Improved HAWT Design –based on "Something old, something new…"

System

Currently the very large commercial HAWTs I've looked at follow a generic structural form:
- a large mass buried concrete foundation, or a large below sea-level supporting structure for marine units;
- a suitably stout, strong, tall metallic tower structure to support the gondola and its internal components and systems plus the rotor;
- a three bladed rotor at the front of the gondola. The rotor blades are directly mounted on the hub/gearbox unit, which passes rotational power on linearly to the generator unit(s).

All well and good, following a general design layout done about a century ago.

Here's my proposal for an improved HAWT design that can trade off weight and cost by employing a little bit more complexity. The design concept is actually a throwback to the design of the early European windmills of yore, where a vertical powershaft descended from the rotor powershaft down to ground level where it transferred wind derived power to rotating grindstones or other implements.

Following that ancient design style, you can revise the current standard wind turbine to employ a 90 degree driveshaft coupler (new) in the gondola connecting to a lightweight aluminum powershaft assembly descending all the way down to ground/sea level. At ground/sea level, rotational power is then transferred to the generator.

Gondola changes:
- the generator is eliminated (removed) from the gondola, but a 90 degree coupler (new) must be added;
- the obvious immediate change would be to the weight and balance of the gondola. If the side loading is excessive due to the missing counterbalancing generator, a traditional response would be the addition of the lightest possible counterbalance on an extended moment arm. A more sophisticated resolution might be the addition of a second smaller rotor assembly extended linearly from the rear of the gondola to harness more wind energy –a rather messy response entailing several operational and design issues. The smaller size but longer moment arm of an additional rotor would again result in a reduced side loading condition at the top of the tower.

Tubular vertical powershaft (new):
- required to transfer power from the horizontal axis powershaft all the way down to ground level, or sea level if employed on ocean-based turbines;
- powershaft assembly is composed of several tubular aluminum members with broad welded flanges at each end. Assembled with standard bolts;
- side support guidance collars with roller bearings would be positioned intermittently down the support tower to contain the power shaft's vibrations and flex;
-at ground level, very large diameter flange(s) is/are welded near the bottom end of the last powershaft. The large diameter flange(s) would run on sets of heavy duty bearings, effectively supporting much if not all of the weight of the entire powershaft assembly. The goal here is to reduce the loading of the tower structure the greatest amount possible in order to reduce its weight and cost.

Generator unit (similar to existing ones):
- if the support tower base is sufficiently large in diameter as many are, the generator can be mounted vertically within the tower base, directly coupled to the powershaft end;
- if the tower base were too small in diameter, a 90 degree transfer coupler would be added to the bottom of the vertical powershaft, which would then transfer rotational power through the tower wall via a short horizontal axis powershaft (new) to a generator housing (new) outside the tower.

Advantages and gains:
- a turbine of a set height could be supported by a lighter, less costly tower structure compared to the conventional design;
- if only a single three bladed rotor were employed, the gondola would be smaller, lighter and less cost;
- if two three bladed rotors are employed, more wind energy can be harvested for the same height tower. The gondola structure can still be made shorter, lighter and less costly since the generator unit would be missing from it, relocated to ground level;
- on marine wind turbine units, the lower centre of gravity would contribute to greater stability in severe weather;
- light weigh generator designs would no longer be required, since a less costly conventional generator would be housed at ground/sea level. Such larger, conventional generators would be less costly, with easier, less time consuming maintenance and repairs;
- single unit generators could be swapped out with only a forklift or truck hoist, compared to gondola mounted single unit generators which require large cranes to swap out.

Disadvantages and losses:
- extra cost and weight of a second three bladed wind rotor if used;
- addition of either one or two 90 degree power couplers;
- additional tubular power transfer shaft members extending the full height of the tower, plus a number of guidance collars and their support members;
- frictional losses of power due to the 90 degree transfer(s) and the bearing supports at the very base of the power shaft;
- if the generator(s) is housed internally within the tower base, a much larger, more complex access door will be required compared to a standard manhatch.

Practical Height Limits:
The calculations of efficacy and cost reduction would consider several factors:
- reduction of structural materials in the tower and the gondola due to the absence of the generator there, vs. the additional new components discussed: the 90 degree coupler(s), and the vertical powershaft assembly and its lateral support collars.
- part of the calculations would involve the total weight of the vertical powershaft and the frictional losses of supporting that powershaft weight on bearing assemblies, plus the frictional losses of the couplers.

Thus, the design may be practical between heights H1 (lower limit) and H2 (upper limit). Above height H2 the cost savings attributed to a lighter tower and gondola structures are outweighed by:
a) the cost of the new components, plus
b) power losses due to support bearing assemblies friction.

(cont'd on Part 2....)

System2

Improved HAWT Design -cont'd

(cont'd from Part 1...)

A minor factor also to be included in cost calculations would be the labour savings of servicing the generator at ground level vs. the increased labour required for servicing the couplers and support collars. Other minor factors would be the reduced capital cost of the generator, which no longer need be of a light weight design utilizing expensive supermagnets, plus a reduction in the size and weight of the supplementary power cables ascending from the ground up to the gondola.

Increasing Tower Height:
If the design goal is to maximize the energy recovered for a given capital cost C, then increasing the tower height allows for increased power generated due to higher wind speeds. But designers have to increase the tower's diameter and its structural strength to make significant gains in tower height, thus increasing the fabrication and construction costs of the entire project.

One method of raising tower height without requiring a significant increase in the tower diameter and structural stiffness would be by employing a guyed tower design, with guy wires, popularly used with radio towers. The upper limit of the guy wire attachments would naturally be below the bottom limit of the rotor blades.

Again there is a trade off: the reduced tower structural weight and cost vs. the increased weight and cost of the guy wires (new) and their separate foundations (new), plus the increased maintenance cost of the guy wire cables over the lifespan of the project. There are likely other losses as well to consider.

What do you think? Comments and feedback would be welcome. It would be interesting to see power vs. height vs. weight vs. cost graphs if you can share it. Please pass this on to pro wind turbine engineers in order to help keep improving renewable energy designs.

Best,


Harry Zilber
Toronto, Canada

BB.

Re: Improved HAWT Design –based on "Something old, something new…"

Actually a right angle drive on HAWT is quite an old concept...

I think Jacobs is still selling them.



The only difference is that they have the generator at the top of the tower instead of at the base.

-Bill

russ

Re: Improved HAWT Design -cont'd

Don't you think this has been gone over many times in years past?

Guyed towers are standard design for small turbines.

The height/wind speed gain is easily available - if I remember right the Danish Wind Association lays it out well. Cost per meter of elevation is going to be hard to come by unless someone does an actual tower design.

I don't think there is a chance in the hot spot of the vertical drive shaft being utilized.

Russ

BB.

Re: Improved HAWT Design –based on "Something old, something new…"

Welcome to the forum...

And by the way, try to keep all related posts in one thread (click on last 24 hour posts to find your previous posting/threads.

-Bill

niel

Re: Improved HAWT Design –based on "Something old, something new…"

power transfers to the ground cause a complexity for the tower design and limit the towers only to those that can transfer the power. this is also a high cost in implementing so towers will skyrocket in price. something like this could be done on a diy basis for the mechanically inclined individual that also has architectural, electrical, and welding skills. that same individual is likely to built his own turbine too.

russ

Re: Improved HAWT Design –based on "Something old, something new…"

The engineers working for all the large wind turbine manufacturers are smart fellows.

Small turbine manufacturers are sometimes just shade tree mechanics with no engineering involved.

The people making commercial turbines have spent a lot of time and money on the most economic design.

Russ

Peter_V

Re: Improved HAWT Design –based on "Something old, something new…"

Zilber wrote: »

Here's my proposal for an improved HAWT design that can trade off weight and cost by employing a little bit more complexity.

you can revise the current standard wind turbine to employ a 90 degree driveshaft coupler (new) in the gondola connecting to a lightweight aluminum powershaft assembly descending all the way down to ground/sea level. At ground/sea level, rotational power is then transferred to the generator.

Advantages and gains:
- a turbine of a set height could be supported by a lighter, less costly tower structure compared to the conventional design;
- if only a single three bladed rotor were employed, the gondola would be smaller, lighter and less cost;
- if two three bladed rotors are employed, more wind energy can be harvested for the same height tower. The gondola structure can still be made shorter, lighter and less costly since the generator unit would be missing from it, relocated to ground level;
- on marine wind turbine units, the lower centre of gravity would contribute to greater stability in severe weather;
- light weigh generator designs would no longer be required, since a less costly conventional generator would be housed at ground/sea level. Such larger, conventional generators would be less costly, with easier, less time consuming maintenance and repairs;
- single unit generators could be swapped out with only a forklift or truck hoist, compared to gondola mounted single unit generators which require large cranes to swap out.

Disadvantages and losses:
- extra cost and weight of a second three bladed wind rotor if used;
- addition of either one or two 90 degree power couplers;
- additional tubular power transfer shaft members extending the full height of the tower, plus a number of guidance collars and their support members;
- frictional losses of power due to the 90 degree transfer(s) and the bearing supports at the very base of the power shaft;
- if the generator(s) is housed internally within the tower base, a much larger, more complex access door will be required compared to a standard manhatch.

Your theory has a major flaw.
The size and strength of the support tower has virtually NOTHING to do with the weight of the turbine. Wind loading on the turbine is the primary concern and since your design doesn't change the rotor diameter, that will remain the same so it will require exactly the same size tower.

Going with two rotors will require INCREASING the size/strength of the support tower and yet will yield far less additional power compared to using two separate turbine&towers.

So what your idea does is add extra cost and materials, PLUS some relatively large losses.
Right angle drives have much higher losses than spur gears, etc. The best right angle drive will have probably 2-3 times the losses of a mediocre spur gear. The big wind turbines don't use mediocre spur gears, they either use very high efficiency ones, or none at all.

solarix

Re: Improved HAWT Design –based on "Something old, something new…"

If I remember right, the magazine Machine Design did an article awhile back on the pros and cons of using hydraulics to transfer the power down the tower to a ground mounted generator.

Peter_V

Re: Improved HAWT Design –based on "Something old, something new…"

solarix wrote: »

If I remember right, the magazine Machine Design did an article awhile back on the pros and cons of using hydraulics to transfer the power down the tower to a ground mounted generator.

Hydraulics or Pneumatics? I remember reading about an idea that was supposed to use compressed air with the generator on the ground.
Apparently the idea was that when the wind died down a gas/diesel powered air compressor would kick in and keep the generator running.

Seemed really stupid to me. In addition to the built in losses from using compressed air, you'd have to truck fuel out to remote locations. since most turbines seem to be in remote areas.

Makes more sense to me to just have the generator on the turbine and when the wind dies down, have a backup natural gas/diesel/whatever generator located close to the point of use (sorta like they currently are).

Cariboocoot

Re: Improved HAWT Design –based on "Something old, something new…"

#1 problem with wind turbines: losses due to inefficiencies.

Any time you store, transfer, make use of, or convert energy there are losses. Therefor the most efficient design is the one with the least amount of complexity in converting the mechanical power to electrical power. More machinery = more losses.

Physics; can't get around it. :cool:

BB.

Re: Improved HAWT Design –based on "Something old, something new…"

There have been a few compressed air solutions tried/offered.

One of the simplest wind power was an air compressor on the turbine, and running the air line to a well... Use the compressed air/bubbles to lift water directly from the well.

The other industrial compressed air method was to compress air into old salt mines (or equivalent) off peak, and use the compressed air as an air source for a natural gas powered peak electrical generator... The "pre-compressed" air reduces loads on the natural gas turbine and allows it to generate more electricity (instead of running its own turbo-compressor).

-Bill