Where's the keel on a solar sail-powered ship? (Score 2, Insightful)

The Physorg article notes: "And like a marine sail, a solar sail could also bring you home. You could use the solar sail to tack your vessel, making it travel "against the wind," back to Earth." But, I thought that do sail across the wind you need something to provide "lift" to counter the lateral force of the sail, which is provided in boats by a keel, or centerboard, or daggerboard, or a fin and rail on a windsurfer, or a skeg, etc. etc. Where's the counterforce in a solar sail in space?