Now that the initial enrollment period for health care is over, it's time to sift through the data and get ready for the next enrollment period.
More than 1,200 MW of wind power capacity was installed in the United States in the third quarter of 2011 alone, bringing new installations through the first three quarters of the year to 3,360 MW, according to the American Wind Energy Association. The U.S. wind industry now totals 43,461 MW of cumulative wind capacity through the end of September 2011.
More than 1,200MW of wind power capacity was installed in the
United States in the third quarter of 2011 alone, bringing new
installations through the first three quarters of the year to
3,360MW, according to the American Wind Energy Association (AWEA).
The U.S. wind industry now totals 43,461MW of cumulative wind
capacity through the end of September 2011. Of this total, more
than 35% of all new generating capacity has been installed within
the past four years.
"Within the international standards, the prescribed design life
is 20 years," says Mike Derby, land-based R&D team lead
(acting), Wind and Water Power Program, Energy Efficiency and
Renewable Energy, U.S. Department of Energy (DOE). "Certainly,
there are some that are older than that."
According to Derby, the first wind turbines, ranging from 40kW
to 100kW, were installed in the early 1980s. "Modern large,
utility-scale wind turbines for commercial production of electric
power are considerably younger than those turbines," he says. "The
latest generation started being deployed in the mid-2000s."
Annual operations and maintenance (O&M) costs for wind
turbines, which include insurance, regular maintenance, repair,
spare parts, and administration, are estimated between 3% to 5% of
the total cost of installation (click
here to see Fig. 1). A different estimate indicates that
costs equal 20% to 25% of the cost per kilowatt hour produced over
the 20-year lifetime of the turbine. If the turbine is still
relatively new, the costs are estimated to reach between 10% to
15%; however, this percentage may increase to at least 20% to 35%
by the end of the turbine’s life cycle. Costs for repair and
spare parts, in particular, increase as the turbine ages. According
to the "2010 Wind Technologies Market Report," released in June
2011 by the DOE and the Lawrence Berkeley National Laboratory,
"Despite limited data availability, it appears that projects
installed more recently have, on average, incurred lower O&M
costs than older projects in their first several years of
operation, and that O&M costs increase as projects age."
Many of the same processes used to reduce O&M costs in
industrial plants apply to wind power projects. However, the
variable environments of both inland and off-shore wind turbine
locations, as well as the height of the turbines themselves, pose
unique challenges. On October 31, Sandia National Laboratories
released the first findings from its Continuous Reliability
Enhancement for Wind (CREW) database. Although the data is
considered "directional" rather than "actionable" because of its
small sample size — current data covers three seasons and
58,000 turbine-days of data of wind turbines at or above 1MW in
size — the dataset provides a "useful initial view of the
U.S. fleet’s operational and reliability performance."
Among the goals of the project are to benchmark reliability
performance, identify technology improvement opportunities, and
enable O&M cost reductions. "The data from the CREW database is
expected to go to the owner/operators primarily," says Derby.
"It’s the same model that’s used for the gas turbine
industry and other power generation."
According to Derby, plants report their reliability statistics
in return for specialized reports about how they’re doing
relative to other generators.
Notwithstanding 19,000 turbine-days of unknown time,
attributable to the pilot status of the program and associated beta
time, the wind farms reported overall performance in line with
expectations. Operational availability, which includes a generating
factor of 78.5% plus a reserve shutdown of 16.3%, totals 94.8%, and
capacity factor equals 33.4% (click
here to see Fig. 2). On a national basis, according to
the 2010 Wind Technologies Market Report, the average
operating capacity, or capacity factor, for wind projects has grown
steadily over the past 30 years to reach a 34% capacity factor in
Reported downtime includes unscheduled maintenance at 3% and
forced outage/unavailability at 1.8%. Scheduled maintenance
accounts for 0.5%. "There are really two categories — planned
maintenance and unplanned events," says Derby.
Newly installed wind turbines fall under manufacturer
warranties, so the manufacturer specifies required service and
maintenance. In addition, next year, AWEA will publish its
Operations and Maintenance Recommended Practices Manual,
which will be distributed to its members and made available for
sale in its online store.
Generally, the entire wind system, including the tower, storage
devices, and wiring, should be inspected at least once a year.
Routine maintenance also includes: changing the gear oil, coolants,
seals, brake pads, and filters; greasing the bearings; adjusting
sensors and actuators; and visually inspecting the blades, tower,
and electrical connections. Although the turbines have a life
expectancy of 20 years, many of their components do not. Preventive
maintenance includes the replacement or refurbishment of these
Unplanned stoppages requiring maintenance, according to Derby,
occur under fault conditions. "If you have some kind of a failure
in the system — for instance, a bearing failure or maybe a
gear tooth breaks — that’s an example of unplanned
maintenance," he explains.
In addition, condition monitoring is emerging in the wind
industry. This method, which uses high-tech multiple sensors in the
turbine, massive data collection, and sophisticated analysis to
track the condition of individual turbine components, is already
being used in more mature energy generation industries, such as oil
and gas, coal, and nuclear. It has also been used in industrial
applications in the aircraft, military, and processing sectors. In
recent years, more sophisticated online monitoring systems have
been introduced to wind turbines, the most common of which are
vibration monitors and fluid contamination monitors. "Condition
monitoring is typically done in large power plants where you only
have one system serving an entire 100MW plant versus a 100MW wind
system that would require 50 such systems that have to be monitored
in order to determine if the turbine components are operating
properly," says John Dunlop, senior technical programs manager,
Studies by the Electric Power Research Institute (EPRI) indicate
a 47% reduction in overall maintenance costs when using predictive
maintenance techniques. When deciding to use any of these condition
monitoring systems, however, an end-user should consider the cost
of installing and commissioning these systems versus the usefulness
of the information.
According to Andy Milburn, gear and bearing consultant, Milburn
Engineering, Inc., Seattle, data collection can lead to data
overload. "There are so many sensors on the gearboxes and the
turbines themselves that owners and operators are getting too much
information," he says. "There’s so much information that
they’re ignoring it. It’s hard for them to pick out
what’s important and what’s not. There’s good
information in there, but it’s not being disseminated in a
way that people can handle."
Within the wind energy system, certain components may require
more critical O&M care than others. Individual components are
known to be more prone to failure, are essential to turbine
operation, or are more expensive or time-consuming to repair.
Although there are variations among components by manufacturer,
configuration, and operating environment, certain items, such as
generators, power converters, and gearboxes, have been singled out
as failure prone by particular studies.
Excluding "other," the CREW findings list the top three
contributors to turbine unavailability as rotor/blades, electric
generator, and balance of plant (BOP), as shown in Fig.
3(click here to see Fig. 3). Surprisingly,
in this study, the gearbox failures, which, in other studies, are
estimated to cause 30% of wind farm O&M costs, don’t rate
in the top five.
A separate study conducted by the German Wind Energy Measurement
Programme tracked the performance of around 1,500 wind turbines in
Germany for 10 years (1997 to 2006). The German study’s
findings pointed to electrical equipment as the cause of most
stoppages, with approximately 5.5 incidents every 10 machine-years
(click here to see Fig. 4). However, these
problems are resolved fairly quickly, and the turbines are back
online in less than two days. In the same study, gearboxes account
for only about 1.5 incidents every 10 machine-years, but the outage
time logs in at more than six days.
A smaller but more recent database from the agricultural
commission of Schleswig Holstein, Germany, which tracked 5,800
turbine-years, indicates similar failure rates for the various
components, but significantly longer outage periods per failure. In
the case of gearboxes, the average outage period was 14 days.
To address the perceived problems with gearbox reliability, in
2009, the DOE launched its Gearbox Reliability Collaborative (GRC).
The department designed and conducted field and dynamometer tests
to evaluate, validate, and develop gearbox analytical tools and
models. The effort also established a database of gearbox failures.
"We engineered a gearbox so that the DOE owned the intellectual
property for that and instrumented it so we could try to understand
what was happening to the inside of a gearbox as it was being
loaded," says Derby.
Although the newer gearboxes don’t yet match the 20-year
lifespan of turbines in general, there have been some technological
advances made that improve their reliability. However, there are
still reasons for gearbox failures specific to wind turbines (see
The Gearbox Problem).
"They’re doing better than they were in the past, but the
longevity at this point is unknown for the newer turbines," says
Milburn, who has been working with gears for 35 years, the last 10
of which have been focused on gearboxes in wind turbines. "Right
now, bearings are the biggest problem. In the old days, they had
lots of gear problems, but those have mostly been solved. Now,
they’re more application problems. The bearings are being
exposed to loads and conditions that no one has seen before."
According to Milburn, the most common problem with gearboxes in
wind turbines is bearing inner race axial cracks (Photo
1). Problems with micropitting, surface temper
(Photo 2), and inclusions on the gear tooth are
also still occurring on megawatt-size turbines.
As an example of engineering away a problem, recent turbine
designs have eliminated the gearbox by using a low-speed,
large-diameter synchronous generator. However, results of studies
of the performance of these direct-drive turbines are mixed. The
Dutch Offshore Wind Energy Concepts (DOWEC) study compared
projected reliability for six design strategies for 5MW machines
and found that the failure rates will increase by approximately 20%
for innovative variable-speed and direct-drive designs. Northern
Power Systems, in its design study for an innovative direct drive
wind turbine, concluded that unscheduled maintenance costs will
decrease by 60% with their design because of the elimination of the
Until all failures in wind systems can be engineered away, there
will be a need for wind turbine technicians. There are no technical
or physical barriers for wind to supply at least 20% of U.S.
electricity by 2030, according to the DOE; therefore, the
organization estimates there will be 80,000 O&M jobs by that
year. As the latest generation of wind turbines is launched, the
skills required of maintenance technicians will increase in scope,
particularly in the areas of diagnostic, control, and power
Currently, the North American Board of Certified Energy
Professionals (NABCEP) does not offer certification on systems
larger than 100kW. "It evaluates the skills of individual workers
and typically has been focused primarily on small turbine
installations," says Dunlop.
However, many additional programs are available. Most turbine
manufacturers, for example, offer comprehensive training for their
own technicians as well for the site owner’s personnel. In
addition, AWEA directs a program that offers its Seal of Approval
to technical training programs. "Our approach, with the cooperation
from the training institutions across America, looks at the
programs themselves," says Dunlop. "The Seal of Approval program is
based on skills that were extracted from our operators. We pushed
them pretty hard to provide us with the minimum skills that they
would expect a graduate of a technician training program to have.
It addresses all of the aspects of how those skills are taught, in
the classroom as well as the hands-on portion."
Medford, Ore.-based wind systems service provider UpWind
Solutions offers its 170 technicians a combination of
manufacturer-provided and independent training. "We’ve got
technicians that have been through the electrical training
programs," says Guy Dees, director of operations at the
firm’s Sweetwater, Texas-based operations office. "Other
technicians have gone through technology schools — one-year
or associate’s degrees."
In addition, the firm employs veteran technicians, with equal or
more experience than Dees, who has been involved with wind energy
since 1998 and with UpWind Solutions since 2008.
The company provides full-service O&M for utility-scale wind
projects. "To make the projects work, especially sites in remote
areas, we bring on promising individuals from local areas and
provide them with OEM training or different types of industry
training that’s available out there," says Dees. "Our
technicians work on everything from BOP to major component
replacement and everything in between."
Therefore, most of the company’s projects are long term.
"We work on day-to-day maintenance activities, preventive
maintenance, and troubleshooting," says Dees. "Our technicians
travel across the United States and do everything from catching up
on maintenance schedules to large-scale retrofits. It just depends
on the location and the work warranted."
These long-term contracts make the work "recession proof,"
according to Dees. Despite the recent lull in new installation,
particularly in 2010, UpWind Solutions remains busy. "Our business
is not tied to development or construction of new turbines," says
Dees. "Our business is all about operations, and we’re still
operating the turbines that were installed during the
According to Andy Milburn, gear and bearing consultant, Milburn
Engineering, Inc., Seattle, gearboxes in wind turbines are prone to
failures stemming from their application in wind energy systems.
The following are the most common problems:
Highly variable load and speed: Wind is an
intermittent energy source. It alternates between gusting and
still. Therefore, the load that these gearboxes are trying to
transmit is a lot more variable than it is in a plant operation.
"There are some applications where the load in plants is pretty
variable," says Milburn. "But I think wind turbines are probably
the worst of the lot."
Low gearbox safety factors: The drive system in
wind turbines is designed to be compact. "They try to make things
as small as they can, so that means the safety factors that
they’re using are low compared to a typical industrial
application where they don’t have to be too concerned about
weight," says Milburn.
Flexible foundation: Typically, a plant gearbox
and motor are mounted on a large concrete foundation or a steel
structure that’s bolted to a concrete foundation. "Up in the
nacelle, we don’t have that luxury," says Milburn. "The
nacelle is flexing and the rotor itself is causing lots of loads in
the whole structure. This causes misalignment between the generator
and the gearbox."
Periods of no rotation: The gearboxes operate
only around 30% of the time, so they are often idle. "Most rotating
machinery doesn’t like to sit at rest," says Milburn. "They
run into problems with lubrication then."
Operating as a speed increaser: Wind system
gearboxes operate as a speed increaser instead of a speed reducer.
"Most gearbox applications use a high-speed motor that drives
something that’s turning slower," says Milburn. "In this
case, you’re taking the blade that’s rotating slowly,
and you’re increasing the speed up to the generator speed. So
that has some affect on things in terms of lubrication."
Extreme operating environment: The turbines
have to operate in extremely cold or extremely hot settings.
Although the gearbox is in a nacelle and protected from rain it can
still be subjected to extreme temperatures.
High operating temperature: Manufacturers are
resistant to adding large radiators to wind turbines. "They allow
these gearboxes to run pretty hot, and that means the oil viscosity
gets low," says Milburn. "When they’re rotating slowly, you
don’t get a thick oil film between bearings and gears, so you
get metal-to-metal contact — and that’s a problem."
Design details: Design flaws may cause
failures, even if they occur slowly over time.