The new 3.0 MW direct drive permanent magnet generator wind turbine from Siemens (image courtesy of Siemens Energy)

There has been much interest in the development of direct drive systems in recent years, since the elimination of the gear box theoretically the turbine system more reliable.  What Siemens appears to have done is to take that a step further – by eliminating half of the components at the top of the tower, there is less maintenance for the service technicians to have to worry about.  This is good for onshore systems, but even more valuable for wind turbines that are to be located offshore, far from land. It also means, in theory, more uptime for each turbine, thus allowing them to produce electricity over wider intervals.

Siemens installed the first prototype of the SWT-3.0-101 at the beginning of December 2009 close to the town of Brande in Denmark. Siemens entered the wind energy business through the acquisition of the Danish company Bonus Energy A/S approximately five years ago, a company that had been in business since 1980, as Danregn Vindkraft. This company was a pioneer in the early days of recent interest in wind power, and was a logical acquisition for Siemens as it looked to enter the market. The Siemens Wind Power business unit is still headquartered in Brande. The permanent magnet generator is being produced by the Large Drives business unit within the Siemens Industry Sector.

The compact nature of the nacelle for the new wind turbine from Siemens means that it is easier to transport than other systems (image courtesy of Siemens Energy)

Siemens first tested direct drive systems in the form of two 3.6 MW concept turbines in July 2008, leading to the 3.0 MW prototype installed late last year. While Siemens acknowledges that they were not the first to market with a direct drive permanent magnet generator system, the company appears to have deliberately taken its time with the development of its own systems. In a news release from late last year, Mr. Stiesdal indicated that rushing to the market with immature technology was not an option for Siemens. While the nacelle contains new technology, the blades, rotor hub, tower and controller were developed from existing products. Full commercial launch of the new turbine through serial production, is expected to commence next year, with a number of systems being installed around the world in the meantime.

One comment from Siemens is worthy of note for the permanent magnet industry and its supply chain. In a promotional video that was released to coincide with the launch of the new turbine, Ernst Frendesen, Director of Global Sales and Proposals for Siemens said that the

“market demand that we expect on this machine will be extremely big and therefore for a period, we think that the market demand will outweigh the production capacity.”

Attempts to ascertain the specific amount of permanent magnet materials used in SWT-3.0-101 turbine design were declined by the company for reasons of confidentiality. It is clear, however, that Siemens is putting the permanent magnet industry [and indirectly, the rare earths supply chain] on notice.

Schematic of the new 3.0 MW direct drive permanent magnet generator wind turbine from Siemens (image courtesy of Siemens Energy)

Mr. Stiesdal has kindly agreed to do an interview with me on the SWT-3.0-101 wind turbine and its direct drive, permanent magnet-based drive system, which I will post to Terra Magnetica once completed, along with any other developments in the area of DD PMG turbines as they happen.

[last updated August 9, 2010, to correct text of Mr. Frendesen's quote from promotional video].

The use of algae as a potential source of fuels is nothing new within the world of renewable energy. As Siemens says:

Algae are a valuable source of raw material. For millions of years throughout the history of the world, they have transformed CO2 into valuable organic molecules. Some species specialized in the production of fatty acids and lipids. Their fossilized remains from the dawn of time are the foundation for the petroleum and natural gas extracted today. Algae continue to harbor enormous potential today as suppliers of biomass, biogas, or biodiesel. They are also easy to cultivate. They don’t need anything more than CO2 and water, and preferably wastewater at that because of the nutrients it contains.

The problem is that while it is relatively easy to grow algae, harvesting it is a real pain. Within a liter of water, only a few grams of algae grows at a time, and so the water has to be filterd and drained, which is time consuming.

The solution, according to Siemen’s Manfred Ruehrig, is to add a fine powder of magnetite – iron oxide – into the water.  The algae latch onto the magnetite and, after stirring, the algae-magnetite combination can be easily removed by using an external permanent magnet. Although this has only been done in the laboratory so far, results have been promising, and could lead to the scaling up of the process, using similar processing equipment to that used for industrial magnetic separation. The magnetite would be re-used after separating it from the algae.

According to Siemens, the process would result in less water loss, and thus it could be used for drying in drier areas.

The use of magnetic particles in this way is not dissimilar to well-establish biomagnetic separation techniques used in the medical sector, to separate blood cells, DNA and other biological entities, using combinations of chemically-active magnetic nanoparticles, and powerful magnetic fields generated by specially-shaped magnetic configurations.

Flywheels work on the basis of imparting energy into a rapidly rotating mass, which can then be tapped for later use.  They are a well-established method of providing back up power for commercial power utilities, and more recently, they have started to see use in regenerative braking applications for vehicles, where the energy from braking is transferred into a flywheel [instead of the alternative electrical generator approach].

It is to this latter application that the Kinergy is apparently being applied.  In Figure 1 we can see a cutaway model showing the insides of the device. The blue-and-yellow components represent the magnetic gear system.

The Ricardo Web site says that:

[t]he range of potential Kinergy applications is significant not least due to its comparatively very low projected production costs. The technology is thus ideally suited for use in road vehicles where regenerative braking and torque assist is employed as a means of improving efficiency and hence reducing fuel consumption and CO2 emissions. Such potential applications range from small, price-sensitive mass-market passenger cars to large luxury SUVs, buses and trucks. Across all of these vehicle categories, Kinergy offers the prospect of enabling effective hybridisation extending into market sectors where the use of conventional electro-chemical battery systems technology would be prohibitively expensive.

They go on to say that:

Further potential Kinergy applications also include low-cost, compact energy management and storage systems for use in industrial and construction equipment, elevators, railway rolling stock, and local electrical substations and power distribution systems.

Magnetic gears of this type are relatively new, and there are not too many commercialized applications for them as yet. The systems generally consist of three concentric sub-systems which allow for the conversion of speed into torque and vice versa, without contact between the sub-systems.  They can also be combined with electrical motors and generators to form some very interesting electrical machines.

Ricardo says in the excerpts above that they anticipate “very low projected production costs“. Magnetic gears are not cheap to build, because of the labour involved, so one would have to surmise from this statement that in relation to the system as a whole, the gear sub-system is not a major cost driver. Certainly there are some significant advantages to magnetic gears over and above mechanical gears, to make them worth considering.

Ricardo is working on the use of the Kinergy concept in a demonstrator FLYBUS vehicle based on an Optare Solo bus, as shown in Figure 2.

Figure 2. FLYBUS demonstration concept, using the Ricardo Kinergy flywheel system. Courtesy of Ricardo (2009)

I’ll be posting more on magnetic gears in the near future, and I will be presenting a review of magnetic gears and related electrical machines at the Magnetics 2010 conference in Florida, next January. In the meantime, you can read the rest of the article on Kinergy here.

The Times Online has just published a story on a technology that apparently “has the potential to revolutionise the renewable energy industry by making wind power cheaper and more reliable and greatly increasing the efficiency of wind turbines for electricity companies.”

The driver behind the work, conducted by Dr Markus Mueller and Dr. Alasdair McDonald of the University of Edinburgh’s Institute of Energy Systems, is the goal of effectively eliminating the gearbox from off-shore wind turbines. Being able to achieve this would increase reliability and reduce maintenance costs, given that off-shore wind turbines are out at sea.

The researchers claim to have been able to reduce the weight of conventional direct-drive generators by up to a half, and have developed a system that is apparently simpler to assembly and manufacture. Unfortunately at this point, there appears to be little in the public domain on the new technology. I was able to find a paper presented at the 2008 European Wind Energy Conference that looks to describe the technology.

Based on this paper, it appear that the NGenTec [not "NGenTech" as originally reported by the Times] technology involves the use of a “C” shaped core generator [see Figure 1] which, according to a University of Edinburgh press release sent out on Nov 23, 2009, they’re calling C-GEN. The team used it to build a 20 kW, 100 rpm prototype. They were able to show that changing the mechanical structure of the generator led to reduce required mass while maintain rigidity and structural integrity. Building on the initial concept, the team were able to show that a generator capable of producing 100 kW, based on this design, would have a total mass of approximately 2,800 kg (6,170 lb) – less than half the 6,600 kg (14,550 lb) mass of the NorthWind 100 commercially-available wind turbine generator, which also produces 100 kW of power.

Figure 1: a) schematic of a conventional permanent magnet, radial flux generator, and b) the NGenTech C core machine. From Mueller & McDonald (2008).

Dr. Mueller and Dr. McDonald have on the last couple of weeks formed a new company to market the device, called. The new company is chaired by Mr. Derek Shepherd, “a former managing director of Aggreko International, a Glasgow-based supplier of mainly diesel-fuelled generators.“

The Times article goes on to say that:

Derek Douglas, an entrepreneur specialising in raising finance for start-up companies, has joined NGenTech [sic] with the aim of raising £4 million to prove that a 6MW generator would work and then a further £10 million to set up an assembly and manufacturing operation.

Mr Douglas goes on to say that the technology has applications for both on- and off-shore systems. This makes sense, although there isn’t necessarily the same cost premium associated with maintenance on-shore, as there is for off-shore installations.

At the moment, NGenTech does not appear to have a Web site up and running yet. NGenTec does have a Web site, and  the Institute for Energy Systems also has an extensive Web site. It shows that this group is doing extensive work in the arena of generators and electrical machines for a variety of renewable energy systems, including wind turbines, wave energy convertors, tidal current systems and the like.

From the NGenTec site:

The Company is presently raising its first round of funding of £4 million. This will enable us to develop, manufacture and build a 1 MW modular unit over the next 12 months. This 1MW modular unit will be specifically designed to form part of a 6MW generator we plan to manufacture and test the following year.

According to the University’s press release, the new company was spun out of the University by Edinburgh Research and Innovation (ERI), the University’s successful research and commercialisation arm, which celebrated its 40th anniversary this month. The University retains a minority stake in the new business.

The initial proof of concept work was funded by Scottish Enterprise.

I’m looking forward to seeing how these chaps progress with this project. You can read the original Times Online article here, incorrect spellings and all…

Jack asks the questions: “why are the components being made in China? Can we do anything to cause them to be made in the USA?“.  He goes on to discuss the opacity of Chinese rare earth mining companies in terms of true cost structures, and how virtual all rare earth permanent magnets used in large scale wind turbines, probably originated in China.

Jack goes on to say:

These are the current consequences of the non-production of any but trivial amounts of the rare earths outside of China, combined with the economic thinking of America’s business and government elites; the former want to maximize profit at any cost, the latter want revenue from the taxes on those profits.

The rest of Jack’s article talks about the issues of investing in hard rock mining, and rare earth mining in particular, in order to exploit the significant natural resources available to us in the USA and Canada. he says that:

Chinese and Japanese companies are now looking at these North American resources for the benefits of the economies of their home countries. They can only do this so long as North America does not any longer have a domestic supply chain to refine, produce metals and alloys, produce components, and assemble those components into end use products.

The article is a good primer on the present problems facing this industry, and how they could impact rare earth permanent magnet supply in the future. You can read Jack’s article here.

]]> http://www.terramagnetica.com/2009/11/12/the-problems-of-sourcing-wind-turbines-and-rare-earth-metals-from-china/feed/ 0 http://www.terramagnetica.com/2009/10/12/wind-turbines-up-close-and-personal/ http://www.terramagnetica.com/2009/10/12/wind-turbines-up-close-and-personal/#comments Mon, 12 Oct 2009 15:56:17 +0000 Gareth Hatch http://www.terramagnetica.com/?p=645 Last week I was in Denmark, and while there I had an opportunity to pay a visit to some wind turbines operated by Aalborg University in Northern Denmark.  Getting to finally see and hear a fully functional 2.3 MW wind turbine “in the flesh” was pretty cool, I have to say.

There was a reasonable wind blowing at the time of my visit and the turbines were moving at around 15-18 RPM.  Standing directly under the blades I could certainly hear them moving, but it wasn’t as loud as I had expected, and after moving just 50-100 yards away the sound diminished significantly.

The University also has a mast close to these turbines in order to measure wind speeds at different heights above the ground, as part of their research into efficiency of production.

Here are some photos…

According to the Humdinger Web site, “[i]nstead of using conventional geared, roating airfoils to pull energy from the wind, the Windbelt™ relies on an aerodynamic phenomenon known as on an aerodynamic phenomenon known as aeroelastic flutter (‘flutter’). While the phenomenon is a well-known destructive force (e.g., a cause of bridge failure), researchers at Humdinger have discovered that it can also be a useful and powerful mechanism for catching the wind at scales and costs beyond the reach of turbines”.

Huh!  ”Sounds pretty bizarre”, I thought to myself, but with a niggling feeling that I actually knew what they were talking about, without understanding why… until I read the very next paragraph on the Web page, where the source of that feeling was resolved. “To picture how this works”, says Humdinger, “think of how you held a blade of grass between your fingers as a kid and made it whistle [Aha!], — or how the strapping on a truck can be seen moving in the wind. That is roughly how the Windbelt can pull energy from the wind – then, it’s a second step to turn that energy of the moving membrane into electricity, which is done by actuating new types of linear generators.”

Clever!

The fluttering of the membrane moves a coil back and forth over a permanent magnet, or vice-versa. The changing field leads to the generation of electricity in the coil, and thus a generator is born.

Humdinger claims that by grouping these fluttering mebranes into modules, cells and panels, they can be used to generate anything from sub-1W to multiple MW of power.  An array of 10 x 1 m x 1m x 5 cm panels could produce 1 kW of power.   On larger installations, Humdinger claims that the “Windcell Panels have an initial projected production cost of $1 per rated watt, “or US$0.03-US$0.05 per kWh (at 6m/s average windspeeds) [...] – four times cheaper than comparable solar systems and far less expensive than similarly-sized turbine-based wind systems”.

A quick search of the US Patent and Trademark Office shows that a patent on the above technology was issued to Humdinger only last month.  Images from the patent show a variety of suggested coil – magnet configurations, a couple of which are shown below:

According to a BusinessWeek article on this technology from late last year, the device’s inventor, Shawn Frayne, came up with the idea while trying to help fishermen in rural Haiti generate cheap, robust electricity. “Unconnected to the local power grid,” said the article, “they relied heavily on dirty kerosene lamps, which are not only costly to operate but also unhealthy and dangerous. [Shawn] decided to devise an alternative—a small, safe, and renewable power generator that could be used to power LED lights and small household electronics, such as radios.”

Mr. Frayne has subsequently worked with communities in rural Guatemala to develop production-ready versions of the Windbelt.  As the concept enters the mainstream of wind generation technology, it will be interesting to see what impact it has on the behemoth that is the wind turbine industry.  At the cheaper rates of electricity generation claimed by Humdinger, and in easy-to-use form factors, one has to think that the technology just might stand a chance of succeeding.

Good luck to them!

As we saw in a previous article in this series, engineers like to increase the given output per turbine, in order to reduce the number of towers that need to be installed.  However, in the process of increasing that output, we run into the challenge of ever-increasing mass at the top of the tower, and problems with mechanical reliability.  Although permanent magnet-based hybrid and direct drive generators can increase the power output with less mass in the nacelle, even these configurations have their limit, as mass inevitable creeps up with increased power rating.  The prevailing wisdom in the utility-scale wind energy industry is that for present technology, this practical limit is somewhere around 6-8 MW. So – how do we go beyond this limit?

Enter the superconductors.  Scientists have known for decades that below a critical temperature, certain materials exhibit zero resistance to electrical current – a phenomenon known as superconductivity.  However, because these material-specific critical temperatures were so low [below 30 K (-405 °F)] these materials had few practical applications.  In the late 1980s, a new family of superconducting materials were discovered, including the synthesis of an yttrium-based [YBCO] material with a critical temperature of 93 K (see Figure 1). Since then, materials with even higher critical temperatures have been discovered.  This family of so-called high temperature superconducting [HTS] materials was hugely significant, because their critical temperatures were greater than the boiling point of liquid nitrogen.  This meant that for the first time, practical applications might be viable since the liquid nitrogen cryogen needed to cool the devices was inexpensive [did you know that the cost of liquid nitrogen is actually less than that of milk?!].

After their discovery, tremendous amounts of effort were spent on producing cost-effective HTS materials that could be manufactured into coils, wires and cables.  As a result, a whole family of superconducting electromagnets came on the market, used for anything from SQUID magnetometers to the control systems in particle accelerators.  HTS coils are today able to carry more than 100-150 times the current of a conventional copper wire of similar size.  It was inevitable, therefore, that attention would eventually turn to the use of HTS materials in motors and generators, particularly in applications where mass and bulk needed to be minimized, such as marine propulsion systems – and wind turbines.

There are a number of companies presently working on the development of HTS generator systems for wind turbines.  In 2007, American Superconductor Corp [ASMC] began work in partnership with TECO-Westinghouse, on the design of a 10 MW wind turbine that would utilize a direct drive HTS generator system, as part of a National Institute of Science and Technology grant.  ASMC has been working on large-scale HTS-based electrical machines for some time.  In early 2009, they completed testing of a 36.5 MW HTS motor for the US Navy, in conjunction with Northrop Grumman (see Figure 2).  Using their proprietary 344 YBCO HTS material, ASMC’s initial data indicates that the 10 MW wind turbine generator will weigh around 120 tonnes [264,500 lb], as opposed to an estimated 300 tonnes [661,000 lb] required for a permanent magnet direct drive generator to produce the same output.

Earlier this year, AMSC started work on a project with the Department of Energy’s National Renewable Energy Lab and its National Wind Technology Center [NWTC], to properly evaluate the economics of the 10 MW wind turbine.  Interestingly, engineers at the NWTC have been quoted as saying that it may take as long as 10-15 years for us to see 10 MW+ commercially-available wind turbines based on HTS materials.

Advanced Magnet Lab and its subsidiary AML Energy [AMLE] are working to incorporate its proprietary Double-Helix technology into a 10 MW direct drive HTS generator system for wind turbines.  AMLE claims that this technology, once proven, will be scalable to 20-30 MW power outputs.  They report that the design will be 75% lighter and 50% smaller turbines than the best turbines available today, with greater efficiency and reliability of operation.  They hope to have a demonstration unit built by 2011-2012.  AMLE is also looking into applying their technology into hydroelectric turbines.

Since 2007, Zenergy Power and its partner Converteam have been working on a UK Department of Trade and Industry [DTI]-sponsored project to develop an 8 MW direct-drive wind turbine, based on Zenergy’s proprietary HTS coils (see Figure 4).  This same team was recently in the news for their work on the world’s first HTS hydroelectricity generator.  According to Zenergy, a key goal is to ramp up the manufacturing of HTS wires, so that the cost of these materials can be reduced.  The first prototype of their turbine is scheduled for production and testing in 2010.

A particularly attractive feature of HTS generators in general,  is that once they have been “charged” by passing current into the coil, so long as the coil remains at cryogenic temperatures, the current will not deteriorate.  This further reduces the weight in the nacelle since the additional power supply needed to energize conventional induction generators, is eliminated.

After reviewing the current state of HTS-based systems, it would seem then, that although we are some years away from viable, 10 MW+ commercially-available wind turbines based on HTS generators, we are well on our way to achieving this output.  If companies like those mentioned above are any indication, we’ll be pushing through to 15 MW and 20 MW in no time at all!

I hope that this article was of some use to you;  I welcome feedback and am always looking to improve the content and quality of the Terra Magnetica blog.  If you missed the previous article in this series, titled “How Does The Use of Permanent Magnets Make Wind Turbines More Reliable?“, you can find it here.

Until relatively recently, almost all commercial wind turbines had the same type of power train features.  A typical configuration is shown in Figure 1. The rotor blades, typically made from fiber glass, are mounted to a cast-iron hub.  The hub is mounted onto the drive shaft which passes into the nacelle via a rotor bearing, into a mechanical gearbox.  The gearbox is then coupled to a doubly fed induction generator [a special electrical machine that uses two sets of electrically-excited windings to create magnetic fields as part of the mechanical-to-electrical energy conversion process].  It does not use permanent magnets.

Figure 1: Conventional commercial-scale wind turbine. 1 - blade; 2 - hub; 3 - rotor bearing; 4 - gearbox; 5 - generator. Courtesy of Nordex GmbH (2008).

The typical rotor speed for commercial-scale wind turbines is anything from 10-20 RPM under normal conditions.  Because doubly fed induction generators of this type require high RPM in order to operate properly [at least 750-1500 RPM], the gearbox is required to convert the low speed of the rotor into the high speed needed by the generator.

Unfortunately – the bigger these gearboxes get, the more prone they seem to be to all kinds of mechanical problems.  In recent years, there have been improvements in the design and manufacture of wind turbine gearboxes, but there are still a variety of issues to be overcome. According to a paper published by the National Renewable Energy Laboratory in 2007, the majority of gearbox failures originate in the bearings.  Without regular maintenance and observation, it doesn’t require an active imagination to see how catastrophic a full gearbox failure would be to the turbine.

These challenges led to a re-think in the structure of the wind turbine power train, and in 2005, the first commercially-available hybrid turbine generator solution came on the market.  This configuration uses an innovative gearbox design in conjunction with a permanent magnet generator, with the end result being a significantly increased reliability for the system as a whole [see Figure 2].

Figure 2: Combined gearbox - permanent magnet generator system. Courtesy of Multibrid (2008).

This type of set up reduces the overall weight in the nacelle, and requires a generator speed of 60-150 RPM – significantly lower than that for the doubly fed inductor generator design. All of this also means that the turbine power train is more reliable, has fewer moving parts to go wrong, and requires less maintenance.

So – the next logical step in the evolution of the turbine power train, would be to come up with a design that removes the need for a gearbox altogether – and this is indeed where we are at with these designs today.  The last couple of years has seen the emergence of commercial-scale, direct drive permanent magnet generator [PMG] systems, with the hub directly connected to the generator. In order to achieve this, we need a much larger diameter generator, to accommodate the required increase in the number of magnetic poles on the rotor.

The result is a system with significantly increased reliability and reduced maintenance costs. Reduced downtime for maintenance also means less non-producing time offline. The elimination of associated mechanical losses that are inevitable with gearboxes, also leads to improved efficiencies in the power conversion process.  The generator itself is also much more robust than conventional systems, and gives greater efficiencies when wind speeds are not at full rating, compared to the earlier designs.

Figure 3: Direct drive neodymium-based permanent magnet generator for 3.5 MW wind turbine. Courtesy of The Switch (2008).

Of course, this being the real world, the direct drive PMG is not entirely without challenges.  Finnish company The Switch produces PMGs for the Scanwind 3500 DL wind turbine, rated to 3.5 MW of power, and shown in Figure 3.  This PMG uses over 2,000 kg [4,400 lb] of high energy neodymium-based [Nd-Fe-B] permanent magnet material.  This equates to approximately 0.6 kg [1.3 lb] / kW produced.  The obvious supply chain implications for these quantities of Nd-Fe-B magnets are beyond the scope of this article, but have been discussed elsewhere at here at Terra Magnetica.

So, I hope that this article has given you some insight into the evolution of wind turbine electromechanical systems, and how the use of permanent magnets has allowed engineers to design more robust, more reliable power trains.

In my next post, the fourth in this series, we’ll take a look at developments in the use of cutting edge superconducting materials, to produce generator systems that might surpass those presently available. Will these new designs be the next step in the evolution of wind turbine systems? We’ll discuss that too. In the meantime, if you missed the previous article in this series, titled “Why Are Wind turbines Getting Bigger?“, you can find it here.

Finally, some of the content of these articles is drawn from a paper that I presented at the Magnetics 2008 Conference in Denver, Colorado, titled “Going Green: The Growing Role of Permanent Magnets in Renewable Energy Production and Environmental Protection“. You are welcome to download a copy of the presentation from here.

First, some data: as the figure below shows, twenty years ago, the largest commercial wind turbines were producing around 0.5 MW of electrical power, with a rotor blade diameter of approximately 40 m [130 feet] and a tower height of a little over 50 m [165 feet]. Ten years ago the largest turbines were producing perhaps 2 MW, the rotor diameter had doubled to around 80 m [260 feet] and the turbine nacelle [the "pod" at the top that contains all the electromechanical components] sat perched on a tower now 100 m [330 feet] tall.   If we fast forward to the near-present day, we would see that last year saw the start of production of turbines generating as much as 7 MW of power, with rotor diameters of over 125 m [410 feet] and tower heights in the order of 115 m [380 feet].

Trend in increasing wind turbine size (EWEA 2007)

I’ll skip the usual comparisons of these lengths and heights to the length of [American] football fields. You get the picture  - these are big mechanical structures.

There are some obvious advantages to being able to produce more power per wind turbine installed, mainly related to economies of scale. Installing 10 X 5 MW turbines instead of of 20 X 2.5 MW turbines means half the towers to be installed, half the nacelles to be placed at the top of the towers, and in theory half the crane time required to get the job done.

Before we turn to the guts of the turbine itself though, sitting so high above the ground, let’s look for a moment at the turbine blades and tower. The larger these structures have become, the more difficult it is to put them into place. Have some sympathy for the poor truck drivers who have to drive the vehicles that carry those enormous rotor blades, 60 m [200 feet] long, into some of the less accessible places on the planet. So why go to all that bother? Why not just build a bigger, beefier bunch of machinery at the top of the tower instead?

Well, we can do that, and it is in fact being done [see my next post in this series for some examples]. However, it turns out that the amount of energy that a wind turbine can extract from the wind, is proportional to the total area across which the blades of the turbine will sweep. This means that longer blades will, in theory, enable us to generate greater power. Of course, you can’t have these blades coming perilously close to the ground as they move, so the center of rotation has to be placed further above the ground, in order to be able to accommodate the increase. So that’s one reason why the blades are getting longer and the towers are getting taller.

Turbine blades en route to the Scout Moor Wind Farm, passing through Edenfield, UK

There is another key reason though, for the increased tower heights. If you have the time and patience to look through the mathematics involved, you’ll see that the energy that our wind turbine can extract from the wind, is proportional to the cube of the speed of the wind that the turbine experiences. This means that, all other things being equal, a doubling of the wind speed, for example, would lead to eight times the amount of energy being extracted at the first wind speed. Wind speeds generally increase as you get further away from the surface of the planet and of course, a taller tower helps us to get there. There are also considerable variations in average wind speed across the globe, and this “cubing effect” helps to explain why seemingly small differences in wind speed from site to another, can have significant ramifications on the viability of a project and its estimated payback period.

A number of recent studies have shown that, setting the technical and logistical challenges aside – and I know that that’s a big aside! – based on average wind speeds at elevated positions, there is enough wind energy potential world wide to provide all of the planet’s energy needs several times over. In the USA alone, a 2005 study showed that there was enough offshore wind energy potential to replace all the conventional power stations in the entire USA!

One final comment: in most stories in the media on renewable energy production, the writer will frequently compare the total power to be produced from a particular installation, to the number of homes that this energy could comfortably power. What’s interesting to me is that this actually depends on where on the planet those houses just happen to be and so needs to be made clear in any given case. For example, a not untypical 5 MW wind turbine produces enough power for the needs of 1,500 average-sized single family homes in the USA. Were we to re-locate the aforementioned wind turbine to the European Union [EU], we would have enough power for 2,500 average-sized EU single family homes. Going even further afield to China, we would see that 5 MW is enough power for 10,000 average single family homes in that country. We can see, therefore, that the impact of a single wind turbine significantly depends on the location and context in which it is being used.

In my next post, the third in this series, I will discuss the evolution of large wind turbine electromechanical machinery, and how permanent magnets are now a crucial element in dealing with the significant mechanical and electrical challenges that come with building these larger turbine systems.   If you missed the first post of the series, you can find it here.

Some of the content of these articles is drawn from a paper that I presented at the Magnetics 2008 Conference in Denver, Colorado, titled “Going Green: The Growing Role of Permanent Magnets in Renewable Energy Production and Environmental Protection“. You are welcome to download a copy of the presentation from here.