A method and apparatus for non-volatile overspeed protection is described. The present invention provides a method and apparatus for non-volatile overspeed detection to provide turbine rotational speed safety during a power outage. In one embodiment, aerodynamic braking is used to slow rotation of a rotor of the wind turbine. If an overspeed condition continues after application of aerodynamic braking, mechanical braking is used to reduce the rotational speed of the rotor. Power is supplied by a non-volatile power source to continue overspeed detection during a power outage. A low-pressure trigger valve is used to apply a mechanical brake when hydraulic pressure in the braking system falls below a predetermined threshold.