Domestic windmills put to bed.

[The Natural Philosopher]

You should. During the construction of this house, the 'lads' would have their afternoon tea, and put it on, and place bets on whether or not the subjects would become violent and abusive, or burst into tears.

The best was one teenage lad who apparently had, proved by DNA testing, got a dreadful sort of 'Vicky Pollard' pregnant with just one abortive knee trembler up against a pub wall. Trisha was telling him to be responsible, mature and look after her. His response was that not only did he actually not like her, but it was not even a proper shag, and he was ****ed if he was going to spend the rest of his life with some weepy cow that didn't know enough to take the Pill, and was a lousy shag to boot.

This got a general cheer from the Portakabin. For honesty if nothing else.

The bets were laid off, as he got violent and abusive, and she burst into tears..

Quite educational all round...

[Steve Firth]

AH HA! So how do ypu know who they are?

[Huge]

You must be joking. I am well aware of the content of these programmes.

[ARWadworth]

They probably should be. But not just for contraception.

The teenager I am seeing said I did not need to use a condom as she was on the pill. I made sure I wore one as she did not have an MOT certificate. Even if she had an MOT it is really only valid for the day it was written as you do not know who else has driven the car.

One in ten teens have some sort of STD. The last thing I wanted was to catch VD give my girlfriend a reason to chop my knob off.

I did read recently that the 40 to 50 year olds have had a massive increase in the number of STDs

Adam

[Andrew Mawson]

certificate.

Ah well ... in my day STD was Subscriber Trunk Dialling .... how things change !!!!

AWEM

[Peter Parry]

Look at

for some real data. For most roof height turbines anything from 50 to 700 Watt/hours a day is all you will get. As the controller consumes

100Watt/hours per day its probably enough to power one energy saving lamp for a few hours.

They need to be very high, 60m is a good starting point.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "ARWadworth" saying something like:

I take it she has all her own teeth? Not so much fun, sometimes.

[The Natural Philosopher]

Model aircraft expereinec confirms this: you need to be that high to get out of the earths surface boundary layer. Or conversely if you fly below

200ft at dusk, you will have smooth still air..but not above..

[Andy Champ]

And when I was a kid, every time I went to the dentist I had a filling. Almost always one, very occasionally two, never none. It was only when I did stats at uni that it ocurred to me that it was kind of suspicious that my 24 individual teeth were cooperating so nicely to spread the workload out.

Of course, after a filling you can't tell if there was a carie or not.

Andy

[Peter Parry]

One thing to bear in mind is that anemometers overestimate the output you are likely to get as they are not affected by turbulence in the same way windmills are. Moreover the manufacturers power curves are often complete works of fiction.

From the Warwick data for 4 sites :-

Predicted yearly output

From NOABL wind speed - 422kWh From measured Wind Speed - 129kWh Actually achieved - 44kWh

From NOABL wind speed - 426kWh From measured Wind Speed - 114kWh Actually achieved - 41kWh

From NOABL wind speed - 545kWh From measured Wind Speed - 146kWh Actually achieved - 44kWh

From NOABL wind speed - 479kWh From measured Wind Speed - 136kWh Actually achieved - 85kWh

the predicted NOABL windspeed for most urban areas allows a more accurate estimate of output.

I notice that the "silent" Windsave has now had to have a mass damper added on the pole to try to reduce vibration.

[dennis]

However you can smell decay burning when they use the drill.

[Roger]

The message from Peter Parry contains these words:

Sorry for the late follow-up.

Oh dear. The address below has a power curve among the "images". Would that have any connection with reality?

had already concluded that average wind speed wasn't a great help in determining power output given the relationship between wind speed and output but I had hoped that something like this power curve was reasonably accurate.

[Andy Dingley]

• site" is the fraction of generation capacity obtained over a year, i.e. total output / (rated power * total hours). This depends on three things: the size of the generator, the amount of time it generates usefully and the power it can achieve whilst doing so.

In an idealised "wind tunnel" environment at optimum windspeed, this is obviously 100% for a wind turbine + generator that's seeing a consistent wind that's enough to achieve rated power. The problem with practical wind turbines is that we can't achieve anything like that. The "Drake equation" version is something like this:

= Fraction_with_any_wind * (1- (Fraction_of_wind_speeds_too_low + Fraction_of_wind_speeds_too_high)) * Inefficiencies_in_de- rating_the_generator_from_optimum_to_actual_windspeed

You can improve this is a few engineeering ways:

• Pick a good site.

• Pick a _consistent_ site, over the windiest

• Design an efficient turbine that delivers good shaft power / windspeed

• Design a turbine that accepts a wide range of useful windspeeds

• Design a turbine that accepts a wide range of useful windspeed by doing _something_ at the limits, not just shutting down completely. (This is arguable - it tends to make #3 difficult)

• Design a turbine that uses a wide range of useful windspeed moderately efficiently. Your ultra-performance blade design is no use if you have to furl it too often

• Design a generator that can make use of what the turbine delivers, it doesn't just sulk if shaft power is inadequate. Don't over-size generators if the rest of the system isn't going to be able to work with it - that'll make your peaks impressive, but hurt the average.

• Use a downside power system that can make use of whatever the generator delivers. This means a modern smart inverter, not falling back onto a load bank or "heat waster" (CAT, I mean you!)

Note that averaging these figures is only slightly better than multiplying their peak values. You have to do integration over the whole year to get any sort of realism. I suspect that failure to do this is the root cause of most of the inaccuracies in quoted figures.

The claimed figures for this site (5kW machine delivers 14,000 kW h over a year) are around 30%. Anyone with real experience only dreams of getting actual figures that high.

[Andy Dingley]

Just to pre-empt the logicians, this one is obviously wrong. It's a good idea in terms of improving overall performance of a wind turbine, but in terms of improving utilisation alone it's actually a negative (as mentioned lower down).

The contradiction is that much of wind turbine design is about trading off peaks vs. averages. Some designs do one better than another, which is why vertical shafts (pretty insensitive to variations) might still have advantages in urban settings.

[The Natural Philosopher]

The very best windmills - large one, well above the boundary layer, do at best 30% load factor.

That one..well their 14Mwh per year assumes a shade over 30%.

at - say - 10p/unit, that's £1400 per year savings.

Assuming you spend £1400 a year on electricity, that is.

Or that te leccy compamny will buy back from you at 10p/unit. Normal commercial cost of baseband power is around 3-4p.

Assuming you get that 30%. That is.

In reality I suspect its about half that in a typical installation. So about 4-5% ROI.

Complete waste of time.

[Roger]

The message

from Andy Dingley contains these words:

I have already discounted that claim as advertising hype. A good many of the full size inland turbines can't manage a capacity factor that high. I had hoped to weight my wind data based on that power curve but if the curve is pie-in-the-sky as well I might as well not bother wasting any more time on it.

[The Natural Philosopher]

what power curve?

[The Natural Philosopher]

Almost all domestic alternative energy solutions are pie in the sky.

The only things that work are insulation, better boilers, and heat pumps.

If you want to play with solar or wind, or install mercury filled bulbs, have fun, but don't expect to actually save money as against what leaving it in the bank would do.

[Andy Dingley]

can see a (slightly) larger version if you faff through their crappy inaccessible Flash-based site and its deliberately obstructive navigation that prevents you getting to the content.

I've blagged the best copy I could and put it here

[The Natural Philosopher]

according to the beeb. Its nowt like that at ground ;llevel. Nor even up at the first floor.

At best 5-8mph (about 3m/s..)

I can accept its better above teh tree line, but thats about 15 meters higher than I would get planning permission for.

And that is still onlt 30% of rated output..