The letters of the sign sway up and down
as if they are bobbing about on the waves.There’s nothing very
complicated about the mechanism – its just one long crankshaft – but
making it work by renewable energy has been less straightforward than I
expected. I originally intended to make it wind powered. No electricity,
just a geared down mechanical linkage to the crankshaft. I was worried
about gales, so my first design was self furling (the propeller blades
turn themselves out of the wind when it gets too strong). I was delighted
to find I had a suitable worm gearbox and even a suitable propeller (from
a petrol powered blower). It was a complete failure. I realised that what
I had made was actually a very highly powered device for turning itself
out of the wind, even in a light breeze.
I tried extending the tail, but there was little improvement.
So then I abandoned the self furling and increased the
diameter of the propeller from .6m to 1.5m. It was still completely
gutless, even in a fresh breeze. My blades weren’t brilliantly
aerodynamic and I hadn’t stuck it on a really tall pole to remove any
possible effects of obstructions, but even if these changes had trebled
the power it would still not nearly been able to power the sign. Next I
attached my propeller to a powerful DC motor. (This acts as an efficient
generator. If you join the wires from one motor to another identical one
and spin the first one by hand, the other will turn nearly as fast as the
one you’re spinning.) Connecting my ‘generator’ to an identical
motor, it did sometimes turn, but still had little power. It was always
easy to stop the 8mm shaft with my fingers.
I went down to our local harbour and was amazed to
see some of the yacht turbines spinning with hardly any wind – but then
I saw that many others weren’t, and realised that the ones that were
cheerfully spinning weren’t charging, they just hadn’t been left
connected to anything. I guess that large windmills (which keep their
speed roughly constant by adjusting the pitch angle of the blades) are
also often turning without generating. I started to wonder if there was
less power in the wind than I had intuitively imagined.
I met up with my friends from Science Projects, who
make exhibits for science centres, and their experience had been very
similar to mine. They just couldn’t get wind power to do anything much.
On one project they had had got an expert from Rutland (who make the UK
yacht wind turbines) to come and see their installation as it wasn’t
working. His advice was that they needed to place it further away from any
possible obstruction, but they were doubtful this would produce a 90%
improvement as it was already in a quite exposed position.
Now curious, I started Googling the subject. I think
the key fact is that power is proportional to the cube of the wind speed.
So when it’s blowing a gale, wind power is good source of energy. But
whenever the wind drops a bit, even if its still a fresh breeze, wind
power becomes pathetic. David Cameron (the leader of the UK conservative
party) got a lot of publicity for fitting a ‘Windsave’ windmill to his
chimney (www.windsave.com). Windsave’s website proudly claims their 2m
diameter blades will generate 1Kw of electricity at a wind speed of only
12 meters per second. 12 meters per second is force 6 or
almost a gale. By the cube law, a moderate breeze of 6 meters a
second would only generate 120 watts, certainly not enough for a freezer
let alone anything else that might be switched on, and a light breeze of 3
meters a second would only generate 15 watts, enough for one energy saving
light bulb. And David Cameron’s windmill certainly isn’t on a high
pole with completely unobstructed windflow so it could only produce much
less than Windsave’s quoted figures. I can’t imagine how they claim it
can save you 33% of your entire electricity bill.
I’m sure bigger is better and the case for offshore
wind farms is probably still fine. However the figure that is often quote
that 10% of our energy comes from renewables is misleading as most of this
comes from long established hydroelectric schemes. Currently, about one
percent of our electricity comes from all UK’s wind turbines.
While I was puzzling about this my sister (who makes
mosaics) was commissioned to design a piece for a Dubai oil company’s
boardroom. She really struggled to find images of oil rigs and oil
production as all the major oil companies now just have pictures of wind
generators on their websites.
So I now think wind turbines are principally green
icons. Until I started playing with wind power I was completely in favour
of them. Wind turbines are elegant structures, and its very clever how
recent development has converted the relatively slow speed of their blades
into significant amounts of power. But if I, who pride myself in having an
intuitive sense of what works, can be so mislead by the power of the wind,
there’s little hope that most other people are more clued up.
Its far too easy to be a grumpy old man, so for the
pier’s sign, I decided to change track and try a motor running from
photovoltaic panels. I bought two Kyocera 12volt, 85watt panels and
connected them to a 2 amp, 24volt motor to drive the sign. It worked
immediately, and slowed down satisfyingly when the clouds came over. For the
pier it’s a much better fit. Its busiest when the weather is bright and
sunny – its not usually busy when there’s a gale. At 12 volts the
motor can only draw 12 watts, so with panels rated at 170 watts, I thought
it should run whatever the weather. We carefully added weights to balance
every letter and reduce the load on the motor. This greatly improved
things, but I should have been more fussy about the bearings as it still
tends to stop in thick cloud.
Its not perfect, but its still very satisfying seeing
it run without connection to the mains or batteries. It doesn’t even
need a timer, its starts up in the morning and stops in the evening
It made me realise how careless we usually are
using energy, even with the recent price increases its still really very
cheap. Making the arch makes me think that if people are serious about
switching to renewable energy, almost all electrical products will have to
be redesigned from scratch.
I hadn't realised how much email this page would
generate, even before it was picked by the BBC: Email me if you want to
get in touch with any of the people quoted:
of any sort reduce the wind even more drastically than I had thought.
just read your page about windpower, your experience is very much like
'It is easy to underestimate the effect of buildings and the landscape.
Even the tallest windmills placed in a random place will give bad result.
Off the coast or on a mountain is the only way to be sure of a constant
useful wind. The formula v2 = v1*(h2/h1)^n Where n ranges from 0.1(flat
surface) to 0.3(trees, houses) is useful for estimating the wind speed at
a new height h2 when the speed v1 at height h1 is known. It is only valid
if the terrain is uniform and where I live it is not accurate except if
the height difference is fairly small.'
Hugh Piggott, who has been building small wind turbines
in Scotland for many years wrote that he agrees that Windsave and other small urban
turbines are pretty useless. However he is concerned that their failure will
persuade people that small turbines are always useless. He has a brilliant
website about how to build good ones: http://www.scoraigwind.com/index.htm
wrote that he had improved the power of his windmill by reducing the
diameter of the blades, so I probably didn't persevere long enough with my
The sails are 700mm long each and it drives
a 100:1 geared dc motor from Maplin. I had to gear it back to 50:1 using
a smaller drive sprocket, as it simply wouldn't turn. The thing needs a
self furling capability, this I'll do on the next one.
It turns well in very light breezes and
comfortably charges small batteries, typically 6volt x 4 ah. It would,
of course, run a similar motor directly. I think your sign is very novel
and was surprised it wouldn't run directly. As I said, mine
improved immediately once I got the gearing right and I also trimmed the
sails back from 1m down to 700mm and that too helped, curiously!
I think it must be something to do with the governor effect of having 3
sails, you'd know more about this I imagine.
I don't know
whether you remember me, I got in touch about wind turbines and mentioned
that I intended to make one from a bicycle dynamo. Well, its done and
works really well. I used a Sturmey Archer Dynohub as the generator,
didn't bother to gear it up as I only need about 4 ah per month. It
trickle charges a car battery that I use to occasionally run a water pump.
The sails are cut from pvc pipe and are 450mm long, so its only small, but
delivers usable current, even at very low revs. All in, its cost me about
£40, less than the price of a battery.
I found this the most interesting reply of all.
Dennis quotes reports from Germany and Canada very skeptical of large
scale wind turbines. Its long, but quite fascinating:
can't find the original link for this Eon Netz report but the pdf is
attached. Worth reading right through but here are a few choice samples:
2004, Germany was once again the global world leader in the production of
wind power. At the end of 2004, wind energy plants with an installed
capacity of 16,400MW supplied the German electricity grids. The greatest
proportion of this capacity, 7,050MW, was connected in the E.ON control
area. E.ON Netz, the transmission system operator of the E.ON Group,
consequently makes a key contribution towards the technically and
commercial optimum integration of wind power into the electricity supply
energy is only able to replace traditional power stations to a limited
dependence on the prevailing wind conditions means that wind power has a
limited load factor even when technically available. It is not possible to
guarantee its use for the continual cover of electricity consumption. Consequently,
traditional power stations with capacities equal to 90% of the installed
wind power capacity must be permanently online in order to guarantee power
supply at all times.
High voltage (HV) grids are increasingly reaching their capacity
limit and they can take no further electricity from wind farms. As a
result, E.ON Netz is currently planning just under 300km of new high and
extra-HV overhead lines in Schleswig-Holstein and Lower Saxony. E.ON Netz
is doing everything it can to implement these grid expansion measures as
quickly as possible
According to grid studies by the Deutsche Energie-Agentur (dena), wind
Germany is expected to increase to 48,000MW by 2020, around a threefold
increase since 2004. The possibility of integrating this generation
capacity into the supply system remains to be seen. There is
a need for considerable changes to the extra-HV grid alone, of around
2004, there was slightly less wind available
than in an average year. In total, German wind farms generated 26 billion
kWh of electricity, which is around
4.7% of Germany’s gross demand. Wind farm
operators were paid a total of €2.35 billion, at an average of
highest wind power feed-in in the E.ON grid was just above 6,000MW for a
brief period, or put another way the feed-in was around 85% of the
installed wind power capacity at the time.
average feed-in over the year was 1,295MW, around one fifth of the
average installed wind power capacity over the year.
Over half of the year, the wind power feed-in
was less than 14% of the average installed wind power capacity over the
In 2004 two major German studies investigated the size of
contribution that wind farms make towards guaranteed capacity. Both
studies separately came to virtually identical conclusions, that wind
energy currently contributes to the secure production capacity of the
system, by providing 8% of its installed capacity.
As wind power capacity rises, the lower
availability of the wind farms determines the reliability of the system
as a whole to an ever increasing extent. Consequently the greater
reliability of traditional power stations becomes increasingly eclipsed.
As a result, the relative contribution of wind power to the guaranteed
capacity of our supply system up to the year 2020 will fall continuously
to around 4%
concrete terms, this means that in 2020, with a
forecast wind power capacity of over 48,000MW
(Source: dena grid study), 2,000MW of
traditional power production can be replaced by these wind farms.
With the continued expansion of the use of wind energy in Germany, demand
for standby reserve capacity will continue to rise, and will increase
around fivefold by 2020.
total electricity consumption (grid load) in North Friesland is between
40MW (low load) and 120MW, wind farms with a total production capacity of
over 500MW are installed in the area. Consequently, even at periods of
high consumption, around four times as much electricity is generated by
wind power on windy days than is used by customers.
surplus wind power has to be transported to consumers over long
distances. The size and operation of the grids must be altered to cope
with this requirement, with the primary objective of avoiding overloading
lines and the resulting losses of supply.
European transmission system operators are also increasingly affected by
the high wind power feed-in in Germany. The reason for this is that power
always flows within the grid according to the laws of physics and seeks
out the route of lowest electrical resistance.
result, sometimes a significant proportion of the wind power in-fed in
Northern and Eastern Germany flows in a loop through the grids of the neighbouring
countries of the Netherlands, Poland and the Czech Republic, where
it leads to significant loads on the operating resources.
thermal power stations do not disconnect from the grid even following
serious grid failures, instead they generally trip into auxilliary
services supply and until then, "support" the grid. Wind farms,
however, have so far disconnected themselves from the grid even in the
event of minor, brief voltage dips. Experience shows that this can lead to
serious power failures:
·On 29 January 2004, a two-phase line fault occurred in the
220kV grid in the Oldenburg region and resulted in split second-long
voltage dips in the region concerned. This produced a sudden loss of
around 1,100MW of wind power feed-in.
·On 15 September 2004, a crane caused an earth fault on an
extra-HV line in Hamburg. The resulting brief voltage dip of a few
tenths of a second meant that approx. 600MW of regenerative power
disconnected from the grid in the Hamburg region.
ten years time there will still be a large number of older wind farms in
Germany feeding into the grid, which do not have the necessary grid
supporting features. There is therefore a risk that even simple grid
problems will lead to the sudden failure of over 3,000MW of wind power
feed-in. In this case, the reserves maintained in
the Integrated European Transmission System, in order to cope with
problems, would no longer be adequate to safely tackle such failures.
the present time, it is not known how to confront this risk."
get even less out their turbines:
Toronto Star, Jul. 24, 2006
"Let's take Ontario during the month of July. Last Thursday, for
example, the output of the province's three operational wind farms, which
at full output can produce 207 megawatts, only generated between 4 and 42
megawatts depending on the hour.
For most of the day last Friday, output was below 10 megawatts, working
out to less than 5 per cent of "nameplate" capacity. So far this
month the typical range is between 35 megawatts to 75 megawatts, with a
top output of 157 megawatts achieved during a single hour.
This is part of the reason why power planning authorities, when
factoring in the contribution that wind makes to the grid, only assume
that an average of about 10 per cent of theoretical output will make it to
the grid during peak times."
ERCOT (The texas power grid) used the same capacity factor of 10%. They
recently dropped that number to 1.9%.
*At low wind speeds (under 5 m.p.h.) wind farms frequently consume more
power than they produce. (to keep electronics running, to yaw the turbines
into the wind, etc.)