Well that all depends on what type of vampires we're talking about here. Are we talking Marvel-style, where any sort of UV radiation will hurt them, or are we talking WoD-style, where it's a mystical quality of the sun that inflicts damage on them. Now, if it's the first one, he should be able to simply defend his mutant garlic farm with a series of UV lights placed at overlapping intervals. If it's the second one, I'd recommend he find a local Etherite or Virtual Adept cabal to set up some equivalent device, only instead of UV lights, you'd have to use a Correspondence effect (probably disciple level at least, more likely adept) to co-locate the sun's rays to the tower, so as to ward off vampires again.

Of course, with the increased radiation from the wi-fi tower AND the solar rays, this will probably cause the garlic to rapidly evolve into some advanced life form heretofore unseen.

I, for one, welcome our new mutant garlic overlords.

What about my dreams of superhero-dom, you insensitive clods!?