Turbotricity

One thing we wanted to avoid like the plague is selling turbines and then having to run around modifying twenty or thirty turbines. We had a few teething problems which, while not critical, needed to be resolves properly. In an earlier post we outlined the vibration issue. We now have a turbine head with two levels of vibration isolation which dramatically reduces the resonance in the tower, and we have beefed up the tower as well.

We have also used a beefed up generator. While the blades (which do all the work) are the same, and output will be much the same, we are using a generator rated at 3kw instead of 2.5kw, with an upper limit of 4.5kw for up to twenty minutes. On most installations, the output will peak at 3.6kw which is the rating of the inverter we are using.

The cowlings are all looking great. However, because the planning exemption only covers components with a matt finish, we have to dull them down a bit in the final version. Our moulding company had gone to great lengths to get a professional mirror finish. Pity….

We went to Bantry Show with our turbine last weekend. There was huge interest in the turbine, particularly amongst farmers interested in doing part of the installation themselves.

In the picture, you can see the finished version of our turbine, complete with its cowling, pinnacle wing etc. Although the resolution on the photo isn’t great, the board at the back shows, clockwise from top-left; Controller (built in Durrus, Co. Cork), Inverter, Resistive load, and wind interface. These components can be mounted inside the house, or if preferred in a custom-made box outside, under the eaves of the roof.

We are saddened to hear that An Bord Pleannala has ordered the removal of a Proven 6kw wind turbine near Dundalk because it believes the planning exemptions did not apply. Many in the industry had not read the small print in the planning exemption.

There are many developments (house extensions, solar panels and some wind turbines) which are generally exempt from planning. However, any general exemption from planning is still subject to certain restrictions which are outlined in Statutory Instrument 600 of 2001). One of the key restrictions is that if the installation is deemed to interfere with the character of a landscape or a view of special amenity it would still require permission.

The conditions for exemption, SI 83 of 2007 clearly state that the exemption is subject to these restrictions. If there is any risk that a wind turbine on your site would interfere with the character of a landscape or a view of special amenity, then you should check with your Local Authority to see if the exemption applies in your case.

In the vast majority of cases, the exemption will apply, however, it is not carte blanche to put turbines everywhere without consultation.

Our new pinnacle wing and cowlings are finally in production after many delays. These mouldings give a superb finish to the appearance of the turbine, but they are more than a pretty face….

The cowling reduces wind drag at the hub, giving a free flow of air over the generator to the root of the blades. However, the important tweaking comes from the pinnacle wing.

Normally, downwind turbines suffer from tower shadow – when each blade passes by the tower, there is a brief moment when it gets turbulent wind caused by the tower which is a major obstacle located a few inches from the blade. On our Proven 2.5kw machine at home, the tower is quite wide at the point where the blade tip passes, and this gives the blade “dirty wind” for quite a few degrees of rotation.

Our pinnacle wing is designed to reduce this drag to an absolute minimum. It also helps to ensure that the turbine is steadily facing downwind. And it looks good….

We apologise to those who had expected us to sell turbines in the third week of April. We hit a technical hitch with vibration and some noise as a result. Because our turbines don’t have an iron core, they have much sharper pole changes as the magnet passes the coil, and this seems to cause a vibration.

On our experimental turbines, this was no problem because we weren’t using a tapered tower. However, when we put the turbine onto the tower we are actually using, the tower amplified the noise from the vibration like some sort of horn.

We could switch to a normal iron core turbine, but the turbine we are using has huge benefits – zero cogging at start-up, and very high efficiency – up to 94%. It is important that we get this right, and take the time to do so properly. We want to maintain a high level of efficiency with a turbine that will work in low wind speeds. Unnecessary noise from vibration is something that can be and must be eliminated.

So we are working on various ways of mounting the turbine with rugged vibration mounts to resolve this issue and expect to be back on track in another few weeks.

We believe it is essential to have a safe and simple way of raising and lowering the wind turbine. There are various systems used, the most popular one being to have an anchor point and winch using a “gin pole”. This requires an extra cubic meter of concrete for the anchor, and a fair bit of work with a tirfor winch.

We have seen other turbines that were lifted with a crane (OK first time, but what about the maintenance costs?) and in some cases turbines that had to be serviced by working aloft – again, reducing the cost of the hardware, but increasing the cost of maintenace.

The most dangerous suggestion we have seen is using a gin pole and attaching it to a car or tractor. The traction between tyres and grass is far too variable, and the forces are colossil when the turbine is nearly horizontal.

We are using a hydraulic ram and mobile hydraulic power pack to raise and lower our towers. This is simple and effective and the tower can be down within about ten minutes of arriving on-site. This method is used by many lampost companies to raise and lower their towers and works perfectly well.

The maximum load is when the tower is nearly horizontal, but the interesting part is when the tower is near vertical. At a certain point, it becomes almost balanced and you could push it into place with your little finger. Because there is a small amount of play in the hinge and at the connections for the hydraulics, this allows the turbine to swing by quite a few degrees at this point.

This is a problem for all lifting systems, particularly if you are behind the tower working a winch. At that point, the tower could swing like a pendulum and if any component failed, it would come down on top of you. Your hard hat would extend your lifespan by milliseconds….

While our hydraulic system can be operated remotely for safety reasons, we prefer not to allow the turbine to swing freely. To prevent this, we attach a rope about 3m from the base and a second person keeps this tight to take up the slack when the turbine is close to vertical. This way, the turbine falls gently onto its base and can be bolted down once in place.

This system is safe, simple and enable easy maintenance. For DIY enthusiasts, it would be possible to purchase a suitable hydraulc ram and operate this using a hydraulic take off from a tractor.

Turbotricity featured on The Business RTEs Sunday business programme on April 19th. (Photo of Tim Desmond interviewing Quentin beside our prototype turbine from RTE website. If you’d like to hear the full interview, you can click here

We’re very proud of the standard of generator we use in our 2.5kw turbine. This is a high efficiency precision built axial flux generator, weighing over 45kg and capable of producing well above its 2.5kw rating. All components are made from stainless steel, aluminium, plastic or copper so the generator is completely corrosion resistant.

It is also unlike any other generator we have ever seen. Generators work because electricity is produced when a magnet passes across a coil of copper. In our case, the coils are on embedded in a drum, with magnets revolving on either side of it. This creates a more efficient, smooth running and longer lasting generator.

We have two sets of neodymium magnets either side of a fixed cage which contains the coils this cage is fixed to the central shaft. The magnets are mounted on the body of the generator and on a second cage. Both sets of magnets revolve on either side of the coils in the stator.

Unusually, the shaft is fixed and the main body of the generator rotates around the fixed shaft. This gives the generator greater momentum and ensures that the shaft and bearings can be protected from the elements, ensuring longer life.

The cables from these windings are brought through the centre of the shaft and carry power from the copper windings out of the generator (and ultimately down the field to your house)

Axial flux generators like ours have movement which his absolutely smooth, with no cogging effect which would be normal with an iron core generator. This means that they begin to generate at lower wind speeds than traditional generators.

Here you can see the shaft of the generator attached to the nacelle, which in turn will be mounted onto the tower of the turbine.

The entire generator assembly is manufactured to very fine tolerances, and SKF bearings are used throughout. This is a generator which should provide many years of trouble-free use, regardless of the working conditions to which it is subjected.

Wind turbines generally don’t work well in built up areas, where they may be placed downwind from houses, tall hedgerows or trees.

An area might still be very windy, but this wind is made up of eddies and gusts with a lot of turbulence. Eddies come from various directions and the turbine cannot respond quickly enough to differing wind directions.

However, turbulence has an even more marked effect. A wind turbine doesn’t really work by wind pushing the blade around – most of the energy happens close to the blade tip which works on the basis of lift coming from areas of high and low pressure, similar to the wing of an aircraft. We all know what happens to the wing of an airplane when it hits turbulence. The same thing happens to the blade of a wind turbine, and the output of the turbine is decimated by this effect.

For this reason, a wind turbine must be as high as you can get it, and as far away from obstacles in the direction of prevailing winds. There are very few instances where a turbine can work effectively in a built up area, so unless you happen to be on the western edge of a housing estate, or have a site which is wide open to wind from anywhere between SW and NW, a turbine won’t work for you.

To assess the effects of obstacles, you should obtain a wind rose from the met office for your area, and estimate the percentage of wind you will lose due to obstacles located at different compass points from the turbine base.

David Cameron notoriously put a turbine on the roof of his house, and many people believed that this is a simple solution to our energy needs. It isn’t – rooftop turbines are the snake-oil of the domestic wind energy market. There are interesting efforts to make vertical axis machines that will work, but none of them are convincing as yet…

We have decided to offer a 2.5kw turbine as a modest turbine that most people can afford, and which will make a meaningful dent in their energy bills

There are some cheap 5kw machines out there, but they are usually Chinese made and are simply not designed for our climate. At the other end of the scale, the 6Kw machines that are well made are costing about €32,000 installed. That is still more expensive per watt than our turbine.

However, there are other issues with larger turbines;

Planning Permission and Turbulence

The planning exemption for domestic turbines is a total height to the tip of the blade of 13m. With our rotor diameter of 3m, the tip of the blade is never less than 10m off the ground. This means that the blade tip is not exposed to turbulence at lower levels.

A 6kw turbine with a rotor diameter of 5.5m can only have a tower height of 10.25m. The blade at the bottom of its stroke will be 7.5m off the ground. This means that the blade tip (which does most of the work on a wind turbine) will suffer a lot more turbulence from surrounding hedgerows.

Effect of the new tariff

The new feed in tariff is set at 9c per KwHr for electricity exported, with a subsidy of 10c for the first 3,000KwHrs per year. Most of the extra power generated by a 5 or 6 kw machine will be exported at a price of 9c, whereas most of the power produced by a 2.5kw turbine will be either exported at 19c, or used by the householder at 16c.

The return on investment for a larger turbine is considerably lower as a result.

How much electricity do you use?

You can look at your ESB bill to see how many units of electricity you use. Of course, you won’t use these at exactly the same time that your turbine is producing, so electricity is constantly being bought and sold seamlessly. But in round terms, you can expect the following production from a 2.5kw turbine on your site, depending on the local wind speed. This assumes that you use 40% of the output from the turbine and export the other 60%;