Recent Advances in Sustainable Energy and Environmental Development

The energy sector, along with the conditions of the natural and built environment, are significantly affected by the tremendous increase in total energy consumption. This dramatic increase is caused by the improvement in the average quality of life and by the continuous increase in the global population. These factors significantly impact on the overall energy demand and the environment. Such harmful effects may be limited by enhancing the use of renewable energy sources. In this context, a sustainable use of energy and careful attention to the environment is crucial for the future development of human civilization and the stability of the Earth.

The aspects concerning energy efficiency, renewable energy utilization and emission reduction are the driving forces in the application of the concepts of sustainable energy, environmental development and new technological possibilities in the energy sector. Researchers, stakeholders, politicians and engineers involved in the analysis of sustainable energy systems are addressing crucial topics related to complex aspects of energy and the environment, such as technological [1], sociological [2] and economic ones [3], at different scales, from small systems [4] to the country level [5].

New knowledge concerning non-renewable and renewable energy sources and technologies, green energy and economy, environmental protection in energy, power generation technologies, alternative fuels and other energy- and environment-related areas of research is constantly provided by the intense research activity of researchers worldwide. Among the possible ways to share new knowledge, an important possibility to actively diffuse the outcomes of research works consists of the participation in conferences, where fruitful networking can take place. An example of this is the International Conference on Sustainable Energy and Environmental Development (SEED) held by the Institute of Sustainable Energy in Cracow, Poland. In particular, this Special Issue is dedicated to selected papers of the third edition of the SEED International Conference, which aims to cover a broad range of topics related to energy and environmental protection. The conference event allowed researchers to present recent research in the field of non-renewable and renewable energy sources and technologies, sustainable energy development, green energy and economy, environmental protection in energy managements systems, power-to-gas and power-to-liquid technologies, alternative fuels and other areas. In the frame of the Special Issue “Selected Papers from 3rd International Conference on the Sustainable Energy and Environmental Development (SEED 2019)”, several papers have been considered, and six papers have been published.

The topics of selected papers concerned the investigation of:

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A hybrid biomass–wind renewable energy system [6];

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The coupling of a gas turbine with an organic Rankine cycle [7];

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Operation flexibility in an energy investment project based on a gas-fired power plant [8];

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An interesting new exergy indicator developed to maximize the energy utilization in an organic Rankine cycle operating with a low-temperature heat source [9];

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The performance of two types of solar collectors assessed under real installation operation conditions [10];

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The optimal design of microgrid systems on the basis of the effects of capital and energy subsidies [11].

The analysis of the operation characteristics and economic energy performance of a small-scale trigeneration system for an application consisting of a household and a zootechnical farm was investigated by Figaj et al. [6]. Technologies such as a biomass-fueled water steam turbine, an absorption chiller and a wind turbine were implemented in the system connected to the electric grid with a bidirectional connection. In this study, the grid was used as virtual storage, allowing the recovery of up to 80% of the electrical energy produced in excess. The system was modeled and simulated by means of Transient System Simulation (TRNSYS) software. The results show that Simple Pay Back time of the proposed system can be below 6 years under some conditions, as free biomass, power of steam and wind lower than 4 kW, and a reference system with a natural gas boiler and electrical grid.

In [7], a low enthalpy geothermal source is coupled with a modified Organic Rankine Cycle (ORC), where a gas turbine is adopted to increase the parameters of the steam from a geothermal well. In particular, the system was modeled to investigate three working fluids (R245fa, R1233zd(E) and R600) on the system efficiency and other performance parameters. The obtained results show that the efficiency and power of the ORC plant significantly improves with the heat recovery from gas turbine exhaust which significantly enhances the geothermal subsystem performance. Moreover, R1233zd(E) working fluid achieves the highest efficiency of the modified ORC plant, with a range between 12.21% and 19.20% for the considered temperatures of the geothermal brine.

In another paper, a combined cycle with gas turbine was assessed from the point of view of operational flexibility of the energy investment [8]. The method used to carry out the research was the Monte Carlo simulation coupled with a real options approach and the net present value method. In the study, the operational flexibility was assumed in terms of a switching option to dynamically shut down and restart gas units. The outcomes of the paper showed that the net present value and the risk profiles of the considered technology are significantly affected by the value of the options. The net present value was USD −169.1 M, while the extended one was USD 102.5 M. In summary, the analysis revealed the need for operational flexibility to achieve a good profitability of combined cycles based on gas turbines.

Advances in the assessment of evaluation criteria of ORC plants were presented in the paper by Jankowski and Borsukiewicz [9]. Within the study, the maximization of the use of an energy source in an ORC system was assessed on the basis of a novel parameter, namely, the exergy utilization index (XUI). The criterion based on this index minimizes the difference between the heat carrier outlet temperature and the ambient one. The optimal operating conditions of an ORC are determined through simulation on the basis of the XUI and the total heat transfer area of the system. As regards the results, it was determined that optimal values of indicators as exergy efficiency, the waste exergy ratio, the environmental effect factor or the exergetic sustainability index are achieved for XUI higher than 80%, while for an XUI in the range of 60 and 80%, a relatively low Simple Pay Back can be achieved.

The comparison between two types of solar technologies (flat plate and evacuated tube) was performed by Olczak et al. [10]. Real measured data were used to analyze the performance of a 120-flat plate collector installation used to produce hot water in a swimming pool facility and a 32-evacuated tube collector system for the production of domestic hot water in a multi-family house. On the basis of the measured data, it was possible to confirm that the evacuated tube solar collectors achieved a significantly better solar energy productivity than flat plate units for the same absorber area. The efficiency was 33.7% for flat plate units while it was 67/3% for the evacuated tube collector.

In the last paper, the optimal configuration of microgrids operating in islanded mode is investigated as a function of different policy measures [11]. Capital and fuel subsidies are considered as factors impacting on the levelized cost of electricity of various systems in the model developed by the authors. In particular, the model was developed to minimize the total life cycle costs of microgrid projects. The result obtained show that the final design of microgrid systems for rural electrification is highly affected by capital subsidies and fuel price variations, and when capital subsidies for all considered distributed generation technologies are above 30%, the levelized cost of electricity drops below USD 0.2/kWh and makes the microgrids fairly feasible from the economic point of view.

The mentioned papers are only some important examples of the interesting topics presented in the context of the third edition of the SEED International Conference. Other areas of research and development were also presented in the frame of the event in the form of oral presentations and posters, such as fuels, energy and environment policies, hybrid energy systems, energy transfer/conversion devices, transport sustainability, environmental protection and others. The editors invite the readers of this Special Issue to attend the future editions of the SEED Conference series and to present cutting edge research results.