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Hitachi

Wind Turbine

Higher efficiency

Differences in the rotor position between the upwind and the downwind.
Differences in the rotor position
between the upwind and the downwind.
Comparison of power generation efficiency in winds blowing up between the upwind and the downwind.
Comparison of power generation
efficiency in winds blowing up between
the upwind and the downwind.
Images of winds blowing uphill.
Images of winds blowing uphill.

Wind turbines are often installed on mountains, hills and other rough terrain.
The winds blowing there surge upward on such terrain.

A downwind rotor has its rotor surface inclined downwards when viewed from upwind, so that it can efficiently catch winds blowing up. Therefore, while the power generation efficiency of a system with an upwind wind turbine installed at the same location will decrease when the wind blows up, those with a downwind wind turbine will increase.

At the same time, the downwind rotor is also advantageous in that it allows a wind sensor to be installed ahead of the rotor.
This makes it possible to obtain data on wind direction free of disturbance, resulting in precise yaw control.

The reduced error in yaw angle control displays has effects equivalent to those of response to winds blowing up and higher generating efficiency, thereby leading to low torque ripple.

The response to winds blowing up and changes in wind direction will increase and, therefore, loads imposed on the main shaft and speed-up gear can be reduced, resulting in higher mechanical reliability.

Toward making downwind a reality

Slip stream simulated on a wind turbine
Slip stream simulated on a wind turbine

In employing a downwind rotor, we have conducted sufficient simulations and verification tests.

Safety at standstill for storm winds

Conceptual diagram of free yaw
Conceptual diagram of free yaw

When at standstill for storm winds after cutting out, the system can be set to free yaw, thereby allowing the downwind rotor to let the winds blow by naturally.
As a result, even in case of power failure, the system will not change in permissible wind speeds for storm winds, which makes maintaining a high degree of safety possible.