Increasing the Reliability of Wind Turbine Gearbox

9:57 PM 1 Comment

The gearbox's reputation for a high failure rate is linked to the extreme engineering challenge that gearbox technology faces in wind applications, and the difficulty in properly assessing the loads – and in particular the non-torsional loads that pass through the gearbox – and how these affect bearings and gears. Some manufacturers have chosen to move to direct drive to reduce the number of moving parts in the wind turbine more exposed to wear. But this has led to wind turbine specific generator designs that are usually more expensive and often come together with a long-term maintenance contract with the Original Equipment Manufacturer (OEM), which does not necessarily meet the operations and maintenance (O&M) concept of flexibility expected by customers.

Of course, much has been done in the last decade to design and manufacture gearboxes ensuring a high quality, often with associated with over-engineering and increased cost. Many efforts are also being put in to performing proper monitoring and maintenance to detect and prevent any avoidable damage. These efforts have limited gearbox breakdowns in infancy, and sometimes allowed some maintenance activities to be initiated earlier than before, but they have not helped resolving a key cause of the problem: the rotor support concept, and how it distributes loads among the wind turbine structure and the gearbox.

Failure in Conventional Rotor Support Concepts

Traditional rotor support concepts typically feature either one or two bearings as shown below.

Gearbox connection

In a one bearing configuration, shown in the left hand image, the rotor shaft is supported by one main bearing and by the proper gearbox that is attached by two torque arms to the bedplate. Generally, the single main bearing does not absorb bending moments which result from the blades acting on the rotor shaft and, as a consequence, the planet carrier bearings transmit loads to the gearbox housing that are absorbed by the torque arms. Using this design principle, a gearbox absorbs additional loads introduced by the rotor shaft bending moment and also, to a lesser extent, those due to deflections of the bedplate and main bearing.

The single bearing concept is basically a three point suspension for the hub, one point is the front bearing and the other two are the gearbox torque arm supports. All forces produced by the wind on the rotor are going through the gearbox to the structure, and therefore the gearbox itself becomes part of this structure. Conventional gearbox design techniques used in other industries have simply been proven insufficient to deliver designs that can bear such highly variable loads in all directions over 20 years of operation.

In the two-bearing configuration B, shown above right, the rotor shaft is supported by two main bearings. With this arrangement the residual bending loads transmitted by the rotor shaft to the gearbox depend essentially on the stiffness of the double main bearing configuration and on bedplate stiffness.

Multistage gearbox

Except in a few cases of major turbine concept issues or gearbox defects, modern wind turbines gearboxes usually do not fail in the first few years of operation. Turbines in the 1.5–3 MW class have been built on the experience of smaller machines where gearbox failure was a chronic issue, and wind turbine and gearbox designs have been improved, allowing gearboxes to work properly in the first years of operation. However, inspections after 3–5 years performed on gearboxes of these large wind turbines usually show that major gearbox overhauls or replacements will be required in the next few years.

With one or two gearbox replacements expected over the 20-year lifetime of the turbine, even more in very windy sites, many customers are required by their lenders to include risk provision for extra material breakdown in the gearbox in their project business plan. 

Improving Reliability with Novel Support Concept

As previously mentioned, the main problem of conventional rotor support structures is that the gearbox is performing structural and mechanical functions at the same time, which makes it challenging to simulate loads properly at the design stage. This is especially critical in a component as complex as a gearbox, which is basically designed to withstand mechanical loads. This challenge is illustrated by the recent debate in the US about whether gearbox failures are due to the gearbox ability to withstand the specified loads, or to the fact that real loads experienced by the gearbox are higher than those specified by the wind turbine manufacturers.

An efficient way to solve this problem is to use a rotor support concept that separates structural behaviour from mechanical behaviour  This allows designers to simplify the way the loads are transmitted in the drive train, and therefore specify the drive train components with figures that are much closer to the real loads.

Wind turbine parts

As shown in above, the rotor, supported directly by a cast frame on two main bearings, is not supported by the gearbox, which is fully separated from the supporting structure. The two bearings divert weight and other loads to the main frame.

The key feature of this arrangement is that torque transmission is performed independently of rotor support. The shaft and gearbox are thus protected from potentially damaging bending loads. The concept decouples bedplate deflexion from the main shaft by means of a front elastic coupling that allows a certain degree of misalignment required in the system. The gearbox is allowed to pivot freely when the bedplate deflects. This ensures that only pure torque is going into the gearbox, allowing higher gearbox reliability without overdesign of the gearbox or unnecessary preventive maintenance costs.

Deflection loads

The figure above: Deflection loads (red arrows) are transmitted directly to the tower whereas only torque (dark green arrows) is transmitted through the shaft to the gearbox

A cast frame goes entirely through the hub to support it and drive all deflection loads (red arrows) to the tower, as it shown above. The shaft, connected to the hub at the front of the turbine, transmits pure torque to the gearbox.

Technical Validation

The technical benefits of this rotor support concept have been exhaustively validated in the field by measuring strains and displacements at several points in the structure and drive train. This experimental information has been used to complete and correlate the global virtual design models based on Finite Element Method-ANSYS and Multibody-SAMCEF design tools.

The figure below shows the most relevant results of this technical analysis in which, in addition to the Alstom Pure Torque validation, the global behaviour of the entire rotor support and the drive train is compared with a standard rotor support concept when a bending load is applied to the hub-rotor. For this comparison a standard rotor support concept with two main bearings has been used. When considering the standard rotor support concept, results clearly indicate the development of strain/stress all along the drive train, mainly in the bearing-shaft contact corners, but also affecting internal parts of the gearbox. In comparison, using same nominal bending moment and colour scale, the Alstom Pure Torque concept distributes strain/stress in the structural parts, isolating the drive train from bending moments.

Ansys result

The above figure: FEM comparison between a standard two bearing rotor support concept (top) and Alstom Pure Torque rotor support and drive train (bottom) when a bending load is applied to the hub-rotor.

Equivalent results have been obtained using multibody numerical analysis.

Results indicate a clear reduction of the radial bearing load for any relevant number of cycles when Alstom Pure Torque is considered compared with the standard configuration.

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Efficiency of Wind Turbine

9:53 PM No Comments

How to improve wind turbines efficiency?

Wind turbines can be improved by having simple flaps that will change in response to the change in wind. This characteristic will help greatly since the turbine blades will be characterized with the wind direction therefore the blades are in automatic control of correct steps of adjusting to the low or high winds.

Wind turbine

In order to get optimum efficiency, it is necessary to improve wind turbines by providing information into the active control system from the sensors to avoid wind turbine break from high winds. Since wind energy is increasingly becoming the electrical power, its efficiency is very much important to identify the work load being exerted on the turbine blades consecutively to predict fatigue and avoid a breakdown of the turbines and therefore avoiding huge expenses that can be used to repair a turbine.

It is also very important to have simple but extra curved than straight blades to make it easier for the sensor records to show how greatly a blade has bent and twisted from the winds. There are some cases where the level of energy might reduce when you most need it. This is attributed to the fact that the wind speed is low, due to this, there is need to improve the efficiency of wind turbines so as to function normally at all times.

Wind speed during the day is said to be slow hence there is need to develop stable power that is generated by this energy producer. Due to this, mechanical experts are working on ways in which stable energy or power will be produced all through the day using this wind turbine irrespective of wind speed.

Hub connection

Another way in which you can increase wind turbine efficiency is to incorporate a concrete base. As much as this is not the best green material to use in this case, it is imperative that you use it due to several reasons;

Why concrete base?

It will cut down the number of concrete that is required to foot a tower by two thirds

• They are more economical when installing
• They offer faster construction times of wind turbines.
• They raise the height of the wind turbine so as to increase the production of power enabling power all through the day.

Wind farm

You need to know that it is also possible to construct wind turbines on your own at home. In this case, you have several options of turbines to choose from such as vertical or convectional wind turbines. It is however recommended that you opt for vertical wind turbine for it is easy to construct and efficient in that it its blades are perpendicular to the ground making it easy to generate energy even if wind power is low.

With the massive climate change that is being witnessed in the entire world, there is need to take early precaution so as to avert any further problems. This is because, these changes are attributed to the fact that the activities of most people in the world do not have the best interest of the environment at heart hence great changes in the weather conditions. We need to derive best ways to produce energy without affecting the environment and the best way is to use wind turbines though we have to ensure they are efficient.

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Wind Energy Potential of Germany

9:51 PM 1 Comment

The partial switch to natural gas also lays the foundations for a feasible solution to the problem of storing excess power: power to gas, in which excess solar and wind power is used make hydrogen. Germany also plans to refine more and more bio-gas into "bio-methane," essentially bio-gas with properties nearly identical to natural gas. For an example, see this presentation of a hybrid plant. Stephen Lacey also discusses “virtual power plants” as one of five things that need to be done in the switch to renewables.

As natural gas becomes scarcer and more expensive, Germany could produce excess solar power in the summer, store it for the winter as gas, store excess wind power as gas for hours and days at a time, and use dispatchable co generation turbines running increasingly on bio methane as natural gas is phased out. No fancy gas storage tanks will be needed; Germany will just use the gas lines it already has.

In 2010, researchers from Germany’s Fraunhofer estimated that the German gas network has a storage capacity equivalent to more than four months of German power consumption. German researchers have also estimated that 100 percent renewable power would only "require up to two weeks at a time to be bridged during the winter," far less than the four months already available. But that two-week gap can only be crossed if Germany gets rid of nuclear and resorts to natural gas as a bridge today.

In other words, Germany actually has an action plan to reach 80 percent renewable power, and natural gas is a temporary part of that plan. In addition, a number of studies have been published to show how Germany could go 100 percent renewable. And let’s not forget the organization called 100% Erneuerbar – or the study called Energy Rich Japan that German researchers and one from Japan did on how Japan could get all of its energy from renewables way back in 2003. Do we Americans have any such plan?

State	No. Turbines	Installed Capacity [MW]	Share in the net electrical energy consumption [%]
Saxony-Anhalt	2,304	3,509.16	52.1
Mecklenburg-Vorpommern	1,356	1,549.10	45.4
Schleswig-Holstein	2,675	3,014.98	44.1
Brandenburg	2,952	4,400.78	42.8
Lower Saxony	5,365	6,664.24	25.1
Thuringia	581	754.18	12.3
Rhineland-Palatinate	1,086	1,421.43	8.6
Saxony	821	943.27	8.5
Bremen	67	120.84	4.1
North Rhine-Westphalia	2,820	2,928.11	4.0
Hesse	613	587.77	2.5
Saarland	80	111.40	2.4
Bavaria	412	521.38	1.0
Baden-Württemberg	368	467.08	0.9
Hamburg	61	50.68	0.6
Berlin	1	2.00	0.0

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Homemade Wind Turbine

2:48 PM No Comments

I started the process of designing my wind turbine by searching for information on home-built wind turbines. There are a lot of them out there in an amazing variety of designs and complexities. All of them had five things in common though:

1. A generator 
2. Blades 
3. A mounting that keeps it turned into the wind 
4. A tower to get it up into the wind 
5. Batteries and an electronic control system

I reduced the project to just five little systems. If attacked one at a time, the project didn't seem too terribly difficult. I decided to start with the generator. My online research showed that a lot of people were building their own generators. That seemed a bit too complicated, at least for a first effort. Others were using surplus permanent magnet DC motors as generators in their projects. This looked like a simpler way to go. So I began looking into what motors were best for the job.
There are probably lots of other brands and models of permanent magnet DC motors available that will work well as generators. Permanent magnet DC motors work as generators, but they weren't designed to be generators. So they aren't great generators. Some types of motor are a lot worse than others. When used as generators, motors generally have to be driven far faster than their rated speed to produce anything near their rated voltage. So what you are looking for is a motor that is rated for high DC voltage, low rpms and high current. Steer away from low voltage and/or high rpm motors. You want a motor that will put out over 12 Volts at a fairly low rpm, and a useful level of current. So a motor rated for say 325 rpm at 30 Volts when used as a generator, could be expected to produce 12+ volts at some reasonably low rpm. On the other hand, a motor rated at 7200 rpm at 24 volts probably won't produce 12+ volts as a generator until it is spinning many thousands of rpm, which is way too fast for a wind turbine. So shop for motors accordingly.

Generator

I managed to score one of the good 30 volt Ametek motors off of Ebay for only $26. They don't go that cheap these days. People are catching on to the fact that they make great wind generators. Other brands will work, so don't fret about the price Ameteks are going for. Shop wisely. Anyway, The motor I got was in good shape and worked great. Even just giving the shaft a quick turn with my fingers would light a 12 volt bulb quite brightly. I gave it a real test by chucking it up in my drill press and connecting it to a dummy load. It works great as a generator, putting out easily a couple hundred Watts with this setup. I knew then that if I could make a decent set of blades to drive it, it would produce plenty of power.
So Blades and a hub to connect them to were the next order of business. More online research ensued. A lot of people made their own blades by carving them out of wood. That looked like an outrageous amount of work to me. I found that other people were making blades by cutting sections out of PVC pipe and shaping them into airfoils. That looked a lot more promising to me. This web site tells you how to make a set of blades for a small wind turbine using PVC pipe.

Blades

I followed their general recipe. I did things a little differently though. I used black ABS pipe since my local homecenter store just happened to have pre-cut lengths of it. I used 6 inch pipe instead of 4 inch and 24 inches long instead of 19 5/8. I started by quartering a 24 inch long piece of pipe around its circumference and cutting it lengthwise into four pieces. Then I cut out one blade, and used it as a template for cutting out the others. That left me with 4 blades (3 plus one spare).

Blades

Then i did a little extra smoothing and shaping using my belt sander and palm sander on the cut edges to try to make them into better airfoils. I don't know if it's really much of an improvement, but it didn't seem to hurt, and the blades look really good (if I do say so myself).

Bearing design

Now I needed a hub to bolt the blades to and attach to the motor. Rummaging around in my workshop, I found a toothed pulley that fit on the motor shaft, but was a little too small in diameter to bolt the blades onto. I also found a scrap disk of Aluminum 5 inches in diameter and ¼ inch thick that I could bolt the blades onto, but wouldn't attach to the motor shaft. The simple solution of course was to bolt these two pieces together to make the hub.

Bearing design

Much drilling, tapping and bolting later, I had a hub.

Hub connection

Here it is assembled and with the blades attached (after drilling mounting holes in them of course).

Blade connection

Here is another view of the hub with blades attached.

Hub connection

On a trip to the homecenter store for some PVC doo-dad or other for another project, I found these dome shaped vent caps.

After connection

I immediately thought of adding a spinner to the hub. Wow, with that on there, it really looks like a professionally made unit. I'd never be able to convince anyone I built it myself out of junk from my workshop and plumbing parts. They'd all look at me when I said I built it myself and go "Yeah, right." Then I found a web site that claimed such spinners disrupt the airflow and hurt the efficiency of the blades. I'm not sure I believe the reasoning behind the claim, but I left the spinner off, at least initially.

Diemensons

Next I needed a mounting for the turbine. Keeping it simple, I opted to just strap the motor to a piece of 2 X 4 wood. The correct length of the wood was computed by the highly scientific method of picking the best looking piece of scrap 2 X 4 off my scrap wood pile and going with however long it was. I also cut a piece of 4 inch diameter PVC pipe to make a shield to go over the motor and protect it from the weather. For a tail to keep it turned into the wind, I again just used a piece of heavy sheet Aluminum I happened to have laying around. I was worried that it wouldn't be a big enough tail, but it seems to work just fine. The turbine snaps right around into the wind every time it changes direction. For those of you always clamoring for me to provide plans, blueprints, schematics, etc., for my projects, I have added a few dimensions to the picture. I doubt any of these measurements is critical though.

Tail connection and generator

Here is another view of the completed head of the unit with the motor and tail attached.

Tower

Next I had to begin thinking about some sort of tower and some sort of bearing that would allow the head to freely turn into the wind. I spent a lot of time in my local homecenter stores (Lowes and Home Depot) brainstorming. Finally, I came up with a solution that seems to work well. While brainstorming, I noticed that 1 inch diameter iron pipe is a good slip-fit inside 1 1/4 inch diameter steel EMT electrical conduit. I could use a long piece of 1 1/4 inch conduit as my tower and 1 inch pipe fittings at either end. For the head unit I attached a 1 inch iron floor flange centered 7 1/2 inches back from the generator end of the 2X4, and screwed a 10 inch long iron pipe nipple into it. The nipple would slip into the top of the piece of conduit I'd use as a tower and form a nice bearing. Wires from the generator would pass through a hole drilled in the 2X4 down the center of the pipe/conduit unit and exit at the base of the tower. Brilliant! (if I do say so myself)

Tower base

For the tower base, I started by cutting a 2 foot diameter disk out of plywood. I made a U shaped assembly out of 1 inch pipe fittings. In the middle of that assembly I put a 1 1/4 inch Tee. The Tee is free to turn around the 1 inch pipe and forms a hinge that allows me to raise and lower the tower. I then added a close nipple, a 1 1/4 to 1 reducing fitting, and a 12 inch nipple. Later I added a 1 inch Tee between the reducer and the 12 inch nipple so there would be a place for the wires to exit the pipe. This is shown in a photo further down the page. I also later drilled holes in the wooden disk to allow me to use steel stakes to lock it in place on the ground.

Tower base

This photo shows the head and base together. You can begin to see how it will go together. Imagine a 10 foot long piece of steel conduit connecting the two pieces. Since I was building this thing in Florida, but was going to use it in Arizona, I decided to hold off on purchasing the 10 foot piece of conduit until I got to Arizona. That meant the wind turbine would never be fully assembled and not get a proper test until I was ready to put it up in the field. That was a little scary because I wouldn't know if the thing actually worked until I tried it in Arizona.

Generator and tail

Next, I painted all the wooden parts with a couple of coats of white latex paint I had leftover from another project. I wanted to protect the wood from the weather. This photo also shows the lead counterweight I added to the left side of the 2X4 under the tail to balance the head.

General overview

This photo shows the finished head unit with the blades attached. Is that a thing of beauty or what? It almost looks like I know what I'm doing.
I never got a chance to properly test the unit before heading to Arizona. One windy day though, I did take the head outside and hold it high up in the air above my head into the wind just to see if the blades would spin it as well as I had hoped. Spin it they did. In a matter of a few seconds it spun up to a truly scary speed (no load on the generator), and I found myself holding onto a giant, spinning, whirligig of death, with no idea how to put it down without getting myself chopped to bits. Fortunately, I did eventually manage to turn it out of the wind and slow it down to a non-lethal speed. I won't make that mistake again.
Now That I had all the mechanical parts sorted out, it was time to turn toward the electronic end of the project. A wind power system consists of the wind turbine, one or more batteries to store power produced by the turbine, a blocking diode to prevent power from the batteries being wasted spinning the motor/generator, a secondary load to dump power from the turbine into when the batteries are fully charged, and a charge controller to run everything.
There are lots of controllers for solar and wind power systems. Anyplace that sells alternative energy stuff will have them. There are also always lots of them for sale on Ebay . I decided to try building my own though. So it was back to Googling for information on wind turbine charge controllers. I found a lot of information, including some complete schematics, which was quite nice, and made building my own unit very easy.

General overview

The first order of business was setting up and bracing the tower. After arriving at my property and unloading my van, I drove to the nearest Home Depot (about 60 miles one way) and bought the 10 foot long piece of 1 1/4 inch conduit I needed for the tower. Once I had it, assembly went quickly. I used nylon rope to anchor the pole to four big wooden stakes driven in the ground. Turnbuckles on the lower ends of each guy-line allowed my to plumb up the tower. By releasing the line from either stake in line with the hinge at the base, I could raise and lower the tower easily. Eventually the nylon line and wooden stakes will be replaced with steel stakes and steel cables. For testing though, this arrangement worked fine.

Tower connections

This photo shows a closeup of how the guy-lines attach near the top of the tower. I used chain-link fence brackets as tie points for my guy-lines. The fence brackets don't quite clamp down tightly on the conduit which is smaller in diameter than the fence posts they are normally used with. So there is a steel hose clamp at either end of the stack of brackets to keep them in place.

Cabling

This photo shows the base of the tower, staked to the ground, and with the wire from the wind turbine exiting from the Tee below the conduit tower. I used an old orange extension cord with a broken plug to connect between the turbine and the controller. I simply cut both ends off and put on spade lugs. Threading the wire through the tower turned out to be easy. It was a cold morning and the cord was very stiff. I was able to just push it through the length of the conduit tower. on a warmer day I probably would have had to use a fishtape or string line to pull the cord through the conduit. I got lucky.

General overview

This photo shows the turbine head installed on top of the tower. I greased up the pipe on the bottom of the head and slid it into the top of the conduit. It made a great bearing, just as I'd planned. Sometimes I even amaze myself.
Too bad there was nobody around to get an Iwo Jima Flag Raising type picture of me raising the tower up with the head installed.
Now I'm just waiting for the wind to blow. Wouldn't you know it, it was dead calm that morning. It was the first calm day I had ever seen out there. The wind had always been blowing every other time I had been there. Well, nothing to do but wait.

General overview

Finally! The wind was up and the turbine was spinning. The winds were actually unusually light the whole time I was on my property this time. The wind turbine still made good amounts of power though, even with winds that at best made it to only a little over 20 mph at times.

Controller, battery

This photo shows the controller, battery and associated electronics all wired up. I have a 120V inverter connected to the battery and a multimeter to keep track of the battery voltage and wind turbine output voltage. Also my electric shaver and battery charger are plugged into the inverter and running off of 120V AC. Later I plugged a long extension cord into the inverter and stretched it back to my camp site. I know this setup is really messy, but I was in a hurry to get up and running to take advantage of the wind once it started blowing. That's my excuse, and I'm sticking to it.

Eventually I decided my setup was too messy and dangerous. Having high current electrical connections and a rat's nest of wires on an Aluminum table wasn't smart. The danger of a spectacular short circuit was too high, so I neatened things up. I set all the electronics on a piece of plywood on top of a plastic storage bin and neatened up the wiring. Then I ran a long extension cord from the inverter back to my camp site and plugged all my stuff into it there.

Homemade wind turbine

Question #1: How do you prevent the power cable coming down the inside of the tower from winding up over time?
Answer: This is by far the most asked question I get from people. The short answer is I don't do anything to prevent it. The cable really doesn't wind up all that badly. The wind is as liable to spin the turbine head around one way as it is the other. So there is no real tendency for the cable to wind up badly. If it does wind up over time, it is no big deal to simply disconnect the wires at the bottom and manually unwind it. I have an idea for a fairly easy to build slip-ring system that would prevent any possibility of winding up the cable. At present though, there is little need to actually try implementing it. Maybe I'll try it out on a future turbine.

I used the wind turbine to power my new popup trailer on my spring vacation. The strong spring winds kept the wind turbine spinning all day every day and most of the nights too while I was in Arizona. The turbine provided enough power for the interior 12V lighting and enough 120V AC at the power outlets to keep my battery charger, electric shaver, and mini vacuum cleaner (camping is messy) all charged up and running. My girlfriend complained about it not having enough power to run her blow-dryer though.

Measured volt

Here my volt meter is showing the turbine producing 14.5 volts in a stiff wind. Although the wind turbine powered the popup fairly well, I think there is room for improvement. I was powering the popup with 120 Volts AC via my inverter. The popup has its own 120V AC to 12V DC power supply for powering the interior lighting and other 12V accessories. The losses involved in converting power to 120V AC and then back to 12V DC probably heavily contributed to the battery running down fairly quickly a couple of times during periods of light wind. Powering the 12V systems directly from the battery would probably work better. The only downside I see is that the DC voltage won't be regulated and could swing a couple of volts up or down with changes in wind speed. That wouldn't bother most kinds of lighting too much. Other devices could have a problem with it though.

General view

This photo shows the turbine spinning away and cranking out the power. I haven't had the time to complete the rebuild of the charge controller in a weather-proof enclosure. So this time I just put all the electronics in a plastic bin to protect them from the elements. Good thing too, since it rained several times while we were there this time. The jug of lamp oil is on top of the bin to prevent the wind from ripping the lid off.

Turbine accident

Disaster! I went into town to pick up some supplies. While I was gone, a wind storm came up. Winds well in excess of 50 MPH blew through my area. When I returned I found the turbine in this condition. Two blades had snapped off, and the third was cracked, but still attached. The blades broke where the mounting tab met the body of the blade. I knew this was a weak spot and always expected they would break there eventually. I don't know for sure if it was over-speed, or just fatigue from repeated flexing that caused them to break. I suspect fatigue though. I could see the blades flexing in strong winds before they broke. Interestingly though, I found that the battery bank was fully charged. The wind turbine must have generated some serious power in those high winds before it failed.
I knew I could get the wind turbine up and running again if I could just drill new mounting holes in the blades. I had no drill or drill bits with me though. I had to think about it for a while before I figured out how to do it. Then, the spirit of MacGyver came over me, and I knew just how to do it.

Reconstruction 

I figured out that if I heated my largest Phillips screwdriver over a fire, it would melt a hole in the PVC blades just the right size for the mounting bolts. So I got some charcoal going and started making holes. It's a terrible abuse of a perfectly good screwdriver, but it was an emergency situation after all.

Reconstruction

I used one of the broken mounting tabs as a template to locate where to make the holes in the bases of the blades. Then it was straightforward to just melt through the blades with the screwdriver. It was very quick and easy, and the holes were very clean.

Hub connection

I then re-mounted the blades on the hub of the turbine. I used the broken mounting tabs as spacers under the blades to prevent them from fouling the heads of the bolts that hold the hub together. The tabless blades are much stronger and less likely to flex in strong winds. I should have done it this way in the beginning. Live and learn.

Hub connection

Here is the turbine all re-assembled and ready to go back up on the tower.

Wind turbine

Here is the wind turbine up and flying again. The loss of two inches of blade length doesn't seem to have adversely impacted the performance of the turbine. It still works great. Not bad for an improvised repair job.

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