Putting a collection of moving and electrical parts on the top of a tower where it is exposed to the whims of the weather can be asking for trouble. Here’s what to do when something goes wrong with your wind turbine. Reasons for a turbine’s poor performance fall into the following problem categories:
There may be insufficient wind. Wind comes and goes, and it is normal to see a wind turbine idle at times. But if it rarely turns, you need to consider whether it is appropriately sited. Does the tower place the turbine 30 feet or higher above any obstacle within 500 feet? Or is it attached to a rooftop or sitting lower than or level with nearby objects?
Just as you would not place a PV module in the shade, you should not site wind turbines in sheltered places. Wind energy is extremely sensitive to wind speed, and wind speed is very much affected by obstructions. A tall tower is almost always essential for good results. If you wish to study the wind speed at your site, low-cost data-logging systems with anemometers are available.
Perhaps the blades are fitted incorrectly. Check that the convex side of the blade is on the downwind side of the turbine. In an airplane wing, this would be the upper surface—the side that lifts the plane. That same lift-force pulls the blade around and its reaction slows the wind. The angle of the blade to the wind is also critical. Check that the blades have been installed according to the manual.
Mechanical problems are usually easy to diagnose. If the blades refuse to budge in a good breeze, something is likely locked. Maybe a main bearing has failed and seized up, or a magnet has come loose and jammed the alternator. Another possibility is that the alternator is iced up. If the blades spin, but slowly, make sure the turbine is facing into the wind. If not, the yaw bearing on which it pivots may have failed or the tail may be stuck in the furled position.
An electrical short-circuit will disable the wind turbine. In the event of a short-circuit, turbines with permanent-magnet alternators deliver a high current. This produces a high torque against the rotation of the turbine, which prevents it from running at normal speed. Many turbines have brake switches that deliberately short-circuit the output for control purposes. If the blades turn very slowly, start by checking if the brake switch is closed.
Measure the output voltage of the turbine if you can, between the rectifier and the turbine. If the voltage between any two of the circuit wires is zero, suspect a short-circuit in the wiring (maybe the brushes) or the alternator. A pulsating or “lumpy” torque holding back the blades indicates a short between two of the three wires.
A low-tech test for finding short-circuits is to disconnect the wires at the base of the tower. If the turbine still does not start, then the short is above—maybe in the slip rings or the tower wiring. If the turbine does start, then the short is elsewhere (maybe in the rectifier or controller). The best tool for tracking down a short-circuit is a clamp-on current meter. Check for current at different points in the system. If there is no current at the point of measurement, the short-circuit is somewhere closer to the turbine. If you do measure a current, then the fault is farther away from the turbine. Be aware that the current from a slow-turning alternator may be more like a series of DC pulses than a steady AC current.
If no current is found, there may be a short-circuit failure of the alternator windings. Excessive current can burn out the coils. High-voltage alternators can suffer insulation failures in wet conditions, leading to the same condition. In both cases, the alternator becomes stiff to turn due to internal currents, even when disconnected.
Tracing the current may lead you to a blown diode in the rectifier (see “Checking a Rectifier” sidebar). Another possibility is multiple grounding. If the battery negative is grounded, and one of the AC phases is also grounded, then other phases will be shorted to the ground by the rectifier during the negative half of their cycle.
Another cause of stalling can occur if battery voltage falls to below half of its nominal value due to heavy battery discharge or failure—the turbine will be loaded with current at low speed and the blades will stall, preventing the turbine from reaching operating speed.
Control problems can manifest in several ways, like a broken spring in the blade pitch-control, a jammed tail-furling system, or maybe the electronic control system is stopping the turbine.
In some cases, the controller at the battery or inverter limits the voltage by diverting AC power directly from the turbine to a dump load. A faulty or blown controller can apply the dump load full-time, drawing a current that stalls the turbine. In some hybrid system cases, a solar-electric array can push battery voltage up enough to activate a dump load on the wind turbine, and stop it from working.
There may be too little wind. Small wind turbines have to run at a relatively high speed before they start to produce power. Their voltage is proportional to speed, and they have to achieve the required cut-in voltage for battery charging or, in the case of batteryless grid-tie, the minimum needs of the inverter.
The turbine may have become disconnected from the load (battery, controller, etc.) so that there is no circuit for current. No current means no torque to hold back the blades, and they will run fast, like an engine in neutral on full throttle. The turbine may spin faster than its components are designed for, and turbine voltage will be high. Higher-than-normal voltage can harm system electronics (controller, inverter, etc.) and be a danger to humans. Measure the voltage in different parts of the system (being careful of shock from bare wires or terminals). If it is abnormally high, there is a break (open circuit) between the point of measurement and the load end of the circuit.
The best course of action is to immediately apply the short-circuit brake and investigate the wiring. If the wind is not too strong, then the turbine should stop. If the brake fails to stop the turbine, then carefully short-circuit the wiring at the base of the tower. If the turbine wiring has become disconnected at the tower top, the short-circuit will not stop it, and unless there is a functioning mechanical shutdown system you will have to wait for the wind to stop.
If the brake does work, then make sure fuses, circuit breakers, and connections are conducting properly. If the turbine was disconnected from its battery, but remained connected to the system electronics, then the inverter and controller will have been exposed to excessive voltages and may be damaged. Always wire the turbine with its own separate fuse at the battery.
A broken connection in one of the DC wires will leave the wind turbine freewheeling. But there are usually three wires in the AC cable—if one is broken, the turbine will be noisy; if two are broken, it can run free.
Poor system design can lead to a chronic energy shortfall. As a rule, a small wind turbine can produce about 20 kWh of energy per annum per square foot of swept area, given a site with 10 to 11 mph average wind speeds.
For example, a turbine with diameter of 8 feet would have a swept area of about 50 square feet and might produce about 1,000 kWh per year, given this average wind speed. All too often, deceptive turbine marketing fosters unrealistic expectations. There may be nothing wrong with the turbine, other than a lack of wind or unrealistic expectations that resulted from marketing hype.
Undersized wiring on a long run also could mean that much of the energy is lost in the wire run.
Incorrectly fitted blades can impair performance and reduce output. But in most cases, the assembly of the turbine is simple and unambiguous. Worn or damaged blades become less efficient at capturing the wind. Another symptom of this problem can be a shaking and rattling machine. A buildup of ice or insects can also have these effects.
Mechanical problems such as failed bearings in the alternator will manifest as noise long before they affect energy production, but a jammed yaw bearing could prevent the turbine from turning to face the wind. Check that the turbine is tracking the wind direction properly.
Electrical issues can certainly impact energy production. A blown diode in the rectifier or a bad connection in one wire also would impact performance. These faults produce a growling vibration in the machine and uneven voltages and currents in the three wires.
Control issues can impair performance when, for example, the turbine furls before it can produce its rated output. But some control systems will only allow the output to reach a peak in a very specific wind speed. Blink and you could miss it! It’s hard to tell whether the control system is working correctly; if in doubt, check for mechanical damage such as worn bushings on the control systems or broken springs.
It is worthwhile to know how your system works, and to take an interest in its behavior and misbehavior. You may not be able to understand it as well as the manufacturer, designer, or installer, but you have the advantage of being on site.
Hiring an expert to fix a simple problem can be expensive—even if only for travel. Being able to diagnose the fault correctly, so that the right part arrives to fix the problem, can save a lot of money. Plus, you’ll get the satisfaction of taking responsibility for—and maintaining—your own electricity supply.
Hugh Piggott has been troubleshooting wind-electric systems for more than three decades at his home in northwest Scotland and around the world.