The Calvin cycle is the process in which glucose is synthesized from carbon dioxide that occurs during photosynthesis.
Glycolysis is the process in which glucose is broken down to produce energy. In absence of oxygen, pyruvate undergoes the process of fermentation. One type of fermentation is called alcohol fermentation and the final product of this process is ethanol.
In this process, pyruvate is decarboxylated to form acetaldehyde.
Then, the acetaldehyde is reduced to form ethanol. During this last reaction NADH is oxidated to NAD+ and the hydrogen atom is used to produce ethanol.