Problems with wind power

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 automatically.

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:

Obstacles of any sort reduce the wind even more drastically than I had thought. Bjorn wrote:

'I just read your page about windpower, your experience is very much like mine.'

'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

Bob 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 design:

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.

bicycle generator

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 Ł40, 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:

I 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:

"In 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 systems.

· Wind energy is only able to replace traditional power stations to a limited extent.

Their 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 power capacity

in 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 2,700km.

In 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 €ct 9/kWh.

1.The 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.

2.The average feed-in over the year was 1,295MW, around one fifth of the average installed wind power capacity over the year.

3. Over half of the year, the wind power feed-in was less than 14% of the average installed wind power capacity over the year.

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%

In 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.

Whereas 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.

This 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.

Neighbouring 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.

As a 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.

Large 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.

....in 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.

At the present time, it is not known how to confront this risk."

http://www.foe.co.uk/forum/index.php?topic=2882.msg20675 This FoE forum attempts to pacify the worried greens asking pertinent questions about this report from a major wind operator.

And they call it "sustainable".

Canada 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.)