From a Bee Keeper:
I have a bunch of experience with solar powered electric fences having been off the grid for seven years and using hot wire to contain my sheep, goats and cattle. The little self contained models that you can purchase at the local farm supply are not the best option IMO. My favorite approach, and I currently run four of these, is to mount a 2" pipe in the ground, mount a 10 or 20 watt solar panel at the top and mount a scrounged outdoor cabinet underneath it. In the cabinet I mount a solar charge controller, 12 volt deep cycle (marine) battery and 12 volt DC powered fence charger. This way you have several discreet components that can be replaced if the unit fails instead of replacing your whole fence charger. I use aluminum wire because it delivers a hotter shock than steel but since you're dealing with bear, steel would be your best bet.
For your fence, I recommend that you ground it very well with three ground rods driven in the soil 10 feet apart. They need a #6 wire between them and then to the ground terminal of your fencer. The ground is what actually delivers the shock to the animal. Think of the ground rods like antennas that send the shock to the offender. Then because you're dealing with bear I'd run pairs of wire, one hot and one tied to ground, so when the bear comes between them he gets the full brunt of your fence charger. You might want to run 3 or 4 pairs of wire. When the ground is dry, it conducts very poorly so this pair of wires will really help deliver a hot shock in the summer when bears are most active.
Buy the biggest fence charger you can afford. It will deliver a hotter shock. Even if you care only surrounding a small yard, get one that does several miles(50 or 100). Bear have thick fur that insulates them from a shock so you need the hottest fence you can get. Keep in mind that any animal can run through a hot wire fence and get through it. A hot wire fence is a psychological barrier. You want the animal to get a very hot shock to their nose the first time they experience it. then they'll avoid it. Once they figure out that they can get through it the gig is up. I once had a cow that didn't respect fence. She would put her nose under the bottom wire and scoot under the fence, taking the shocks when they came until she was through it. The only solution for her was a change of address.
When you stop learning you're dead.