The energy needed to overcome the drag of the turbines will be...

The energy needed to overcome the drag of the turbines will be more than they can produce due to efficiences being less than 100%,

eg. Engine pulling train at 100kph needs 5,000Nm

Stick a wind turbine up above a carriage which produces 50Nm and the engine would need to throttle up to 5,100Nm to overcome the extra drag.
Therefore an overall loss of 50Nm. If everything were 100% efficient the engine would still nedd another 50Nm to overcome the drag of the turbine as it produced its 50Nm.

Sorry If I appeared flippant before but I see these things easily, other things I find harder.