A novel fermentation process was developed in which renewable electricity is indirectly used as a fermentation substrate, synergistically decreasing both the consumption of sugar as a first generation carbon source and emission of the greenhouse gas CO2. To achieve this, a glucose-based process is co-fed with formic acid, which can be generated by capturing CO2 from fermentation offgas followed by electrochemical reduction with renewable electricity. This ‘closed carbon loop’ concept is demonstrated by a case study in which co-feeding formic acid is shown to significantly increase the yield of biomass on glucose of the industrially relevant yeast species Yarrowia lipolytica. First, the optimal feed ratio of formic acid to glucose is established using chemostat cultivations. Subsequently, guided by a dynamic fermentation process model, a fed-batch protocol is developed and demonstrated on laboratory scale. Finally, the developed fed-batch process is proven to be scalable to pilot scale. An extension of this proven concept to also recycle the O2 that is co-generated with the formic acid to the fermentation process for intensification purposes, and a potential further application of the concept to anaerobic fermentations are discussed.