How do you protect solar panels from hail?
Smaller panels are one way to go; see this article Hail Damage and your Solar Panels:


  If you decide to install photovoltaic
  modules and worry about hail damage,
  there are a couple of things to
  consider. One of the most important
  concerns the size of the modules. If
  the region you live in is subject to
  frequent or serious hail storms,
  smaller modules are easier and less
  costly to replace. Also if a large
  module sustains damage, it will
  seriously reduce the power output, or
  even cause the system to fail
  completely. The drawback with using
  smaller modules is that they are often
  more expensive to install.


But of course there is not much that would withstand very large size hail but then your home insurance should cover the damage (just like the damage that would happen to your car and/or house during one of those hail storms).  I do not think it is very expensive to get your solar panels added onto your home insurance policy (if they are not covered already).  See this answer too: Do roof solar panels and hail mix?