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Meta
nice email received:
From: Mike Allen
Subject: Re: A Wind Turbine Recipe Book
Date: 12 April 2013 10:53:18 BST
To: jytteI recieved the book yesterday and when it arrived I thought ‘this isn’t worth £12’.
But how wrong I was once I’d opened the envelope and settled down to read the contents with a cup of coffee. 3 hours later the coffee was stone cold and I was still reading the book.
Loads of info to be getting on with.
I’ll email Hugh when my terbine is up and running with some pics.
Thanks a lot.
Michael.
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Answering some questions about rooftop wind
My answers to some questions:
(1) We’re looking at some of the design problems of rooftop turbines, and we had an expert installer tell us that in a best-case scenario, a rooftop turbine can generate 18 to 33 percent of a household’s power. Is that an accurate assessment?
It’s a very vague promise. The best case would be a house on a bare hilltop with nothing around it. A realistic case would be dramatically less productive. For real examples see this study
http://www.warwickwindtrials.org.uk/resources/Warwick+Wind+Trials+Final+Report+.pdf
(2) Is it true that a rooftop turbine generally creates 2 to 3 times as much noise as a tower turbine? And, if so, what can be done about this?
All wind turbines produce some noise and vibration. The amount varies, but whatever level of noise and vibration is produced, the associated problems will be much worse if it is connected with a building. Only a very massive concrete building can absorb this noise and most buildings will transmit it. The occupants will be subjected to this noise. The building may be damaged by the vibration in some cases.
(3) An installer told us that a tower turbine generally requires a consistent 10 mph wind to work. Is that true?
Most properly designed turbines are optimised for the range 3 – 12 m/s in which most of the energy will be produced. (that would be 7 – 25 mph in layman’s terms). Below 7 mph (3 m/s) the density of power is extremely low, so one would need a very large turbine working for a very long time to produce useful amounts of energy.
And by “work” do they mean to generate their maximum power capacity, or to generate power at all?
Most small wind turbines will start to produce at 6, 7 or 8 mph (around 3 m/s) but obviously the power has to start from zero. Maximum output is achieved at 20 – 30 mphs (9 -14 m/s) depending on the make but such winds are relatively rare so they do not contribute a lot to the overall energy production.
Are there any tests that indicate that tower turbines ever hit their maximum capacities?
Of course a wind turbine on a good site will hit its maximum. But the more important thing is the average power it can produce, which can also be expressed as the energy produced over the year. This basically depends on the swept area of the rotor and on the windspeed ‘regime’ that it is exposed to. Rooftop turbines are usually rather small and cannot access good winds, so they are incapable of producing the best results in terms of energy per year.
(4) What good do you think will come out of the Small Wind Certification Council’s certification program for power, sound emission and durability? Will the SWCC truly act in the consumer’s behalf, or will they accede to manufacturer demands? Will we see less models, better models?
Independent testing of wind turbines is long overdue. I hope that it will not impose overly onerous burdens on small wind manufacturers, but it can only be a good thing to obtain independent test results for performance, noise and safety. I hope we will see plenty of models and that we will also get past the hype and learn what they can do for us.
(5) I heard that WindTronics will be releasing a turbine this fall that generates power in winds as low as 2 mph. Have you seen it, and does it work?
while it is possible to generate power in such low winds, the amount of energy will be relatively pathetic. The laws of physics determine the maximum power available per unit of size in a turbine and a very small turbine with very little wind can only produce a negligible amount of energy.
Is it a big step forward in rooftop turbine designs, or is there still much to be done to make sure these things work?
I would rather describe such products as a big step backwards (a disaster even) as they will encourage unrealistic expectations in the consumer, who will later decide that wind energy is a waste of time and money, based on one bad experience.
Two follow-up questions:
* Is it accurate to say that unless your home fits the (location, wind and zoning) requirements for successful wind generation, that a residential wind turbine (tower or rooftop) won’t pay for itself completely in its average 20-year lifespan?
Yes, I would say that it is unlikely that a rooftop wind turbine will pay for itself unless the site if unusually windy, and the property is very open to the wind.
* According to National Renewable Energy Laboratory, a 1.5-kW rooftop wind turbine will meet the needs of a home that requires 300 kWh per month in a location that has an annual average wind speed of 14 mph. ————Are any of those numbers reasonable?
The numbers might add up, yes, provided you can find a house with that sort of wind at rooftop level. I have to say that such houses are very unusual indeed! And the turbine would need to have a diameter of at about ten feet.
Is a 1.5-kW turbine an average size,
The power rating doesn’t really tell you anything about the size, so it is not a good description for a wind turbine. A better description would be the rotor diameter.
and a is a 300 kWh monthly requirement typical for a family?
Yes in The UK that would be sufficient for a very small, energy efficient family. It’s a little less than a typical North American family.
Moreover, I found a chart that says that only 5 of 275 American communities averages an annual wind speed of 14 mph. So how can that “14” number be used as a realistic benchmark?
I don’t think that anyone could claim that it’s a realistic benchmark, no.
===
See the full article in Consumers Digest
Posted in Rooftop madness
2 Comments
Treadle Powered Computer
Posted in People
2 Comments
Real world data
Here is a site with some real world kWh per month as generated by Eoltec, Proven and Bergey machines in the UK. Data uploaded by users.
http://www.renew-reuse-recycle.com/
Direct link to spreadsheet
Posted in UK small wind scene
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Courses in England and nearby
Some course dates in England for imminent courses that I will not be teaching but they are based on my design:
V3 are doing the following:
Introduction to Building a Wind Turbine -Weekend Course
16th – 18th July, Workhouse, Wales
How to Build a Wind Turbine – 5 Day Course
26th – 30th July, Nottingham
transitioncambridge are doing
Friday 9 – Sunday 11 July 2010 (3 full days), 9am to 7pm (some nights may be later); finishing by 5pm on Sunday At Cambridge GreenTech Workshop, Harvest Way, Cambridge
£150 (bookings before 25 June); £180 (bookings after 25 June).
My own next course that I will be teaching is at CAT in Wales
29th August – 3rd September 2010
This will be my last course in the UK this year,
but I am also doing one in Ireland
13-18 September Ballinamore Co Leitrim with Eirbyte
A full calendar of my courses is here including several in the USA.
Posted in Notices, UK small wind scene
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Blade hub question
Hercule writes:
Hello I’m trying to sketch in CAD the blades for a 3m turbine using your 2009 metric recipe book (I’m enjoying the read so far). For some reason I am getting an overlap of 76mm (see image attached). Have I misinterpreted your instructions (Metric Guide – Page 16) or is this intentional? Thankshi Hercule,
It is not important whether there is an overlap or not. It depends on the width of the wood and in some cases the edges of the blades will meet each other but there is no advantage to that and it makes no difference. I suggest that you use the widest wood that you have but at least as wide as the minimum size quoted in the manual. So there is no ‘right answer’ for the width of the wood and sometimes the overlap will be large and other times there will be none.
I hope this helps.
Hugh
Posted in Books
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Galvanised disks
I have just received a batch of galvanized disks for making magnet rotors.
Some ten 300 mm diameters and a pair of 660 mm for my big windmill.
Some ten 300 mm diameters and a pair of 660 mm for my big windmill.
It cost me 64 pence per kg, which comes to about £3 per small disk (about $5).
Transport was a bit more expensive going via the galvanizers,
but I think it will be worth it.
Cost per disk:
cutting £10
galvanizing £3
transport (in total) £7
Total was £20 per galvanized disk delivered to me in a batch.
Posted in Books, my own projects
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Bike pedal power project at school
Here is a nice video from Delaware about a bike using the axial flux alternator for a school class project.
Posted in pedal power, People
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Videos of French courses
I have just produced a video of the course in Normandy in April, building a 3.6 metre (12 foot) battery charger and a couple of smaller machines. I was helping Thomas Plassard and Tripalium with this course for CIER
Patrick Chalmel also put some other videos on youTube of the same event.
Posted in Video links
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Siting of small VAWT turbines in the UK
Factors affecting the success of a wind turbine are :reliability, windspeed, swept area, cost and efficiency. I found a Quiet Revoluiton QR5 turbine at the botanic gardens in Edinburgh and I am checking out these criteria.
There is a good rule of thumb that says a wind turbine should be 30 feet above any obstruction within 300 feet. Windspeed is highly critical for energy production since the energy depends on the cube of the windspeed. There is hardly any wind for turbines sited below the ‘canopy layer’ of the tree tops. For more details check the Carbon Trust wind siting tool. The company state that “Please note that the minimum recommended average wind speed for a QR5 is 5m/s.” But they were willing to sell one to go on this site, maybe just for “demonstration purposes”?
Reliability is very important since the kilowatt hours of energy generated will depend on the hours the turbine is available. The QR5 is out of action so far as I am aware due to problems with the blade attachments. Vertical axis turbines do have intrinsic fatigue problems which along with the problems of starting and stopping, and the problems of putting them on proper towers have made them a poor choice for wind energy.
The turbine is a nice size (5m high x 3.1m in diameter) but in relation to its cost it will not produce much energy even on a good 5 m/s site. The turbine alone costs £25,000. It does not matter how efficient it is it can never produce more than about 12,000 kWh per year at a 5m/s site, and the manufacturers claim 7,500 kWh per year. A HAWT of similar size and a fraction of the cost would do the same.Nice ornament? Or a big waste of money, and another big embarrassment to the small wind industry?
Posted in Rooftop madness, UK small wind scene
6 Comments