You're right, panels are generally ganged together in battery to avoid the 'thick copper cable' problem.

However, the individual panel assemblies do run at lower voltages (individual cells run at the band gap of the semiconductor, 1 or 2 V).

It should be noted that placing the panels in series has a significant effect on panel performance when some of the panels are shaded (The entire string outputs at the rate of the shaded panel), so it would be much better to place panels in parallel when possible.