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Northern wind: ScanWind has installed turbines along the Norwegian coast.
GE
"Eliminating the gearbox from the wind turbine [removes] the technically most complicated part of the machine, inherently improving reliability," says Henrik Stiesdal, chief technology officer of Siemens AG. Furthermore, if a permanent magnet is used in the generator, as is the case with newer turbines, the efficiency goes up even more. That's because, unlike today's electromagnetic generators, permanent magnets don't need power.
Direct-drive generators currently cost more than geared systems and are 15 to 20 percent heavier. Still, GE's decision to buy ScanWind is smart, says Butterfield. "Offshore machines are so expensive in terms of maintenance that some people are thinking the tradeoff tilts in favor of direct-drive generators," he says. "I am optimistic that there is technology out there that's going to help bring direct-drive generators down in parity with the weight and cost of geared systems."
Siemens certainly believes so. The leader in offshore wind energy has been testing two 3.6-megawatt proof-of-concept direct-drive turbines near Denmark for over a year now. Stiesdal says that the technology has proven to work just as well as gearboxes in terms of power, vibrations, temperature, noise, and reliability. Now it's a matter of bringing down its cost.
GE, meanwhile, expects to have a market-ready product by late 2012. It is targeting the European market initially because nearly all of the 1,473 megawatts of offshore wind power currently available come from installations along European coasts. According to industry analysts, this capacity must reach 30,000 megawatts by 2020 if the European Union is to meet its renewable-energy targets. One of the reasons for choosing ScanWind, says GE, is because of the company's footprint in the Nordic countries, which, along with the U.K. and Germany, are the brightest spots for offshore wind energy.
Department of Energy funds companies developing superconducting, "gearless" turbines.
Approval of Cape Wind could signal a boon in offshore wind projects.
I would assume that if the rotor was larger it would also have more coils? But how much larger would the rotor have to be to get the same electrical energy as the gear box versions.
Also whatever happened to the vertical wind generators, they looked like a simpler concept to me, I have seen articles on prototypes but not much follow up?
Dave
The vertical wind turbines have so far had far lower efficiencies than the large tree bladed turbine designs that are the most common today.
The dramatic reduction in efficiency is a much bigger economical disadvantage than the advantage in very slightly lower maintenance cost by having the generator at ground level, and eliminating the minor cost of the yaw mechanism...
What's needed is an efficient design.
It looks like a major reason for the high cost of direct drives is the low volume at which these things are currently (no pun intended) produced.
They should actually cost about the same as gearboxes for the same volume production. Technical advancements that reduce the weight of the drive can help further reduce the cost (it has to do with greater mechanical stresses in the drive and generator equipment right?).
Has anyone thought of fluid drives for the turbines? They could still mount the units high to gain more wind speed but have a fluid drive down to the ground level generators with a risistance built-in the line to obtain more pressure to the generator? Just a thought!
Artemis Wind is promoting a fluid drive for wind turbines, http://www.artemiswind.com/
A few years ago, Parker Hannifin received a grant from the Canadian government to develop a fluid power gearbox for wind turbines. I haven't heard of any progress on it.
Simplicity whenever possible and gearless is very desirable. Seems to me that either design requires power line conditioning? Frequency, lead, and lag adjustments are done electronically for any grid connected wind machine?
A really puzzling question for me is: Can not the speed of the turbine be controlled by the load on the generator? (i.e. controlling the excitation field) Can permanent magnet generators have controllable excitation fields?
Why do GE designs have a cutout speed at high wind conditions? Why not feather the blade pitch and balance against the generator loading? What is the limiting design feature that requires parking during high wind conditions?
Thanks for any insights.
I believe the main disadvantage of all direct drive wind turbines, and most variable speed geared turbines with a fixed ratio gearbox, is that the generator speed must change directly with the rotor speed. This produces "wild" AC, which must be converted by power electronics into constant frequency power for the grid, as you mentioned. In other words, there is no way to eliminate the power electronics with direct drive or conventional geared variable speed wind turbines.
AAER and DeWind, possibly others, offer geared turbines with a variable speed gearbox, in order to drive the generator at constant speed even though the rotor speed is variable. This eliminates the power electronics and allows the use of a synchronous generator, which is the kind used in central power stations. Voltage and power factor are controlled by varying the field. The synchronous generator is directly connected to the grid. They are simpler, more efficient and, I understand, intrinsically more robust than the induction type that must be used with power electronics when the generator speed is variable, as it is in most wind turbines today, geared or direct drive.
About twenty years ago, in order to obtain constant frequency power with a fixed ratio gearbox, some designers achieved constant rotor speed by varying the load on the generator, as you suggested. I believe the NASA turbine at Plum Brook on Lake Erie was of this design. It was razed several years ago because it had long since been outmoded, and maybe because it was an eyesore with its two-bladed rotor, crude exterior and stumpy profile, although this is only speculation. These turbines used synchronous generators for full control of the load and power characteristics. In other words, they did not use power electronics, which was probably the main point of this simple arrangement. In those days, and I am old enough to consider them recent history, power electronics were crude, expensive, inefficient and unreliable. The problem with this old technique is that, compared to modern variable speed turbines which have the advantage of decent power electronics, it is not efficient. To extract the most power from the wind, the rotor speed must change with the wind speed. Therefore, power production in a turbine of the old design would have been considerably less than that of a modern variable speed turbine of similar size. I doubt that any turbine of the old design is available today, although modern variable speed turbines probably control rotor speed to some extent by varying the generator load. Mostly they use other techniques to match rotor speed to wind speed.
I doubt that direct drive is the best solution for wind turbines. The generators are very large. This makes them more difficult to seal against the weather, especially offshore. A large generator also increases tower stress, hence cost, from the wind load - top hamper, to use a sailing term. They are very heavy, and it doesn't seem likely that they can be made much lighter. The greater the tower top weight, the more costly the tower, foundation and erection, although elimination of the generator might be enough to offset the additional weight of the generator.
However, if a standard synchronous generator is installed at the bottom of the tower, where it should be, driven by a vertical drive shaft connected to a variable speed gearbox at the top, then there is no need for power electronics. The tower top weight, size and windage is minimum, hence cost is much reduced. Maintenance is easier. Therefore I predict that direct drive turbines will go the way of those constant speed wind turbines of twenty years ago, at least for turbines of more than 2 MW.
Improved Gearless Wind Turbine Design
Gearless Wind Turbine from GE will be an improved version of Wind Turbine which may be efficient . Earlier there were some companies which have gearless wind turbines.
Dr.A.Jagadeesh Nellore(AP),India
Wind Energy Expert
E-mail: anumakonda.jagadeesh@gmail.com
Re: Improved Gearless Wind Turbine Design
Respected Sir, we are building a vertical wind mill for powering a street light, (for eg : 100w bulb). How to control the generator speed, if we are using a direct drive.
our company,Shandong Swiss Electric Co.,Ltd, has gearless wind turbines with capacity of 1.5MW, 2.0MW. Anybody who is interested in permanent magnetic direct drive wind turbines pls feel free to communicate with us via email:eric@ruiqineng.com.
Re: gearless wind turbine from
Hi,
I could not reach you via email, can you please contact me back in this email
nathan@ http://topmagneticgenerator.com
Re: gearless wind turbine from
hello dear John,i can not approach you by your email id nathan@topmagneticgenerator.com and john@topmagneticgenerator.com, so can you pls send email to Erichesuccess@gmail.com or eric@ruiqineng.com. Thanks.
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ms
190 Comments
current? torque?
"In a turbine generator, magnets spin around a coil to produce current--the faster the magnets spin, the more current is induced in the coil. To make up for a direct-drive generator's slower spinning speed, the magnets in ScanWind's turbine circle with a larger diameter, boosting the amount of current that is induced in the generator by increasing the torque."
I think the following is a better explanation:
By Faraday's law, a magnet moving past a coil generates an electric field, i.e. a voltage. The voltage is directly proportional to the magnet's speed. Increasing the radius of rotation increases the speed proportionally (for the same rotation rate), and thus the voltage.
Current is directly proportional to voltage and load (Ohm's law).
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willknight
37 Comments
Re: current? torque?
@ms
Thanks for the suggestion. That sentence has been fixed to make it a bit clearer.
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