If you have a fixed run and not a tractor, you can semi freeze proof your waterpan. Take post hole digger and dig as deep a hole as you can to get below the frost level. Put a capped plastic 6in pvc pipe into hole with uncapped end up. Fill pipe with crushed stone or clean gravel and then fill with water. Place watering pan on top of buried pipe. The temperature of the water in the pipe should stay a constant 52-57 degrees year round. The heat will rise from this pipe and warm your watering pan, keeping it above 32 degrees. Some ice crusting can occur, but is easily pecked thru by the birds. This will work just about everywhere, some areas you just have to go deeper with your pipe than in other areas. I suggest a hole at least 4ft deep.
If you want to go solar, get a solar powered, low voltage water pump and solar panel big enought to run the pump. You dont need a lot of flow, just enough to keep the water moving. Dig a hole below the frost line, and bury some pec tubing filled with RV antifreeze. Run the pec tubing into and out of your waterbowl or trough. Hook each end of the pec tubing to your solar powered water pump. You want a close loop system. Use a marine battery as backup power. The battery will run the pump all nite as long as you dont use a high amperage type 12v pump and the solar panel will recharge the battery during the day. All you want to do is keep the water flowing thru the pec tubing, even a half gallon a minute pump will be more than enough to do this. This setup is a lot more expensive than the buried pipe and will probably cost you $400 to build.
If you are real handy with tools. Edmunds Scientific has individual solar cells you can buy and put together yourself for about $3 each. You can build as big a solar panel as you want a lot cheaper than you can buy ready made solar panels. A 18v, 3 amp, 54w solar panel will cost you about $125 in materials, but you have to be willing to solder each individual cell together and build a glass covered frame to put them in. Compare that to similar sized solar panels you buy at Lowes, or Northerntool or
Tractor Supply, or anywhere else for that matter, and I think you can see the cost savings for a DIY project.