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The
7.5 kW Bergey EXCEL-R Wind
Turbine
The
EXCEL is a 7 meter (23 ft) diameter three-blade upwind turbine that achieves
high reliability through rugged construction and a minimum of moving parts.
The
rotor on the EXCEL has three pultruded fiber reinforced plastic (FRP) blades
which are rigidly attached at their hubs. The
EXCEL blades are flexible in torsion and have a unique pitch weight attached to
their outboard leading edge. The
patented Powerflex®
blade system provides passive blade pitching as a function of rotor speed.
Thus, the blades are set for a higher pitch to aid start-up, but
“flatten out” at speed to improve operating aerodynamic efficiency.
The airfoil used on the EXCEL is a proprietary design (BW-3) developed
specifically for low Reynolds Number conditions.
This thin, highly cambered section is not affected by normal dust and
residue build-up on the blade leading edge.
BWC offers an Extra-Stiff Blade Option for high-turbulence or high icing
conditions. These blades are often
painted black for ice-shedding.
As
can be seen in the attached parts drawing (Sorry, drawing will be added shortly),
the blades attach directly to the outside shell of the EXCEL’s purpose-built
direct drive 38-pole permanent magnet (PM) alternator.
The alternator has an “inside-out” configuration in that the outer
shell (containing the magnets) rotates about the fixed internal stator
structure. Thus, the alternator
incorporates the rotor hub, has no central rotating shaft, puts the front
bearing in the rotor plane, and has no brushes.
The output is a sinusoidal three-phase alternating current that varies in
voltage and frequency with wind speed.
The
EXCEL wind turbine series is nominally rated at 10 kW.
In a battery charging application,
however, there is an inherent load matching problem between permanent magnet
alternators and battery banks. The
EXCEL-R is optimized for low wind speed performance, which maximizes energy
production. But providing the best
performance in low winds results in some reduction in peak power under high wind
conditions. Therefore, the EXCEL-R
is rated at 7.5 kW.
The
turbine is aligned into the wind by a tail assembly. The tail boom and and integrated rotor/alternator assembly
attach to the mainframe assembly, which incorporates the yaw-axis slip-rings and
the tower interface. The geometry of the mainframe creates the passive Autofurl®
high wind speed protection. The
mainframe offsets the rotor and yaw axes such that rotor thrust produces a
furling moment about the yaw-axis. The
weight and inclined pivot of the hinged tail provides a preset resistance to the
rotor furling moment. Overspeed
control is initiated at 13-15 m/s (30-34 mph) when rotor thrust overcomes the
tail resistance and restoration is caused by gravity as the wind speed subsides.
The EXCEL has no shut-down wind speed.
The turbine can be manually shut-down using a furling winch installed at
the base of the tower.
Corrosion
protection for the EXCEL is provided by hot-dip galvanizing (mainframe, tower
adapter, and tail boom), electro-zinc plating, and polyurethane paint systems.
FRP components, such as the blades, are protected by
ultraviolet-inhibiting resin additives and sub-surface “scrim cloth” UV
barrier. The blades have
polyurethane leading edge tape for protection against erosion.
The EXCEL’s four sealed bearings are provided with static drain brushes
to protect against discharge pitting. A
Marine Corrosion Option is available which substitutes stainless steel hardware
and provide full encapsulation of the stator windings.
The
EXCEL has only four moving parts, no adjustable elements, and no grease
fittings. No scheduled maintenance
is required beyond biannual inspections and replacement of the outer three feet
of blade leading edge tape every 4-5 years.
Static components of the EXCEL are designed for a 50 year life and
dynamic components are designed for a 30 year life. Predicted major overhaul
requirements include blade refinishing and alternator bearing replacement at 15
years or 225,000 kWh’s.
The
VCS-10 controller, which comes with the EXCEL-R wind turbine, provides
controlled rectification through a three-phase semi-converter.
The semi-converter uses phase modulation to control charging voltage and
current based upon the battery bank voltage.
Safe operation of the EXCEL turbine is independent of the load
conditions, allowing the controller to unload the turbine during regulation.
No auxiliary load is required. The
VCS-10 is fully solid-state and is passively cooled.
It incorporates an LCD display of DC bus voltage and status lights to
indicate the charging mode of the unit.
Since
its introduction in 1983 the EXCEL has distinguished itself as the one of the
most reliable wind turbines ever produced.
The Wisconsin Power & Light SWECS test program, the largest of its
kind (involving SWECS from UTRC (Windtech), Windworks, Jacobs, Enertech, and
Carter), showed a 99.1% availability (9.0% higher than any other unit) and an
O&M cost of $0.0026/kWh for the EXCEL over a five year test program.
This is less than half the O&M costs that have been typically
reported for grid-intertied photovoltaic systems (eg, PG&E test
program).
Another
utility, Pacific Power & Light, through its subsidiary OnSite Energy,
installed leading remote wind turbine products (3 kW Northern Power Systems
HR-3, 10 kW BWC EXCEL, and 17.5 kW
Jacobs 10-23) on a telecommunications site at Duncan Mountain, Idaho in
November, 1984 for the purposes of product and technology evaluation.
The site is very remote and accessible only by helicopter during the
winter. Since installation, over
fourteen years now, the BWC EXCEL has achieved nearly 100% availability.
The next most reliable turbine in the PP&L test program had an 84%
availability in the first five years. The
other turbines at the site have now been decommissioned and the EXCEL is
providing prime power to the telecommunications facility.
The
BWC EXCEL is the best selling wind turbine in the size range of 2-20 kW in the
world. Over 600 units have been
installed in more than 30 countries.
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