RENEWABLE ENERGY & THERMAL IMAGING
the electricity to be sent back to the ground. A power station on the ground controls the winches that hold the tethers and pulls in
the power fromthe turbine before sending it to amicrogrid connection.
KILL WIND TURBINES The other basic option for AWE developers is as an alternative to the offshore wind farms withmuch lower cost of electricity over conventional Gigawatt level wind farms. Again, AWE taps the stronger andmore consistent winds higher up. Offshore sites offer safety, availability of real estate and no-fly zones for aircraft. Offshore AWEs containingmotion harvesters could fly from
unstabilised buoys without incurring the huge cost of decommissioning enormous wind towers in the sea at end of life, and without presenting a hazard to shipping. Investors in AWE such as Conoco Phillips, Shell, E-On and Alphabet (parent company of Google) are pushing to concentrate on power station replacement, which they see as the big opportunity. However, Dr PeterHarrop, leader
of the teamof IDTechEx analysts that researched AWE and alternatives, says: “As Altaeros reports, there is also a $17bn remote power andmicrogridmarket that could benefit fromthe technology. Many off-grid sites, including small islands,mining sites ormilitary bases rely on expensive diesel generators to provide some or all of their power needs. There aremany projects that are trying to develop integrated solutions to tackle this market, particularlymicrogrids that integrate some type of renewable energy. The International Renewable Energy Association (IRENA) finds that 400GWof gensets of 0.5MWand above is a candidate for replacement as new emissions laws kick in but 150GWof that is where there are long intervals of no sun or low level wind: AWE uses stronger wind higher up.
WINDMILL INSPECTION Another role for unmanned aerial vehicles (UAVs) lies not in the power generation process itself, but in the inspection of generators, such as windmills. UAV infrared (IR) cameras for the oil, gas and utility industries are already in service, providing exceptional results in areas previously considered impossible to survey. Wind turbines promise to be an enormousmarket for drone
inspection. As the industrymatures, a growing number of wind turbines are operating out of warranty andmust be servicedmore frequently tomaintain productivity and avoid downtime. Preventativemaintenance by inspecting blades before a failure actually occurs costs 25 per cent less than reactivemaintenance, while predictivemaintenance costs 47 per cent less. According to UK thermography consulting company iRed,
inspection of windmills using drones combines visual and infrared techniques, looking for visual characteristics and thermal signatures. Thermography (otherwise known as thermal imaging) uses infrared-sensitive cameras to inspect buildings, electrical equipment and rotatingmachinery to find faults associated with heat loss or gain. Infrared cameras have developed significantly
12 /// Environmental Engineering /// April 2017
Lightweight infrared cameras attached to drones are finding use in helping maintenance teams pinpoint failure locations in wind turbine nacelles
over recent years:modern thermal imaging cameras are now so small they can fit in the palmof the hand. These smaller and significantly lighter infrared cameras are ideal for integration with aerial platforms. A thermal imaging cameramay look like a normal video
camcorder, but it operates somewhat differently. Rather than using a CMOS or CCD technology detector which (in a normal camera) records different levels of a range of visible light colours, a thermal imaging camera uses a device called amicrobolometer array to accuratelymeasure levels of infrared radiation across a scene. Glass is opaque tomost wavelengths of infrared light, so in place of conventional glass lenses, exoticmaterials such as germaniumor sapphire crystalsmust be used. Germaniumlenses are quite fragile, so often have a hard coating to protect against accidental contact – one reason why thermographic cameras are more costly. UAVs are able to fly at an optimumdistance fromthe structure,
usually from3-10m, and can circle around it to cover the whole surface area. The data they gather can then be used in conjunction with photogrammetry software and used to build a three-dimensionalmodel of the blade, delivering a level of accuracy and detail that is hard to achieve withmanualmethods.When and if repairs are needed, the team knows exactly which part of the turbine needs attention and, because the UAV has GPS, it also points to the structure’s exact location. Both visual and thermal analysis
play a useful role in the inspection of wind turbines. Blade damage and gearbox failure are the two factors responsible for the greatest amount
of energy loss, with poormaintenance and lightning strikes being themost frequent causes.While inspection of themain tower is primarily a visual job, thermography can play a useful supportive role in examining nacelles and the turbine blades themselves. Nacelles house themechanics of the turbine, including the gearbox, generator, brake, controller and yawmechanism. Visual inspections are carried out to ensure there is no damage and that no debris has
built up around themoving parts. In the worst case, if there were debris in the nacelle, it could ignite. If the yawmechanismis damaged then the turbinemay not be able to turn its blades against the wind, which could result in greater damage. Although visual inspection ismost significant, aerial thermography on wind turbines is also useful for quickly discovering excessive heat being generated fromthe nacelles. Exposed to whatever the weather throws at them, spinning at
10-22 rotations aminute and designed to enduremore than 120,000 operating hours, the blades are some of the hardest working parts of a wind
turbine.Made of glass fibre reinforced composite and weighing around 12 tonnes each, there is a need to ensure they are structurally safe. Thermographic cameras can be used to identify areas of the
blade which are delaminating, as they can detect variances in the heat of the blade structure. Inspection of the blades can be carried out using drones, or a telescopicmast and a zoomcamera, which can examine the blade in detail. EE
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