Solar Sail pin wheel generator

I have gotten into an argument with someone, who came up with the idea
of setting up a Solar Sail as a windmill with rotating about a generator.
His thought process going along the lines of the sunlight provides a
constant acceleration so the sail will just keep rotating faster and
faster and generate electricity in greater amounts.

To me it seems intuitive that it would not work, at least not in the way
he is thinking of, but I am not sure how to go about showing that, or
showing that I am wrong.

So does anyone have any ideas about how to work out if it is feasible or
not ?

(I have mentioned parabolic dish mirrors to him.)

Thanks
Brett