Realizing urban energy systems with net-zero CO₂ emissions by 2050 is a major goal of global societies in building sustainable and livable cities. Developing cities hold a key to meeting this goal, as they will expand rapidly in the next decades with increasing energy demand, potentially associated with rising CO₂ emissions and air pollution if fossil fuels continue to be utilized. Therefore, identifying equitable, cost-effective, and deep decarbonization pathways for developing cities is essential. Here, we analyzed Bangkok City, Thailand, using the System Advisor Model (SAM) for techno-economic analysis to evaluate the decarbonization potential of rooftop photovoltaics (PV) integrated with electric vehicles (EVs) as batteries on a city scale. The analyses took into consideration hourly local weather conditions, electricity demand, electricity tariffs, feed-in-tariffs, degradation, declining costs of PV and EV, etc., specific to Bangkok. As the prices of PV and EVs decrease over the next several decades, the “PV + EV” system may provide a basis for new urban power infrastructure with high energy efficiency, low energy cost, and large CO₂ emission reduction. The results show that the “PV + EV” scenario in 2030 has the highest CO₂ emission reduction of 73% from electricity and vehicle usage, supplying 71% of the electricity demand of the city. The “PV + EV” system may reduce energy costs by 59% with estimated technology costs in 2030. Most of the energy generated from rooftop PV is consumed owing to large EV battery capacities, which can contribute to the rapid decarbonization of Bangkok City by 2050.

Molybdenum (Mo) is a critical industrial metal valued for its corrosion resistance and strength-enhancing properties. However, increasing demand necessitates more efficient and sustainable recovery methods. Bio-recovery of Mo by biosorption is a promising resolution, especially by the use of surface-engineered microbes that express metal binding proteins on its cell surface. This study investigates the potential of Saccharomyces cerevisiae strain ScBp6, which displays a molybdate-binding protein (ModE) on its cell surface, immobilized on porous materials. Our findings reveal that polyurethane sponges (PS) significantly outperform ceramic materials in yeast immobilization, entrapping 1.76 × 10⁷ cells per sponge compared to 1.70 × 10⁶ cells per ceramic cube. Furthermore, the yeast–PS complex demonstrated superior Mo adsorption, reaching 2.16 pg Mo per yeast cell under 10 ppm Mo conditions, comparable to free yeast cells (1.96 pg Mo per yeast cell). These results establish PS as an effective and scalable platform for Mo recovery, offering high biosorption efficiency, reusability, and potential for industrial wastewater treatment applications.

Ulaanbaatar, Mongolia, relies heavily on coal for winter heating, and continued urban expansion is expected to increase heating demand. This study investigated heating demand and rooftop PV potential in Ulaanbaatar from 2016 to 2025 using Google Earth Engine. Nighttime light intensity, heating degree days (HDD), and solar radiation datasets were integrated to evaluate changes in human activity, climate-driven heating demand, and rooftop solar resources. Electricity-equivalent heating demand, rooftop PV generation, coal displacement potential, and techno-economic performance under different policy scenarios were assessed. The results reveal a clear increase in urban built-up area during the study period, accompanied by rising nighttime light intensity, indicating growing urban activity. Despite relatively stable HDD, urban expansion implies increasing potential heating demands. Under the main rooftop PV deployment scenario, surplus electricity could theoretically offset approximately 10.9% of coal-based heating demand and reduce CO₂ emissions by 1.126 MtCO₂ yr⁻¹ through resistance heating. When the same surplus was converted through heat pumps with COP = 1.86, the theoretical coal-heating offset increased to 20.3%. However, economically viable large-scale deployment remained strongly dependent on feed-in tariff support. These findings indicate that continued urban expansion may lead to higher heating demand in Ulaanbaatar and highlight both the opportunities and structural limitations of rooftop PV for decarbonizing coal-dependent heating systems in cold-climate cities.