I'm not sure how many turnouts you are talking about or where they are in relation to electricity but I use a deicer in my tank. They are not expensive tho they do use electricity of course. Another way to keep them from freezing as quickly is to build an insulated box to fit around the tank. You can cover the top of the tank also, leaving enough room for the horses to get a drink.
Solar ones are about $100 a piece. We'll have them at our new barn but one of my friends is at another barn that refuses to allow power to the turnouts. So was just trying to come up with a way to help keep them well.. not frozen lol.
Movement or heat are the two ways to keep the water from freezing. Movement can be accomplished by adding a bubbler or other device (such as the filter idea above). Heat would be accomplished by adding a de-icing device or purchasing a contained heated water container. We use the electric tub system and love it.
I'm in Northern Indiana - I have a tank heater (like this one: Allied Sinking De-icer - 2170712 | Tractor Supply Company) in my tank, I have a heavy duty, outdoor use rated extension cord running it from my garage. Will they let you run an extension cord from the barn out to the paddocks? Make sure you get an outdoor-rated extension cord that can withstand the weather. (I prefer the sinking ones to the floating de-icers, personally, my horses play with the floating ones and pull them out of the tanks)