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• Retrospective analysis of varying impacts of European electricity generation. • Environmental impact of electricity generation varies considerably over time. • Provision of hourly environmental retrospective profiles of electricity generation. • Comparison of dynamic production-based and consumption-based electricity mixes. The composition of electricity varies significantly throughout the year. As a result, the environmental impact of the electricity mix is also highly variable. However, most LCA studies assume a static annual average electricity mix and neglect these fluctuations. Therefore, this study examines the time-varying environmental impacts of electricity generation in Germany, France, Italy, Spain, and Poland using a dynamic life cycle assessment. It shows that the impacts of environmental categories vary considerably depending on when the electricity is generated, resulting from the different energy generation patterns throughout the day and year. In particular, the integration of renewable energy sources such as photovoltaic systems and wind turbines leads to significant fluctuations of environmental impacts. To determine the magnitude of the variation, coefficients of variation are calculated for each environmental impact category for a representative year. High coefficients of variation of more than 20% can be observed for several environmental impact categories. In addition, both a production-based and a consumption-based approach were used for the dynamic life cycle assessment. Comparing these two approaches shows significant differences in impact category results, for example, for Italy, with an average of 15%. These differences highlight the importance of including cross-border electricity flows in assessing the environmental profile of electricity. Overall, the results of the study emphasize the need to implement dynamic electricity mix models in life cycle assessments, especially for systems with time-varying electricity consumption. The provided Excel spreadsheet files with hourly time profiles of environmental impacts for the countries studied facilitate the adoption of the developed models by other practitioners and provide a valuable tool for assessing environmental impacts. [ABSTRACT FROM AUTHOR]

• Optimal design of hydrogen-based storage considering uncertainties. • Integrated system of hybrid renewable power generation system and hydrogen refuelling station. • MIQCP and MILP modelling of green integrated energy system. • Comprehensive techno-economic model for hydrogen and electricity supply. • Robust optimisation sizing of electricity and hydrogen system. Hydrogen and electricity derived from renewable sources present feasible alternative energy options for the decarbonisation of the transportation and power sectors. This study presents the utilisation of hydrogen generated from solar and wind energy resources as a clean fuel for mobility and backup storage for stationary applications under economic and environmental uncertainties. This is achieved by developing a detailed techno-economic model of an integrated system consisting of a hydrogen refuelling station and an electric power generation system using Mixed Integer Quadratic Constrained Programming (MIQCP), which is further relaxed to Mixed Integer Linear Programming (MILP). The model is implemented in the Advanced Interactive Multidimensional Modelling Software (AIMMS) and considering the inherent uncertainties in the wind resource, solar resource, costs and discount rate, the total cost of the three configurations (Hybrid PV-Wind, Standalone PV, and Standalone wind energy system) was minimised using robust optimisation technique, and the corresponding optimal sizes of the components, levelised cost of energy (LCOE), excess energy, greenhouse emission avoided, and carbon tax were evaluated. The levelised cost of the deterministic optimisation solution for all the configuration ranges between 0.0702 $/kWh to 0.0786 $/kWh, while the levelised cost of the robust optimisation solution ranges between 0.07188 $/kWh to 0.1125 $/kWh. The proposed integration has the advantages of affordable hydrogen and electricity prices, minimisation of carbon emissions and grid export of excess energy. [ABSTRACT FROM AUTHOR]

• Hourly analysis of the Italian electricity production mix is performed. • Evaluation of the electricity produced by each fossil and renewable source with a hourly time resolution. • Four power plant efficiency indicators are defined and evaluated. • Three equivalent carbon dioxide emission factors are determined. The power system has faced unprecedented challenges in the last decade caused by many factors: the introduction of the open electricity market, the diffusion of distributed generation, the growth of the electricity production from the no-programmable renewable energy sources, etc. In this framework the power generation system turned extremely varied and complex. In addition, European Union highlighted the need to increase the energy efficiency to achieve the goal of 30% savings in primary energy consumption by 2030 compared to 1990 levels. Since the goal is defined on primary energy level, the electric efficiency indicators are central issues in the assessment of energy saving measures that affect electricity demand and involve different processes. However, all European Directives set electric efficiency indicators and carbon dioxide emission factors to fixed values neglecting their intrinsic time-variability due to the primary energy source mix used in the electricity generation hour by hour. The use of a fixed value for these parameters could lead to inaccurate or wrong results in various processes. Indeed, they have an impact on the choice of electricity versus fossil-fuel based technologies. In particular, they affect both the possibility for a product to retain access to European market, and its specific rating in an energy labelling class. Moreover, in the case of the modelling of any energy system that interacts with the power grid the electric efficiency indicators are the crucial factors to assess the potential primary energy savings of the technologies. On another level, the use of an incorrect value of energy and environmental indicators in the evaluation of the primary energy savings of those energy efficiency measures supported by economic mechanisms (as white certificates, policy mechanisms supporting renewables, tax deductions), could lead to an underestimation or an overestimation of the economic support. In this context, the aim of this paper is to perform an hourly analysis of the Italian electricity production mix evaluating the contribution of each primary energy source. The novelty of this approach is related to the evaluation of the electricity produced by each fossil and renewable source with an hourly time resolution over the years 2016 and 2017. Four power plant efficiency indicators and three carbon dioxide emission factors have been also defined and determined on hourly basis for both considered years. The results of the analysis have showed the strongly variability of the considered parameters across the years, the seasons and hour by hour depending upon the hourly power generation mix. [ABSTRACT FROM AUTHOR]

Highlights • The efficiency of the renewable energy integration is improved. • Overall power production increases while fulfilling transmission system restrictions. • Wind energy spillage is reduced without modifying the yearly hydropower dispatch. • Real case study in Argentina shows benefits of the minute-by-minute control policy. Abstract This work aims to analyze the complementary operation between an existing hydropower plant and a projected wind farm in a remote area of Argentinean Patagonia. With this new generation, the grid element sizes will be insufficient to handle both generation sources at rated. Particulary, a bottleneck will be present at the transmission line and the coupling transformer with the main grid. To avoid this situation, a coordinated dispatch policy of both generation sources is proposed. With this aim, a heuristic algorithm is developed that improves energy generation under the transmission system restrictions. The proposal is assessed and compared with other operation policies on the basis of real data collected over nine years. The benefits of the proposal, that basically consists in reducing wind and hydro power spillage are highlighted. Furthermore, the impact of enlarging the wind farm on the overall power system production is also evaluated. [ABSTRACT FROM AUTHOR]

Hybrid photovoltaic-wind energy systems are being designed and implemented as stand-alone or grid connected generation systems, due to the need to use local, environmental friendly and low cost energy sources. In this study, a novel methodology to optimize the size of an autonomous hybrid photovoltaic-wind power system with battery storage is presented. A multi-objective optimization problem is considered with two objective functions, the total net present cost and a new reliability indicator called maximum expected energy not supplied, which is calculated using a probabilistic approach. The non-dominated sorting genetic algorithm-II was utilized to find the model solution. The results obtained with the presented methodology were compared with those from traditional methodologies, with the proposed methodology generating a set of feasible solutions, with respect to the system economy and reliability, which maximizes the use of renewable sources and reduces the size of the system backup. [ABSTRACT FROM AUTHOR]

The wind industry is currently facing a major challenge due to the ageing of the wind turbines that were first commissioned. Recent wind turbine designs present higher power performance and lower maintenance requirements than older wind turbines. Furthermore, most of the old wind turbines are installed in the best sites for wind resource exploitation. Under this framework, the repowering of wind farms with the replacement of the old machines by new designs is recognised as a focus area for the wind industry. This paper performs a techno-economic analysis of a real wind farm repowering experience at the Malpica wind farm, located in the Northwest of Spain. Results show the annual energy production of the repowered wind farm increases up to twofold that of the old wind farm with the same rated power. Moreover, the economic analysis reveals the project yields satisfactory profitability, even without reliance on public subsidies as currently happens in Spain. In addition, a sensitivity analysis allows us to understand the effects of the uncertainties over the lifetime of the wind farm, and how they affect the projects performance and profitability. [ABSTRACT FROM AUTHOR]

The increase of power plants’ conversion efficiencies, together with the high share of renewable energy sources in the electricity production for some countries, pushes for the use of heat pumps for space heating when aiming at reducing the associated primary energy consumption. However, the effective reduction of primary energy consumption should be supported by careful evaluations, as a number of parameters influence the heat pumps performance, including outdoor temperature, supply temperature, heat load and electricity primary energy factor. The variability of such parameters increases the complexity of the analysis, and annual or monthly average calculations might lead to incomplete evaluations and thus to sub-optimal solutions. This paper performs a hourly simulation of the operation of an air-source heat pump for space heating, relying on the available heat demand data of real buildings currently connected to a district heating network. In addition, the paper proposes the calculation of the hourly primary energy factor of the electricity supplied by the power grid, as the variability of the generation sources plays a key role in the global analysis of the energy system’s conversion efficiency. The results show that in all the considered cases the heat pumps provide potential primary energy savings compared to natural gas boilers, thanks to the combined effect of their high coefficient of performance and the low electricity primary energy factor in the analyzed context. The primary energy consumption reduction obtained in each case is in the range 10–40%, with a median value close to 30%. Moreover, the comparison between average and high-resolution calculations of primary energy factors shows the possible underestimation of the potential primary energy savings when yearly or monthly data are adopted. [ABSTRACT FROM AUTHOR]

In the present paper, a novel method is proposed to enhance the power production and resolve the inconsistent electricity generation of solar chimney power plants (SCPPs) during nighttime. For this purpose, an integrated renewable cycle is proposed by incorporating two technologies: solar chimney and waste-to-energy. The combination is performed by exploiting the warm air of the condensers outlet into the SCPP. The waste-to-energy (WTE) plant in Tehran is thermodynamically analyzed and the mass flow rate of the condensers cooling air is found. Results indicate that by decreasing the humidity of the municipal solid waste (MSW) from 40% to 30% or by increasing MSW feeding rate (0.934–1.146 kg/s), the mass flow rate of the condenser cooling air increases from 190.3 kg/s to 233.7 kg/s. In addition, by increasing the feeding rate or by decreasing the humidity of MSW in the mentioned range, net power output of the WTE plant increases from 1350 kW to 1650 kW. The best injection method is proposed for the warm air of the condensers outlet into the SCPP. Subsequently, the average power increase is examined in different months and parametric study is performed to assess the influence of the effective WTE parameters and meteorological variables on the power output of the SCPP. The final power of the SCPP reaches 20–70 kW (even at the hottest night of the year with 5% relative humidity) and increases 20–1200% and 65–94% (monthly average) compared to the case of without injection. Results demonstrate that in the integrated system, by a 22% increase in the MSW feeding rate (from 0.934 kg/s to 1.146 kg/s) or by decreasing the MSW moisture content (from 40% to 30%), power output of the WTE plant and SCPP increases by 22% and 7%, respectively. Additionally, relative humidity of the surrounding air can increase the SCPP power production by 25%. In addition, the results indicate that wind speeds higher than 12.5 m/s will not affect power production of the SCPP, while relative humidity of the surrounding air, ambient temperature, the MSW feeding rate, and humidity of the MSW have considerable effects on the SCPP power production. In average, total energy and useful exergy efficiency of the proposed system is increased by 0.15% and 0.12% compared to the standalone WTE plant during nighttime. The integration of SCPP with the WTE plant is an applicable method to enhance the power generation and overcome the inconsistent power production of SCPP during nighttime. [ABSTRACT FROM AUTHOR]

Renewable sources of energy are providing an increasing share of the electricity generation mix, but their intermittency drives a need for energy storage. At the same time, water resources are increasingly scarce due to changes in demand, such as from population growth, supply side pressures such as climate change and governance challenges relating to poor management. Large storage reservoirs are used for water management and for energy storage. However, some existing and proposed hydropower reservoirs require vast areas of land and have considerable social and environmental impacts. Growing concerns on water and energy storage from a water-energy-land nexus approach motivated this study. Our objective is to compare how energy and water storage services, such as hydropower generation, electricity grid and water management, are provided with Seasonal Pumped-Storage (SPS) and Conventional Reservoir Dams (CRD) plants. Our case study region is Brazil, a country with extensive hydropower capacity and development plans, for which we compare the cost, land requirement and social impacts between CRD and potential SPS plants. Whilst seasonal pumped-storage have higher capital costs than conventional reservoir dams, given the much lower land requirements and evaporative losses, they are a valuable water and energy storage alternative especially in locations with plain topography and high evaporation. Results show that if Sobradinho CRD was built today it would result in a $USD 1.46 billion loss, on the other hand, Muquém SPS plant would result in a $USD 0.67b revenue. [ABSTRACT FROM AUTHOR]

Renewable energy systems can play a key role in sustainable energy supply. Because of the fluctuating electricity generation, storage technologies are needed to close the gap between demand and supply. Besides the electricity sector, the transport sector causes high energy demand. In this context, because of their remoteness, islands can be seen as blueprints for possible energy transition pathways. The objective of this paper is to analyse different principle concepts that come into question for a 100% renewable subtropical island from the distribution system operator’s point of view. This perspective offers the possibility to account all system costs needed to transfer a centralised energy system into a 100% renewable one and to assume the macroeconomic costs of such a transfer. For the case of La Gomera the economic competitiveness of renewable energy, particularly solar PV and wind power, is shown. All evaluated sustainable scenarios lead to lower annual cost and primary energy demands than the business-of-usual (BAU) scenario based on the cost assumptions used in this study. The analysis underlines that the combination of different technologies will lead to the lowest primary energy demand and to the lowest annualised cost of 10.89 M€ for the entire island energy system, which is 37.2% lower than a BAU scenario. [ABSTRACT FROM AUTHOR]

The solar energy share in Sweden will grow up significantly in next a few decades. Such transition offers not only great opportunity but also uncertainties for the emerging solar photovoltaic/thermal (PV/T) technologies. This paper therefore aims to conduct a techno-economic evaluation of a reference solar PV/T concentrator in Sweden for building application. An analytical model is developed based on the combinations of Monte Carlo simulation techniques and multi energy-balance/financial equations, which takes into account of the integrated uncertainties and risks of various variables. In the model, 11 essential input variables, i.e. average daily solar irradiance, electrical/thermal efficiency, prices of electricity/heating, operation & management (OM) cost, PV/T capital cost, debt to equity ratio, interest rate, discount rate, and inflation rate, are considered, while the economic evaluation metrics, such as levelized cost of energy (LCOE), net present value (NPV), and payback period (PP), are primarily assessed. According to the analytical results, the mean values of LCOE, NPV and PP of the reference PV/T connector are observed at 1.27 SEK/kW h (0.127 €/kW h), 18,812.55 SEK (1881.255 €) and 10 years during its 25 years lifespan, given the project size at 10.37 m 2 and capital cost at 4482–5378 SEK/m 2 (448.2–537.8 €/m 2 ). The positive NPV indicates that the investment on the selected PV/T concentrator will be profitable as the projected earnings exceeds the anticipated costs, depending on the NPV decision rule. The sensitivity analysis and the parametric study illustrate that the economic performance of the reference PV/T concentrator in Sweden is mostly proportional to solar irradiance, debt to equity ratio and heating price, but disproportionate to capital cost and discount rate. Together with additional market analysis of PV/T technologies in Sweden, it is expected that this paper could clarify the economic situation of PV/T technologies in Sweden and provide a useful model for their further investment decisions, in order to achieve sustainable and low-carbon economics, with an expanded quantitative discussion of the real economic or policy scenarios that may lead to those outcomes. [ABSTRACT FROM AUTHOR]

Rising penetrations of variable renewable generation in electric power systems can raise operational challenges. One is that renewables can increase the need for dispatchable generation with fast-ramping capabilities. This can be costly, because in many instances flexible generators can be more expensive than baseload units that have slower ramping capabilities. If ramping capacity is not available, renewable curtailment may be needed. An alternate solution to this need for ramping is to use energy storage. A question that this raises is how renewable and conventional generators and energy storage would interact in a market environment, and whether certain asset-ownership structures would result in more efficient coordination. To this end, this paper presents a multi-period market-equilibrium model of interactions between these different types of market agents. The impacts on renewable integration of conventional generators having limited ramping capabilities are studied through an illustrative case study. We also examine a variety of structures for the participation of energy storage in the market. We find that co-ownership and co-operation of renewable generators and energy storage brings about the best results from the perspective of alleviating market inefficiencies. Having energy storage directly controlled by the market operator or participating as an independent profit-maximizing firm is less efficient. [ABSTRACT FROM AUTHOR]

Wind power is one of the most promising renewable energy sources that has gained enormous attention, especially in the electricity generation sector over the past decade in the United States. In this study Data Envelopment Analysis (DEA) is implemented to quantitatively evaluate the relative efficiencies of the 236 large utility-scale wind farms. Input- and output-oriented CCR (Charnes, Cooper, and Rhodes) and BCC (Banker, Charnes, and Cooper) models are applied to pre-determined three input and three output variables. The sensitivity analysis is conducted for the robustness of DEA by introducing seven new models with the various combinations of input and output variables of the original model. Tobit regression models are developed for the second stage of the analysis to investigate the effects of specifications of the wind turbine technologies. DEA results indicate that two-thirds of the wind farms are operated efficiently. On average, 70% of the wind farms have a considerable potential for further improvement in operational productivity by expanding these wind farm projects, 24% of them should reduce their operational size to increase their productivity level, and 6% of them are operating wind power at the most productive scale size. Nonparametric statistical tests show that the most efficient wind farms are located in Oklahoma because of the relatively high wind speed resources. Tobit regression model indicates the selection of the brand of the wind turbine has a significant contribution to the productive efficiency of the wind farms. The results of this study shed some light on the current efficiency assessments of the 236 large utility-scale wind farms in the United States and the future of wind energy for both energy practitioners and policy makers. [ABSTRACT FROM AUTHOR]

A promising way to electrify regions lacked to reliable access to electricity is the employment of stand-alone photovoltaic power systems (SPPSs). Recently, the cost of electricity from such systems has fallen, and it is expected that this tendency will continue in the future. Within this paper, a new design methodology of highly reliable and sustainable SPPSs is presented. The approach consists of the following processes: prediction of the load demand, characterization of the PV performance on site, sizing the SPPS considering different storage technologies, and forming the most effective design. On the other hand, a new dimensionless number will be introduced to characterize the PV performance at a particular location. In order to demonstrate the methodology, an intention to electrify 93 households in a rural community is given as an example. The results show that a SPPS configuration including compressed air energy storage and supercapacitor may be the most effective SPPS design. [ABSTRACT FROM AUTHOR]

In this paper, an alternative renewable energy concept, i.e. concept of solar power plant with short diffuser (SPD) was investigated through the development of a numerical model with simplifications due to general complexity. The mentioned alternative energy concept is based on the possibility of utilizing an artificially created and maintained convective vortex system in the surrounding atmosphere. Finally, it is assumed that the specific vortex system would able to deliver useful mechanical work which then can be used to produce carbon-free electricity via turbine assembly. Preliminary numerical results were presented as a case study for SPD plants using a solar collector diameter of 600 m with a diffuser of 30 m in maximal and 25 in minimal diameter. According to the obtained numerical simulations, for the considered case, it was found that pressure potential should be below 5 kPa in general (with mass air flow rates less than 31 t/s) in order to enable reasonable operating conditions for commercial wind turbine technologies (a specific pressure potential range was defined in order to provide reasonable parameters related to the vortex system). Namely, for pressure potentials ranging between 3.5 kPa to 5.0 kPa, and mass air flow rates from 26 to 31 t/s, the plant would be able to deliver between 5.17 MW to 16.95 MW of nominal electric power output with an associated range of wind turbine operating air velocities from 30 m/s to 50 m/s. A comparison of the numerical results was obtained by using available observation data and reasonable matching was achieved, i.e. partial validation of the developed numerical model due to the non-existence of an experimental plant. Current research related to SPD concept development is still in the stage of numerically based experiments, which are crucial and important towards the consideration of a prototype plant. Therefore, the gained and presented findings in this paper are certainly valuable for the further development of the herein analyzed alternative renewable energy concept and provide a base for the final experimental realization of a prototype plant. [ABSTRACT FROM AUTHOR]

This study presents the energetic performance of the biomass to produce power for micro scale domestic usage. Human excreta are chosen as the subject of the study to investigate their potential to produce biogas under ambient conditions. Furthermore, the research examines the approaches by which biogas production can be enhanced and purified, leading to a high-power generation system. The experimental work focuses on the design and fabrication of a biogas digester with a reverse solar reflector, water scrubbing tower, and a dryer. Anaerobic digestion has been considered as the decomposition method using solar energy which is a heat providing source. Specifically, two types of experiments have been performed, namely, feces to water weight proportion and continuous feeding experiments, each involving a set of six samples. The effect of parameters such as pH, ambient temperature, and biogas upgradation reveals that volume of biogas and power generation can be best obtained when an 8:2 feces to water weight sample is employed and when the feeding is applied every fifth day. In addition, this study discusses the environmental prospects of the biogas technology, which is achieved by using the water purification method to improve the methane percentage to 85% and remove undesired gases. The motivation behind this work is to understand the potential of human excreta for the development of domestic power generating systems. The results obtained reveal that 0.35 m 3 /kg of biogas is produced with 8:2 weight proportion sample, which generates 26.8 kW h power from 35 kg of waste. On the other hand, continuous feeding on the fifth day produces 0.7 m 3 /kg biogas and generates 60 kW h power. [ABSTRACT FROM AUTHOR]

Different storage technologies enable an increasing share of variable renewable generation in the electricity system by reducing the temporal mismatch between generation and demand. Two storage ratings are essential to time-shift delivery of electricity to loads: electric power, or instantaneous electricity flow [W], and electric energy, or power integrated over time [Wh]. An optimal storage portfolio is likely composed of multiple technologies, each having specific power and energy ratings. This paper derives and explains the link between the shape of the time-varying demand and generation profiles and the amount of desirably installed storage capacity, both energy and power. An analysis is performed for individual storage technologies first, showing a link between the necessary power and energy capacity and the demand and generation profile. Then combinations of storage technologies are analyzed to reveal their mutual interaction in a storage portfolio. Results show an increase in desirability for storage technologies with low cost power ratings when the mismatch between generation and demand occurs in daily to weekly cycles. Storage technologies with low cost energy ratings are preferred when this mismatch occurs in monthly to seasonal cycles. The findings of this work can help energy system planners and policy makers to explain results from generation expansion planning studies and to isolate the storage benefits accountable to temporal arbitrage in broader electricity storage studies. [ABSTRACT FROM AUTHOR]

Renewable energy technology-based power generation is considered to be environmentally friendly and to have a low life cycle greenhouse gas emissions footprint. However, the life cycle water footprint of renewable energy technology-based power generation needs to be assessed. The objective of this study is to develop life cycle water footprints for renewable energy technology-based power generation pathways. Water demand is evaluated through consumption and withdrawals coefficients developed in this study. Sixty renewable energy technology-based power generation pathways were developed for a comprehensive comparative assessment of water footprints. The pathways were based on the use of biomass, nuclear, solar, wind, hydroelectricity, and geothermal as the source of energy. During the complete life cycle, power generation from bio-oil extracted from wood chips, a biomass source, was found to have the highest water demand footprint and wind power the lowest. During the complete life cycle, the water demand coefficients for biomass-based power generation pathways range from 260 to 1289 l of water per kilowatt hour and for nuclear energy pathways from 0.48 to 179 l of water per kilowatt hour. The water demand for power generation from solar energy-based pathways ranges from 0.02 to 4.39 l of water per kilowatt hour, for geothermal pathways from 0.04 to 1.94 l of water per kilowatt hour, and for wind from 0.005 to 0.104 l of water per kilowatt hour. A sensitivity analysis was conducted with varying conversion efficiencies to evaluate the impact of power plant performance on water demand. Cooling systems used in power generation plants were also studied and include once-through, recirculating, dry, and hybrid cooling. When only the power generation stage is considered, hydroelectricity and nuclear power generation with once-through cooling systems showed the highest water consumption (68 l of water per kilowatt hour) and water withdrawals coefficients (178 l of water per kilowatt hour), respectively. [ABSTRACT FROM AUTHOR]

The growing need for the clean and renewable energy has led to the fast development of grid-connected tidal stream power generation systems all over the world. These large scale tidal stream power generation systems are going to be connected to power systems and one of the important subjects that should be investigated is its impacts on power system stability. Hence, this paper investigates the possibility of tidal stream power generation system on damping inter-area oscillations, as a new contribution to earlier studies. As tidal farms are mostly installed far from conventional power plants, local signals do not include good quality to alleviate inter-area oscillations. To overcome the problem, a novel damping controller is developed by employing wide-area measurement system and added to base controllers of doubly-fed induction generator through tidal stream power generation system. The proposed wide-area damping controller includes efficient means to compensate for the incompatible performances of wide area measurement based delayed signals. Robustness of the designed damping controller has been demonstrated by facing the study system with faults leading to enough shifts in power system operating point, and tidal farm generation. [ABSTRACT FROM AUTHOR]

Urban systems account for about two-thirds of global primary energy consumption and energy-related greenhouse gas emissions, with a projected increasing trend. Deep geothermal energy and woody biomass can be used for the production of heat, electricity and biofuels, thus constituting a renewable alternative to fossil fuels for all end-uses in cities: heating, cooling, electricity and mobility. This paper presents a methodology to assess the potential for integrating deep geothermal energy and woody biomass in an urban energy system. The city is modeled in its entirety as a multiperiod optimization problem with the total annual cost as an objective, assessing as well the environmental impact with a Life Cycle Assessment approach. For geothermal energy, deep aquifers and Enhanced Geothermal Systems are considered for stand-alone production of heat and electricity, and for cogeneration. For biomass, besides direct combustion and cogeneration, conversion to biofuels by a set of alternative processes (pyrolysis, Fischer-Tropsch synthesis and synthetic natural gas production) is studied. With a scenario-based approach, all pathways are first individually evaluated. Secondly, all possible combinations between geothermal and biomass options are systematically compared, taking into account the possibility of hybrid systems. Results show that integrating these two resources generates configurations featuring both lower costs and environmental impacts. In particular, synergies are found in innovative hybrid systems using excess geothermal heat to increase the efficiency of biomass conversion processes. The application to a case study demonstrates the advantages of using a system approach for the analysis over a stand-alone comparison between options. [ABSTRACT FROM AUTHOR]

Renewable energy systems are proving to be promising and environment friendly sources of electricity generation, particularly, in countries with inadequate fossil fuel resources. In recent years, wind, solar photovoltaic (PV) and biomass based systems have been drawing more attention to provide electricity to isolated or energy deficient regions. This paper presents a hybrid PV-wind generation system along with biomass and storage to fulfill the electrical load demand of a small area. For optimal sizing of components, a recently introduced swarm based artificial bee colony (ABC) algorithm is applied. To verify the strength of the proposed technique, the results are compared with the results obtained from the standard software tool, hybrid optimization model for electric renewable (HOMER) and particle swarm optimization (PSO) algorithm. It has been verified from the results that the ABC algorithm has good convergence property and ability to provide good quality results. Further, for critical case such as the failure of any source, the behavior of the proposed system has been observed. It is evident from the results that the proposed scheme is able to manage a smooth power flow with the same optimal configuration. [ABSTRACT FROM AUTHOR]

In this paper, a method for designing hybrid electricity generation systems is presented. It is based on the Modified Electric System Cascade Analysis method. The Power Pinch analysis is used as a guideline for development of an isolated power supply system, which consists of photovoltaic panels, wind turbines and energy storage units. The design procedure uses a simulation model, developed using MATLAB/SIMULINK and applies the developed algorithms for obtaining an optimal design. A validation of the Modified Electric System Cascade Analysis method is performed by comparing the obtained results with those from the Homer Pro software. The procedure takes as inputs hourly wind speed, solar radiation, demands, as well as cost data, for the generation and storage facilities. It is also applied to minimize the loss of power supply probability and to minimize the number of storage units. The algorithm has been demonstrated with a case study on a site in Oujda city, with daily electrical energy demand of 18.7 kWh, resulting in a combination of photovoltaic panels, wind turbine and batteries at minimal cost. The results from the Modified Electric System Cascade Analysis and HOMER Pro show that both tools successfully identified the optimal solution with difference of 0.04% in produced energy, 5.4% in potential excess of electricity and 0.07% in the cost of the energy. [ABSTRACT FROM AUTHOR]

Providing a cost-efficient, eco-friendly and sustainable energy is one of the main issues in modern societies. In response to this demand, new features of microgrid technology have provided huge potentials while distributing electricity more effectively, economically and securely. Accordingly, this paper presents a new multi-objective generation management model for optimal day-ahead operational planning of medium voltage microgrids. The proposed model optimizes both pollutant emission and operating cost of a microgrid by using multi-objective optimization. Besides, a seamlessness-selective algorithm is integrated into the model, which can be adopted to achieve the desired self-sufficiency level for microgrids along a specified planning horizon. Furthermore, the model is characterized by a reserve-assessment strategy developed to handle the load and renewable energy resources estimation errors. The introduced model is solved using a combination of numerical and evolutionary methods of species-based quantum particle swarm optimization to find the optimal scheduling scheme and minos-based optimal power flow to optimize the operating cost and emission. In addition, the suggested solution approach also incorporates an efficient mechanism for considering energy storage systems and coding the candidate solutions in the evolutionary algorithm. The proposed model is implemented on a test microgrid and is investigated through simulations to study the different aspects of the problem. The results show significant improvements and benefits which are obtained by applying the proposed intelligent management. [ABSTRACT FROM AUTHOR]

High shares of intermittent renewable power generation in a European electricity system will require flexible backup power generation on the dominant diurnal, synoptic, and seasonal weather timescales. The same three timescales are already covered by today’s dispatchable electricity generation facilities, which are able to follow the typical load variations on the intra-day, intra-week, and seasonal timescales. This work aims to quantify the changing demand for those three backup flexibility classes in emerging large-scale electricity systems, as they transform from low to high shares of variable renewable power generation. A weather-driven modelling is used, which aggregates eight years of wind and solar power generation data as well as load data over Germany and Europe, and splits the backup system required to cover the residual load into three flexibility classes distinguished by their respective maximum rates of change of power output. This modelling shows that the slowly flexible backup system is dominant at low renewable shares, but its optimized capacity decreases and drops close to zero once the average renewable power generation exceeds 50% of the mean load. The medium flexible backup capacities increase for modest renewable shares, peak at around a 40% renewable share, and then continuously decrease to almost zero once the average renewable power generation becomes larger than 100% of the mean load. The dispatch capacity of the highly flexible backup system becomes dominant for renewable shares beyond 50%, and reach their maximum around a 70% renewable share. For renewable shares above 70% the highly flexible backup capacity in Germany remains at its maximum, whereas it decreases again for Europe. This indicates that for highly renewable large-scale electricity systems the total required backup capacity can only be reduced if countries share their excess generation and backup power. [ABSTRACT FROM AUTHOR]

The increase in distributed renewable energy supply offers new opportunities to improve the performance of local energy systems. In line with this, research and development has begun to broaden its scope from the building scale towards the neighbourhood and district scales. The formulation and comparison of potential energy solutions in different contexts at different scales of analysis demands well-defined concepts and robust decision support tools. This paper studies the concept of energy positive neighbourhoods, which it defines as areas “ in which the annual energy demand is lower than annual energy supply from local renewable energy sources. … The aim is to support the integration of distributed renewable energy generation into wider energy networks and provide a functional, healthy, user friendly environment with as low energy demand and little environmental impact as possible. ” Key performance indicators for energy positive neighbourhoods are proposed along with an ‘energy positivity label’. A decision support tool, called AtLas, designed to inform the long term planning of neighbourhood energy solutions is described and used to evaluate the energy positivity level of a Finnish residential neighbourhood and part of a French university campus. [ABSTRACT FROM AUTHOR]

As the demand for alternative sources of energy has increased, harvesting abundant environmental energy such as vibration energy including track vibrations in railway systems has attracted greater attention. In this study, we develop a portable high-efficiency electromagnetic energy harvesting system with supercapacitors that converts the energy of track vibrations into electricity. The generated electricity is stored in the supercapacitors and used in remote areas for safety facilities or in standby power supplies for rail-side equipment. The proposed system consists of a mechanical transmission and a regulating circuit. Acting as the energy input and transmission, Gears and a rack amplify the small vibrations of the track, and one-way bearings enhance efficiency by transforming bidirectional motion to unidirectional rotation. Supercapacitors are used in the vibration energy harvesting system for the first time. The supercapacitors permit the storage of energy from rapidly changing transient currents and a steady power supply for external loads. The proposed system is demonstrated through dynamic simulations, which show the rapid response of the system. An efficiency of 55.5% is demonstrated in bench tests, verifying that the proposed electromagnetic energy harvesting system is effective and practical in renewable energy applications for railroads. [ABSTRACT FROM AUTHOR]

Increasing attention has recently been drawn to energy consumption in manufacturing plants. Facing the challenges from reducing emissions coupled with rising raw material prices and energy costs, manufacturers are trying to balance the energy usage strategy among the total energy consumption, economy, and environment, which can be self-conflicting at times. In this paper, energy systems in manufacturing environments are reviewed, and the current status of onsite energy system and renewable energy usage are discussed. Single objective and multicriteria optimization approaches are effectively formulated for making the best use of energy delivered to the production processes. Energy supply operation suggestions based on the optimization results are obtained. Finally, an example from an automotive assembly manufacturer is described to demonstrate the energy usage in the current manufacturing plants and how the optimization approaches can be applied to satisfy the energy management objectives. According to the optimization results, in an energy oriented operation, it takes 35% more in monetary cost; while in an economy oriented operation, it takes 17% more in megawatt hour energy supply and tends to rely more on the inexpensive renewable energy. [ABSTRACT FROM AUTHOR]

A prototype of a solar power tower system was designed and constructed to produce electricity from solar energy. This prototype of a solar power tower system was constructed and installed at King Abdulaziz University in Saudi Arabia where solar intensity is excessive. Heliostats were implemented to capture the solar rays during daylight. These mirrors are used to direct the solar energy to a solar receiver that is made of alloy steel so that thermal energy is conveyed to a thermal fluid inside the receiver. Based on a detailed selection procedure presented in this article, a final number of ten heliostats were chosen to direct the solar energy to the solar receiver. In addition; two motors were used to control the heliostat rotational and elevation movements. The thermal fluid is a molten salt mixture (which consists of 60% NaNO 3 and 40% KNO 3 ). Cold and hot storage tanks were manufactured from steel and they were insulated with calcium silicate from all sides. A one-meter high and one and a half-meter cylindrical vessel was adopted for each of the cold and hot tanks. In this article, a detailed design analysis of each component is presented. The thermal power transferred to the water in the heat exchanger as it is heated by the molten salt was measured and found to be 11.26 kW. The thermal power given by the molten salt in the heat exchanger was also measured and found to be 12.31 kW. The design thermal power was 13 kW. The percentage error in the thermal power obtained is about 5.3%. [ABSTRACT FROM AUTHOR]

Wind speed forecasting aids in estimating the energy produced from wind farms. The soaring energy demands of the world and minimal availability of conventional energy sources have significantly increased the role of non-conventional sources of energy like solar, wind, etc. Development of models for wind speed forecasting with higher reliability and greater accuracy is the need of the hour. In this paper, models for predicting wind speed at 10-min intervals up to 1 h have been built based on linear and non-linear autoregressive moving average models with and without external variables. The autoregressive moving average models based on wind direction and annual trends have been built using data obtained from Sotavento Galicia Plc. and autoregressive moving average models based on wind direction, wind shear and temperature have been built on data obtained from Centre for Wind Energy Technology, Chennai, India. While the parameters of the linear models are obtained using the Gauss–Newton algorithm, the non-linear autoregressive models are developed using three different data mining algorithms. The accuracy of the models has been measured using three performance metrics namely, the Mean Absolute Error, Root Mean Squared Error and Mean Absolute Percentage Error. [ABSTRACT FROM AUTHOR]

This paper proposes an adaptive control algorithm for grid-interfacing inverters in renewable energy-based distributed generation systems. The proposed control algorithm functions in two different modes: basic power generation mode, harmonics compensation mode. In basic power generation mode, the inverter pumps desired amounts of active and reactive powers into the grid at the point of common coupling. In harmonics compensation mode, the control algorithm ensures sinusoidal grid current through load current harmonics mitigation in addition to desired power generation. Moreover, the proposed control algorithm does not use any detection methods for compensation of harmonic currents. Hence, it results in low computational burden. Based on the requirements, the proposed control algorithm can be operated in either of the modes. A proportional–integral controller-based closed loop control is employed for accurate control of the power injected into the grid. A frequency adaptive notch filter is used to synchronize the grid-interfacing inverter with the fundamental component of grid voltage without using any phase locked loop. The effectiveness of the proposed control algorithm in reference active and reactive powers generation, current harmonics compensation is demonstrated successfully by simulation and experimental results. [ABSTRACT FROM AUTHOR]

The increase in applications related to solar energy is making it necessary to study those factors related to improving system efficiency and final production. Electricity generation in solar power systems, such as concentrated solar power and photovoltaic plants is governed by meteorological conditions. The presence of attenuating atmospheric factors determines the sun’s intermittent character, causing electricity generation instability. Consequently, these fluctuations cause problems when integration the generated electricity into the public electricity grid, resulting in variability and unpredictability in the electricity market. Therefore, choosing a climatologically optimal place to install solar plants is fundamental for optimizing the final electricity generation. Besides this, constantly-updated solar information can contribute to take transcendental decisions and, consequently, in the performance of solar applications. Accordingly, a real-time solar radiation estimation is presented using satellite images, where beam, diffuse and global components have been evaluated in real time for all sky conditions. [ABSTRACT FROM AUTHOR]

Chinese Kang is widely used as heated bed and for heat recovery of cooking stove in Northern China. However there are main drawbacks of indoor and outdoor air pollutant generation and heavy demands on solid fuel handling. A novel combined Kang system, which integrates solar Kang and solar air collector, is here proposed. Experiments were conducted to examine the alternative operating modes: (i) only solar air collector in service, (ii) only solar Kang in service, and (iii) both solar Kang and solar air collector in service. The results show that these three modes behave differently and have distinct effects on room thermal environment in winter. When this pollution-free system operates under the third combined mode, the room temperature increases significantly and the vertical temperature gradient reduces. The Kang surface temperature increases and its uniformity is improved. It is also found that the room air temperature is closely related to the Kang surface temperature. Furthermore, most of the time the thermal environment meets the occupant need. This paper reports the experimental work and investigates into the effects on indoor thermal environment as in rural residences in Northern China. [ABSTRACT FROM AUTHOR]

Renewable energy resources increased their importance in the last decades due to environmental pollution problems. Additionally, the fact that fossil fuels such as oil, coal, and natural gas will be depleted in near future encourages researchers to make investigations on alternative energy resources. Wind energy, which is one of the most used alternative resources, has a great potential. In this study, Weibull parameters at İncek region of Ankara (the capital city of Turkey), where Atılım University campus is located, were determined for four different seasons and for twelve months in order to accomplish wind speed characterization at the region. Wind speed data at 20 m and 30 m heights were collected from a measurement station installed at Atılım University campus area. The data were taken as 1 min average values for a one year period between June 2012 and June 2013. Hourly average wind speed values for each height were derived using the collected wind data. Weibull parameters were calculated with five different methods using the derived hourly average wind speed values. According to root mean square error analyses, the best methods for which Weibull distribution fits the actual wind data were determined as power density and empirical methods. The power and energy density values for the region were also calculated for each season and each month. It was revealed that the maximum power density is encountered in March with about 98 (W/m 2 ). Since this power density indicates that large scale wind turbine use is not a good option at the region, the performances of three different small scale wind turbines were evaluated. According to the results, two of the investigated wind turbines were found to be capable to generate all yearly energy need of an average household in Turkey. [ABSTRACT FROM AUTHOR]

One of the most pressing issues in the study of the power generation and distribution is the characterization of the grid behavior, whether a relevant fraction of the connected power plants relies on Renewable Energy Sources. Indeed, because of the discontinuous power supply and the limited presence of energy accumulators, concerning power imbalances may take place on the grid. The power plants ensuring high reliability performance should be ready to feed the loads when the Renewable Energy Sources are not available. In order to ensure the grid stability and the sustainability of nuclear energy, the possibility of operating Generation-IV nuclear reactors in a flexible way should be considered, i.e., the Nuclear Power Plants should adjust the mechanical power produced so as to comply with the sudden grid frequency variations. In the present work, this opportunity is assessed for the Lead-cooled Fast Reactors, adopting the Advanced Lead Fast Reactor European Demonstrator (ALFRED) as a representative of Lead-cooled Fast Reactor technology. For this reactor concept, because of the large thermal inertia that characterizes the system, the adoption of the “reactor-follows-turbine” scheme (currently employed in the Pressurized Water Reactors) is not feasible. An alternative solution is proposed, i.e., the set-point for the thermal power produced in the core is kept constant at the nominal value (or slowly variable), and the set-point for the mechanical power available to the alternator is adjusted according to the load demands. In order to assess the performance of the developed control scheme, two case studies are simulated. In the first one, a frequency profile of the synchronous Continental European grid is provided. In the second simulation, the possibility of performing the islanding operational transient is evaluated. Such an operational transient needs the connected power plants to perform relevant power variations in few seconds in order to deal with the abrupt change in the grid powered configuration. The simulation outcomes show that the proposed control scheme allows achieving prompt mechanical power variations. As for the quantitative results, in both simulations the frequency value is maintained below the upper safety threshold (50.8 Hz). On the other hand, the control scheme complies with the technological constraints set for the safe operation of the primary circuit of the ALFRED reactor. In particular, the Balance of Plant pressure-induced feedbacks on the primary circuit dynamics are effectively dampened, i.e., the temperature in the cold leg is effectively maintained close to its set-point (i.e., 400 °C) and the plant is almost insensitive to the variations of the grid power demands. [ABSTRACT FROM AUTHOR]

Buildings space conditioning is a key sector with a high potential for cost effective energy and carbon savings, in which high efficient heat pumps can have a significant contribution. Besides consuming electricity increasingly produced by renewable energies, heat pumps can also have an important role to balance supply and demand, allowing the integration of intermittent renewable generation in smart grids. The aim of this paper is to demonstrate that ground source heat pumps are a very high efficiency technology for buildings space conditioning, and present a high potential for electric load management as a flexible load, when combined with the thermal storage capacity of the building. The very high efficiency of an advanced ground source heat pump system, which integrates state of art components in an optimal manner, was assessed considering the seasonal performance factors for one complete heating season and one complete cooling season, calculated based on the monitored data of an experimental site installed in a service building in Portugal. Innovative load management strategies to control the heat pump coupled with the thermal mass of the building were tested and its associated benefits, including integration for intermittent generation, were evaluated. The thermal response of the building was analyzed applying a model based on the lumped capacitance method, and it was validated with experimental data. A load shifting strategy by preheating the building and avoiding peak periods is proposed to allow the use of lower electricity rates leading to a reduction of electricity costs of 34%. Additionally preheating the buildings also contributes a larger integration of the renewable generation surplus (19–30% of the surplus generation). The implementation of Demand Response actions by switching off heating loads, during some periods of time, to compensate the variations and forecasting errors of wind power is also evaluated with positive impacts. [ABSTRACT FROM AUTHOR]

Solar direct steam generation is considered as a promising technology for steam production in thermal power generation due to high temperature levels that can be achieved compared to other technologies that use indirect steam generation. This paper demonstrates exergy and exergoeconomic analysis of commercial-size direct steam generation parabolic trough solar thermal power plant. For steam power cycles, reheating might be necessary to avoid great wetness of steam which shortens the lifetime of the turbines. Therefore, two configurations have been considered in this study; the non-reheating configuration as well as reheating by steam–steam heat exchanger. For each component, exergy and exergy-costing balance equations have been formulated based on a proper definition of fuel–product–loss. Exergy results show that particular attention should be paid to solar field, condenser, low pressure turbine and high pressure turbine (in a descendant order) as they constitute the major sources of exergy destruction. Results from exergoeconomic analysis, however, show that the condenser should be the fourth component in the order of importance after the solar field and low/high pressure turbines. Increasing the temperature at the inlet of the low pressure turbine by 100 K using steam–steam reheating is shown to result in 9.1% increase in the vapor fraction at the exit of turbine. This increase in steam quality, however, would be achieved by drop less than 1.5% in thermal and exergetic efficiencies, and about 2% increase in cost of electricity. Moreover, the effect of degree of reheating on exergetic exergoeconomic parameters has been investigated. The results revealed that there is a specific value of degree of reheating for which the exergetic efficiency would be on it’s lowest value. This point would be of importance during optimization procedure of reheating direct steam generation solar plants. [ABSTRACT FROM AUTHOR]

In this study, several Angström-type regression models, namely the linear, quadratic, cubic, logarithmic and exponential models, are compared to estimate the global solar radiation on horizontal surfaces over a territory. The country of Tunisia is used as a case study for the methodology. The models studied were calibrated using four meteorological stations that are providing global solar radiation and sunshine duration data. The statistical analysis showed that the models assessed are well suited to accurately estimate the solar potential. Overall, the cubic model showed the best regression fit and performed slightly better than the others. However, since the difference between the models studied is insignificant, the linear model has been preferred for the mapping of the solar potential of the study area, mostly because of its simplicity. Two approaches were assessed for the use of the Angström–Prescott parameters: the classical approach which consists of using generic parameters for the whole study area, and a spline interpolation of these parameters. Both methods gave very similar results with a slight improvement for the classical approach which has been employed to map the spatial and temporal distribution of the solar potential of the study area using spline interpolations at a 500 m × 500 m resolution. In application to the territory of the case study, the monthly mean daily global solar radiation in Tunisia varies between 6.9 MJ/m 2 /day in the north of the country during January and 28 MJ/m 2 /day in June, in the surroundings of the Gulf of Gabes. Annually, the monthly mean daily solar radiation ranges from 15.7 to 19.4 MJ/m 2 /day, increasing from north to south. [ABSTRACT FROM AUTHOR]

This work is focused on the analysis of the wave resource and its exploitation by means of a proposed 12 MW wave plant in Northwestern Spain. For this purpose, a total of four current technologies of wave conversion are analysed at three different sites located at different water depths, which correspond to one of the European areas with the greatest wave energy resource and where its electric production is still underdeveloped. To carry out the research, the wave data recorded at an offshore buoy near the area and the power matrices of the four selected wave energy technologies are used. The offshore wave conditions—representing 95% of the total energy of an average year—are propagated through spectral numerical modelling towards the coast. On the basis of the results, two of the four selected technologies forming the 12 MW power plants and one of the three considered points emerge as the ones allowing the greatest energy production and, at the same time, having a minimum area of occupation which, in turn, is crucial to reducing the visual impact. Finally, this research discusses the energy supply capacity of the proposed plants to satisfy the energy consumption required by nearby communities. [ABSTRACT FROM AUTHOR]

The increasing share of intermittent renewable electricity production leads to operational challenges in the electric power sector. Storage will be needed, among other options, to ensure an efficient and reliable operation of the electric power system. The power to gas (PtG) concept provides a possibility to store excess renewable electric power and as such it can increase the utilisation of RES-based electricity generation. The renewable methane, produced via PtG, can be stored in the gas system and used e.g. for electricity generation. The gas system has a much larger storage capacity compared to current electricity storage technologies. However, PtG introduces extra couplings between the gas, electricity and carbon ( CO 2 ) sector and it is not known what the effect of these new interactions could be. Therefore, an operational model has been developed that includes the gas, electricity and CO 2 sector to analyse the effects of PtG on these sectors and on the interactions between them. Based on a case study, it is found that PtG partially transfers capacity and flexibility problems, triggered by the introduction of intermittent RES-based electricity generation, from the electricity to the gas sector. Moreover, a downward pressure on the gas prices is observed. However, the effects of PtG are generally smaller than those of the large-scale introduction of intermittent renewable electricity generation. Also, complex inter-sector dependencies are introduced through the CO 2 that is required in the PtG process. If PtG is to be deployed at large scale, the study of these effects is relevant for policy makers, regulators, energy markets’ participants and system operators. [ABSTRACT FROM AUTHOR]

Low inertia stack, high penetration levels of renewable energy source and great ratio of power deviations in a small power delivery system put microgrid frequency at risk of instability. On the basis of the close coupling between the microgrid frequency and system security requirements, procurement of adequate ancillary services from cost-effective and environmental friendly resources is a great challenge requests an efficient energy management system. Motivated by this need, this paper presents a novel energy management system that is aimed to coordinately manage the demand response and distributed generation resources. The proposed approach is carried out by constructing a hierarchical frequency control structure in which the frequency dependent control functions of the microgrid components are modeled comprehensively. On the basis of the derived modeling, both the static and dynamic frequency securities of an islanded microgrid are provided in primary and secondary control levels. Besides, to cope with the low inertia stack of islanded microgrids, novel virtual inertia concept is devised based on the precise modeling of droop controlled distributed generation resources. The proposed approach is applied to typical test microgrid. Energy and hierarchical reserve resource are scheduled precisely using a scenario-based stochastic programming methodology. Moreover, analyzing the results verifies the impressiveness of the proposed energy management system in cost-effectively optimizing the microgrid ancillary service procurement. [ABSTRACT FROM AUTHOR]

Reliable and inexpensive electricity provision is one of the significant research objectives since decades. Various Economic Dispatch (ED) methods have been developed in order to address the challenge of continuous and sustainable electricity provision at optimized cost. Rapid escalation of fuel prices, depletion of fossil fuel reserves and environmental concerns have compelled us to incorporate the Renewable Energy (RE) resources in the energy mix. This paper presents Combined Emission Economic Dispatch (CEED) models developed for a system consisting of multiple Photo Voltaic (PV) plants and thermal units. Based on the nature of decision variables, our proposed model is essentially a Mixed Integer Optimization Problem (MIOP). Particle Swarm Optimization (PSO) is used to solve the optimization problem for a scenario involving six conventional and thirteen PV plants. Two test cases, Combined Static Emission Economic Dispatch (SCEED) and Combined Dynamic Emission Economic Dispatch (DCEED), have been considered. SCEED is performed for full solar radiation level as well as for reduced radiation level due to clouds effect. Simulation results have proved the effectiveness of the proposed model. [ABSTRACT FROM AUTHOR]

Highlights: [•] The energy system of whole of Japan is analyzed in this study. [•] An advanced model based on MARKAL is used for the energy system analysis. [•] The impact of charge patterns of EVs on electricity generation mix is evaluated. [•] Technology competitiveness of the next generation vehicles is also evaluated. [Copyright &y& Elsevier]

Highlights: [•] We investigate H2/O2 production from large hydraulic plant by water electrolysis. [•] We produce methanol and hydro-methane from H2/O2 obtained. [•] We investigate two different configurations of the plant. [•] We perform a thermo-economic analysis for three scenarios in Paraguay. [•] We find plants optimal size using a time-dependent thermo-economic approach. [Copyright &y& Elsevier]

Abstract: Renewable energy sources are presently being considered as alternatives to fossil fuels, because they are perpetual, environmentally friendly, and release negligible amounts of greenhouse gases to the atmosphere while producing energy. A disadvantage of renewable energy systems, however, is that continuous energy generation is not possible by using only one type of renewable energy system, since renewable energy resources depend on climate and weather conditions. Two or more renewable energy systems can be integrated into a hybrid system to overcome this problem so that when one resource is not available, the other can continue producing energy. Another disadvantage of renewable energy sources is that they are not available at every geographic location. Their use is mostly advantageous at remote locations that often are of high ecological value. Thus, identification of preferable locations for renewable energy systems is a decision-making problem that requires evaluation of the potential of the resource together with economic and environmental limitations. This paper introduces a methodology for site selection of hybrid wind solar–PV renewable energy systems. First, environmental acceptability and economic feasibility objectives are identified through a comprehensive review of the literature, current Turkish laws and legislations, and interviews with the General Directorate of Electrical Power Resources Survey and Development Administration of Turkey. Second, viable locations in terms of environmental acceptability and economic feasibility are determined through a fuzzy decision-making procedure that uses ordered weighted averaging algorithm for aggregating multiple objectives. Then, priority sites are identified separately for wind and solar energy systems by using Geographic Information System (GIS) and finally associated maps are overlaid to obtain the most feasible locations for hybrid wind solar–PV systems. [Copyright &y& Elsevier]

Abstract: This paper presents an approach for solving the generation scheduling problem of a complex system consisted of conventional and renewable energy sources (RES). Wind power plants are integrated into the system in order to minimize the total thermal unit fuel costs. The gained results for wind farm power production are used as input in the system to determine the optimal amounts of generated power for the thermal generating units and hydro generating units over the study period. The optimization problem consists of minimizing the total production costs, respecting power balance equations for each time interval and all operational system constraints. The proposed approach is applied on a specific system consisted of thermal power plants (TPPs), storage hydro power plants (HPPs), pumped-storage hydro power plant (PSHPP) and wind power plant (WPP). The benefits of energy production from WPP, in terms of reducing the production costs of conventional thermal power plants are also investigated. In the proposed paper two cases are analyzed. In the two analyzed cases power unit’s generation, thermal unit’s fuel costs and stream flows of hydro units are calculated over the study period. [Copyright &y& Elsevier]

Abstract: Wells turbines can represent important source of renewable energy for many countries. An essential disadvantage of Wells turbines is their low aerodynamic efficiency and consequently low power produced. In order to enhance the Wells turbine performance, the present research work proposes the use of a symmetrical duct in the form of a venturi tube with turbine rotor located at throat. The effects of duct area ratio and duct angle are investigated in order to optimize Wells turbine performance. The turbine performance is numerically investigated by solving the steady 3D incompressible Reynolds Averaged Navier–Stocks equation (RANS). A substantial improve of the turbine performance is achieved by optimizing the duct geometry. Increasing both the duct area ratio and duct angle increase the acceleration and deceleration upstream and downstream the rotor respectively. The accelerating flow with thinner boundary layer thickness upstream the rotor reduces the flow separation on the rotor suction side. The downstream diffuser reduces the interaction between tip leakage flow and blade suction side. Up to 14% increase in turbine power and 9% increase in turbine efficiency are achieved by optimizing the duct geometry. On other hand, a tangible delay of the turbine stall point is also detected. [Copyright &y& Elsevier]

Abstract: The present paper reports the results obtained on a carbon dioxide transcritical power cycle using an energy and exergy analysis. The procedure consisted of modifying the inlet pressure to the turbine from 66bar, by means of the software HYSYS®, maintaining constant each evaluated turbine inlet temperature (60, 90, 120 and 150°C) until the net work was approximately zero. As a result, an increase up to 25% for the exergy efficiency, and up to 300% for the energy efficiency are obtained when the inlet temperature to the turbine is risen from 60 to 150°C. Consequently, the analysis shows the viability of implementing this process as alternative energy, because of the possibility to recovery energy from waste heat from industrial processes. [Copyright &y& Elsevier]

In this study, a multistage interval-stochastic integer programming model is formulated for managing greenhouse gas (GHG) emissions and planning electric-power systems under uncertainty. The developed model can reflect dynamic, interactive, and uncertain characteristics of energy systems. Besides, the model can be used for answering questions related to types, times, demands and mitigations of energy systems planning practices, with the objective of minimizing system cost over a long-time planning horizon. The solutions can help generate electricity-generation schemes and capacity-expansion plans under different GHG-mitigation options and electricity-demand levels. Tradeoffs among system cost, energy security, and emission management can also be tackled. A high system cost will increase renewable energy supply and reduce GHG emission, while a desire for a low cost will run into risks of a high energy deficiency and a high GHG emission. [Copyright &y& Elsevier]

Abstract: In this paper, an ammonia–water based Rankine cycle is thermodynamically analyzed for renewable-based power production, e.g. solar, geothermal, biomass, oceanic-thermal, and nuclear as well as industrial waste heat. Due to the nature of the ammonia–water mixture, changes in its concentration allow thermodynamic cycles to adapt to fluctuations in renewable energy sources, which is an important advantage with respect to other working fluids. The non-linearity of the working fluid’s behaviour imposes that each cycle must be optimized based upon several parameters. A model has been developed to optimize the thermodynamic cycle for maximum power output and carry out a parametric study. The lowest temperature state of the system is fixed, and three other parameters are variables of study, namely, maximum system temperature, ammonia concentration and energy ratio, which is a newly introduced parameter. Energy ratio indicates the relative position of the expansion state and is defined in terms of enthalpies. The study is conducted over a concentration range of 0–0.5, the maximum temperature studied varies between 75°C and 350°C for extreme cases, and the energy ratio from saturated liquid to superheated vapour. As a result, the optimal expansion energy ratio is predicted. The cycle efficiencies are drastically affected by the concentrations and temperatures. Depending on the source temperature, the cycle energy efficiency varies between 5% and 35% representing up to 65% of the Carnot limit. The optimal energy ratio has been determined for several concentrations and reported graphically. [ABSTRACT FROM AUTHOR]

Abstract: Growing of PV for electricity generation is one of the highest in the field of the renewable energies and this tendency is expected to continue in the next years. Due to the various seasonal, hourly and daily changes in climate, it is relatively difficult to find a suitable analytic model for predicting the performance of a grid-connected photovoltaic (GCPV) plant. In this paper, an artificial neural network is used for modelling and predicting the power produced by a 20kWp GCPV plant installed on the roof top of the municipality of Trieste (latitude 45°40′N, longitude 13°46′E), Italy. An experimental database of climate (irradiance and air temperature) and electrical (power delivered to the grid) data from January 29th to May 25th 2009 has been used. Two ANN models have been developed and implemented on experimental climate and electrical data. The first one is a multivariate model based on the solar irradiance and the air temperature, while the second one is an univariate model which uses as input parameter only the solar irradiance. A database of 3437 patterns has been divided into two sets: the first (2989 patterns) is used for training the different ANN models, while the second (459 patterns) is used for testing and validating the proposed ANN models. Prediction performance measures such as correlation coefficient (r) and mean bias error (MBE) are presented. The results show that good effectiveness is obtained between the measured and predicted power produced by the 20kWp GCPV plant. In fact, the found correlation coefficient is in the range 98–99%, while the mean bias error varies between 3.1% and 5.4%. [ABSTRACT FROM AUTHOR]