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The 7.5 kW Bergey EXCEL-R Wind Turbine
The EXCEL is a 6.7 meter (22 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. Pultrusion is a continuous forming process that allows for a very high glass fiber content, which results in a very high strength, yet flexible rotor blade. The basic material strength in ~ 100,000 psi or approximately twice the strength of low carbon steel. Though the blades are not tapered or twisted, they nonetheless operate at ~ 80% of the maximum theoretical aerodynamic efficiency and produce very low sound levels due to the proprietary Bergey SH3035 airfoil. The SH3035 airfoil was developed using advanced computer modeling verified by wind tunnel testing by the National Renewable Energy Laboratory (NREL). The blades are protected from abrasion with a special polyurethane leading edge tape and the blades are painted with an aircraft-quality polyurethane paint after being very carefully balanced. The blades are typically painted white, but are often painted black for cold climates to promote ice-shedding.
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 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 4-10 years. Static components of the EXCEL are designed for a 50 year life and dynamic components are designed for a 30 year life.
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 (except for 24 and 48 VDC versions). 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 1,000 units have been installed in more than 30 countries.
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Excel R/120 7.5kW Battery Charging Wind Generator
Bergey WindPower's BWC Excel-R/120: Peak power of 7.5kW. 120 VDC output. Includes VCS-10 charge regulator. Optimized for low wind speed.
Bergey wind turbines used in combination with a back-up diesel generator, and with optional photovoltaics (PV), provide a cost-effective and reliable alternative to conventional methods of electricity supply in remote areas. For home and village power applications Bergey technology includes advanced system architectures featuring state-of-the-art sine-wave, bi-modal DC-AC power inverters. For telecommunications and smaller village power applications, Bergey hybrid systems often incorporate photovoltaic subsystems to take advantage of the complimentary seasonal variations in wind and solar power.
Bergey hybrid power systems are designed around a DC bus, which forms the common connection point for all of the DC sources and loads. A DC Power Center, which includes protective fuses, controls, and monitoring, forms the heart of the system. Wind turbines and PV arrays are connected to the DC Power Center through separate charge regulators. One or more battery strings are also connected to the DC Power Center to provide the short-term (typically 0.5 - 2 days) energy storage. The inverter system and any DC loads are also connected to the DC Power Center. The back-up diesel is connected to the inverter, which can double as a battery charger during diesel operation.
Village power systems usually incorporate one or more 7.5 kW BWC EXCEL wind turbines. The turbines supply variable power to the DC bus, where it is converted to constant voltage, constant frequency AC power in the inverter, and used to supply the load. Any excess wind turbine power is stored in the batteries until they become fully charged. During short-term low wind periods this stored energy is available to supply the loads. If the battery voltage falls below a pre-set limit the back-up diesel is started and operated until the batteries again reach full charge. Battery charging from the diesel is provided by the bi-modal (DC-AC or AC-DC) inverter. In larger systems the inverter can also synchronize with the diesel generator to share peak loads. Diesel run time is kept to a minimum and the diesel is fully utilized when it is operated.
Battery charging BWC EXCEL's can be supplied with outputs of 48, 120 or 240 VDC. They are well suited for large rural homes, remote villages and facilities, eco-tourism resorts, and larger telecommunications sites.
The BWC EXCEL is most often installed on a guyed lattice tower, which is available in heights of 18 m (60 ft.) to 37 m (120 ft.). Tilt-up versions of these towers are available for sites without crane access. Non-guyed lattice type towers and monopoles (tapered tubular) towers are also available to heights of 37 m (120 ft). You may also supply your own tower if you follow BWC's technical requirements for Excel towers.
Specifications
Start-up Wind Speed: 3.4 m/s (7.5 mph)
Cut-in Wind Speed: 3.1 m/s (7 mph)
Rated Wind Speed: 13.8 m/s (31 mph)
Rated Power: 7.5 kW for battery-charging
Cut-Out Wind Speed: None
Furling Wind Speed: 15.6 m/s (35 mph)
Max. Design Wind Speed: 54 m/s (120 mph)
Type: 3 Blade Upwind
Rotor Diameter: 6.7 m (22 ft.)
Blade Pitch Control: None, Fixed Pitch
Overspeed Protection: AUTOFURL
Gearbox: None, Direct Drive
Temperature Range: -40 to +60 Deg. C (-40 to +140 Deg. F)
Generator: Permanent Magnet Alternator
Output Form: 3 Phase AC, Variable Frequency (Regulated 48 - 240 VDC after VCS-10).
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