Use of SODARs as a reliable tool for wind power resource evaluation

 

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Motivation

An positive trend on the height of the wind turbines in order to reach optimal levels for power generation made necessary to find alternatives for wind profiling besides anemometer towers. Higher towers mean a considerable increase in the cost of equipment, civil works, structures and permits. Besides this, towers are fixed structures and additional costs are produced if want to be removed or changed in location.

Even though using remote techniques like SODAR or LIDAR where quite new in the sector, the advantages they have make worthwhile to give them a try. Among other advantages, these techniques are fast to deploy in the field, are easy to change in location, are less environmental impacting and their measuring technique imply that a higher volume of air is taken for measurement compared to an an anemometer, that could be also affected by the tower itself.

In the case of SODAR, a tool that has been used since many years for air pollutant dispersion and for airport management, there some additional advantages that needed to be explore and compare in relation with conventional anemometer towers.

Objective

The main objective of this project was to confirm if SODAR could be a solid tool for win power resource evaluation.

Also to check if this tool is valid for determining the wind profile for the first meters (200m) of the planetary boundary layer with enough precission and representativity in order to be useful for wind power assessment.

Finally to explore the weakness and advantages of this technique in relation with classical anemometer tower.

Methodology

A REMTECH PA0 (remtech.com) phased array sodar was first tested at laboratory. This meant hardware, software and communications checks. These included the integration with a GPRS SAGEM router as gateway. For that time, this kind of routers were not very common in field experiments.

Two developments were made for this project, first a housing and powering solution based on solar power. These SODARS where first design for AC continuos powering and were considerably power demanding. The second development was a datalogging and sensor system for ancillary information such temperature, precipitation and currents, in order to learn as much as possible about the consuming patterns.

SODAR was installed in a location characterized by extreme temperatures, with freezing temperatures during winter and temperatures above 30ºC in summer. It was installed at a reasonably distance of a 80 m anemometer tower.

Data was received through internet to a central server, processed and sent to our client. This survey lasted for some years and preventive and corrective maintenance was done by our personnel. The client was very involved in all the processes.

Results

Thanks to this project our client was able to get some conclussions about this technique. Nowadays this company has SODAR measurement as a standard service and is a powerfull actor in this kind of measurment. Some of the results are:

The SODAR used in this project can be considered portable and useful for field deployment. This makes this instrument, and others of their family, suitable for:

  • Preliminar wind power assessment
  • Extrapolation of results obtain by towers.
  • Completing and verify assessments done using towers.
  • Assess wind power resources at locations where tower cannot be installed due to technical, environmental, economical or legal constrains
  • Wind profiling up to 200 m and more

Some disadvantages are inherent to this measuring technique such some noise in the vicinities of the installation, aditional fragility in terms of vandalism if not well protected, interference from noise sources, slight influence of precipitation and more power demanding than towers.

Obviously mostly of these disadvantages have being considerably reduced in the last products available in the market.

AppNote

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