RES-based System Research Articles

A Transformerless Enhanced-Boost Quasi-Z-Source Inverter with Low Input Current Ripple for Stand-Alone RES-Based Systems

The main drawback of DC-source-based renewable energy sources (RESs), such as photovoltaic (PV) panels or fuel cells (FCs), is that the voltage generated by a panel or cell is less than the required voltage for connection to a DC–AC inverter for grid applications. In this paper, a single-switched DC–DC boost converter equipped with a quasi-impedance source inverter (QZSI) with a modified switching model is proposed to increase the output voltage of these RESs and convert it to a fixed AC grid voltage for loads. By changing the position of the inductor in a classic step-up converter and using a switched-inductor block, the input current ripple is significantly decreased, and the reliability and long-life of the input sources are increased, which is the main contribution of this work. The quality of the generated AC voltage and the low amount of total harmonic distortion (THD) in the projected topology are significant, and no overshoot and undershoot have been reported for both output voltages and currents under different operating conditions with variable loads. Theoretical analysis, simulation results, and comparison with similar topologies are examined and a prototype with a power of 200 to 400 watts is presented. Experimental results confirm the theoretical studies.

Problems of development of innovative power supply systems of Ukraine in the context of European integration

Purpose. To analyse problems and features of the formation of perspective concepts and scenarios for the development of the latest structures of energy supply systems for Ukraine in the context of the energy transition and European integration. Methodology. Theoretical studies, analysis, and generalization of scientific and practical results along with the comparative analysis. Findings. The European Green Deal contributes to the wide development of relevant RES-based systems in the EU countries. Ukraine has also declared its active position regarding the issues of low-carbon development and green transition with the formation of relevant implementation scenarios until 2035, 2050, and 2070. The paper analyses the current state and structure of the electricity supply system in Germany and Ukraine on their ways to low-carbon development of the energy sector and economy. As a result of the conducted research, it is possible to determine further rational steps for effective transformation of the electric power industry according to the strategy of pragmatic or low-carbon development with further measures to modernize the nuclear and thermal energy sectors and moderate RES development. Development of rational structures of electric power systems of new technological order is a constantly relevant, science-intensive direction, which brings serious changes to the traditional raw-resource economy and energy industry. Originality. The conducted comprehensive analysis of the current state and prospects for the development of the structure of electric power complexes of Ukraine and Germany makes it possible to formulate high-priority rational steps in achieving energy independence and energy security, taking into account low-carbon development of the national economy. Practical value. The represented analytics can be used to ensure sustainable development of Ukrainian energy industry, to form an outlook on problems, prospects, and aspects of optimistic and pessimistic scenarios of the generation system development.

Life cycle assessment of a renewable energy system with hydrogen-battery storage for a remote off-grid community

Remote areas usually do not have access to electricity from the national grid. The energy demand is often covered by diesel generators, resulting in high operating costs and significant environmental impacts. With reference to the case study of Ginostra (a village on a small island in the south of Italy), this paper analyses the environmental sustainability of an innovative solution based on Renewable Energy Sources (RES) integrated with a hybrid hydrogen-battery energy storage system. A comparative Life Cycle Assessment (LCA) has been carried out to evaluate if and to what extent the RES-based system could bring environmental improvements compared to the current diesel-based configuration. The results show that the impact of the RES-based system is less than 10% of that of the current diesel-based solution for almost all impact categories (climate change, ozone depletion, photochemical ozone formation, acidification, marine and terrestrial eutrophication and fossil resource use). The renewable solution has slightly higher values only for the following indicators: use of mineral and metal resources, water use and freshwater eutrophication. The climate change category accounts for 0.197 kg CO2 eq./kWh in the renewable scenario and 1.73 kg CO2 eq./kWh in the diesel-based scenario, which corresponds to a reduction in GHG emissions of 89%. By shifting to the RES-based solution, about 6570 t of CO2 equivalent can be saved in 25 years (lifetime of the plant). In conclusion, the hydrogen-battery system could provide a sustainable and reliable alternative for power supply in remote areas.

Spatial analyses of smart energy system implementation through system dynamics and GIS modelling. Wind power case study in Latvia

Major concern in utilising renewable energy sources, such as solar or wind, is their intermittent nature. Therefore, whether they can be reliable energy sources to provide uninterrupted energy demand when reaching a high share of renewable energy in the system depends on the whole energy supply network. Higher flexibility of RES-based systems can be reached through the development of smart energy concepts.The system dynamics model coupled with a geographical information system platform has been used to analyse space and time dimensions of RES potential using geo-referenced information. This approach allows analysing the whole energy system by determining the best-suited development scenario for each region separately, based on their resource, economic, and technological capabilities. Furthermore, the system dynamics model is complemented with different policies to evaluate their impact on renewable and local energy resource development and economic potential. The results show that the potential for large-scale onshore wind farm capacities with suitable land conditions could be around 5.5 GW, but the forecasted necessary wind power capacity to reach climate neutrality in 2050 is 1.55 GW. Therefore, onshore wind turbines should be promoted to move toward a smart and renewable power system in Latvia.

Optimization of On-Grid Hybrid Renewable Energy System: A Case Study on Azad Jammu and Kashmir

Expansion of modern power systems due to increasing energy demands face the challenges of grid reinforcement cost, size and complexity, transmission losses, and environmental factors. Placement of renewable energy sources (RES) based generation systems addresses these challenges. However, the size and placement location of RES-based system require optimization of installation and operational cost with better return on investment and reduction of greenhouse gas emissions. This paper presents an optimized solution for RES-based generation system to be installed with the existing power system of Azad Jammu and Kashmir (AJK) region that is facing power shortfall and load shedding. The weather and climate data from NASA and National Renewable Energy Laboratory (NREL) have been used and various models of on-grid hybrid renewable energy system (HRES) are compared to highlight their techno-economic benefits. An optimal hybrid photovoltaic, wind, and hydroelectric energy-based generation system is proposed with a significant reduction in cost of energy, net present cost, initial costs, and GHG emissions. Installation of the proposed hybrid RES-based generation system guarantees reduction in system power losses and line flows with an improved voltage profile of the system.

Effects of decarbonization on the energy system and related employment effects in South Africa

This paper assesses the impact of decarbonization on the energy system and related employment in South Africa. The cost-minimizing, global energy system model (GENeSYS-MOD) is utilized to project two energy mix scenarios and their associated employment implications at provincial level. While the business as usual (BAU) scenario shows a continuous use of coal capacity in the South African power sector until 2050, the 2 °C scenario exhibits a phase-out of coal by 2040 and a higher diversification of power generation dominated by solar and wind capacity.The increase in renewable energy sources (RES) generates employment in the energy sector which can partially substitute the decline in coal related jobs in affected regions. However, it is not certain that the employment created by RES will directly benefit those negatively impacted by the transition. The results of a sensitivity of the 2 °C scenario provide a near cost-optimal energy system in line with a just transition towards a 2 °C world that limits the employment impacts for former coal regions. Thus, a technological transition from a coal- to a RES-based system needs comprehensive plans for job-transfers, policy formulations, support mechanisms and structural transformation.

Global sensitivity analysis for assessing the economic feasibility of renewable energy systems for an off-grid electrified city

This study aims to develop a global cost map to provide comprehensive understanding and practices for the preliminary assessment and implementation of renewable energy source (RES) based energy systems. Using an optimization technique to minimize the system cost, we first assessed technical and economic feasibility of six RES energy systems of three RES types (solar-powered, wind-powered, and solar/wind hybrid) in two cities (Barcelona, Spain and Jeju Island, Korea). Based on the results of the case studies, we then performed the global sensitivity analysis to develop a cost map which is capable of assessing the levelized cost of energy (LCOE) for the design and operation of the RES-based system in a wide range of regions of different RES potentials and demand levels. As a result, the hybrid RES energy system shows the lowest LCOE ($0.11–0.14/kWh) compared to the single source-based energy systems ($0.12–0.26/kWh) because it requires the fewest energy storage systems by offsetting the temporal intermittence of solar and wind availabilities. In addition, it was revealed that the RES technology cost as well as regional RES potentials is critical to determine the LCOE, while the effect of a regional demand level on the LCOE is relatively negligible.

Economic and environmental benefit analysis of a renewable energy supply system integrated with carbon capture and utilization framework

The recent focus on energy-related environmental issues, such as the depletion of fossil fuels and the climate change, has led to a pressing need for sustainable energy supply systems. Existing systems may, in theory, be revamped into sustainable systems by including new components such as renewable energy sources (RES) and carbon capture and utilization (CCU) frameworks. However, economically and environmentally optimal mechanisms for the integration of RES and CCU frameworks into existing energy systems have yet to be determined. Therefore, this study presents a new approach to sustainable energy supply systems by integrating a RES-based system with existing technologies, coupled with a CCU framework. To address both economic and environmental benefits of the proposed system, a multi-objective optimization technique comprising two objective functions (total daily cost and the total CO2 emission) was developed using a mixed integer linear programming (MILP). The capability of the proposed model is illustrated by a case study of the future transportation sector in Korea. The Pareto solutions for the optimal energy supply system were identified according to CO2 reduction targets under different energy price scenarios.

A novel multiobjective generation and transmission investment framework for implementing 100% renewable energy sources

Over the last decade, it has been considerable attempts to replace thermal power plants by renewable energy sources (RESs), mainly to reduce harmful gaseous emissions. Ubiquitous nature of these sources in the emerging smart grid, demands a dominated RES power system for a long-term horizon. This study proposed a model for 100% RES-based system which is tractable and flexible enough to be used for any mixture of generation unit types with any level of uncertainty needless of the correlation between their random and unpredictable behaviours. To overcome the complex nature of RESs, an efficient stochastic multiobjective mixed-integer linear programming framework is proposed. The efficacy of the proposed model is evaluated via numerical simulation.

Feasibility and impact analysis of a renewable energy source (RES)-based energy system in Korea

In this study, we analyze the feasibility and impacts of a renewable energy source (RES)-based electricity supply system of future Korea. To achieve this goal, we first developed different scenarios for increasing the contribution of RES by lowering the rate of i) nuclear power, ii) thermal power, iii) both nuclear and thermal power, and iv) these scenarios with real-world constraints. Based on the generated scenarios, we then specified the established systems with practical strategies which encourage different renewable sources (wind, solar photovoltaic, biomass, and waste). Finally, we analyzed the impacts of the established RES-based systems according to various criteria: the total required cost, the dependence on imported energy, CO2 emissions, and land use. The results show that the RES-based system that utilizes wind energy as its main source by steadily decreasing the rate of thermal power for electricity generation is the most affordable for future Korean electricity system. We also identify the merits and drawbacks of the analyzed systems and provide relevant recommendations for the establishment of a sustainable energy system for Korea. These findings will support policy makers in integrating quantitative assessments into energy-related policy design and implementation.

Simulations of economical and technical feasibility of battery and flywheel hybrid energy storage systems in autonomous projects

This paper deals with the feasibility of a Renewable Energy Sources (RES)-based stand-alone system for electricity supply based on a Flywheel Energy Storage System (FESS) located on the Greek Island of Naxos. The innovative use of flywheels in parallel connection with electrochemical batteries, as an integrated storage device in the same power plant, was selected to be simulated as it is a necessary buffer covering the load of a typical house. The optimal configuration for the electromechanical connection between the electrochemical batteries and flywheels is also considered in this study. Operational characteristics of the new storage systems were estimated and used in the simulations, while the financial aspects of the projects finalized using hand-made calculations and the HOMER software was used only for the energy calculations. It was found that an off-grid project using advanced and totally “green” technologies is possible and comparable to more conventional RES-based systems, in terms of energy and economical feasibility. Finally, it can be concluded that systems with low price flywheels are equivalent to those with electrochemical batteries.

A comparative feasibility study of stand-alone and grid connected RES-based systems in several Greek Islands

This paper deals with the feasibility of RES-based systems for electricity supply in four different Greek Islands. Three specific typical loads were selected to be covered, where the grid connection was considered as optional. An optimization procedure in terms of energy efficiency and economical feasibility has also been applied, using the HOMER software for the energy part and a hand-made calculation procedure for the financial aspects. It is found that an off-grid project is not economically feasible and the grid connection is necessary only for the sale of excess electricity (not as a backup source). Finally, the relationship between environmental potential and produced energy is found to be linear, with almost constant behaviour for solar systems.

Energy consumption of a residential building: comparison of conventional and RES-based systems

The energy needs of a typical one-family house in the Thessaloniki area for heating, cooling and domestic hot water production are calculated. The calculations are based on the typical average daily consumption of hot water and on the degree-day method for heating and cooling. The results are finally translated into thermal energy consumption, assuming the typical Greek situation (heating with diesel oil boilers and conventional radiators, cooling with local air-to-air split-type heat pumps and hot water production with electric heaters). The same energy needs are assumed to be covered by a vertical closed loop ground heat exchanger combined with a water-to-water heat pump system with fan-coils for heating and cooling and a thermosyphonic solar system for domestic hot water production. The ground heat exchanger/heat pump system efficiency is determined using data from an existing and continuously monitored similar system installed in the broader area of Thessaloniki. The solar system load coverage is calculated using the f-chart method. The energy consumption of the renewable energy systems is calculated and compared to that of the conventional system. The results prove that significant energy savings can be achieved.