Solar-powered birdbath heater?

In preparation for winter here in Maine, I'm wondering about the feasibility of keeping a birdbath accessible for the birds that stick around. An Internet search for a solar-powered birdbath heater didn't yield anything useful. Has anyone ever found or created one?

Maybe search for solar powered live stock waterers?
If you are thinking of a photovoltaic heater,  I think it would be hard pressed to keep up, especially since most birdbaths are not insulated,
A solar powered fountain might keep the water from icing over.
Running the water from the fountain through a  solar thermal water heater could do the trick.

Thanks, William. I saw some strategies for heating livestock waterers, specifically one using an old tire stuffed with an insulating material. I might be able to adapt this to use a more shallow container.

William Bronson wrote:Maybe search for solar powered live stock waterers?
If you are thinking of a photovoltaic heater,  I think it would be hard pressed to keep up, especially since most birdbaths are not insulated,
A solar powered fountain might keep the water from icing over.
Running the water from the fountain through a  solar thermal water heater could do the trick.

The easiest way is to place a basin with heated water and replace it each time you notice any formation of ice. You can find one in hardware stores, bird feeder stores, or any electrical supply shops. Just make sure to install it properly and plug it in a fault circuit interrupter to deter electric shock.

If you have the financial resources, installing a winter birdbath in your backyard can be a good idea. These are winter birdbaths that are designed to be effective in cold weather because this equipment comes with built-in heaters usually located in the basin so that the water will always stay liquid even if the temperature is going down.

Have you tried passive solar approaches to your birdbath challenge? Bird enthusiasts can harness the sun’s power without buying solar panels and other store-bought technology fixes. Passive solar takes advantage of sun exposure when and where needed. During the cold months, for example, my solar powered bird bath is a shallow black 3’ diameter 6” deep repurposed rigid pond liner with a 6” deep pile of black basalt river stones in the center. The birdbath is nestled into a decomposing pile of warm straw and horse manure compost. The bath is tilted slightly southward toward the sun’s lower position on the horizon. The water pools at the south or low end of the pond. Because both rocks and edges are black, the passive solar system absorbs and stores the sun’s heat. The evening’s ice and snow melts within an hour of even moderate sunlight hitting the black central stone pile and dark edges of the bird bath. Shallow pond depth means quicker melt. Experimenting with black (heat absorbing) recyclables, southern sun exposures, and insulating base materials is a virtually free way to capture passive solar heat while helping wildlife in winter.

Thanks to all who posted suggestions here. Great ideas!