Sodar: Operation and Limitations (1/2)

February 18, 2012

On last post I explained briefly some features related to this Remote Sensing (RS) apparatus, but I consider that it should be explained further. Therefore, I am going to detail other considerations related to Sodar’s technology through two posts based on the academic paper of S. Bradley, I. Antoniou et al. (2005). By now, physical principles and uncertainties will be described. Next post will focus on its calibration methods.

Sodar is a Remote Sensing apparatus that measures 3D wind speeds at high altitudes. By emitting vertical sound beams of sound, it is possible to interpreter the backscattering frequencies due to the Doppler Effect and thus, wind components can be decoded (See Fig. 1). Usually, three or five beams are necessary to obtain reliable raw data measurements. Each of them is usually tilted 15-20º (ϕ) to the vertical (See Fig. 2). Though the emitted signal produces a continuous backscattering echo after crossing the infinite turbulent layers in the atmosphere, the echo generated at the studied altitude (Z) can be recognized according to the following formula. This means that among the continuous echo signal received, the specific signal generated at the Scattering Volume at Z height is generated at t (time) moment. The same principle is used by pulsed lidars.

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Sodar’s Overview

January 3, 2012

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Sodar (Sonic Detection And Ranging) is device for measuring remotely wind profiles from the ground by projecting sound waves. By sending an acoustic pulse away at sound velocity, it interacts with density fluctuations in the air and the frequency of backscattered signal is interpreted. This is possible due to the Doppler Effect that means frequencies between the sent signal and the backscattered one are different. Hence, wind speed can be interpreted.  Hence, wind profiles (wind speed and wind directions in function of height) at that place can be obtained.

Reliable Sodar ranges are typically around several hundred meters and basically, it depends on ambient noises and atmospheric humidity. First Sodars were developed in late 1950’s, but the first commercial ones appeared in 70’s in California (AeroVironment, Inc). Prizes are around 50.000 USD per unit.

Advantages:

– Higher altitudes than met masts.

– Cheap and easy-to-install.

– Accurate at appropriated atmospheric conditions.

Disadvantages:

– Not accurate under rainy, noisy, and low humidity conditions (sound is attenuated more rapidly in dry air).

– Data are obtained by averaging the received data. Hence, wind speed and wind direction standards are not reliable.

– Not appropriate when high obstacles are nearby (buildings, trees, towers).

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New reports

February 15, 2011

Since the beginning of this program, we made many reports and assignments. I don’t want to upload all of them, but I would like to share the articles that I personally wrote:

Improvements in the transmission grid network for a succesful wind power integration: In this report I analyzed how the wind power development can be improved in Europe. j

Spatial planning in the region of Galicia. This region in Spain has a lot of installed wind power capacity. Why?

Spanish Wind Power Policy: A brief and simple diagram.

Leassons learned at Gotland University

February 15, 2011

From the last time I posted, we have learnt many things about the wind power industry. Here is a short summary of what we studied on this Master:

  • Principles of wind turbines: Components of wind turbines and the differences between synchronous and asynchronous generators must be known to understood the basic principles.
  • Climatology and Boundary Layer Theory: Kinetic energy from wind moves the blades, and thus electrical energy can be produced.
  • Aerodynamics: The shape and chord of blades are optimized by using formulas. Lectures provided by some accademics of Risoe and Uppsala universities were useful to understand these phisical principles.
  • Measurements Methods: Linear, non linear, CFD (Computational Fluids Dynamics) are useful to predict the wind resources at a determinated place by using MCP (measurement correlate and predict) techniques. Hence, software such as WindPro or WinSim are useful tools.
  • Wind Power potentials: Places located in cold climates or offshore wind farms have high potential in future but there are some considerations they must be valorated.
  • Grid Network: Before starting a new wind power project four words must be considered: Wind, wind, wind and infrastructure/grid network. Hence, it is important to know the point of common coupling (PCC) to connect the wind farm to the grid network.
  • Logistic: The other leg of the four words is obvious; roads, docks, and so on.
  • Public acepttance and environmental impact: Visual impact, flicker shadows, noises, consequences to the wildlife are other important aspects.
  • Policy and Legal Planning: Incentives and subsidiaries from administrations, legal frameworks… These frameworks can explain why some countries as Germany has such installed wind power capacity.

First reports.

September 16, 2010

Master is running fast. After the Power Point presentations which were useful to know the rest of students and analyze the energetic situation in our countries, now it is time to write the reports. I must recognize writing technical reports in English is more demanding as I had expected.

However, I am proud of my work with the few time we had to write them. Here are posted:

Spain: Energy Situation: Briefly report about the Energetic situation in Spain with personal comments.

Spain: Wind Power Situation: Wind Power policies, forecasts, present situation, so on.

Spain Wind Power Development

September 6, 2010

Today Monday, we had another presentation. This time we had to speak about the Wind Power industry in our countries. As you can guess, Spain holds a privileged position in the world with our fourth place.

Again, here is the presentation I have just shown to teachers and the rest of students. Now we need to write the reports and they must contain further information. So, let’s start as soon as possible. :-)

Spanish Energy Comsuption & Production.

September 4, 2010

Finally, we started our Master on Wind Power at Gotland University. After the student presentations, we had some lectures, readings and homeworks. A lot of homeworks.

In our first week, we need to introduce our country and the present situation related to the Energy Comsuption and Production. Here is my presentation.

Google and its cero-carbon emissions policy.

July 31, 2010


According to the Google’s blog, yesterday, 30th July, the Mountain View’s company will start purchasing 114MW from a wind farm at the NextEra Energy Resources Story II facility in Iowa for 20 years. This decision is related to the Google’s purpose to become a carbon neutral company.

On one hand, they try to reduce the carbon emissions by optimizing their data centers, and on the other hand, they power their facilities with renewable energy (they own one of the largest corporate solar installations) and buying the remaining energy from wind power farms.

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The World’s largest wind power farm.

July 30, 2010


Alta Wind Energy Center (AWEC) will be the world’s largest wind power farm with its 1.550 MW. It will be located in the Tehachapi-Mojavi region (about 100 miles north of urban Los Angeles, U.S.) The wind farm is being developed by Terra-Gen Power and will consist of 300 turbines manufactured by Vestas. This Mega-project will replace the current “largest wind farm” which is in Texas (Roscoe Wind Farm).

The company in charge of this project is Terra-Gen Power, which primarily sells the output of the renewable energy projects to load serving entities under long-term power purchase agreements. In this case, Southern California Edison has agreed to a 25-year power purchase agreement for the power producer. The project is planned to finish in 2011.

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Nuclear against Wind Power

July 26, 2010

TED (Technology Entertainment and Design) is a small Californian nonprofit organization devoted to “Ideas Worth Spreading”. It was founded in 1984 and now their events are in Long Beach and Palm Spring as well in Europe and Asia offering live streaming of the talks. They address a wide range of topics within the research and practice of science and culture. Past presenters include Bill Clinton, Al Gore, Bill Gates, Google’s founders and many Nobel Prize winners. A website I really recommend to you if you like Science and Culture.

This time, I would like to pay attention on the video that is about Wind and Nuclear Energy. Firstly, we have the nuclear supporter, Stewart Brand, who shows to us actual data about the disadvantages of each energy source, from solar to coal energy. On the other hand, Mark Jacobson, focus his speech on the nuclear problems and then, on the advantages of the Wind power.

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