technology watch
French company EAD looks to remote sensing as the way forward
Éole Avenir Developpement (EAD) and Natural Power completed the first ever French installation of ZephIR®, the revolutionary laser anemometry device for the wind energy industry. The installation at the Carentoir wind farm in Brittany, means that France joins a growing list of countries worldwide which have successfully deployed the device, including Canada, Denmark, Scotland, England, Wales, Norway, Germany, Spain, New Zealand, the US and Greece.
ZephIR® was chosen to overcome a tricky shear-uncertainty problem that commonly affects wind analysis in Brittany. The rolling, agricultural landscapes of the region may be aesthetically pleasing, but planted field boundaries and tree shelter belts often interfere with the passage of the wind, leading to surprisingly high levels of surface roughness. This leads to uncertainty in the modelled shear profile and encourages banks to apply greater uncertainty and developers to require greater equity.
In order to address the problem, ZephIR® was installed adjacent to an existing 60m anemometer mast that is logging long-term wind data. Data was then collected for a month by ZephIR®, with sampling of data at multiple heights from ground level up to 150m. This allowed analysis of shear wind speeds not only at the hub height, but across the whole width of the rotor, improving the accuracy of shear correlation calculations and providing greater analysis certainty for the developer.
Oisin Brady, director of Natural Power, France, said of the deployment:
"The Carentoir deployment neatly demonstrates the exceptional flexibility and accuracy of ZephIR®. In less than an hour, the unit was installed and logging data with a significant commercial value to EAD. With minimum fuss, it can then be redeployed elsewhere on the site or removed altogether."
In many people's view, the ease of deployment combined with multiple functionality of the unit, where it can operate equally well as a long-term anemometer or for short-term correlation work (such as at Carentoir), means that ZephIR® will rapidly become an indispensable tool for wind energy developers.
written by Donald Speirs
Marine Energy Technology – Too early for Convergence?
"According to law of averages, one day, all cars will be the same….."
Many of us remember this tag line for a brand of motorcars in the mid nineties and the advert that went with it, featuring hundreds of identical vehicles, plodding their way along an imaginary highway. The message was simple enough; motorcar design will converge inexorably towards a hypothetical end point, where all cars will be uniform and an 'optimum' design is achieved. Whether or not this was happening in motor car design at the time is largely irrelevant, the scenario gave the brand an opportunity to suggest that their product alone was fresh and exciting, and was breaking the trend. Nevertheless, the concept of design convergence remains powerful and is a recurring theme throughout all sectors of technology, from small products like mobile phones and home computers, right through to large scale systems like gas turbines and aeroplanes.
In the renewables sector too, there are examples of design convergence. Within wind power, it is today taken for granted that large-scale commercial wind turbines have a singular appearance, the so-called 'Danish' model. This consists of a tapering tubular tower with three slender blades fixed to the hub, ahead of the nacelle. This belies however the conceptual diversity that has developed since Charles Brush first unveiled his 'home generator' turbine in the 1880's. The Brush wind turbine was the forerunner of modern horizontal axis machines and featured a whopping 17m wooden rotor and a 12kW generator (paltry by today's standards). Since then a huge variety of horizontal and vertical axis wind power configurations have been tried, many with highly exotic appearances and names to boot. Not all designs have been successful, but many have found niche applications. The Savonious turbine for example is great for reliability, but the low overall efficiency rules it out of commercial-scale electricity production.
But is the Danish model a triumph of function over form? Not necessarily it seems. In fact the solid tubular-tapering tower, regarded as so aesthetically appealing, uses more steel than a lattice tower would and is thus more expensive to manufacture. Consider also that a two bladed or single bladed turbine could actually be more efficient than three bladed designs, except that consensus has grown that the three bladed turbine results in a more 'balanced' and 'soothing' appearance. Nevertheless, engineering considerations do hold sway as well. For example, the conventional induction generator coupled to helical gearboxes has for many manufacturers, presented the most feasible method of maintaining a viable connection to the AC grid network at the same time as managing the fluctuating power from the wind, along with the rotor stresses that this generates.
For marine renewables development, many people are comparing the current boom in interest to the pioneering wind energy days of yesteryear. Dr Ross Halliday, wave energy specialist with Natural Power, has been impressed by the level of conceptual diversity:
"We are really in a phase of conceptual jockeying for position when it comes to marine energy devices. The global requirement for renewables has stimulated a lot of thought about the most effective way of harnessing marine power, all the way from your back garden inventor through to your multi-million pound research facility. We are in a period of proving at the moment, when the strengths and weaknesses of the different concepts and developers are yet to emerge clearly"
The diversity on offer in the marine sector is apparent in the devices on offer, although there are still scant few fully commercial devices, and none proven. In the tidal sector, an early concept that came to fruition was the Engineering Business's 'Stingray' device, employing an underwater aerofoil that drove a pressurised hydraulic generator. This is vastly different in appearance and engineering to the more recent 'Open hydro' turbine, which dispenses with complexity (at least in appearance) and opts for a novel outer ring, stator/generator concept. Another device, different again from the Stingray and the Open Hydro but founded on well established principles, is the Seagen device from Marine Current Turbines. This uses an approach not dissimilar to that of wind energy devices, utilising elements such as variable pitch blades mounted on a horizontal axis rotor.
Within the wave sector the diversity is even greater, with a seemingly unlimited number of potential configurations for oscillating water columns, hinged contour devices, floating point absorbers and over-topping devices, all of which could do the job of extracting power from the sea. Having undertaken technical and commercial evaluations of all the key marine devices that are being developed, Dr Halliday has developed a thorough understanding of the key issues related to marine devices:
"The marine environment is very hostile and has influenced the design of marine devices to the extent that the first considerations of the designer have to be a) how will it survive?, and b) how much maintenance will it need? The paradox is that developers who wish to boost project economics by deployment in higher energy waters run a greater risk of damaging their devices, pushing up capital costs to cope with this…"
Conventional wisdom suggests that much like the wind sector, the current embryonic period of testing and evaluation for marine will eventually be overtaken by a period of design convergence with a single concept or style dominating. However, with the huge variety of factors to consider at sea and the relative difficulty in testing and deployment, such convergence may be a long way off, if it happens at all. As Dr Halliday puts it:
"Predicting a concept 'winner' is an especially difficult exercise when it comes to marine devices because of the wide range of factors that must be considered. It is entirely possible that the device which achieves the best commercial success in the long run will do so not because of the underlying concept, but because of the thorough engineering and development testing that has gone into it. Hence the real factor for success may rest with the determination and skill of the developers.…"
In which case, it would seem that the development of successful commercial marine technologies will come back firmly to the preserve of those who have the resources and tenacity to develop them. Bad news for the back garden enthusiast then, but encouraging for those already engaged in device development who, instead of a 'Danish model' for marine energy emerging, can perhaps look forward to finding their niche within a diverse array of successful devices.
Technology Spotlight - Protection Relays
Time to upgrade your wind farm protection relays?
With ever more stringent grid code requirements in the UK, an increasingly sophisticated approach is being applied to protection relay systems and their use with renewable energy. Natural Power's Asset Management business, which has quietly grown since their inception in 2003 to managing over 285 MW across 13 sites, provide an insider's perspective on where the technology has got to.
Protection relays are effectively the brain of the wind farm protection system and guard against power surges or other undesirable electrical events that could harm people or damage capital equipment. Essentially consisting of an electrical switch, the relay will trigger a signal to the main circuit breakers to operate if any of the key wind farm electrical parameters (e.g. voltage, current, frequency or power) stray above or below set limits. The setting of these limits, including the system response time, is of crucial importance to their effective operation. If the settings are too sensitive, then the relay will trigger frequently, interrupting power flow for spurious reasons. Conversely, if the settings are not sensitive enough, or the response time slow, then damage to generating equipment can occur along with wider grid instability.
In recent years, technical advances in digital signaling and micro processing has moved protection relay technology on from single function non-communicating devices into multi-function protection, control and measurement units. Arthur Daly, Chief Technician with Natural Power explains:
"In a relatively short space of time traditional protection relay systems, consisting of a large rack of relays, all individually operated, programmed and controlled, have been replaced by single integrated units that provide the necessary protection functionality along with the ability for end-users to interrogate historic events. This has brought protection relays into the realm of Intelligent Electronic Devices (IEDs), increasing automation and reducing the need for substation personnel."
Commercially available systems can communicate both protection signals along with system measurements to the wind farm Scada system, giving on-site technicians real-time data at their fingertips. In the course of servicing the thirteen sites under his charge, Arthur is convinced there are tangible benefits available as a result of using integrated protection systems.
"We saw immediately the benefits of full functionality protection relay systems when we set about fault finding on two sites, the first with the up to date electronic protection system and the second without. On the latter, the requirement was for two days of cable testing until the fault was identified and then further wind farm down-time to rectify the problem. On the former, the location of the fault was identified instantly from the condition monitoring record, which showed the exact circuit that had caused the trip, and more importantly where the responsibility lay for the problem."
Modern protection relay systems it would seem, with their enhanced ability to identify problems, reduce downtime and reduce owner liabilities, have come a long way from the inflexible electromagnet switches of yesteryear that could merely insulate electrical systems from the very worst rigours of the grid.
Natural Power have trained personnel in the use of the principal commercially available relay systems.
Wind Farms and Radar - Co-existence through Technology?
Wind energy developers and air traffic controllers are pressing hard to follow through on encouraging early predictions that a solution to radar interference from wind turbines would be developed.
At the heart of the radar problem are the fundamental and somewhat opposing characteristics of wind farming and air traffic control radars. On the one hand, air traffic control radar systems are designed to sweep vast areas of the sky and search carefully for the very smallest of aircraft. Modern radar systems are so powerful, that they can pick up flocks of birds tens of kilometres away as well as large waves in the ocean at similar ranges. A radar is deliberately designed to gather information about objects in the sky instead of ignoring them, which means suppressing returns from wind turbines is against their fundamental ‘raison d'etre’. On the other hand, wind turbines have been designed for the single purpose of the maximising of energy production from the wind and has driven designers to focus on achieving the most efficient turbines, but without necessarily considering radar reflection properties.
Broadly the UK air traffic picture can be described as a hotchpotch of different radar systems, of varying ages, that have arisen over many years to meet the specifications of a variety of end users. For example, overall civilian air traffic responsibility falls to NATS En Route Ltd (NERL). Nevertheless, their system may be a different specification and manufacturer to individual aerodromes, or to specific armed force service radars which may be different again. Therefore, a ‘catch-all’ radar solution is difficult to find, since each radar system needs to be configured individually. And with stringent CAA air safety requirements that must be met, each system must be individually certified before adoption.
The Whitelee project near Glasgow provided a technological solution to radar impacts through the erection of a brand new radar system. The new radar system was cleverly positioned in a location where it would have sight of airspace above the Whitelee site, but would be blocked from viewing the turbines. Thus, where air traffic controllers would have had clutter from wind turbines, this can now be blanked out and replaced by a feed from the alternative radar to ‘fill in the gap’. The idea of a composite radar picture, taking multiple feeds from different radar stations, has been mooted as a possible method of mitigating against cumulative clutter for air traffic systems here.
On the turbine side UK firms BAE Systems and QinetiQ are both involved in developing low Radar Cross Section (RCS) turbine components using a combination of Radar Absorbing Materials (RAMs) and designing the exterior surfaces and shapes to be of low reflectivity. BAE Systems are also working with the University of Sheffield to develop a highly novel technique that will use an electrical pulse to reduce the Doppler shift of returns from moving blades. Most air traffic radar systems are specifically configured to detect such Doppler shifts as evidence of moving aircraft and hence eliminating this from the signature would help the radar processor to identify the return as a wind turbine rather than aircraft. Trials of these systems have so far demonstrated effectiveness at reducing the RCS. BAE Systems are scheduled to make public the final results of lab trials of the measures in early 2008, which they hope will also mark the start of a phase of final validation and testing before implementation.
One spin-off benefit of the drive to examine such stealthy turbine solutions has been significant advances made in modelling software used to predict the effectiveness of mitigation measures. In addition, within the realm of the more established line of sight modelling techniques used to predict visibility, there appears to be general confidence within the aviation industry that the prediction tools achieve a good degree of accuracy.
With both turbine and radar side technologies being developed it seems clear that when it comes to solving the radar and wind farm conundrum, no single solution to the problem is going to emerge. Rather the solutions that are adopted will be a mixture of stealthy turbines, regulatory reform, composite radar displays and sophisticated radar processing upgrades.