More than solar panels at that distance from the sun, hence the likes of Perseverance using one.
Earth has stronger sunlight but a thick wet soupy atmosphere that aborbs and scatters solar energy.
Mars has weaker sunlight (less than half as strong), but its atmosphere is near-vacuum, with hardly any absorbption/scatter.
Put those things together, and there's not much difference between a solar panel on Mars and a solar panel on Earth.
I expect the Watney character had the best panels available, surely a few kilowatts here?
The perseverence RTG only generated 110 watts when brand new. That's two headlamp bulbs.
The larger Voyager RTG managed about 400 watts.
He must have had a much larger RTG.