Environmental Analysis 11
Data recorded at the mast cannot be assumed to be rep - resentative of the whole site especially for large projects or where there is a lack of homogeneity in the terrain and therefore complex modelling may be undertaken to better assess the whole site.
Once long term wind speeds have been calculated for the hub height of the proposed turbine, the gross electrical energy production can be calculated by using the manufactures power curve. There are six main factors which then need to be factored into the equation to derive a net production figure which will be significantly lower than the theoretical gross. These factors are:
•Wake loss •Availability of the turbine •Electrical efficiencies •Reduction in the blade aerodynamics due to ice, dirt or insects •Shut down due to environmental factors •Curtailments
Once a turbine has been installed measurements continue to be taken on-site and used to compare turbine output to live wind data – this is to both verify manufacturers output claims but also to identify any problems. Ongoing data is also fed back into wind models for the site which, along with weather forecasts and live verification data, is used to forecast electricity output for the coming 24-72 hours.
Ice Storms – Sensor based warning system
The accretion of ice on turbine blades reduces output as the blades become less aerodynamic and slow down. Additionally the extra weight can cause damage to the gearing and there is a potential risk of injury from ice shearing off the blades at speed. Ice accretion is commonly a feature of a freezing rain event, or ice storms as they are sometimes called. Freezing rain occurs when rain, is 'supercooled' to below freezing
as it passes through cold air in the atmosphere, yet remains liquid as it falls. If the turbine blades are at or below 0°C the rain freezes instantly on contact to coat the blades with a 'glaze' of ice which can quickly build- up. Ice can also be caused by low temperatures and high humidity – freezing fog conditions for instance.
As turbine blades are designed to be aero - dynamically efficient even a small amount of ice quickly causes imbalances to develop which dramatically slows the rotation. Turbines are normally turned off during icing to prevent damage. However, if ice is still present on a blade when the turbine is restarted it could shear off at speed presenting the risk of damage or injury in a sizeable area around the turbine.
So the early detection of icing can prevent damage and reduce the risk of injury. Specialist instruments such freezing rain or ice detection sensors can be used in conjunction with temperature and relative humidity sensors to form an ice warning system whereby a data logger and modem might be used to, for example, send a warning via SMS text or even to trigger the shut down and re-start of the turbine based upon pre-set conditions being met.
Conclusion
Measurements matter in wind energy – for prospecting and validating new sites, for modelling wind patterns and forecasting output, for monitoring turbine performance and for ensuring the safe operation of turbines during ice events. The data acquisition system chosen needs to be power efficient and reliable; it must be robust enough to work in challenging environments and flexible enough to cope with multiple makes and types of sensors and provide a choice of communication options. Campbell loggers offer all the above and are widely used by specialist wind consultants around the world – to find out more please get in touch.
Soil Moisture Plus Temperature Sensor
The SM300 from Delta-T Devices (UK) measures soil moisture and temperature with research grade accuracy.
The SM300 offers outstanding performance in mineral, organic and saline soil conditions, and it is stable across wide ranges of temperature and salinity. The SM300’s construction uses industrial grade connectors and high specification materials throughout to produce a soil moisture sensor of outstanding quality. The built-in temperature sensor simplifies soil temperature measurement and achieves 0.5°C accuracy.
The SM300 minimises soil disturbance, preserving the original soil structure around the measurement rods. It is easy to insert and install whether at the soil surface or at depth. The SM300’s circular shape facilitates installation in augered holes – extension tubes are available.
The SM300 is a dual-purpose probe – it can be used both with the Delta-T HH2 hand-held Moisture Meter for instant moisture readings, or left in situ for data logging of moisture and temperature. The SM300 is compatible with all Delta-T data loggers; they provide cost effective solutions for recording up to 60 sensors. In fact the SM300 can be connected to most types of data logger (simple 0 to 1V DC output for water content).
Reader Reply Card no 27 New Handheld XRF Analyser
Bruker Elemental (USA) introduces the S1 TURBOSDR handheld XRF analyser for in-situ measurement of heavy metals and other restricted materials. The S1 TURBOSDR’s elemental chemistry reports provide fast and accurate results for many types of restricted materials screening, including all RCRA pollutant metals. Because the S1 TURBOSDR is portable (2 kg), the analyser can easily be taken to the job-site rather than collecting samples and transporting them to the laboratory. In fact, the S1 TURBOSDR is GPS compatible to allow for mapping the results.
Bruker’s S1 TURBOSDR uses X-Ray Fluorescence (XRF) for a quick and safe method of testing for heavy metals at contaminated sites. With point-and-shoot ease, the S1 TURBOSDR makes the analysis fast and simple.
XFlash®
The key to the success of the new S1 TURBOSDR handheld XRF analyser is Bruker’s Silicon Drift Detector (SDD) technology, which offers count rates and resolution far
superior to alternative SiPIN detector technology. The large solid angle and the high count rate capability of the industry-leading XFlash® SDD allows the user to
take full advantage of the fluorescent radiation emitted from the sample, resulting in lower detection limits and shorter measurement times.
Reader Reply Card no 28 Reader Reply Card no 29
Ice detection sensors and freezing rain sensors can be used to warn operators of ice glazing occurring allowing early shut down of turbines.
New Food Probes Range
Sentek (UK) are pleased to confirm the availability of a range of probes suitable for the use within the food industry. These include Jam Probe: pH measurement in jam and Fruit preserves; Dairy Products Probe: pH of milk, sauces, mayonnaise; pH Knife Probe: For direct measurement of frozen and semi defrosted meat products; and Penetration Food Probe: pH of meat, cheese, and solids.
Reader Reply Card no 26
Annual Buyers Guide 2010
IET
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