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Course Title
100 Home
101 Introduction
102 FAQ Page
103 Course Catalog
104 Green World
105 Demand & Supply
106 Conservation Careers
107 Solar Careers
108 Wind Turbine Careers
109 Entrepreneurs
110 Employee or Employer?
200 Demand Management
201 Summary
202 Residential Energy Profile
203 Ten Conservation Rules
204 HVAC System
205 Kitchen Appliances
206 Water Heater
207 Lighting
208 Laundry Appliances
209 Calculating Savings
300 Renewable Technology
301 Solar Energy
302 Solar Collectors
303 Solar Water Heating
304 Stirling Engines
305 Basic AC-DC Electronics
306 Silicon Solar Panels
307 Thin Film Solar Panels
308 Wind Turbines
309 Inverters
310 Grid Tied and Off Grid
311 Solar Site Survey
312 Solar Site Diagram
313 Sun Path Chart
314 Site Survey Worksheet
315 Wind Turbine Site Survey
316 Wind Turbine Worksheet
400 Solar Thermal Design
401 Solar Heat Overview
402 System Configuration
403 Site Survey
404 SRCC Compliance
405 System Specification
406 Bill of Materials
407 System Installation
408 Solar Heat Incentives
409 Document Package
410 Future Products
500 Solar PV Design
501 Solar PV Overview
502 System Configuration
503 Site Survey
504 Grid Tied & Off Grid
505 System Specification
506 Bill of Materials
507 System Installation
508 Solar PV Incentives
509 Document Package
510 Future Products
600 Wind Turbine Design
601 Wind Turbine Overview
602 System Configuration
603 Site Survey
604 Grid Tied and Off Grid
605 System Specification
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Green Collar Careers - Wind Turbine System Overview

Nacelle is the official wind industry term for the unit containing:
  • Turbine Blade Hub & Bearings
  • Generator/Alternator
  • Gearbox (if equipped)

A gear reduction and direct drive (gearless) units are shown to the right.   Currently gear reduction units are selling at lower cost although that will soon change as the direct drive units cost less to produce.   Direct drive units usually include the inverter unit as an integral component of the nacelle.  Most wind turbines require a form of braking or retarding when high wind conditions persist.  Some direct drive systems will use the inverter to retard the turbine speed which is the most efficient way to control overspeed events.

Click picture to expand

Gearboxes are generally lubricated with grease to simplify sealing and minimize leakage.  Grease tends to thicken in lower temperatures and adds a significant drag below about 20 F.  Where oil may be used in some gearboxes seals are crucial to maintain.  Grease will tend to last longer between changes where oil will need to be changed periodically. 

Direct drive has no gearbox and the only lubricated parts are the sealed bearings.  These will generally last 20 years.

DC output systems are almost always a brush type generator.  Brushes are a wear component adding to service requirements.

AC output systems use alternators and don't require brushes.  Inductively coupled alternators require a circuit that controls excitation voltage; this circuit may be integrated into an inverter which will be mounted inside the nacelle.  Inductively coupled alternators will require a gearbox with at least a 10:1 ratio. 

Permanent Magnet alternators can operate at direct drive speeds.  Inverters with an integrated control circuit will be installed in the nacelle.
As the wind direction changes the nacelle will need to rotate to point the turbine blades into the wind.  Directional changes are known as "yaw".  Most nacelles have a rotary yaw table on the bottom side for mounting to the tower.  Nacelle units equipped with a tail fin position the unit so the wind strikes the blades and the tower is downstream (leading), where units without a fin position the blades downstream of the tower pole (trailing).  Both leading and trailing flows have their benefits.

Towers come in a variety of styles and heights.

  • Monopole towers have the least maintenance and highest price
  • Guy Wire poles are the least expensive and the highest maintenance
  • Telescoping poles are the easiest to erect and some allow easy nacelle access

Heights range from 20 - 100 feet.