Commonly Asked Wind Energy Questions
WindLogics experts answer commonly asked questions about wind resources and wind energy in general. To submit a wind energy question of your own, please send it to us at asktheexpert@windlogics.com.
Is there a cost-effective way to measure the wind at hub height?
Erecting Met towers continues to be a common practice, and some developers are spending the significant dollars needed to put up 80-meter towers to measure the wind at hub height. However, both sonic and laser wind profilers show great promise for accurate measurement of wind speed and direction at and above a turbine's blade height. A key advantage of these devices is their low profile, which eliminates zoning and permitting concerns in most locations.
SODAR (or Sonic Detection and Ranging) technology bounces sound waves off particles in the atmosphere to calculate wind speed and direction from the feedback. The devices can be deployed with solar panels to provide power for operations and communications. Current SODAR devices cost about half of the price of an 80-meter tower installation.
LIDAR (or Light Detection and Ranging) is a similar remote sensing technology using a laser beam to bounce light waves off particles in the atmosphere. Compared to SODAR, current LIDAR units are quite a bit more expensive and require more power, typically from existing electric service or remote generators.
Why is a wind study needed?
With continued growth in the wind market and increasing need to control project cost, wind farm stakeholders must be sure of the economic feasibility of each opportunity. A detailed understanding of the expected return on investment will drive the right business decisions. The cornerstone of that analysis is an accurate assessment of the wind, the fuel for the plant. And wind energy production is related to the cube of the wind speed, so any variance in wind speed measurement impacts the projected output.
What is normalization and why is it important?
Normalization refers to a scientifically based analysis of the long-term wind resource at the study point by combining detailed modeling of one year of wind data with 40 years of the WindLogics reference information. This analysis is particularly useful for understanding the inter-annual wind variability which impacts wind project cash flow risk, and therefore wind project financing.
What is the Buffalo Ridge?
The Buffalo Ridge is an elevated land form running northwest to southeast through eastern South Dakota, southwestern Minnesota and northwestern Iowa. It is an excellent area for wind farms because of its consistent wind speeds with little interference. Wind speeds in this area average as high as 9 meters per second or 20 miles per hour, when measured at 80 meters above ground surface. In addition to its excellent wind resource, wind farm projects in this area often have convenient access to electrical transmission lines. Other areas of the Midwest may have even better wind regimes, but lack essential transmission capability.
What is the value of diurnal/monthly data?
Because the transmission grid has a fixed capacity, wind-generated electricity should ideally match demand for electricity as closely as possible. In many cases it does not. For example, the best wind speeds at utility-scale hub heights often occur at night when demand is reduced. Seasonal variations also occur. So, understanding a site’s wind variability is essential for negotiating power purchase agreements and planning for utility wind integration. Annual average wind speed can be helpful in initial stages, but proceeding with only that understanding could move marginal projects forward and possibly eliminate very favorable locations.
What is a P-value and why is it important?
The prediction level values (P90, P95, etc.) are probability values, in percent, that indicate the likelihood of a given event happening. The P values in wind analysis reports are the lower interval bounds, in the units of the measured data (wind speed in m/s, GW/yr, etc.). They are important because they quantify the inter-annual variability of wind speeds and gross energy production to help in making key project financial decisions.
What is a Virtual Tower?
A Virtual Tower is WindLogics nomenclature for a hub-height point of reference on a project site. From this point, which can be virtually anywhere on the site, WindLogics can extract hourly wind speed data for a full year (8760 time steps) for further detailed analysis. The results are comparable to having a met tower erected and collecting data for a full year, except of course the WindLogics approach takes only a few weeks to complete.
