Design Tradeoffs

There are some interesting design tradeoffs evident in the Vestas V82 and V80.  The tradeoffs no doubt affect the overall lifetime costs of the equipment.

My project has a V80, built in 2002, and 2 V82’s, built this year.  I continue to await permission to operate from the Electrical Safety Authority, and am hopeful provisional permission to operate may come tomorrow.

The V80 has 40 m blades, a 78 m tower, and a 1.8 MW generator.  It has a cut in wind speed of 4 m/sec, and a cut out wind speed of 25 m/sec.  The V82 has 41 m blades, an 80 m tower, and 1.65 MW generator.  It has a cut in wind speed of 3.5 m/sec, and a cut out wind speed of 20 m/sec.

The V82 will be produce more at all wind speeds across the power curve until winds are above 12 m/sec, when the V80 will be more productive.  Over a year, this will give about 3-4% more production from the V82, and the main reason for its greater productivity is its longer blades, which catch more wind.  This result is site specific, but likely applies across most of Ontario.  1 Point for the V82.

When the wind is blowing on the wind turbine, the nacelle will have a tendency to turn.  But in order to produce at the maximum, the turbine must be pointed into the wind, and so this tendency to turn must be overcome.  The V82 has a yaw bearing, which the nacelle sits on.  There are mechanical brakes to prevent the nacelle from turning.  In the V80, the nacelle sits on teflon pads – there is no bearing.  And no brakes are required, as nacelle is held into the wind by friction.  Very elegant.  No bearing, no brakes means less points of failure.  And failure of a nacelle bearing would be very costly to repair, as both the rotor and the nacelle would have to be removed.  1 point for the V80

The V80 has a transformer in the top to boost voltage.  In some cases, this can eliminate the need for a transformer at the substation, which is a significant savings (the biggest transformer they can install is 34,500 V, and my project attaches to 44,000 V lines, so an intermediate transformer will always be required).  Also, it reduces line losses on the way from the top of the tower to the bottom, and greatly simplifies the cabling.  My V80 has a single power cable that runs down the ladder, whereas the V82 has 10 cables.  The drawback of having the transformer at the top is that the weight of the nacelle is much greater.  In addition, transformer service would be very costly if required.  With the heavier nacelle, a larger crane is required to erect the turbine.  I estimate that V82’s cost about $75,000 less in crane mobilization fees to erect than V80’s, but cost $20,000 more in cable to connect to the padmount transformer.  V82’s, because of lower crane mobilization charges get a point for small projects.  V80’s don’t lose a point for large projects, because a large crane mobilization charge amortized over many turbines becomes less important.

The V82 uses an ultrasonic sensor to measure winds, and it is supposed to be highly reliable.  The V80 uses a heated cup based anemometer.  So the V82 has no moving parts.  But the V80 has had no problems for the past year.  So no points awarded.

Of course, the true comparison will be the total operating cost and production over 20 years.  That’s a long time to keep reading a blog, and even longer to keep writing it.

On another note, we are in the midst of a big wind event.  Winds have been as high as 26.5 m/sec (95 km/hr) at the V80 today, and the turbine is producing at capacity.  The same is true of the large wind farms across Ontario, with production averaging about 270 MW, which is close to capacity.  Interestingly, at this time, 6 of Ontario’s operating nuclear reactors are off line, including 4 out of 6 at Pickering, and 1 each at Darlington and Bruce.  That’s 3400 MW of nuclear that is unavailable.

Seems like the system is able to cope with intermittent suppliers.

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