@article{RoueguiBellabairElAslietal.2025, author = {Rouegui, Meryem and Bellabair, Hind and El Asli, Abdelghani and Amar, Amine and Z{\"o}rner, Wilfried and Rachidi, Fouad and Lghoul, Rachid}, title = {Bio-Methanization of Sheep Manure and Beet Waste in the Meknes-F{\`e}s Region, Morocco: Effects of Pretreatment and Machine Learning Applications for Biochemical Methane Potential Prediction}, volume = {10}, pages = {213}, journal = {Recycling}, number = {6}, publisher = {MDPI}, address = {Basel}, issn = {2313-4321}, doi = {https://doi.org/10.3390/recycling10060213}, year = {2025}, abstract = {Sheep manure and beet waste (the uneatable leaf part of the beet) are promising feedstock for biogas production due to their abundance and organic richness. However, their high lignocellulosic content reduces anaerobic digestibility and controls methane yield. This study investigates the effect of various pretreatment strategies, namely physical, thermal, and combined physical-thermal methods, on the Biochemical Methane Potential (BMP) of sheep manure and beet waste. Batch anaerobic digestion experiments were conducted under mesophilic conditions, with BMP values recorded for each treatment. The highest BMP for sheep manure, 125 Nml CH4/g VS, was achieved using combined physical and thermal pretreatment. This approach enhanced methane production by 16\%, 25\%, and 60\% compared to physical pretreatment (PP) alone, thermal pretreatment (TP) alone, and no pretreatment, respectively, while the one BMP for beet waste is 80 Nml CH4/g VS and obtained with thermal pretreatment. To predict BMP outcomes, three machine learning approaches are applied, namely Linear Regression (LM), Random Forest Regression (RFR), and Gradient Boosting Machine (GBM), using digestion time (N days), total solids (Ts), volatile solids (Vs), pretreatment type, and biomass type. The variance analysis confirmed that the interaction between pretreatment and biomass type significantly improved model performance. While diagnostic checks revealed non-linear patterns limiting the linear model, ensemble methods achieved stronger results. The RFR model explained 79.5\% of the variance with a Root Mean Square Error (RMSE) of about 15.7, whereas the GBM model achieved the lowest RMSE of 5.05. GBM captures complex non-linear interactions. In addition, variable importance analyses identified digestion time, solid content, and pretreatment as the most influential factors for methane yield, with the combined chemical and physical pretreatment producing the highest biogas outputs. These findings underscore the potential of advanced machine learning models, particularly GBM (Gradient Boosting Machine), for optimizing anaerobic digestion strategies and maximizing biogas recovery from sheep manure and beet waste.}, language = {en} } @article{MehtaJainZoerner2025, author = {Mehta, Kedar and Jain, Rushabh Bansilal and Z{\"o}rner, Wilfried}, title = {Agrivoltaics Around the World: Potential, Technology, Crops and Policies to Address the Energy-Agriculture Nexus for Sustainable and Climate-Resilient Land Use}, volume = {18}, pages = {6417}, journal = {Energies}, number = {24}, publisher = {MDPI}, address = {Basel}, issn = {1996-1073}, doi = {https://doi.org/10.3390/en18246417}, year = {2025}, abstract = {The urgent pursuit of climate-resilient agriculture and clean energy systems, central to the Energy-Agriculture Nexus and the UN Sustainable Development Goals, has accelerated global interest in agrivoltaic (Agri-PV) technologies. This paper presents a global systematic review and meta-analysis of 160 peer-reviewed studies, structured through a five-stage thematic synthesis: (1) mapping global and regional Agri-PV deployment and potential, (2) analyzing system design and modeling methodologies, (3) evaluating crop suitability under partial shading, (4) reviewing enabling policies and regulatory frameworks, and (5) assessing techno-economic feasibility and investment barriers. Results reveal that Europe and Asia lead Agri-PV development, driven by incentive-based policies and national tenders, while limited regulatory clarity and high capital costs constrain wider adoption. Despite technological progress, no integrated model fully captures the coupled energy, water, and crop dynamics essential for holistic assessment. Strengthening economic valuation, policy coherence, and standardized modeling approaches will be critical to scale Agri-PV systems as a cornerstone of sustainable and climate-resilient land use.}, language = {en} } @article{MehtaLwakatareZoerneretal.2025, author = {Mehta, Kedar and Lwakatare, Bertha and Z{\"o}rner, Wilfried and Ehrenwirth, Mathias}, title = {Mini-grid performance in Sub-Saharan Africa: case studies from Tsumkwe and Gam, Namibia}, volume = {12}, pages = {30}, journal = {Sustainable Energy Research}, number = {1}, publisher = {SpringerOpen}, address = {Singapore}, issn = {2731-9237}, doi = {https://doi.org/10.1186/s40807-025-00174-y}, year = {2025}, abstract = {This paper investigates the performance analysis and operational challenges of mini-grids in Sub-Saharan Africa, focusing on the Tsumkwe and Gam mini-grids, the only officially recognized mini-grids in Namibia. The study addresses a critical gap in understanding mini-grid efficiency, technical difficulties, and future potential. The key research questions focus on assessing mini-grid performance, identifying technical and operational challenges, quantifying the relationship between electricity demand and supply, and providing recommendations for enhancing rural electrification through mini-grids. These insights are crucial for evaluating the effectiveness of mini-grids in the African context and understanding their role in advancing rural electrification. By using a mixed-method approach, the research combines quantitative and qualitative data to offer a comprehensive analysis of these two mini-grid systems of Namibia. The data collected from 2017 to 2022 include metrics on energy supply, consumption, photovoltaic generation, community load, and meteorological conditions. Qualitative insights were gathered through field visits, surveys, and interviews with mini-grid operators, allowing for a thorough examination of community perspectives, operational issues, and technical performance. The findings reveal that the Tsumkwe mini-grid has seen a decline in efficiency due to maintenance problems and battery overheating, while the Gam mini-grid, initially oversized, now struggles with increased demand and new connections. This study provides the first detailed technical insights, identifies consumer archetypes, and evaluates the energy dynamics of mini-grids in Namibia. Recommendations include improved maintenance protocols, advanced battery management, and enhanced data monitoring. By analyzing Tsumkwe and Gam, this paper offers valuable lessons for mini-grid development in Sub-Saharan Africa, stressing the need for continuous evaluation and strategic improvements to achieve sustainable rural electrification.}, language = {en} } @article{MehtaEhrenwirthZoerneretal.2023, author = {Mehta, Kedar and Ehrenwirth, Mathias and Z{\"o}rner, Wilfried and Greenough, Richard}, title = {Need of energy transition at roof of the world}, volume = {2023}, pages = {101271}, journal = {Energy for Sustainable Development}, subtitle = {Correlative approach to interpret energy identity of high-altitude Central Asian communities}, number = {76}, publisher = {Elsevier}, address = {Amsterdam}, issn = {2352-4669}, doi = {https://doi.org/10.1016/j.esd.2023.101271}, year = {2023}, language = {en} } @article{NgetunyBaldaufZoerner2026, author = {Ngetuny, Joshua Kiplagat and Baldauf, Tobias and Z{\"o}rner, Wilfried}, title = {Evaluating Feedstock Pretreatment Methods to Unlock Co-Digestion in Small-Scale Biogas Systems: A Multi-Criteria Approach to System Integration and Decision Making}, volume = {19}, pages = {1303}, journal = {Energies}, number = {5}, publisher = {MDPI}, address = {Basel}, issn = {1996-1073}, doi = {https://doi.org/10.3390/en19051303}, year = {2026}, abstract = {Small-scale biogas plants in developing countries present a viable alternative to traditional polluting energy sources, particularly in rural and underserved communities. These systems typically rely on locally sourced livestock manure; however, inconsistent supply often results in underfeeding, reduced biogas production, and, in many cases, system abandonment. Co-digestion with crop residues presents a promising strategy to enhance feedstock availability and system resilience. However, the recalcitrant nature of lignocellulosic biomass and limited access to suitable pretreatment technologies have constrained its adoption. This paper evaluates feasible pretreatment methods for integrating crop residues, especially straw, into small-scale biogas systems. Using the Analytic Hierarchy Process (AHP), pretreatment methods are assessed based on five criteria: (i) technology simplicity, (ii) energy requirements, (iii) capital and operational costs, (iv) effectiveness, and (v) environmental impact. The analysis identifies microbial pretreatment using the liquid fraction of digestate, combined with mechanical size reduction, as the most suitable approach for small-scale implementation, utilizing low-cost, simplified mechanical devices adaptable to various crop residues with minimal energy input. A conceptual design of a demonstration plant is proposed to validate this integrated pretreatment approach and assess its impact on biogas yield, system performance, and technology adoption. The design incorporates an on-site digestate separation unit to supply microbial inoculum and emphasizes simplicity and cost-effectiveness in material handling and energy use. Pilot trials are proposed to evaluate key performance indicators, including specific methane yield (LCH4/gVS added), volatile solids reduction (\%), and methane content increase (\%), ensuring evidence-based adoption and practical applicability of the design.}, language = {en} } @article{NgetunyBaldaufZoerner2025, author = {Ngetuny, Joshua Kiplagat and Baldauf, Tobias and Z{\"o}rner, Wilfried}, title = {Optimizing Feedstock Selection for Sustainable Small-Scale Biogas Systems Using the Analytic Hierarchy Process}, volume = {18}, pages = {1739}, journal = {Energies}, number = {7}, publisher = {MDPI}, address = {Basel}, issn = {1996-1073}, doi = {https://doi.org/10.3390/en18071739}, year = {2025}, abstract = {Small-scale biogas systems can play a pivotal role in sustainable energy provision, particularly in developing countries. However, their dependence on livestock manure as the only feedstock poses challenges to their adoption and long-term viability. This often leads to insufficient biogas production and plant abandonment. This study proposes co-digestion of livestock manure with other farm residues to enhance the technical sustainability of small-scale biogas systems by ensuring adequate and consistent biogas production throughout the plant's lifespan, minimizing the risks associated with reliance on a single feedstock. A novel feedstock selection approach is developed using the Analytic Hierarchy Process (AHP), a multicriteria decision-making method, to prioritize feedstocks based on adequacy, supply consistency, and logistical ease. AHP is chosen due to its capability to handle both quantitative and qualitative evaluation criteria. This approach is applied to the F{\`e}s-Mekn{\`e}s region of Morocco, which offers abundant livestock and crop residues alongside product utilization pathways. The prioritization and ranking of the potential feedstocks identified in the region reveals cattle manure as the top-ranked feedstock due to its consistent supply and ease of collection, followed by straw, valued for its storability and nutrient stability. Sheep, horse, and chicken manure ranked third, fourth, and fifth, respectively, while household food waste and fruit and vegetable residues, limited by seasonality and perishability, were ranked lower. Based on these findings, co-digestion of cattle manure and straw is proposed as a sustainable strategy for small-scale biogas plants in F{\`e}s-Mekn{\`e}s, addressing feedstock shortages, enhancing biogas production, and reducing plant abandonment. This approach strengthens technical sustainability and promotes the broader adoption of biogas technologies in developing countries.}, language = {en} } @article{NgetunyHsaineMabroukietal.2025, author = {Ngetuny, Joshua Kiplagat and Hsaine, Jalal and Mabrouki, Abdelaalim and Rachidi, Fouad and El Asli, Abdelghani and Z{\"o}rner, Wilfried}, title = {Assessment of agricultural residues for small-scale biogas plants and adoption drivers: a case study of the F{\`e}s-Mekn{\`e}s region in Morocco}, volume = {15}, journal = {Biomass Conversion and Biorefinery}, number = {22}, publisher = {Springer}, address = {Berlin}, issn = {2190-6815}, doi = {https://doi.org/10.1007/s13399-024-06443-y}, pages = {29207 -- 29223}, year = {2025}, abstract = {Small-scale biogas systems hold promise as reliable renewable energy sources in developing nations; however, adequate and consistent supply of feedstock remains a challenge. Agricultural residue, due to their lack of competition with food crops for resources, is touted as a dependable feedstock choice. This article therefore examines agricultural residues as potential biogas plant feedstocks in the F{\`e}s-Mekn{\`e}s region of Morocco, using a structured farm survey to evaluate livestock types, crop varieties, and residue utilization. Additionally, the study explores the challenges and drivers influencing biogas technology adoption in Morocco. Findings indicate a predominance of small-scale farms with livestock (averaging 11 cattle, 45 sheep, and 20 chicken) and mainly subsistence crop production, making these farms suitable candidates for small-scale biogas plants. Key barriers to adoption include a lack of awareness about the technology, along with technical and financial constraints. However, raising awareness, establishing demonstration plants, and offering financial and non-financial incentives are identified as potential drivers of adoption. This research provides a foundation for implementing biogas technologies in the case study area and other developing nations, guiding researchers and governmental and non-governmental organizations in disseminating small-scale biogas systems as a reliable energy source and a method for converting agricultural residues into sustainable energy (biogas) and fertilizer. Graphical Abstract}, language = {en} }