In the article, “Small Wind Turbine Standards Increase Consumer Confidence,” I explain how third-party standardization and certification programs are striving to help consumers determine the most effective distributed wind systems for their needs. However, until formal standards are set consumers are left with the need to determine the value of a system on their own, and are often misled on how to accurately assess the system’s performance. Therefore, in this article, I will discuss how consumers can make accurate assessments of personal wind turbine performance.
When considering the installation of a distributed wind energy system, how do consumers properly determine the capacity and size of a system? Most people look at the power rating of the wind turbine – an instantaneous measurement – in kilowatts (kW). Wind manufacturers often rate their systems by power, measuring the peak output of the system in individual test environments, regardless of the wind speed. Manufacturers then name systems based on these ratings. In most cases, however, power is not a useful figure for this purpose.
If all wind turbines were power-rated under the same conditions, this might be a helpful starting point in choosing the system, but maximum power rating really has very little to do with the amount of energy a system will produce in the winds at a consumer’s actual location. A wind turbine rated at a high kW power output in high winds may be very poor at producing energy over an entire year as the high speeds at which it is rated will not sustain, given very few people live in areas with consistent 28-30 mph winds. Even worse, power ratings can be misleading if the manufacturer uses higher wind speeds or reports only momentary outputs. Thus, the peak power rating of a wind turbine should not be used as selection criteria. If peak power ratings between different wind turbines are compared, it should be done at a standard wind speed, typically 11 meters per second (m/s), or 25 mph.
A much more accurate measurement for determining a personal wind turbine’s actual use is the amount of usable energy (power produced over time) which the wind system will produce in the wind conditions at your site. Energy – measured in kilowatt-hours (kWh) – is what does the work and what is purchased from (or sold to) the utility company, and, ultimately, is what really matters in a wind energy system.
To obtain an accurate measure of a turbine’s energy production, first determine the wind resource available in the designated area. Reliable and statistically generated wind energy assessment tools are available online to help determine the wind resource and average wind speeds in a particular area. Resources such as Sitelook can calculate personalized estimates of the wind potential at an exact location. Local governments also often have historical wind speed statistics for a particular area.
Once the area’s average wind resource is confirmed, a consumer should turn to the turbine manufacturer’s advertised energy curve or chart. With accurate energy production information, consumers can properly estimate how much energy a proposed system will produce. And, of course, this is critical to designing a system that will meet their individual needs.
Consumers should look for products whose energy charts show output levels ideal for their personal needs, at the point that meets the average wind speed in the area. Power curve and energy production estimates for wind turbines should be used cautiously. Only power and energy curves based on testing certified by an independent industry-accepted test facility should be considered.
March 2011 marked the third anniversary of an independent wind turbine test off the coast of Zeeland in The Netherlands. Over the past 36 months, 11 wind turbines were tested side-by-side and measured for their energy output. An important observation from the results of this ongoing test is that, out of the 11 turbines tested, only one met (or exceeded) the manufacturer’s energy production estimate. And those that fell short of meeting their advertised claims didn’t miss by a small amount. The best of the 11 turbines only produced 60 percent of what their manufacturer indicated it would, and some produced as little as 10 percent of their manufacturer’s estimated energy production.
The lone exception in this group was the Skystream 3.7 distributed wind generator, which produced 53 percent more useable energy than the advertised energy figures predicted by the manufacturer.
All of the 11 turbines are undergoing testing on short towers and in less-than-ideal wind conditions, so in all cases, their energy production should be improved by a taller tower or installation in a better wind location. But it’s important to note that the energy production estimates provided by the turbine’s manufacturers were based on the wind conditions that exist at the test site, and if the energy prediction from a manufacturer is inflated or inaccurate at one wind speed, it’s safe to assume that the estimates for other wind speeds should also be viewed with some skepticism.
The most important lesson from this test is that consumers should evaluate any wind turbine’s potential performance based on independent and long-term test data. By understanding how to best assess the true performance of distributed wind systems, users can make informed purchasing decisions, thus leading to an alternative energy system design that is optimal for individual use and overall customer satisfaction. For more information on uses and applications of distributed wind energy visit windenergy.com.
Written by Andy Kruse. This article was written with information provided by the Dutch government and each turbine’s manufacturer. Please refer to the individual web sites or product specification documents for each listed turbine manufacturer. The Zeeland test data can be found here. For Paul Gipe’s article on the Zeeland test click here.