^^^ Jack: the other little known problem with wind turbines is the lack physical mass in their rotors (compared to the rotor mass of genuine base load generators). Rotor mass is what provides frequency stability (your 60 hertz stuff) and frequency stability is a crucial factor in the security of the entire network
Synchronous generators, such as large coal-fired generators, are a source of inertia in the power system. When a frequency disturbance occurs, the inertia of synchronous generators inherently resists the change in frequency.
The renewable generation replacing conventional generation is mostly non-synchronous, and does not provide inertia. So as the mix changes, the overall system inertia is reduced, and the ability to maintain frequency deteriorates. This means that the cost of wind power needs to increase beyond the cost of the generator itself to pay for additional "ancillary services" to retain the previous status-quo for system security.
It's complicated stuff - but alas societies in first world countries tend to demand that the lights stay switched-on !!
Don