| Xenon | A heavy gas used in specialized electric lamps. |
| X-Ray | A type of electromagnetic radiation having low energy levels. |
| Xyloid Coal | Brown coal or lignite mostly derived from wood. |
| Yaw | Rotation parallel to the ground. Generators Yaw to face the wind as the wind changes direction. |
| Yaw Axis | Vertical axis through the center of the generators gravity. |
| Yaw Bearing | The bearing that sits under the generator to allow the generator to rotate and follow the wind direction. |
| Zenith Angle | The angle between directly overhead and a line through the sun. The elevation angle of the sun above the horizon is 90° minus the zenith angle. |
| Zephyr | A gentle breeze. Also the West Wind in Greek mythology. (“Favonius” in Latin.) |
| Zonda | A warm, dry wind that blows westerly off the Andes of South America and across the plains of Argentina. |
