In this study, the possibility of sector coupling with biological Power-to-Methane to support and stabilize the energy transition of the three major sectors of electricity, heat, and gas was addressed. For this purpose, the energy cell simulation methodology and the Calliope tool were utilized for energy system optimization. This combination provides detailed insights into the existing dependencies of consumers and fossil and renewable energy suppliers on a local scale. In this context, Power-to-Methane represents an efficient technology for quickly and effectively exploiting unused electricity potential for various sectors and consumers. It was found that, even in regions with low wind levels, this surplus electricity potential already exists and depends on various influencing factors in very different ways. The solar influence on these potentials was considered in connection with gas-fired cogeneration plants for district heating. It was found that the current heat demand for district heating produces a large amount of electricity and can generate surplus electricity in the winter. However, in the summer, large amounts of usable waste heat are dissipated into the environment, owing to the low consumption of district heat. This problem in the heat sector could be reduced by the expansion of photovoltaics, but this would require further expansion of storage or conversion systems in the electricity sector. This demonstrates that the consideration of several sectors is necessary to reflect the complexity of the sector coupling with Power-to-Methane properly.