I think that they will
work quite well as they are.
Several possibilities are
coming into my mind.
You might even make a darrieus of
them, because they are very
strong things. You could
put them skewed so that you
could take an advantage
of the twisted blades.
(Please see my recent post
of a VAWT idea.)
You might also cover
the blades partly
with for example
polyurethane and some
kind of plastic cloth
to make the airfoils
asymmetric.
You can also use
them as they
are with a VAWT.
As they are very strong
you might use them
as they are instead of
cutting them shorter.
Here the thumb rule
among the old guys with
big wind turbines is that
the rotor axle thickness
should be at least 1/100
the diameter of the wind rotor.
So for a 7,5 m diameter wind
rotor your rotor axle should be
at least 7,5 cm thick.
- Hannu