Renewable energy systems provide a resilient access pathway to affordable and sustainable energy for millions of people in regions with no or undeserved grid. In this work, a multi-objective Hybrid Optimization Model for Electric Renewables (HOMER) software has been applied to design and assess the techno-economic feasibility of Hybrid Renewable Energy Systems (HRESs) for Malawi’s off-grid communities. The study targeted the use of decentralized photovoltaic (PV), wind, diesel generator, and battery storage technologies to electrify three villages of Chigunda, Mdyaka, and Kadzuwa, which had estimated daily electrical energy peak demands of 14.53, 8.09, and 6.40 kW, respectively. Wind and solar resource data were used as inputs to generate multiple combinations of energy systems in HOMER. The sensitivity of the output systems was tested by varying the wind velocity and diesel pump prices. The optimization results showed that for Chigunda, the optimal configuration comprised PV-wind-battery, while for Mdyaka and Kadzuwa, the PV-battery combinations were ideal. In all the cases, the optimal systems were more sensitive to changes in wind velocity. The systems were, however, found to be infeasible economically as the costs of energy were higher than the per kilowatt-hour cost of US$ 0.120 for electricity in Malawi.

It is of strategic significance to extract germanium (Ge) in an ecological way for sustainable development. Adsorbents that already adsorb Ge have disadvantages such as poor selectivity and low adsorption capacity. In this study, a novel adsorbent material based on rice husk functionalized with tannic acid was developed for the efficient extraction of Ge from simulated coal fly ash leachate. The adsorption capacity of tannic acid-functionalized rice husk (TA-EPI-ORH) for Ge was 19.9 times higher than that of untreated rice husk, demonstrating significantly improved performance. The results showed that the adsorption process of Ge by TA-EPI-ORH is consistent with pseudo-second-order kinetic and Freundlich isotherm model. TA-EPI-ORH had excellent selective adsorption properties, with adsorption of 1.40 mg L⁻¹ Ge exceeding 95% and solid-liquid partition coefficients of 4380 mL g⁻¹, even in the presence of nine impurity metal ions (average concentration: 479.08 mg L⁻¹). When compared with the two main coexistence ions—aluminum (Al) and calcium (Ca)—both of which have the relatively highest concentrations (Al: 1594.20 mg L⁻¹, Ca: 1740.13 mg L⁻¹), the separation factors for Ge still maintain relatively high level with SF(Ge/Al) = 42.57 and SF(Ge/Ca) = 39.93. Compared to existing studies, TA-EPI-ORH exhibits superior selective adsorption performance even with the presence of more interfering ions. After elution of the adsorbed Ge from TA-EPI-ORH, the extraction rate of Ge with low initial concentration (1.40 mg L⁻¹) reached 85.17%, while the extraction rates of Al and Ca were only 1.02% and 1.18%, respectively. Further research revealed that the catechol groups on the surface of TA-EPI-ORH formed stable complexes with Ge, whereas the complexes with coexisting ions (e.g., Ca and Al) were unstable, thereby ensuring high selectivity for Ge. This green chemistry-based functionalization of rice husk not only enables high-value utilization of agricultural waste but also provides a sustainable and eco-friendly strategy for efficient Ge separation and recovery.