Certification indicates which certification(s) the turbine has, or if certification is in process. See the “Why Certification is Important” sidebar for more information.
AWEA rated power is in kW at 11 meters per second (25 mph). Note that this is power at only one point on the power curve. Comparisons between machines at any one point on the curve are not apples to apples. More useful are energy (kilowatt-hours) measurements at the average wind speed at tower top at your site.
AWEA rated AEO (annual energy output) in kWh at a 5 meters per second (11 mph) average wind speed. This is useful information for comparing, but is only at one average wind speed, while residential wind sites may range between average wind speeds of 7 to 13.
Estimated AEO is predicted for 8–14 mph average wind speeds. These can give you an idea of what energy production to expect at your site, assuming:
This section of the table is perhaps the most useful because it can help you be realistic about what a wind turbine might produce at your site. Rated power (watts) or power at any specific point on the turbines’ power curves cannot give you this information.
Source of AEO is the source of the annual energy output data. The sources include data derived from the field-verified energy curves on the certified turbines—i.e., Certified Energy Curve; manufacturer-supplied data, such as from Windcad, Bergey’s proprietary, Excel-based spreadsheet calculator; and the use of an AEO calculator, depending on the turbine.
Rpm is the turbine’s rotational speed at rated power. This may indicate two important aspects of the wind turbine’s performance. A lower speed for a similarly sized rotor usually translates into less wear and tear on the turbine, and less noise.
Governing system is the type of overspeed control. Turbines should have a method to protect themselves in high winds. Because wind power increases with the cube of wind velocity, enormous forces bear on a turbine in high winds. The top end of an accurate power curve can show you how well a machine protects itself. At regulation wind speed, the power curve of a furling machine will show a significant drop as the turbine turns itself out of the wind and slows down. In high winds, a machine with active blade pitching will show a flat line on the power curve, with little or no power reduction. Turbines with auto shutdown are designed to come to a complete stop.
Governing wind speed (mph) is the speed at which the machine is fully governed. Conservative designers choose to govern at lower speeds, knowing that long-term reliability is more important than capturing rare high winds.
Grid-tie only (GTO) or battery-based (BB) indicates whether the machines are designed for direct batteryless connection to the utility or are for battery charging. Battery-based systems can also be utility-intertied, but besides needing batteries, may need additional equipment. GTO machines will not operate without a live utility connection.
Cost is shown in U.S. dollars, but doesn’t include shipping. Prices include various controls and sometimes even towers or more. Inquire with manufacturers for details of what you’ll get for your dollars.
Warranty details should be carefully scrutinized to see what is covered, and what the fine print reveals.