Wind resource assessment
Encyclopedia
Wind resource assessment is the process by which wind power
developers estimate the future energy production of a wind farm
. Accurate wind resource assessments are crucial to the successful development of wind farms.
, where the modern wind power industry
first developed.
equipped with anemometer
s, wind vane
s, and sometimes temperature, pressure
, and relative humidity sensor
s are installed. Data from these towers must be recorded for at least one year to calculate an annually representative wind speed frequency distribution.
Since onsite measurements are usually only available for a short period, data are also collected from nearby long-term reference stations
(usually at airports). These data are used to adjust the onsite measured data so that the mean wind speeds are representative of a long-term period for which onsite measurements are not available. Versions of these maps can be seen and used with software applications such as windNavigator, FirstLook and Vortex.
Many data logger manufacturers offer wind data management software that is compatible with their loggers, such as NRG Systems' Symphonie Data Retriever Software, SecondWind's Nomad 2 Desktop Software, Kintech Engineering's EOL Manager Software (http://www.kintech-engineering.com), or Campbell Scientific's LoggerNet software. These software packages will typically only gather, store, and analyze data from the manufacturer's own loggers.
Third party data management software and services exist that can accept data from a wide variety of loggers and offer more comprehensive analysis tools and data validation. One example is GENIVAR's WindServer http://www.windserver.com.
and WindRose http://www.wcc.nrcs.usda.gov/climate/windrose.html.
, created at Risø National Laboratory
in Denmark. WAsP uses a potential flow model to predict how wind flows over the terrain at a site. Meteodyn WT, WindieTM and WindSim
are similar applications that use CFD
calculations instead, which are potentially more accurate, particularly for complex terrains.
, WindPRO
, and WindSim
.
Wind power
Wind power is the conversion of wind energy into a useful form of energy, such as using wind turbines to make electricity, windmills for mechanical power, windpumps for water pumping or drainage, or sails to propel ships....
developers estimate the future energy production of a wind farm
Wind farm
A wind farm is a group of wind turbines in the same location used to produce electric power. A large wind farm may consist of several hundred individual wind turbines, and cover an extended area of hundreds of square miles, but the land between the turbines may be used for agricultural or other...
. Accurate wind resource assessments are crucial to the successful development of wind farms.
History
Modern wind resource assessments have been conducted since the first wind farms were developed in the late 1970s. The methods used were pioneered by developers and researchers in DenmarkDenmark
Denmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...
, where the modern wind power industry
Wind power industry
The wind power industry is involved with the design, manufacture, construction, and maintenance of wind turbines. The modern wind power industry began in 1979 with the serial production of wind turbines by Danish manufacturers...
first developed.
Wind resource maps
Government agencies publish maps of estimated wind resources for most areas with active wind power development. Wind prospecting can begin with the use of such maps, but the lack of accuracy and fine detail make them useful only for preliminary selection of sites for collecting wind speed data. With increasing numbers of on-site measurements, as well as operating data from built wind farms, the accuracy of wind resource maps has improved over time. Maps are available as commercial products through resource consultants, or users of GIS software can make their own using publicly available GIS data such as the US National Renewable Energy Laboratory's High Resolution Wind Data Set (http://www.nrel.gov/gis/data_analysis.html). Although the accuracy has improved, it is unlikely that wind resource maps, whether public or commercial, will eliminate the need for on-site measurements for utility-scale development projects.Measurements
To estimate the energy production of a wind farm, developers must first measure the wind on site. Meteorological towersMeasurement tower
A measurement tower is a free standing tower or a removed mast, which carries measuring instruments with meteorological instruments such as thermometers and wind velocity measurers. Measuring towers are an essential component of rocket launching sites, since one must know exact wind conditions for...
equipped with anemometer
Anemometer
An anemometer is a device for measuring wind speed, and is a common weather station instrument. The term is derived from the Greek word anemos, meaning wind, and is used to describe any airspeed measurement instrument used in meteorology or aerodynamics...
s, wind vane
Weather vane
A weather vane is an instrument for showing the direction of the wind. They are typically used as an architectural ornament to the highest point of a building....
s, and sometimes temperature, pressure
Barograph
A barograph is a recording aneroid barometer. It produces a paper or foil chart called a barogram that records the barometric pressure over time....
, and relative humidity sensor
Hygrometer
A hygrometer is an instrument used for measuring the moisture content in the environmental air, or humidity. Most measurement devices usually rely on measurements of some other quantity such as temperature, pressure, mass or a mechanical or electrical change in a substance as moisture is absorbed...
s are installed. Data from these towers must be recorded for at least one year to calculate an annually representative wind speed frequency distribution.
Since onsite measurements are usually only available for a short period, data are also collected from nearby long-term reference stations
Weather station
A weather station is a facility, either on land or sea, with instruments and equipment for observing atmospheric conditions to provide information for weather forecasts and to study the weather and climate. The measurements taken include temperature, barometric pressure, humidity, wind speed, wind...
(usually at airports). These data are used to adjust the onsite measured data so that the mean wind speeds are representative of a long-term period for which onsite measurements are not available. Versions of these maps can be seen and used with software applications such as windNavigator, FirstLook and Vortex.
Calculations
The following calculations are needed to accurately estimate the energy production of a proposed wind farm project:- Correlations between onsite meteorological towers:
- Multiple meteorological towers are usually installed on large wind farm sites. For each tower, there will be periods of time where data is missing but has been recorded at another onsite tower. Least squaresLeast squaresThe method of least squares is a standard approach to the approximate solution of overdetermined systems, i.e., sets of equations in which there are more equations than unknowns. "Least squares" means that the overall solution minimizes the sum of the squares of the errors made in solving every...
linear regressionLinear regressionIn statistics, linear regression is an approach to modeling the relationship between a scalar variable y and one or more explanatory variables denoted X. The case of one explanatory variable is called simple regression...
s can be used to fill in the missing data. These correlations are more accurate if the towers are located near each other (a few km distance), the sensors on the different towers are of the same type, and are mounted at the same height above the ground.
- Multiple meteorological towers are usually installed on large wind farm sites. For each tower, there will be periods of time where data is missing but has been recorded at another onsite tower. Least squares
- Correlations between long term weather stations and onsite meteorological towers:
- Because wind is highly variable year to year, short-term (< 5 years) onsite measurements can result in highly inaccurate energy estimates. Therefore, wind speed data from nearby longer term weather stations (usually located at airports) are used to adjust the onsite data. Least squares linear regressions are usually used, although several other methods exist as well.
- Vertical shear to extrapolate measured wind speeds to turbine hub height:
- The hub heights of modern wind turbines are usually 80 m or greater, but cost effective meteorological towers are only available up to 60 m in height. The power law and log law vertical shear profiles are the most common methods of extrapolating measured wind speed to hub height.
- Wind flow modeling to extrapolate wind speeds across a site:
- Wind speeds can vary considerably across a wind farm site if the terrain is complex (hilly) or there are changes in roughness (the height of vegetation or buildings). Wind flow modeling software, based on either the traditional WAsPWAsPWAsP is a PC program for predicting wind climates, wind resources, and power productions from wind turbines and wind farms. The predictions are based on wind data measured at stations in the same region. The program includes a complex terrain flow model, a roughness change model, and a model for...
linear approach or the newer CFDCFDCFD may refer to:Science and computing* Computational fluid dynamics, a branch of fluid dynamics* Counterfactual definiteness, the ability, quantum mechanics, to consider results of unperformed measurements* Cfengine Daemon, the process that runs Cfengine...
approach, is used to calculate these variations in wind speed.
- Wind speeds can vary considerably across a wind farm site if the terrain is complex (hilly) or there are changes in roughness (the height of vegetation or buildings). Wind flow modeling software, based on either the traditional WAsP
- Energy production using a wind turbine manufacturer's power curve:
- When the long term hub height wind speeds have been calculated, the manufacturer's power curve is used to calculate the gross electrical energy production of each turbine in the wind farm.
- Application of energy loss factors:
- To calculate the net energy production of a wind farm, the following loss factors are applied to the gross energy production:
- wind turbine wake loss
- wind turbine availability
- electrical losses
- blade degradation from ice/dirt/insects
- high/low temperature shutdown
- high wind speed shutdown
- curtailments due to grid issues
- To calculate the net energy production of a wind farm, the following loss factors are applied to the gross energy production:
Software applications
Wind power developers use various types of software applications to assess wind resources.Wind data management
Wind data management software assists the user in gathering, storing, retrieving, analyzing, and validating wind data. Typically the wind data sets are collected directly from a data logger, located at a meteorological monitoring site, and are imported into a database. Once the data set is in the database it can be analyzed and validated using tools built into the system or it can be exported for use in external wind data analysis software, wind flow modeling software, or wind farm modeling software.Many data logger manufacturers offer wind data management software that is compatible with their loggers, such as NRG Systems' Symphonie Data Retriever Software, SecondWind's Nomad 2 Desktop Software, Kintech Engineering's EOL Manager Software (http://www.kintech-engineering.com), or Campbell Scientific's LoggerNet software. These software packages will typically only gather, store, and analyze data from the manufacturer's own loggers.
Third party data management software and services exist that can accept data from a wide variety of loggers and offer more comprehensive analysis tools and data validation. One example is GENIVAR's WindServer http://www.windserver.com.
Wind data analysis
Wind data analysis software assist the user in removing measurement errors from wind data sets and perform specialized statistical analysis. Popular applications are WindographerWindographer
Windographer is wind data analysis software. It reads and presents wind speed and direction data recorded at potential wind farm sites by meteorological towers, sodar, or lidar...
and WindRose http://www.wcc.nrcs.usda.gov/climate/windrose.html.
Atmospheric Simulation Modeling
Wind flow modeling methods, described in the following section, named 'Wind flow modeling', provide insights into very high-resolution wind flow behavior, often, at horizontal resolution finer than 100-m. Because of such finest resolution computational fluid dynamics (CFD) modeling application, the typical model domains used by these small-scale models have a few kilometers in the horizontal direction and several hundred meters in the vertical direction. The above mentioned model domain limitations by small-scale CFD models, need to be addressed and are often addressed by atmospheric CFD models, that could cover horizontal model domains on the order of 100's of kilometers and vertical domain depths of 10's of kilometers. In other words, any atmospheric processes that occur within such large-scale atmospheric model domains, that will influence site-specific wind and its temporal variation should be captured for successful wind resource assessment. This class of atmospheric CFD models and their contribution has not been fully explored and adopted yet, although the aforementioned atmospheric influences captured by such models are highly relevant and critical for the overall wind resource assessment efforts. There are a few such atmospheric CFD models being applied for wind resource assessments today.Wind flow modeling
Wind flow modeling software aims to predict important characteristics of the wind resource at locations where measurements are not available. The most commonly used such software application is WAsPWAsP
WAsP is a PC program for predicting wind climates, wind resources, and power productions from wind turbines and wind farms. The predictions are based on wind data measured at stations in the same region. The program includes a complex terrain flow model, a roughness change model, and a model for...
, created at Risø National Laboratory
Risø National Laboratory
Risø DTU National Laboratory for Sustainable Energy is a scientific research organization north of Roskilde, Denmark. From 1 January 2008 it was made an institute under Technical University of Denmark...
in Denmark. WAsP uses a potential flow model to predict how wind flows over the terrain at a site. Meteodyn WT, WindieTM and WindSim
WindSim
WindSim is wind energy software that uses CFD to optimize wind turbine placement in onshore and offshore wind farms.WindSim is used worldwide by wind resource assessment professionals to help design more profitable wind farms.-History:...
are similar applications that use CFD
Computational fluid dynamics
Computational fluid dynamics, usually abbreviated as CFD, is a branch of fluid mechanics that uses numerical methods and algorithms to solve and analyze problems that involve fluid flows. Computers are used to perform the calculations required to simulate the interaction of liquids and gases with...
calculations instead, which are potentially more accurate, particularly for complex terrains.
Wind farm modeling
Wind farm modeling software aims to simulate the behavior of a proposed or existing wind farm, most importantly to calculate its energy production. The user can usually input wind data, height and roughness contour lines, wind turbine specifications, background maps, and define objects that represent environmental restrictions. This information is then used to design a wind farm that maximizes energy production while taking restrictions and construction issues into account. There are six wind farm modeling software applications available: Meteodyn WT, openWind , WindFarm , WindFarmerWindFarmer
WindFarmer is wind energy software used to calculate turbine wake impacts, energy yield, and site conditions for determining turbine suitability. WindFarmer uses wind modeling inputs from WAsP or CFD software. WindFarmer is developed internally by the independent renewable energy consultant GL...
, WindPRO
WindPRO
WindPRO is wind energy software used to model wind farms. Users are able to design wind farms, including wind turbine layout and electrical design. Energy production, turbine noise levels, turbine wake losses, and turbine suitability can be calculated. WindPro uses wind flow modeling inputs from...
, and WindSim
WindSim
WindSim is wind energy software that uses CFD to optimize wind turbine placement in onshore and offshore wind farms.WindSim is used worldwide by wind resource assessment professionals to help design more profitable wind farms.-History:...
.
External links
- http://www.windserver.com WindServer website