New SODAR makes the wind visible
NIWA’s new SODAR trailers reveal the complexities of the wind.
The SODAR (Sonic Direction and Range) trailers constructed by NIWA Instrument Systems are proving their worth gathering wind information for a variety of purposes.
One trailer is currently carrying out wind measurements near Wellington as part of the multi-agency Topographic Multiplier Project. It will gather information about how much the wind speeds up around hills, which will be used to review the wind loading standards in building regulations. Another use is assessing the viability of potential wind power sites.
How the SODAR works
SODAR (Sonic Direction and Range) is like radar, but uses sound rather than radio waves. It beams sound pulses up from an array of acoustic aerials. From the relative strength and Doppler shift of the received echoes, the SODAR provides information about wind speed, direction and turbulence, thermal structure and mixing at different heights. It can produce a continuous vertical profile of the wind in the column of air above the trailer, up to five kilometres high.
The SODAR trailer is easy to set up and relocate. It is powered by two clean energy sources: methanol and sunlight. The SODAR derives wind statistics and other information not readily available from conventional wind measurement technologies.
SODAR powered by alcohol
The new improved SODAR trailer is powered by a methanol Fuel Cell. Methanol is the simplest of the alcohols and, while toxic, is safe when handled properly. For safety, we currently contain the methanol in certified 28 litre plastic cartridges. The fuel cell connects directly to these.
Superior to its predecessor, the new SODAR power supply requires little maintenance, does not get hot or vibrate, is quiet, has a clean exhaust (mostly water) and is light - you can lift it with one finger.
The fuel cell
The fuel cell converts chemical energy stored in the methanol fuel into electrical energy.
It can supply up to 65 Watts of power continuously. A 28-litre cartridge of methanol will power the SODAR 24 hours a day for around three weeks. To reduce the amount of methanol needed and to extend the time between site visits the power supply is supplemented with solar panels.
The fuel cell uses methanol and oxygen from the air, to produce electricity and a small amount of water and carbon dioxide. It exhausts this through a plastic tube under the trailer.
Designed for remote operation
The SODAR trailer is designed to carry out unattended operation in remote environments. We monitor and control its operation via either cellular communications or satellite.
The trailer has its own weather station
The SODAR trailer has a self-contained weather station that can easily be erected on a mast placed near the trailer.
The weather station has no moving parts. It measures wind speed and direction, air temperature, relative humidity, barometric pressure and rainfall. It continuously records this local weather data, usually at a height of two metres above the ground, and can be used to enable the SODAR to start up at the onset of a predetermined weather event.
Where to from here?
We’ll conduct further experiments with local sources of pure and less expensive methanol. Impure methanol can poison the catalyst and degrade the performance of the fuel cell, so we’ll measure this to see how it might affect the longevity of fuel cells.
Those involved in the Topographic Multiplier Project are: GNS, NIWA, Opus, and the University of Auckland.