I’ve just been to the wind turbines talk at the Climate Camp on Blackheath. It was really well attended. The organisation who ran the talks are called v3power.co.uk. They often run courses explaining how to build your own wind turbine, but they’ve never held one in London. If anyone is interested, they would need to find some workshop space for a 3 day course… It sounds great to me.
Anyway, below are my notes from the talk:
All the hand made turbines at the camp were based on Hugh Piggott’s books. He is seen as the master of handmade wind farms. His book costs £12. Older versions of his book are free to download as pdf files from the website.
The ethos behind the turbines is that they can be built by hand. Almost no electricity is required to construct any parts, except for a small amount of welding. This means that they can be built and fixed anywhere in the world.
The amount of energy required to make one of these turbines is “paid back” (ie regenerated from the wind) in about 1 year. All the turbines are built to last much longer than that, but regular annual servicing is recommended.
The organisation is more interested in considering energy payback than the economic payback, as they believe that it is a more valid criteria by which to assess wind power.
These turbines are not the most efficient. But what they lack in efficiency they make up for in ease of manufacture – anyone with some DIY skills could make these by following the instructions in the book. All the measurements in the book are to an accuracy of milimetres, whereas commercial turbines are built to much higher degrees of accuracy, to squeeze out more efficiency.
The electricity generated is stored using lots of batteries. This is done because wind power is massively variable.
The most important equation is this:
Electrical power = windspeed cubed.
(Hence their company name v3power.co.uk).
Power generated by wind farms can be stored either in batteries, or fed back into the grid. It is very useful to store the power, because of the extreme variability of wind generation – it effectively allows you to average out the fluctuations in power very easily.
However, storage in batteries (or any other method) is inherently less efficient than using the power there and then. So if you can use the power as it is generated, then do so.
The power is generated by a series of magnets spinning around some coils of wire. When they pass over the coils, current is created.
Can you use magnets from old computer hard disk drives?
Yes you can, in smaller wind turbines. The magnets inside hard disc drives are neodymium rare earth magnets. But they are a strange shape, and quite small, so you would need around forty disc drives to build one turbine. This sounds like a lot, but old disc drives are often thrown out by universities, companies, etc.
You have to be careful where you source your batteries from. Old batteries don’t hold their charge as well as newer ones.
Is it possible to connect DIY wind turbines to the mains electricity grid?
Yes. But you need a device called a “Grid Tie Invertor”. These are made by a German technology company called SMA. The model is called a a “Windyboy”. This company has pretty much cornered the market. Windyboys are quite expensive – around 2000 Euros.
The good news is that it is relatively simple to get permission to connect to the national grid. If your equipment (eg a Windyboy) meets a set of specifications called the G83 and G59 rules, then all you need to do is get a qualified electrician to install it. No complicated permissions are required from the actual electricity company. He recommended a company called Goodenergy who let you feed your power in very easily, and pay you for the privilege! Interestingly he mentioned that Ecotricity generate around 30% generated 18% of their energy from nuclear power last year!
UPDATE: Ecotricity dispute the 30% number. Last year 18% of their energy was nuclear – more here.
On a slightly ironic note – massive banks and corporations are excellent sources of high quality batteries, because they are used to maintain their computer server rooms, and have to throw away perfectly good batteries after 2 years of use!
We then split in to two smaller groups to look at a turbine more closely.
The batteries used on this site are called “Sealed Deep cycle gel batteries”. They used to be used in the Telecom Tower.
These are good quality batteries. They will give you around 1000 full charges and discharges. People often assume that Lithium Ion batteries would be good for turbines, but in fact they are not. They are designed to recharge quickly and be light in the pocket (for mobile phones etc), so do not suit the needs of a wind farm very well. Environmentally they are also very bad. Lithium is a very scarce resource only found in a small number of countries.
A single turbine like these can only run about 3 x 100 Watt lightbulbs. But the key thing to remember use of windfarms in conjunction with reduction of energy use. For example 100 Watt lightbulbs are a Victorian era technology, easily replaced by much much higher efficiency light sources.
The turbines here are relatively short, and there are many obstacles nearby (ie the tents on the camp). These causes turbulence, and turbulence causes less power to be generated. Cities have a lot of turbulence. A company called Windsave sold a lot of low cost turbines in B&Q. They were criticised at the time for allowing people to place them in very poor positions generating very little powr. This gave a rather bad name to wind turbines for a while. Some of the material on their website in the past, showed turbines mounted lower than the roof of the house, rather like a satellite dish. This is almost completely pointless!
The speaker said that Blackheath is an extremely good spot for turbines.
The turbines here are called “Three blade horizontal axis wind turbines”.
Vertical axis wind turbines are beloved by architects because they look attractive. Wild claims are often made about their efficiencies. The speaker said that horizontal axis turbines are tried and tested technology. They work. Really well.
Savonius wind turbines look like split oil drums. They work only by using the drag of the wind, which means that the wind can come from any direction. However, they don’t use lift, unlike normal turbines so are less efficient.
So, back to our wind farms. The shape of the blades is absolutely critical. They are complex shapes, built in four stages. Notice that the shape is twisted from tip to root. To build them, lines are drawn on your piece of wood every 6th of the way down the block, then instructions are followed for each of those segments. This simplification makes the blades slightly less efficient, but makes them easier to build by hand.
An important part of their ethos is to make them with hand tools, avoiding electricity where possible.
Carving blades is a really fun part of the process.
Notice the classic aerofoil shape at the tips. This curve is made by eye. Use good quality wood without knots. These ones are plywood with a little linseed oil applied to them. They have tried varnish it in the past, but water still seeps in, then seeps out to the tips and causes problems. Linseed oil is an experiment.
Why is 3 the optimum number of blades?
More blades gives greater torque but lower top speed. If you are driving mechanical equipment directly, greater torque is often desirable. This is why you often see wind turbines with loads of blades on farms. More blades will start at lower wind speeds. But the turbine will run at a slower speed.
Single bladed turbines look funny but are usable. Three blades are also efficient due to gyroscopic effects. They balance out the gyroscopic forces so that they add up to zero. (?)
Blades can be made out of guttering, but wood is easier. Shaping the blades take about a day. Maybe 10 hours a blade. When they have been shaped, they are are sandwiched between two pieces of plywood.
Then this is attached to a steel disc. Can use break drums from car brakes can be used for the steel disc.
Then there is a resin layer, which we’ll come back to in a moment.
Beneath the resin layer, there is a second disc, which has magnets glued to it. They are positioned opposite to one another, ie the first one has its north pole facing upwards, and the next one has its south pole upwards. In this turbine only one of the discs contains magnets, but some models have magnets on both discs. In our example only one disc contains magnets, which are attracted to the steel disc. The whole apparaturs is held apart by nuts. There are very strong forces between them, trying to pull them together. This can be very dangerous when working with them – it is easy to get your hands caught.
The resin layer contains six coils. These coils are built by winding wire around a another tool that you can build youself – a piece of plywood with nails in. The wire is wound around nails, by spinning the piece of plywood. The nails in the tool are the same distance apart as the magnets. It is vital to count the turns made. This is very monotonous. Then they are sellotaped in place, and put inside the resin mold. Nasty toxic resins are then poured into the mold. Polyester resin is used. This is also used to build boats and canoes. Other catalysts are also mixed into it, and also some talcum powder. The Talcum powder is a bulking agent, it is cheaper than resin (and makes it smell nice!) It’s a bit like baking an incredibly toxic cake! The resin coils are the only part of the turbine that is not easy to reuse or recycle, but thankfully rarely goes wrong (compared to all the moving parts).
There are 6 coils and 8 magnets in this turbine. They are laid out in a very symetrical pattern so that each coils are being acted on by the correct magnet at the right time. The layout produces electricity at three different phases from the coils, but the combination of the coils combines nicely so that it can be fed straight onto a battery with a simple rectifier. No charge control system required. It might seem silly to turn what is three phase AC power into DC for a battery, when our mains grid is based on AC, but don’t forget that the period of the phase of this power is constantly shifting with the speed of the wind. Sticking this straight into the mains would be bad!
The whole thing sits on a bearing. Someone asked “are they twin cones bearings?” Yes. You can use lost automotive bearings e.g. another of our turbines used a bearing from a Vauxhall Astra. They sometimes need greasing or running in a bit.
Welding is necessary beneath the bearings. This is a downside. The tower (bit pole that the turbine sits on) can often cost more than the turbine. Even a small one costs £90. Scaffold poles are easy to get, but to go taller than this is difficult. Shackles and wire for the tower are not cheap.
In a storm a turbine would snap – they cannot go infinitely fast! So all turbines have a furling mechanism. This means that if the wind gets too high, the turbine will be automatically turned away from the wind. The bearings are offset to one side of the tower. So it is always trying to spin itself out of the wind. With very high force, the wind will hinge and lift the tail through half a metre which makes he blades turn out of the wind. It is also possible to short circuit the terminals. This slows down the blades too.
These turbines are built over a weekend with 12-15 people. Not too intensive. Most of it is DIY techniques only.
Could you use off-the-shelf alternators?
Sort of. Tape drive units from massive old mainframe computers are good because they are low speed. Car alternators are not good because they are designed for thousands of revs per minute. So you would need gearing, which reduces efficiency. You could use the wire from an existing alternator, and rewind he wire. But this is really fiddly. It is easier to make it yourself.
How close together can you place them?
It depends – the air downwind of a turbine is “dirty” ie turbulent, so you have to take account of this.
How big can you build them?
Biggest one they’ve build is 3.6m radius. Biggest in the world is 5m built to this specification.
Will you be running courses in London?
They want to come to London. They’ve built a turbine in Hainault before, but want to do more. Need a venue. Also doing some later this year in Wales and elsewhere. V3 power are based in Nottingham.
Do you build these in the developing world?
Many people are developing these skills in Nicaragua and other places, and Hugh goes touring to different countries. They encourage anyone who attends a course to go off and spread the word. Many places in Africa run off batteries based on diesel generators. These are ideally suited to wind farm solutions.
What about planning permission?
Planning permission is very region specific. These ones are temporary structures so no planning required. It is much easier to get permission on agricultural land than anywhere else.
How tall can you build them? Do you ever use foundations for the tower?
We’ve but them as high as 50m tower using only guy ropes. Concrete is very bad environmentally, so we don’t use it.
Great short film about the designer: