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World's Largest Wind Turbine
PeteJones writes "'Construction work on the REpower 5M was successfully completed last night with the installation of the rotor. Thus the main work on the prototype of the 5-megawatt, world's largest wind turbine has finally been completed.' The pictures are quite impressive. With 3 18-ton rotor blades pumping out 5 MW I wonder if my neighbours would mind one in my backyard?"
http://www.biggleszx.com/slashdot/5m_01.jpg
http://www.biggleszx.com/slashdot/5m_02.jpg
http://www.biggleszx.com/slashdot/5m_03.jpg
Regards.
$ mv *.sig >/dev/null
This is a great idea. Why aren't we fully exploiting the power of the wind?
This is an example of the obstacles that American power generating windmills are facing. If ever there was a NIMBY group it's these people. Someone wants to build an offshore set of windmills to power about 3/4 of Cape Cod and surrounding areas in Massachusetts. Since Massachusetts is heavily dependent on important electricity and oil, this seems like a great solution.
Undoubtedly there are some ecological implications, but the NIMBY group clearly is magnifying these issues in order to shoot down the whole idea; they're fishing for excuses. They don't want to have to look at windmills. This is where some federal leadership may be required in order to get the U.S. off its foreign energy dependency.
it's = "it is"; its = possessive. E.g., it's flapping its wings.
The noise you mention is a problem. It is caused by the blade passing close to the tower supporting the turbine. There are a few solutions to this, each with its complications. One that I have thought of is to make the tower streamlined, with the sharp ends at a right angle to the rotation of the rotors. What others have done is to move the blades further 'out' from the support structure. A third alternative is to use one of the so-called 'egg-beater' designs, which have no need for a support structure.
In the end, my idea is probably the easiest. But it won't be 100% effective. It is best to locate large-scale turbines away from areas where sound will be a problem.
As regards taking energy out of the wind, the atmosphere's about 11km high, and the wind profile goes up from zero at ground level to pretty fast up in the jetstream. A turbine's wake is mostly dissipated at about 8 turbine diameters downwind, too. So even a wind turbine of this size might only affect less than 1% of the total atmosphere's height, for less than a kilometre horizontally.
When wind power started to come back after the 1973 energy crisis, useful sizes were much smaller. There were a few big machines, but they were one of a kind prototypes. Most of the turbines of the 1970s and 1980s were in the 100KW range. That's a convenient size, because all the components can be shipped easily. The entire hub/generator unit can be shipped assembled.
But all those little turbines are a maintenance headache. Farms of big mills generate more power per acre than little ones, because the blades are higher and catch more wind. So size has been creeping up. As the 1970s units wear out, they're being replaced with fewer, but larger, machines. New wind farm machines are running around 1.5MW. That's a commercial technology. General Electric alone has 2300 units of its 1.5MW turbine installed.
Offshore, much bigger machines are the norm. Setting a pylon in the ocean is a big job, so the fewer the better. Big components can be moved in by ship, so the truck size limit goes away. So offshore machines are running around 5MW. But there aren't many of them. Most of the really big machines are still experimental.
Wind power is like hydroelectric power. There are a limited number of good sites. Most of the ones in California, the major passes through the coastal mountain range, are already taken. The East Coast doesn't have a long coastal mountain range, so installing wind farms in passes is out. So the East Coast systems tend to be offshore.
Total installed wind turbine capacity worldwide is about 40 gigawatts, although that's peak, not average, output. This is up by a factor of 10 in the last decade. Much of this is due to better power conversion technology. Early wind turbines synchronized the blade itself to the power grid. Newer ones have inverters and better controls, so they interface much better to each other and the power grid. Many of the early turbines were only tolerable on grid because they were such a minor portion of generation. They were a destabilizing influence, forced into synch by bigger generators elsewhere. With improved controls, wind generators can contribute to frequency stability, rather than stressing it. As wind power becomes a larger fraction of generation, that's essential.
..but it depends where you are (local average wind speed, depends heavily on topography) and how much power you need.
If you can find a way of levelling the load (e.g. batteries) with only moderate conservation you'd need the equivalent of a constant 1kW output, about 1.4 Hp. Power abstracted from a windmill follows the formula k*0.5*A*V^3, where A is the area of the blade disc, V the windspeed, and K is the fudge factor. There's a theoretical limit of about 59% efficiency, due principally to retaining enough momentum to carry the air on the downwind side away from an axial turbine.
Anyway... say you have a mean wind speed locally of 10mph, which is constant, because you have the device up a tower. That equates to 4.45ms^-1, so working backwards, and assuming 50% efficiency for the 'k' factor - hey, we're geeks, we'll buy th every best - you'd need a blade disc, um, 5.4 metre diameter. Of course the conversion to electricity incurs losses, sy 80% overall... so a (*very* efficient) wind genny rated for1Kwh output at 10mph would imply a 5.9m diameter swept area. Pretty small!
In fact, in the interests of minimising noise and improving part-speed efficiency, you'll find 1kW rated wind generators are slightly bigger, and rely on rather higher mean windspeeds. Beware the windspeed measurement though, that V^3 term will kill ya. If the mean windspeed locally turns out to be just half what you measure, you'll get, at best, only 1/8th the output expected. The actual design considerations for wind turbines (disc solidity, operating range windspeed etc) are wonderfully technical and pretty interesting in their own right.
As to why not...well small wind gens are rather expensive , and Planning control (local ordinances, US) tend to restrict the possibility to rural areas.
Compared to other sources of bird fatalities, windmills rank pretty low.
My patience is infinite, my time is not.