Wouldn't magnifying or focusing (same thing) mean it would need to be gyro stabilized? Now we are talking serious money
. The beauty of solar
cells is that they still work even when they are not directly pointed at the sun.
The average energy the Earth gets from the sun is 164 Watts per square meter
over a 24 hour day. More so at the Equator and less so at the poles and of course, nothing at night. 164 watts/ 746 watts per horsepower is 0.21 horsepower per square meter. So if you want to develop one horsepower we are going to need about 5 square meters of surface area....and that's assuming the conversion of the suns heat energy to stored battery
energy is 100% efficient....which it is not even close to that.
Perhaps somehow 5 square meters of an energy collecting device could be applied to the sail somehow? Most small boats are not going to have the deckspace.
I could though imagine a large barge like catamaran
with nothing but solar cells on deck
that putts along on its own power at a knot
or two. But then who would want to ride on that when the wind
is much more capable of propelling a boat?