My understanding is that the utility company will not pay you any money. they will give you credit for future energy usage. But they will not actually send you a check. Therefore, you can only save what you would spend for each month. You can't actually make any money with an at home windmill. I don't know if this is still factual but it came from a reliable source at one time.
I read an article about some different people who put up private windmills on their property for their own personal use and even with the cost savings on energy it was going to take nearly 20 years to pay it off. I think until energy prices go way up it takes a long life for some of these green ideas to pay off.
I haven't studied wind turbine design in any depth, but the idea of a hydraulic transmission sounds brilliant to me. Sort of analagous to the automatic transmissions in cars instead of manual, I suppose. Efficiency should be good, but the maintenance, nacelle design, etc. should all be greatly simplified. It would be interesting to have someone in the industry comment on why this path hasn't been taken.
The trasmission is a high-wear and quite heavy device, and presently it is the one item that has a definite lifetime. In addition, it takes up a fair amount of space and the connection to both prop and generator must be quite precisely aligned. REplacing the gearbox in the upper assembly is a very big deal task. The generator, generator controls, gearbox, and gearbox cooling hardware comprise more than half the weight of the upper end, and so moving all of them to ground level would produce quite a savings in space and weight. An added advantage of the hydraulic approach is that all of the cooling could be located on the ground, since cooled oil would also cool the topside pump assembly. The piping losses can be minimized using techniques that have been well known in the hydraulics industry for many years. The somewhat reduced efficiency of using hydraulics would certainly be offset by the increased reliability and the reduced servicing costs associated with having much of the system at ground level.
Using ground hydraulics is an interesting approach and I believe the reason it hasn't been tried would be the losses in moving all that fluid such a great distance. Up top you would still need something to control the blade pitch and positioning, so you may as well have the transmission up there too.
The challenge with low speed alternators and generators is that they need a whole lot of poles to be "low speed". Each time the number of poles doubles the speed iscut in half, and to get to a 600 RPM synchronous speed one is already up to 16 poles. That winds up being a large device. Putting the generator on the ground allows for whatever speed and number of poles is convenient. Plus, the added advantage of being able to adjust the ratio almost instantly is a handy side benefit.
There does exist an alternative for putting the gearbox and the generator up in the nacele where they are very hard to get to and expensive to service. The solution is to have the turbine directly driving a large variable displacement hydraulic pump, and then use a variable displacement hydraulic motor to turn the generator down on the ground. This wold avoid using a gearbox and also allow generation of power at lower wind speeds, with the added advantage of being able to run the generator at whatever speed was desired. The generator and associated support and control equipment would be at ground level, making them cheaper to install, maintain, and repair, and the power would already be at ground level, making the grid connectionssimpler. Moving the weight down to the ground would reduce the required strength for the base and support, so that would add to the savings. One more potential advantage is that hydraulics does offer a way to store energy in an accumulator, which could potentially assist in a method of longer term energy storage.
What I don't understand is why this approach has not been used very much so far.
- rate life isn't the primary metric... it's return on investment (ROI). Life span has an impact, but so long as it is not different that expected, it remains just one of several variables impacting ROI.
- already (6 years ago) designed in processing power for monitoring the vibration with active pitch control for minimizing wear on the minimal transmission involved. (4 generators around one large gear - balanced torque on frame, made easier generator swap out inside nacelle - no crane or helicopters involved). Amazing to "listen" to difference in the system with high freq adjustments being made vs without any active control. The basic controls already have the maintenance monitoring , data logging, high level access across networks, etc. to minimize costs.
- Pitch is constantly changing based on location of blade in a single rotation. Why? because on really large diam systems, the speed of wind is significantly different at the top of the arc vs the bottom of the arc.
- smaller systems? Great, but they will always have some significant disadvantages to big systems. a- closer to the ground (slower wind speeds and near birds of prey food source) b- higher blade speeds (noise/bird strike) c- distributed maintenance over larger area (higher maintenance per watt) d- majority of population does not have a reasonable location for installation (limited urban options) e- most people will not want to take responsibility for their own power source (most don't want to be responsible for their own plumbing!) .
In many locations it can make sense... but for majority of population in US and Europe, it isn't an option. Centralized power (and all of it's weaknesses) is likely to be with us for a long while. And yes, this will waste power in distribution and be a major cost in maintenance of transmission lines.
I wish it wasn't so.,,. (in general, I prefer de-centralized systems)
Regardless, the real changes in this industry will come when all the energy sources operation on a "level" playing field, not because of 50 year product lives. It is amazing to see the gov incentives still being paid out to oil/gas .. while many alternative energy incentives have dried up.
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