The increasing global demand for electricity has accelerated the integration of renewable energy sources, including solar photovoltaic (PV) systems, wind energy conversion systems (WECS), and battery energy storage systems (BESS), into modern power networks. Although these resources improve sustainability and reduce dependence on fossil fuels, their intermittent and variable nature introduces significant challenges related to system reliability, power quality, operational costs, and energy management, particularly in standalone and off-grid applications. This study presents a comprehensive review and analysis of both standalone and grid-connected renewable energy systems employed in distributed generation. Special emphasis is placed on evaluating the impact of renewable energy variability on system performance and reliability. Furthermore, the study investigates the role of green hydrogen technologies, including electrolyzes and fuel cells, as long-term energy storage solutions in hybrid renewable energy systems. The findings indicate that integrating green hydrogen with solar and wind resources can significantly enhance energy reliability, improve system flexibility, and ensure a continuous power supply in off-grid environments. The study highlights hybrid green hydrogen-based renewable energy systems as a promising pathway toward sustainable, reliable, and resilient future energy infrastructures.
This study provides a comprehensive long-term energy performance evaluation comparing traditional solar space heating systems (water and air collectors) with emerging alternatives, namely photovoltaic (PV)-driven heat pumps and photothermal solar heat extractors. The comparison is performed per unit collection area under idealized heat use and storage assumptions, rather than as a full building-level heating system analysis. Utilizing hourly meteorological and radiometric data from Rock Springs, US (2001–2022), the results reveal that while solar water heat extractors are more efficient than traditional heaters, their heating gain factor remains below 1.2, whereas emerging solar air heat extractors demonstrate low future potential. Over annual cycles, crystalline silicon PV-driven heat pumps outperform traditional solar water heating due to their superior efficiency under the low-to-moderate solar irradiance levels that dominate the heating season, despite traditional systems performing better at peak heat fluxes. Ultimately, this underscores that long-term technology dominance is strictly non-linear and governed by local radiative climates. Complementing the technical study, a preliminary economic screening is performed based strictly on component capital costs, without factoring in long-term operational dynamics such as maintenance, degradation, or discounting. Within this simplified financial framework, the analysis indicates that crystalline silicon or CdTe PV-driven heat pumps can viably replace solar water collectors (unless domestic hot water is a primary requirement) or expensive closed-circuit air collectors. Conversely, solar heat extractors remain viable only in niche applications with exceptionally high thermal energy costs exceeding 0.25 USD/kWh. By establishing these boundary thresholds, this work provides a streamlined decision-making framework that identifies the economic domains in which emerging PV-heat pump configurations achieve market viability relative to traditional thermal systems.
This study applies an integrated water–energy–food (WEF) nexus approach to melon and grape value chains, combining life cycle assessment, water footprinting (blue/green/grey), carbon footprint, and exergy analysis within a circular economy framework. Türkiye, the fourth-largest melon producer (~1.7 Mt/yr) with over 80 indigenous grape cultivars, serves as the primary case study, supplemented by global data. In the wine chain, cultivation (37%) and glass packaging (28%) dominate global warming potential (GWP), with a baseline of 1.38 kg CO2eq per 0.75 L bottle (ReCiPe 2016-H). Recovering pomace bioethanol, polyphenolic extracts, grape seed oil, and tartaric acid in a circular economy scenario lowers the footprint to 1.12 kg CO2eq (−19%). Turkish wine grapes exhibit blue-water shares of 38–41%, well above the global 25%, reflecting irrigation reliance in semi-arid Anatolia (Elazığ, Diyarbakır, Cappadocia). Exergy analysis identifies refrigeration as the top energy sink (280 MJ/t grapes, 32%) and primary exergy destruction site (193 MJ/t; second-law efficiency: 31%). Fermentation records the lowest exergy efficiency (28%) due to the irreversibility of sugar-to-ethanol conversion. These findings demonstrate that combining WEF nexus management with circular bioeconomy strategies can substantially reduce the overall environmental burden, particularly in water-stressed agricultural regions.
