There could be an issue between watts, and watt-hours. That would make me off by a factor of 24, assuming Wikipedia averages in time the sun is not shining. However, if you can also look at the rated hydrogen output of 240 liters per day. That’s about 2700 watt hours of energy per day per panel. That’s only 4 times as much.
Just did some real world research. https://www.gogreensolar.com/products/30000-watt-30kw-solar-panel-ground-mount-installation-kit?s=recomatic
30 kW system takes about 2000 sq feet and would cost just south of $100K installed with no batteries. It throws your numbers into question.
15 watts per square foot at 20% efficiency would mean 75 watts solar energy per sq foot reaching the ground. About 800 watts per sq meter.