From the cell to the panel
From the Photovoltaic Effect to Photoelectric Solar Cells

The short-circuit voltage of a pn junction is on the order of the bandgap divided by the electron charge, or on the order of one volt. The maximum power output from a 1 cm ² cell with a 20% efficiency under standard conditions is approximately 5 mW. Thus, the current delivered by such a cell is on the order of a few milliamps. A 10 × 10 cm ² Si cell thus delivers approximately 1.5 W under standard test conditions.