Utilization Of Renewable Energy Sources Research Articles

Geoscientific research's influence on renewable energy policies and ecological balancing

Geoscientific research plays a crucial role in shaping renewable energy policies and promoting ecological balance. This review explores the impact of geoscientific research on renewable energy policies and its role in ecological balancing. Geoscientific research provides valuable insights into the geological and environmental factors that influence the feasibility and sustainability of renewable energy projects. By studying the earth's processes, geoscientists can identify suitable locations for renewable energy installations, assess potential risks, and develop strategies to mitigate environmental impacts. One of the key ways in which geoscientific research influences renewable energy policies is through its contribution to resource assessment. Geoscientists use various techniques, such as geological mapping, geophysical surveys, and remote sensing, to identify and quantify renewable energy resources, such as solar, wind, and geothermal energy. This information is essential for policymakers to develop effective policies that promote the development and utilization of renewable energy sources. Furthermore, geoscientific research plays a crucial role in ecological balancing by providing insights into the environmental impacts of renewable energy projects. By studying the interactions between renewable energy installations and the surrounding environment, geoscientists can identify potential ecological risks and develop strategies to minimize them. This information is essential for policymakers to develop policies that ensure the sustainable development of renewable energy projects while protecting the environment. In conclusion, geoscientific research plays a crucial role in shaping renewable energy policies and promoting ecological balance. By providing valuable insights into renewable energy resources and their environmental impacts, geoscientists help policymakers develop effective policies that promote the sustainable development of renewable energy projects.

Origin of deactivation of aqueous Na–CO2 battery and mitigation for long-duration energy storage

The development of long-duration energy storage technology is crucial to facilitate the efficient utilization of renewable energy sources while mitigating carbon dioxide production. In this study, we investigate the deactivation and reactivation mechanisms of the aqueous Na–CO2 battery during extended cycling. We have designed the cathode to include non-precious intermetallic catalysts. As the cell undergoes repeated cycles, the voltage polarization during discharge progressively rises, eventually leading to the cell's deactivation and formation of decomposition products clogging the electrode surface. Results obtained from comprehensive characterization techniques, including conductive atomic force microscopy (cAFM), Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and inductively coupled plasma-mass spectrometry provide insight into the decomposition products. We also showcase an electrochemical approach for regeneration of these aqueous cells. Our findings, along with the insights we have gained, provide a path toward creating long-duration systems with self-healing properties.

Review of Cloud-Based Smart Energy Meters

Abstract: Smart meters represent a pivotal advancement inenergy management, offering numerous benefits to consumers and utility providers. This report provides an overview of smart meters, their functionalities, advantages, challenges, and broader implications for the energy industry. A smart meter is an advanced device that accurately measures electricity consumption. It's better than traditional meters, providing efficient tracking and insights into energy usage habits. Upgrade to a smart meter to make informed decisions and save money on electricity bills. These devices are a vital component of smart grid technology, which aims to enhance energy distribution and consumption efficiency, reliability, and sustainability. Modern technologies, such as the Internet of Things (IoT), have many applications in the energy sector. IoT can help to improve energy efficiency, increase the utilization of renewable energy sources, and reduce the environmental impact of energy use. It can achieve these goals in energy supply, transmission, distribution, and demand. This paper reviews the literature on IoT in energy metering systems and its essential components, functionality, and advantages over conventional metering systems.

Schottky Junctions with Bi@Bi2MoO6 Core-Shell Photocatalysts toward High-Efficiency Solar N2-to-Ammonnia Conversion in Aqueous Phase.

The photocatalytic nitrogen reduction reaction (NRR) in aqueous solution is a green and sustainable strategy for ammonia production. Nonetheless, the efficiency of the process still has a wide gap compared to that of the Haber-Bosch one due to the difficulty of N2 activation and the quick recombination of photo-generated carriers. Herein, a core-shell Bi@Bi2MoO6 microsphere through constructing Schottky junctions has been explored as a robust photocatalyst toward N2 reduction to NH3. Metal Bi self-reduced onto Bi2MoO6 not only spurs the photo-generated electron and hole separation owing to the Schottky junction at the interface of Bi and Bi2MoO6 but also promotes N2 adsorption and activation at Bi active sites synchronously. As a result, the yield of the photocatalytic N2-to-ammonia conversion reaches up to 173.40 μmol g-1 on core-shell Bi@Bi2MoO6 photocatalysts, as much as two times of that of bare Bi2MoO6. This work provides a new design for the decarbonization of the nitrogen reduction reaction by the utilization of renewable energy sources.

Empowering sustainable energy communities: Optimizing multi-carrier energy systems with green energy, uncertainty management, and demand response

Energy management has emerged as a pressing concern in the planning and operation of smart cities, driven by the escalating demand for energy. Concurrently, demand response programs (DRPs) have gained significant attention in recent years, owing to their profound impact on the power system. This paper introduces an approach aimed at minimizing operational costs and environmental emissions within a smart city reliant on grid-connected power. A novel green energy scheduling for a multi-carrier energy community is presented to achieve a sustainable development. The proposed method places a premium on maximizing the utilization of renewable energy sources. Recognizing the inherent uncertainty associated with green energy resources, this approach seeks to enhance system reliability by addressing this challenge. This paper's primary objective is to tackle the intricate problem of power management in a smart city while factoring in the uncertainty stemming from green energy resources and the integration of DRPs. To address these complexities, the paper leverages the CPLEX solver embedded in the GAMS software application, while uncertainties in the system are modelled through the application of the Monte-Carlo algorithm. The results show that considering the uncertainty of green energy resources, the total cost of the system can be reduced by $504 by performing the DRPs.

Data-Driven Strategies for Optimizing Albania’s Utilization of Renewable Energy Sources from Urban Waste: Current Status and Future Prospects

Albania is now implementing a range of steps as part of its journey towards European Union integration, based on agreements that have been achieved. Key to these initiatives is the extensive adoption of circular economy concepts through comprehensive waste management systems. This collaboration is based on systematically implementing measures that align with the fundamental principles of the waste management hierarchy. Albania wants to lead in waste-to-energy conversion exploration by focusing on trash minimization, reuse, recycling, and energy generation from residual waste. Although there has been notable advancement, especially in aligning laws with EU requirements, there are practical obstacles, especially in the execution of waste-to-energy projects. The challenges involve the need for effective waste segregation, higher recycling rates, and the use of advanced waste-to-energy technologies. The essay utilizes meticulously selected data on Albania’s waste generation from reputable organizations and the legal framework regulating waste management to assess the current situation and predict future possibilities, which may be advantageous for government ministries and agency platforms.

Innovative Compact Twin Whirly Bird-based Wind Turbine: A Sustainable Solution for EV Charging Infrastructure

The global adoption of whirly bird vent roofs across various industries underscores their utility in harnessing wind energy for cooling purposes within warehouses and similar environments. The innovation proposed in the current study builds upon this established technology by integrating semi-perpetual motion principles into a compact twin whirly bird-inspired wind turbine design. This novel approach aims to enhance power generation efficiency, thereby offering a sustainable solution for energy production. The compact twin whirly bird turbine concept represents a significant advancement, particularly in the context of powering electric vehicle (EV) chargers. As the demand for EVs continues to surge, concerns persist regarding the availability of charging infrastructure. By integrating the proposed innovative wind turbine technology into the EV charging ecosystem, we address this critical issue while simultaneously promoting the adoption of renewable energy sources. The key to our proposal is the deployment of small-scale wind turbines in diverse public locations, thereby democratizing access to clean energy generation. Unlike conventional large-scale wind turbines, our whirly bird-inspired turbines boast versatility in installation, akin to streetlamps, facilitating widespread deployment across urban landscapes. While these turbines may yield comparatively modest power outputs relative to megawatt-scale counterparts, their strategic placement ensures a decentralized network capable of powering EV charging stations. In summary, our research presents a compelling solution that bridges the gap between EV charging infrastructure availability and the utilization of renewable energy sources. By leveraging the inherent advantages of whirly bird-inspired wind turbines, we offer a practical pathway towards sustainable energy provision in public spaces, thereby facilitating the widespread adoption of electric vehicles.

Determinants of Green Energy Use: Household Level Comparative Analysis of Southern Khyber Pakhtunkhwa

In recent times, the utilization of renewable energy sources has gained significant traction and garnered widespread attention across diverse social segments. The prominent driver behind this surge in popularity is its cost-effectiveness and long-term durability. Notably, even individuals with limited financial means are increasingly drawn toward various forms of renewable energy. This research endeavor aims to draw comparisons between users and non-users of green energy and their corresponding household behaviors. Upon conducting a rigorous data analysis, the study will present a comprehensive and well-founded conclusion, along with offering pertinent recommendations. This study is slated to take place in the rural regions of Southern Khyber Pakhtunkhwa, Pakistan. The study employed random sampling to select a sample from the population and focused on examining the relationship between the utilization of green energy, its characteristics, conventional green energy use, and the quality of solar energy. The primary objective of the study was to explore the choices made by individual households concerning green energy consumption and the factors that influence this choice. The analysis was carried out using Ordinary Least Squares (OLS) regression. This research gap presents a significant opportunity for advancing the promotion and adoption of renewable energy sources.

Current Scenario and Future Perspectives of Renewable and Sustainable Energy in India: Progress and its Challenges

Energy is a key force behind both social and economic advancement. The scientific advancements in numerous industrial, governmental, and municipal activities have significantly increased the energy demand. The main reasons behind the efficient utilization of renewable energy sources (RESs) are the rapidly increasing rates of energy demand and fuel prices, as well as the requirement to control greenhouse gas emissions. In reality, meeting the world’s growing energy requirements and preventing climate change are now of greatest concern. This review paper provides a thorough overview of the creation and growth of renewable and sustainable energy sources, including information on their types, traits, benefits, and drawbacks. This review specifically discusses the situation and future potential of renewable and sustainable energy sources in India. The growth of RESs can have a substantial impact on the economic development of India, in addition to creating employment possibilities related to harnessing energy from RESs.

Design and optimization of battery and thermal management system for AC photovoltaic energy module

The utilization of renewable energy sources has increased due to concerns about climate change. However, injecting the power from renewable energy sources into grid-tied systems is challenging. The techno-economic analysis a photovoltaic (PV) energy systems is investigated. As a result, this paper presents AC-PV module for Grid-Tied and Off-Grid Scenarios via optimization, modeling, and test results. Even though the output of a PV panel is DC voltage, a three-port inverter and a lithium-ion battery pack are integrated with the back of the PV panel. They are packaged as a PV system module that makes the module output have AC voltage. Therefore, an optimized AC-PV module can be a solution for residential and commercial use, which are grid-tied systems; it can be very efficient for those without access to electricity, which is an off-grid system. An integrated battery and thermal management strategy is crucial for this AC-PV module. In the article, the battery capacity optimization, the electrical and the thermal model of the battery pack, battery heat generation model are discussed by using stochastic analysis techniques; the battery test results are also obtained to identify the models’ parameters and a control algorithm is proposed to extract the battery information such as temperature, current, voltage, SoC and SoH of the battery pack.

ANALYSIS OF THE SHARE OF RENEWABLE ENERGY SOURCES IN THE GROSS FINAL ENERGY CONSUMPTION OF EUROPEAN COUNTRIES

This article provides an analysis of the shares of renewable energy sources in the gross final energy consumption for European countries over several years. The study encompasses various renewable energy sources, including overall solar energy, solar thermal and solar electricity individually, biomass, biofuels and waste, wind power, geothermal energy, hydropower, and heat pumps. The analysis was conducted for the Netherlands, Germany, France, Poland, and Ukraine. The article examines not only the actual data on the utilization of renewable energy sources in these countries but also analyzes their plans for further increasing their usage. The findings of the analysis are crucial for understanding the trends in renewable energy development in Europe and can serve as examples for other countries. The analyzed data includes historical figures as well as future projections. The collected graphical data illustrates the real achievements of countries in terms of renewable energy utilization, as well as their intentions and plans for the future. This information can serve as a valuable guidebook for those interested in renewable energy development and seeking to implement similar strategies. The final results of the research provide insights into the state of renewable energy development in Europe, highlighting the prospects and opportunities for further growth. The article emphasizes the significance of utilizing renewable energy sources as a path towards sustainable development and contributes to the dissemination of knowledge about them for other countries aiming to reduce their reliance on traditional energy sources and transition to more environmentally friendly alternatives. Bibl. 37, Fig. 11.

Chaotic‐quasi‐opposition based whale optimization technique applied to multi‐objective complementary scheduling of grid connected hydro‐thermal–wind–solar‐electric vehicle system

AbstractThe sources of fossil fuel are impoverishing in upcoming future. In the current research scenario, sincere effort has been taken worldwide to explore the use of renewable energy sources in electrical power system for the economic benefits and environmental consciousness. The main contribution of the proposed work is first, to find optimal hydro‐thermal scheduling (HTS) with wind, solar, and electric vehicles (EVs) for variable load. The target is to find out maximum utilization of renewable energy sources for economic power generation with less emission. Thus, a new approach of EV to grid has been adopted with wind–solar based HTS system for improving grid reliability and resilience. Second, there is a requirement to overcome the local optima problems with less convergence speed. This is obtained by employing a relatively new methodology, known as chaotic‐quasi‐opposition‐based whale optimization algorithm (WOA) (CQOWOA). The proposed algorithm is tested on HTS and wind–solar‐electric vehicle‐based HTS (HTWSVS) for three different cases. Different nonlinearities like valve point effect of thermal units, transmission losses, spillage rate of hydro reservoir units and uncertainties of wind, solar as well as EV are considered to judge the effectiveness of the proposed CQOWOA technique on realistic problems. The presence of wind, solar, and EV energy sources with HTS is evident from the test results of CQOWOA, for multi‐objective problem where cost and emission both are reduced significantly. The robustness of the proposed solution has been verified by implementing the statistical analysis on two systems with least variation of mean and optimal values of cost with the tolerance of less than 0.025%. The comparative analysis of CQOWOA with the other optimization techniques validates its superiority on both the test systems by minimizing the generation cost and emission.

Thermodynamic and thermoeconomic analysis and optimization of a renewable-based hybrid system for power, hydrogen, and freshwater production

To address environmental pollution effectively, it is crucial to promote the increased utilization of renewable energy sources. Furthermore, an appealing opportunity arises from enhancing the efficiency of renewable-based power plants while diversifying their product output. This study introduces a hybrid system that revolves around renewable resources, with a primary focus on evaluating power generation, hydrogen production, and freshwater extraction. The designed system seamlessly integrates a flash-binary geothermal power plant with a solar system, incorporating cutting-edge phase-change material storage technology. Hydrogen is generated through a combination of steam-methanol reforming and pressure swing adsorption processes. Freshwater is procured utilizing humidification-dehumidification and multi-effect desalination units. In terms of power generation, the system leverages the capabilities of the geothermal power plant alongside a modified Kalina cycle. The performance of this integrated system is rigorously evaluated through a combination of thermodynamic and thermoeconomic approaches. An exergy-economic optimization scenario is employed to determine the most efficient operational mode. The results of this comprehensive analysis reveal that the system can produce 0.0224 kg/s of hydrogen, 8.017 kg/s of freshwater, and generate 215.9 W of net power. Impressively, it achieves an exergy efficiency of 58.3% at a unit cost of $32.23/GJ in the base mode. Furthermore, the optimal operating state boosts efficiency to 60.59%, with a unit cost of $32.22/GJ. Notably, adjustments in the selling price of hydrogen have a significant impact on the system's financial metrics. As the price of hydrogen rises from $5 to $6/kg, the payback period reduces from 4 to 3 years, and the net present value surges from $5.81 million to $10.16 million.

A case study of multi-energy complementary systems for the building based on Modelica simulations

The utilization of renewable energy sources and the development of energy storage technologies have enhanced the interconversion of various energy sources to slow down global warming. The building sector, as the main bearer of energy consumption, is essential for its energy saving and emission reduction. Integrating natural gas-based combined cooling, heating, and power systems with renewable energy generation facilities is an effective solution. For that, different scenarios are designed to provide energy for a specific office building and compared with the current scenario of depending only on the municipal grid. Equipment models for photovoltaic, battery, gas engine, absorption chiller-heater, and electric heat pump are created. The results show that the multi-energy complementary system has better economic and environmental characteristics, with a primary energy ratio of over 80 % and emission reduction of over 17 %; the advantages of configuring the unit capacity to meet the cooling and heating loads for 80 % of the year are obvious, and in this scenario abandoning battery storage has higher economics for users, with a static payback period from 7.3 years to 4.4 years, but the primary energy ratio decreased by 3 % and carbon emissions increased by 7.2 tCO2. It is recommended to consider the principle of gas-electricity complementarity, relying on the combined cooling, heating, and power system to meet part of the loads, with the remaining loads being supplemented by the municipal grid. The installation of batteries should be considered comprehensively based on the price of the batteries and the requirement for energy-saving and emission-reduction.

Assessing the biennial conference on science and technology (BICOST IX) 2023 technical output on renewable energy, energy storage, and green hydrogen in line with UN SDG commitments

Abstract The development, production and utilization of renewable energy, energy storage and green hydrogen and the associated technologies in Sri Lanka have great potential to contribute to the United Nations’ Sustainable Development Goals (SDGs). The island aims to achieve 70% electricity generation from renewable energy sources by 2030 (within the target of 40% utilization of renewable energy sources for the entire energy generation of the country by 2030). The power sector has to invest US$11 billion from 2023 to 2030 to contribute to reaching this target. This commentary aims to provide a critical perspective on the recommendations of the report from the National Science and Technology Commission’s 9th biennial conference in 2023 on science and technology, the sub-thematic technical report on clean energy, energy storage and green hydrogen in line with the SDGs in the Sri Lankan context. The technical report provides insightful recommendations for Sri Lanka’s energy sector under three main sections: renewable energy, energy storage and green hydrogen. Also, it explores the potential of various renewable energy sources, energy storage systems and green hydrogen as sustainable solutions to address the country’s energy challenges while emphasizing the spillover effects of them, which could contribute to the enterprise’s job creation and uplift the economy.

Assessment of a combined heating and power system based on compressed air energy storage and reversible solid oxide cell: Energy, exergy, and exergoeconomic evaluation

The electricity grid with high-penetration renewable energy sources has urged us to seek means to solve the mismatching between electricity supply and demand. Energy storage technology could accomplish the energy conversion process between different periods to achieve the efficient and stable utilization of renewable energy sources. In this paper, a hybrid energy storage system based on compressed air energy storage and reversible solid oxidation fuel cell (rSOC) is proposed. During the charging process, the rSOC operates in electrolysis cell (EC) mode to achieve the energy storage by converting the compression heat to chemical fuels. During the discharging process, the cell operates in fuel cell mode for electricity production and the gas turbine is conducted to recover the waste heat from cell. To evaluate the comprehensive performance of the proposed system, the energy, exergy, and exergoeconomic studies are conducted in this paper. Under the design condition, the results indicated that the proposed system is capable of generating 300.36 kW of electricity and 106.28 kW of heating; in the meantime, the energy efficiency, exergy efficiency, and total cost per unit exergy of product are 73.80%, 55.70%, and 216.78 $/MWh, respectively. The parametric analysis indicates that the increase in pressure ratio of air compressor, steam utilization factor of rSOC stack under EC mode and current density of the rSOC stack under EC mode reduce exergy efficiency and total cost per unit exergy of product simultaneously, while the increment of operating pressure of rSOC stack under FC mode enhances the exergy efficiency and decreases total cost per unit exergy of product. The multi-objective optimization is carried out to improve the comprehensive performance of the proposed system, and the results expressed that the best optimal solution has the exergy efficiency and total cost per unit exergy of product of 65.85% and 187.05 $/MWh, respectively. Compared to the basic operating condition, the improvement of the proposed system has led to the maximum enhancement of 20.32% in exergy efficiency and 18.60% in total cost per unit exergy of product.

The improved aquila optimization approach for cost-effective design of hybrid renewable energy systems

The growing demand for renewable energy systems is driven by climate change concerns, government support, technological advancements, economic viability, and energy security. These factors combine to create a strong momentum towards a clean and sustainable energy future. Governments, governments, and individuals are increasingly aware of the environmental impacts of traditional energy sources and adopting renewable energy solutions. Hybrid Renewable Energy Systems (HRES) are developed as an effective way of meeting the energy demands in remote locations. The complexity of the system components and the fluctuation of renewable energy sources make it difficult to design an economical and effective HRES. In this study, the Improved Aquila Optimization (IAO) approach has been suggested as a powerful tool to optimize the HRES design. The study addresses the implementation of the IAO approach in the design of HRES and emphasizes its advantages over other optimization techniques. Through extensive simulations and analyses, our findings demonstrate the superior performance of the IAO algorithm in improving the efficiency and cost-effectiveness of HRES. The optimization process using IAO resulted in a significant reduction in overall system costs, achieving an estimated Net Present Cost (NPC) of $201,973. It translates to a cost reduction of 25% compared to conventional optimization techniques. Furthermore, our analysis reveals that the IAO approach enhances the utilization of renewable energy sources, leading to a 15% increase in overall energy generation efficiency. These results highlight the effectiveness of the IAO approach in addressing the challenges associated with designing HRES. By significantly reducing costs and improving efficiency, it facilitates the adoption of sustainable energy systems in remote areas. The outcomes of this study emphasize the importance of utilizing advanced optimization techniques, such as IAO, to ensure the economic viability and environmental sustainability of HRES.

Rancang Bangun Thermoelectric Generator (TEG) Sebagai Suplai Daya Alternatif Germinasi Kacang Hijau

The central government has established the National Energy Policy (KEN) to increase the utilization of renewable energy sources (EBT) by around 23% by 2025 and 31% by 2050. In an effort to support the government's program, researchers have developed a Thermoelectric Generator (TEG) as an alternative power supply to replace the energy source from PT PLN for electrical equipment used in the green bean germination process such as lights, fans, and water pumps. This prototype consists of two chambers: a combustion chamber that generates electrical energy and a control room for the germination process. These two areas are separated to ensure that the control device and germination process are not affected by the heat from combustion. The main components of this prototype include ten TEG units with a maximum power of 5.2 W, a 33 Ah battery, an 8A Buck-boost converter, a 3A Buck converter, a 6W Full Spectrum LED, four DC fans, and a DC pump. The TEG functions effectively as the germination process proceeds smoothly.

Research on the path of building carbon peak in China based on LMDI decomposition and GA-BP model.

The building sector contributes significantly to carbon emissions, impeding China's progress toward its 2030 carbon emissions peak target due to the limited utilization of renewable energy sources. This study aims to forecast the peak and timing of carbon emissions in China's construction industry to chart a low-carbon roadmap for the sector's future. Initially, an extended logarithmic mean divisia index (LMDI) decomposition model, based on the Kaya identity, is proposed to gauge the contribution levels of driving factors affecting building carbon intensity. Subsequently, a hybrid prediction model (IGA-BP) is constructed, employing an optimized two-hidden-layer neural network via a genetic algorithm, to forecast building carbon emissions and intensity. Additionally, four scenarios are outlined, each defining pathways to simulate emissions peak, carbon peak timing, and intensity within the Chinese building sector from 2020 to 2050. The research findings reveal: (1) The final emission factor of buildings primarily drives the surge in building carbon intensity, while the industrial structure stands as the most significant limiting factor. (2) Compared to alternative models, the proposed hybrid prediction model more effectively captures the evolution pattern of carbon emissions. (3) The prediction results indicate that China's building carbon intensity has reached its peak. Pathway 12 closely aligns with the sector's carbon emissions peak, projecting a peak value of 5.609 billion tons in 2029. To attain this pathway, China needs to develop more precise and feasible emission reduction strategies for its buildings. Overall, the research outcomes furnish robust references for decision-making in future efforts aimed at reducing building emissions.

Energy Transition in Vietnam: A Strategic Analysis and Forecast

Energy landscapes in Asia and other regions are currently undergoing a transformation aimed at increasing the share of clean energy sources. This article analyzes and forecasts the electricity demand in Vietnam, examining existing constraints that necessitate the shift from coal to renewable energy sources. The rapid economic growth in Vietnam is driving a substantial surge in electricity demand, projected to reach 124 thousand MW by 2030 according to the National Electricity Plan, positioning Vietnam second in Southeast Asia. This surge poses a significant challenge to national energy security, given the impracticality of effective coal mining in the country and the imperative to develop renewable energy sources. Anticipating the changes in Vietnam’s energy mix by 2050, this study foresees a substantial reduction in dependence on coal production. Government investment and green energy investment funds such as JETP are strategically directed towards renewable energy sources, including solar, wind, biomass, hydrogen energy, and efficient energy storage technologies. Consequently, this research substantiates the viability of an energy transition from coal to green energy in Vietnam. The article presents an assessment of the rate of replacing coal with renewable energy sources, taking into consideration various scenarios for economic development, energy consumption growth, and the utilization of renewable energy sources.