Certain embodiments herein relate to a method of electroplating copper into damascene features using a low copper concentration electrolyte having less than about 10 g/L copper ions and about 2-15 g/L acid. Using the low copper electrolyte produces a relatively high overpotential on the plating substrate surface, allowing for a slow plating process with few fill defects. The low copper electrolyte may have a relatively high cloud point.