovative technological means of work. It has been proven that to achieve maximum efficiency from the functioning of the energy security system in the field of renewable energy sources; it is expedient to observe the following four criteria, which necessarily include: decarbonization as one of the ways to get Ukraine out of the energy crisis; development of a new Strategy for the energy sector of Ukraine in the conditions of post-war recovery; the availability of systematic energy security through the introduction of renewable energy sources are programs and sources of financing; the availability of the routine scope of the application of renewable energy sources with the use of state-market instruments for the regulation of renewable energy in Ukraine. The author's model of regulation of compliance with the efficiency of the energy security system in the practical application of renewable energy sources is proposed.

THE REGULATORY MODEL OF COMPLIANCE WITH THE EFFICIENCY OF THE ENERGY SECURITY SYSTEM IN THE SPHERE OF APPLICATION OF RENEWABLE ENERGY SOURCES IN UKRAINE

This article outlines that for most countries of the world, the practical application of renewable energy sources is one of the most priority directions for developing the national energy industry. The annual increase in the volume of energy resources from various renewable energy sources was also noted. The forthcoming book on the growth of the specified indicator was also noted. The countries of the world that currently occupy leading positions in the practical implementation of renewable energy sources on national markets are outlined, including the European Union, the United States of America, China, and India. The fact that energy policy formation is implemented based on the complete domination of non-traditional energy sources over the usual and established fossil and destructive forms for humanity is noted. The strengths of renewable energy sources that should be taken into account are outlined, among them: internal energy characteristics of the potential, which by their content are necessary to satisfy the needs of humanity. Experience convincingly proves that the most significant development of alternative and renewable energy sources should be expected in those countries that today are energy-dependent on fossil and traditional fuels, supplying them to other countries while having a significant external debt burden. It is this circumstance that stimulates own extraction of energy resources through the use of RES; renewable energy sources are available and have an unlimited term and reserves of their use; the economic and ecological component of replacing fossil and dangerous, high-cost energy resources with more accessible, safe resources of non-traditional origin; optimization of price policy by limiting the cost of hydrocarbon resources and minimizing unforeseen losses; complete greening of the environment through the use of environmentally friendly technologies and the use of innovative technological means of work. It has been proven that to achieve maximum efficiency from the functioning of the energy security system in the field of renewable energy sources; it is expedient to observe the following four criteria, which necessarily include: decarbonization as one of the ways to get Ukraine out of the energy crisis; development of a new Strategy for the energy sector of Ukraine in the conditions of post-war recovery; the availability of systematic energy security through the introduction of renewable energy sources are programs and sources of financing; the availability of the routine scope of the application of renewable energy sources with the use of state-market instruments for the regulation of renewable energy in Ukraine. The author’s model of regulation of compliance with the efficiency of the energy security system in the practical application of renewable energy sources is proposed.

Hole transport layers in organic solar cells: A review

Thanks to huge research efforts, organic solar cells have become serious candidates in the field of renewable energy sources, with reported power conversion efficiencies above 19% and operating lifetime surpassing decades. In the thin film stack composing the organic solar cell, the transport layers at interfaces play a key role, as important as the photoactive material itself. Both electron (ETL) and hole (HTL) transport layers are indeed directly involved in the efficiency and stability of the devices, due to the very specific properties required for these interfaces. Focusing on the HTL interface, a large number of materials has been used in organic solar cells, such as 2D materials, conductive polymers or transition metal oxides. In this review, we present the evolution and recent advances in HTL materials that have been employed in manufacturing organic solar cells, by describing their properties and deposition processes, and also relating their use with the fullerene or the new non-fullerene acceptors in the active layer.

Study of Influence of IT-Technologies on Indicators of the Energy Sector of the Economy

Introduction. Energy is an essential branch of the economy, which needs not only reconstruction but effective, innovative solutions, one of which is the wide implementation of digital technologies. It is important to investigate possible cross-industry changes to adjust macroeconomic scenarios of industry development. The purpose of the study is to assess the degree of influence of the introduced 'smart' technologies in the energy industry on the level of inter-industry relationships according to the developed algorithms of the econometric and static Input-Output models. Results. The main consequence of calculations according to the proposed methodology is the possibility of assessing the impact of the introduction of 'smart' technologies on structural dynamics in the energy sector. However, the statistical data for the selected time interval is not enough for analysis by types of renewable energy. Since the share of 'green' energy in the total amount of energy produced remains insignificant, its influence on the accumulation of 'smart' technologies is insufficient. Conclusions. The analysis of statistical calculations allows us to state that the increase in 'smart' technologies implementation in the energy industry of Ukraine has a direct functional impact, albeit insignificant, and demonstrates the positive dynamics in the IT services inter-industry use. The negligible impact is caused by reduced allocations for the renewal of fixed assets in traditional energy sectors. There is a certain use of the latest technologies in the field of renewable energy sources, but their share in the energy structure is insignificant, although it has positive dynamics. Calculating the macroeconomic scenarios of the industry development according to the direct and inverse Input-Output models, which are promising for developing economic equalization measures in the energy sector, remains relevant. Keywords: econometric model of Input-Output tables, direct and dual problems of the IO model, inter-industry flows, types of economic activity, regression analysis.

State-of-the-art: Multi criteria decision making variables on solar PV business potential

Most developing countries, such as Indonesia, have increased targets for renewable energy. These developing countries still have limited framework alternatives that can be used as a business assessment tool or guideline for renewable energy. The characteristics in developing countries are different from developed countries, there are some challenges in adopting the global renewable energy tools that do not suit the characteristics of developing countries. Several literatures describe several variations of methods for decision making in the field of renewable energy sources, particularly the multi-criteria decision analysis (MCDA) method. The Analytic Hierarchy Process (AHP) method has been at the forefront as the most widely used method for evaluation of the best location. Due to the climate, proximity to other facilities, and the existence of protected environmental areas, the location of photovoltaic power plants is a key issue for large-scale projects. There are some papers that analyze and research about the selection process and method to choose the best location. This research has compiled and analyzed the state-of-the-art in MCDA variable in energy business potential decision making research that has been conducted in the past years and looks for research gaps that can be used as a reference for conducting further research. From the analysis, there is still a gap in current research that fulfills all aspects (technical, politic, economy, social, legal, environmental) into one assessment. Technical aspect is the most used variable and the legal aspect is the least used variable. Analyzing all six aspects into one integrated risk assessment to select the potential location for floating solar PV will be the novelty of the research. In addition, the existing studies are dominated by land solar PV objects and very few have raised the topic of floating solar PV. This is something that needs to be studied because the risk character of floating PV is different from land PV.

Selected Characteristics of Municipalities as Determinants of Enactment in Municipal Spatial Plans for Renewable Energy Sources—The Case of Poland

The article proposes methods by which an in-depth analysis of the factors determining the planning activity of municipalities for renewable energy sources can be carried out. The article aims to determine the relationship between the number of local spatial plans specifying designation for renewable energy sources and the municipality’s area, population and planning situation. All local spatial plans in Poland (a total of 104,720 plans) were analysed, distinguishing in each municipality the number of plans with designation for renewable energy sources and micro-installations (a total of 11,338 plans). Then, using quantitative methods, this data was matched with data on the municipalities’ population, area, and planning activity. At the same time, the article provides a literature review of the critical problems concerning the relationship between investments in renewable energy sources and local planning. The barriers encountered are transnational in nature. The discussion section indicates how the proposed research methods can address identified barriers. Further possible research directions are also identified. The study shows a correlation between the planning activity of municipalities in the field of renewable energy sources and both population and population density. The higher the population density (highly urbanised areas), the higher the planning activity as well, and with it, the associated planning activity for renewable energy sources. The results in this respect are spatially differentiated. The main contribution of the research is to identify the relationship between the spatial and demographic characteristics of the municipalities and the way spatial plans are approached. This research identifies how local spatial policies toward renewable energy sources can be assessed.

Integration of solar and wind power generation in the BRICS countries: An analysis of investment parameters and challenges

Subject. This article explores the technological and economic barriers to the integration of solar and wind-driven electric power stations into the electric power system, and it analyzes the options for choosing the optimal investment project when comparing parameters in the format of the BRICS countries. Objectives. The article aims to define and systematize the parameters of investment efficiency of solar and wind power generation construction projects in the BRICS countries. Methods. To assess investment indicators, we used well-established measures in international practice: Net Present Value (NPV), Internal Rate of Return (IRR), Payback Period (PbP), and Aggregate Capital Expenditures (CAPEX). Results. The article identifies and systematizes the fundamental barriers in the implementation of projects in the field of renewable energy sources (RES), among which there are political and institutional, informational, market, and cognitive ones. The article also considers options for overcoming these barriers through improving the institutional environment and State support. Conclusions and Relevance. Means to achieve economic efficiency and reliability of energy supply of the electric power system are getting transformed as the share of renewable energy sources increases and the transition to a new stage of the energy market's development gets actualized. The materials of the article can be used as a tool to determine the level of investment efficiency of renewable energy projects, taking into account the macroeconomic context.

Development of Bioenergy as One of RES Development Areas in Russia

Bioenergy is among the rapidly developing areas in the field of renewable energy sources. Russia (formerly the Soviet Union) has always had extensive practical experience in the development and setting up of industrial technologies and production of the entire range of biofuels, heat and electricity from biomass, primarily from organic waste generated by agro-industrial complexes, forestry and woodworking, and waste from housing and communal services: solid biofuels, including pellets, wood chips, charcoal, and peat briquettes; liquid biofuels, including bioethanol, biobutanol, bioisobutanol, biodiesel, bio-gasoline, bio-kerosene, vegetable oils, tar, and dimethyl ether; and gaseous fuels, including biogas (biomethane), biohydrogen, and synthesis gas (syngas). The potential capacities of Russia in the production of biofuels are estimated at more than 800 million tce. The Soviet Union was the world’s first country, which in the late 1960s mastered large-scale industrial production of biofuels (biobutanol, bioethanol, bioacetone, biohydrogen, and biogas) from biomass (molasses, which is the waste of sugar production from sugar beet).

Experience of the Ural Federal University in Training Specialists in the Field of Renewable Energy Sources

The article describes the long-standing experience gained at the Ural Federal University (UrFU) with training engineering personnel for research and development of renewable energy sources. Quantitative indicators characterizing the numbers of specialists trained in the period from 1997 to 2021, areas and results of scientific researches carried out at the Department of Nuclear Power Plants and Renewable Energy Sources are presented. Information on the test benches and installations used in the educational process is given. The effectiveness of using experimental research and design work of students in the educational process is shown.