Rafal Damian Figaj

The energy transition of the building sector requires the implementation of high-efficiency solutions that increase the share of renewable energy sources while addressing environmental, technical, and economic constraints. Among available technologies, solar air collectors represent a simple and robust option for direct thermal energy generation. This study experimentally evaluates the performance of a prototype solar air collector under laboratory and field conditions and compares its thermal energy yield with the electrical output of photovoltaic panels. Under laboratory conditions, the tested solar air collector achieved a maximum thermal power of 1305 W and an air temperature increase exceeding 40 K. Field measurements conducted under near-standard test conditions demonstrated an average thermal efficiency above 60%. Winter analyses confirmed that, despite lower solar irradiance, the system maintained relatively high efficiency, although the total energy yield strongly depended on atmospheric stability. Comparative results showed that, for an equivalent installation area, the solar air collector generated more usable thermal energy than photovoltaic panels under favorable solar conditions. On the other hand, the limited flexibility of direct thermal energy storage reduces the operational versatility of solar air collectors. These findings confirm the technical feasibility of integrating solar air collectors with photovoltaic systems in hybrid renewable installations. Such combined configurations can improve building energy performance and support decarbonization strategies within sustainable development frameworks.

The power-to-X strategy for passenger car applications offers a viable solution for using the surplus electrical power from renewable energy sources instead of exporting it to the grid. The innovative system proposed in this study allocates surplus electrical power from a building-integrated biomass-based Combined Cooling Heating and Power (CCHP) system to on-site applications and evaluates the energetic and economic benefits. The system comprises two key components: a 50 kW electric vehicle (EV) charging station for EVs and a 50 kW alkaline electrolyzer system for on-site hydrogen production, which is later dispensed to fuel cell electric vehicles (FCEVs). The primary goal is to decrease the surplus of electricity exports while simultaneously encouraging sustainable transportation. The system’s economic viability is assessed through two scenarios of fuel (e.g., biomass) supply costs (e.g., with and without fuel market costs) and compared to the conventional approach of exporting the excess power. The key findings of this work include a substantial reduction in surplus electricity exports, with only 3.7% allocated for EV charging and 31.5% for hydrogen production. The simple payback period (SPB) is notably reduced, enhancing economic viability. Sensitivity analysis identifies the optimal hydrogen system, featuring a 120 kW electrolyzer and a 37 kg daily hydrogen demand. The results underscore the importance of prioritizing self-consumed energy over exports to the national grid, thereby supporting integrated renewable energy solutions that enhance local energy utilization and promote sustainable transportation initiatives.

The present study investigates the energy efficiency of different container house configurations across thirty European locations. By employing Heating Degree Days (HDDs) and Cooling Degree Days (CDDs), the research delves into climatic zone exploration, providing a simplified climatic classification for residential purposes and comparing it with the Köppen–Geiger model. The authors use specific hourly climatic data for each location, obtained through dynamic simulations with TRNSYS v.18 software. Initially, the CDDs are calculated by using different base temperatures (comfort temperatures that minimize energy demand) tailored to the specific conditions of each case. Then, the thermal loads of container houses are evaluated in different climatic scenarios, establishing a direct correlation between climatic conditions and the energy needs of these innovative and modular housing solutions. By comparing stacked and adjacent modular configurations in container housing, particularly in post-disaster scenarios, the study underscores the importance of adaptive design to optimize energy efficiency. The analysis conducted by the authors has allowed them to propose a climate characterization model based on HDDs, CDDs, and solar irradiance, obtaining an effective novel correlation with the Köppen–Geiger classification, especially in extreme climates. The present model emerges as a powerful tool for climate characterization in residential applications, offering a new perspective for urban planning and housing design. Furthermore, the results reveal a significant correlation between climate classification and the specific energy needs of container houses, emphasizing the direct influence of regional climatic characteristics on energy efficiency, particularly in small-sized dwellings such as container houses.

Reduction or elimination of reliance on traditional fossil fuels and of the emission of greenhouse gases and pollutants into the environment are affecting energy technologies, systems, and applications. In this context, one potential approach to achieving sustainability, decarbonization, and ensuring the energy and economic viability of existing and future energy systems involves adopting one or more renewable sources. The presented paper concentrates on examining the performance of a small-scale hybrid renewable polygeneration system. This system utilizes biogas produced through anaerobic digestion, which is then supplied to an internal combustion engine, along with solar energy converted into electrical energy by photovoltaic modules and wind energy harnessed through a wind turbine. A small-scale user, represented by residential buildings and a zootechnical farm with heating, cooling, and electrical energy demands, serves as the case study. TRNSYS software is employed to design and model the system, considering realistic assumptions about technical aspects and user energy requirements. The investigation involves analyzing the system’s operation, considering both energy and economic perspectives. The paper discusses the pros and cons of combining biogas, solar, and wind energy in the proposed hybrid system under the considered case study. Despite non-satisfactory economic profitability without incentives, the proposed system allows one to save significant amounts of primary energy and carbon dioxide equivalent emissions.

The energy sector is nowadays facing new challenges, mainly in the form of a massive shifting towards renewable energy sources as an alternative to fossil fuels and a diffusion of the distributed generation paradigm, which involves the application of small-scale energy generation systems. In this scenario, systems adopting one or more renewable energy sources and capable of producing several forms of energy along with some useful substances, such as fresh water and hydrogen, are a particularly interesting solution. A hybrid polygeneration system based on renewable energy sources can overcome operation problems regarding energy systems where only one energy source is used (solar, wind, biomass) and allows one to use an all-in-one integrated systems in order to match the different loads of a utility. From the point of view of scientific literature, medium- and large-scale systems are the most investigated; nevertheless, more and more attention has also started to be given to small-scale layouts and applications. The growing diffusion of distributed generation applications along with the interest in multipurpose energy systems based on renewables and capable of matching different energy demands create the necessity of developing an overview on the topic of small-scale hybrid and polygeneration systems. Therefore, this paper provides a comprehensive review of the technology, operation, performance, and economical aspects of hybrid and polygeneration renewable energy systems in small-scale applications. In particular, the review presents the technologies used for energy generation from renewables and the ones that may be adopted for energy storage. A significant focus is also given to the adoption of renewable energy sources in hybrid and polygeneration systems, designs/modeling approaches and tools, and main methodologies of assessment. The review shows that investigations on the proposed topic have significant potential for expansion from the point of view of system configuration, hybridization, and applications.

Island energy systems are becoming an important part of energy transformation due to the growing needs for the penetration of renewable energy. Among the possible systems, a combination of different energy generation technologies is a viable option for local users, as long as energy storage is implemented. The presented paper describes an energy-economic assessment of an island system with a photovoltaic field, small wind turbine, wood chip gasifier, battery, and hydrogen circuit with electrolyzer and fuel cell. The system is designed to satisfy the electrical energy demand of a tourist facility in two European localizations. The operation of the system is developed and dynamically simulated in the Transient System Simulation (TRNSYS) environment, taking into account realistic user demand. The results show that in Gdansk, Poland, it is possible to satisfy 99% of user demand with renewable energy sources with excess energy equal to 31%, while in Agkistro, Greece, a similar result is possible with 43% of excess energy. Despite the high initial costs, it is possible to obtain Simple Pay Back periods of 12.5 and 22.5 years for Gdansk and Agkistro, respectively. This result points out that under a high share of renewables in the energy demand of the user, the profitability of the system is highly affected by the local cost of energy vectors. The achieved results show that the system is robust in providing energy to the users and that future development may lead to an operation based fully on renewables.

The energy sector, along with the conditions of the natural and built environment, are significantly affected by the tremendous increase in total energy consumption

The availability of freshwater and energy is a serious issue in remote and islanded areas, especially at a small scale, where there may not be the possibility to access the grid and/or water distribution systems. In this context, polygeneration systems operating on the basis of local, renewable energy sources can be an answer to the users’ demand for electricity, heating, cooling, and domestic hot water. The scope of the proposed paper was to investigate, numerically, the energy and economic feasibility of a novel hybrid polygeneration system powered by biomass, solar, and wind energy for a micro-district of households. The proposed system consists of a biomass-fueled steam cycle, wind turbine, photovoltaic field coupled with thermal and electrical energy storage, adsorption chiller, and a reverse osmosis water desalination unit. The system is also assisted by an LPG generator set running as backup. The system provides space heating and cooling, electrical energy, and fresh and domestic hot water to 10 households located on Pantelleria Island, Italy. The proposed system is modelled and simulated through TRNSYS software with realistic user demand. The energy and economic performance of the proposed system are assessed with respect to a reference system in different scenarios, taking into account islanded operation, connection to the grid, and biomass tariffs. The results show that the proposed system achieves an excellent primary energy saving performance in all the investigated scenarios, with savings of more than 94% for all the investigated scenarios. Excluding any kind of funding, in case of new investment for the system, the simple payback oscillates between 7 and 12 years, showing that the developed alternative is fairly valid with respect to traditional solutions.

Among all the energy production technologies based on renewables, the photovoltaic panels are the ones with the highest rate of development and applications worldwide. In this context, significant efforts are put into research on innovative materials in order to improve the performance of photovoltaic cells. Nevertheless, possibilities available to enhance the energy yield of existing technologies also exist and are explored, such as the cooling of photovoltaic modules. This approach can decrease the mean operation temperature of photovoltaic cells, leading to an increase in efficiency and energy produced. In the present paper, this method is investigated by developing and testing a dedicated water cooling system for photovoltaic panels. In order to investigate the performance of the cooling system, two market-available monocrystalline photovoltaic panels with a power of 50 and 310 Wp were tested under laboratory and real operation conditions, respectively. Based on the results obtained under laboratory conditions, the most promising variant of the cooling system was selected and assessed under real operation conditions. For this system, the maximum temperature of the water-cooled 310 Wp panel was lower by approx. 24 K compared to an uncooled panel, as pointed out by a measurement performed during a typical sunny day when solar irradiation was approximately 850 W/m². This improvement of the cell temperature led to a 10% increase in power generated by the water-cooled photovoltaic panel compared to the uncooled one. The economic analysis revealed that the estimated simply payback time for installing the cooling system in typical domestic photovoltaic installations can be less than 10 years, while from the point of view of net present value, the introduction of the water cooling system can be a profitable option for a 10-year period when a discount rate of 5% is considered.