Conversion of biomass into energy carriers or chemical building blocks generally is hydrogen-deficient. With green hydrogen produced from surplus renewable electricity via electrolysis, CO2 can be converted to supplementary biomethanol. The benefit of the proposed integration of biomass-to-liquid (BtL) and power-to-liquid (PtL) technologies comes from the reduced flexibility requirements and avoided heat losses for the methanol reactor compared to a stand-alone PtL plant and a much higher carbon ratio of original biomass converted into the desired product. During full-load operation of the electrolyzer, the methanol yield can be more than doubled. The typical size of such an installation will lie in the range of 100 MW electrical power, providing a relevant capacity of controlling power for the stabilization of the electrical transmission grid instead of supplying controlling power for the distribution grid of today's power-to-gas (PtG) demonstration plants.