Batgung

I really like this idea. The people that are arguing against the windmills are exaggerating greatly.

What about typhoons though? are there any chances that the typhoons that Hong Kong face will tear those things apart and have windmill debris flying everywhere? I think chances of that happening are slim but I hope they put some thought into it.

Chocolove, I can't find any mention of typhoons on their website, but I can't imagine you can design a large structure in Hong Kong without taking typhoons into account. There is a form to leave feedback / ask questions if you'd like to ask them for more information.

Phil, you might be interested in the Environmental Impact Assessment, which talks about the effects on marine life and fisheries in more detail. As you mention, they don't believe it's a very important site for fish: 'Uniform and exposed muddy seabed with no habitat diversity is unattractive to fish as a shelter or feeding area. (8.8.3.2)'

Looking at the proposed foundation, do you think there is any value in asking them to make it a more irregular shape? If it looked more like a christmas tree with articificial branches, would it increase the surface area, and so increase the reef effect?

I have limited success looking for structural design and considerations in the EIS.   But from looking at the diagram, I expect there will be a tremendous amount of bending moment at the joint between the substructure and the superstructure (credit goes to tngan).   It might be able to withstand severe storms including those of climate change, but what about metal fatigue over a period of decades with salt water action taken into consideration?

T, there are some more comments about the foundations on the project's website. They say they will use a 'suction caisson'. In the following page the diagram shows the foundations don't reach down to the rock layer, so perhaps the condition of that rock is less important?

I'm not sure about the effects of sea-water on corrosion. You'd probably find some useful information by searching for information from the oil industry. They've been building metal structures in this environment for many years, so should have a good understanding of the problems.

regards, MrB

Hi there,

I did a casual search and found this piece of document.  I am not an engineer so I am not in the capacity to verify it.  In layman terms, I just don't understand how it works.  Anyway the document mentioned Suction caisson is quite common for drill platforms in areas with a depth of 1000m to 3000m.  I guess the great water pressure at that depth helps the ancorage quite a bit.  Hmm..... there is hardly anywhere place around Hong Kong with such depth, I would say.  Would it work in so shallow waters?  I wonder.

Best Regards,

T

I've got mixed feelings about windmills, I have to admit.

A couple of concerns that no doubt have been brought up in relation to the ones proposed in HK:

First, birds. Windmills are notorious for shredding birds in flight, and since HK is such a haven for migratory species, what will the potential impact (pun intended, unfortunately) turn out to be? Admittedly, the proposed wind farm is on the opposite side of HK from Mai Po and the main wetlands, but still . . . .

Second, I really don't think of Hong Kong as a windy place. There are lots of still days here -- especially in summer -- when those turbines will sit absolutely stationary. And whatever power they're counted on to generate will need to be compensated for by other power plants. In particular, I think about HK's hideous pre-typhoon days, when the air is stagnant, and demand for electricity for air conditioning peaks in the heat. Getting a workable balance of sources to support the grid under these conditions must be quite a trick.

On a related note, I've noticed that wind power has taken off big time in my ancestral homeland, as these two articles from the Atlantic magazine describe: part 1 and part 2. Iowa, I should note, is a fairly windy place, and it certainly doesn't have the world's most interesting landscape, so perhaps it's an ideal location for wind turbines. But it's interesting to note that the author of the pieces seems tacitly to approve of wind farms in Iowa, but firmly rejects the possibility of the same structures marring the landscape of her own childhood home in southern Indiana. You can look at the photos included in the articles, and see what you think . . . .

This NIMBY-ism (i.e. 'I like wind power, but Not In My Back Yard') has popped up quite frequently in discussions of wind power in the USA. The most famous case was of the Kennedys promoting wind power like crazy in their public politicizing, but then surreptitiously working to undermine plans to situate sea-bed turbines near Cape Cod, Nantucket and Martha's Vineyard, where they keep their holiday homes -- because they would spoil the view, of course.

Cups of coffee

My kettle is rated at 2,000W. The wind-farm is described as generating 200MW, or enough to run 100,000 kettles at the same time.

However it's not clear what's the average actual power generation they expect to get from the farm. Even if you only get 10% of that, it's still a lot of cups of coffee, but it would be good to know the number they are assuming, and then compare it with the actual results they get.

Typhoons

As T notes, the turbines are shut down if the winds are too strong. eg the Lamma Winds turbine quotes a cut-in wind speed of 3m/s, and a cut-out wind speed of 25 m/s.

Notorious bird shredders?

Not really. Britain's Royal Society for the Protection of Birds (RSBP) 'supports a significant growth in offshore and onshore wind power generation in the UK.' However the same page also notes that 'Poorly sited wind farms have caused some major bird casualties'.

So windmills don't suck birds to their destruction from far off locations, but they will do damage if they're in the wrong place. The RSPB say they object to around 7% of the hundreds of wind-farm proposals they review each year.

For the Hong Kong project, the EIA has a long section that discusses the effects on bird life. It concludes:

7.10.1.4  The impact assessment suggests that potential impacts on all birds resulting from construction and operation of the proposed wind farm will not be significant. The SNH model has been used and predicts negligible collision risk for all the most sensitive species in the Study Area based on their distribution and abundance information obtained from boat based field surveys. The significance of construction and operation impacts on avifauna is anticipated to be very low.

Windy enough?

Good question - closely related to the 'how much actual electricty can we expect'. I can't see it quoted in their documents, but let's make a rough guess.

• Start with table 1 in Technical note #77, Wind Statistics in Hong Kong in Relation to Wind Power, from the HK Observatory. It gives the average wind speed for Waglan Island (I'll assume it has similar conditions to the wind farm site) as 6.7m/s. (Second only to Tai Mo Shan among the locations they monitored)
• The project website uses the Vestas V90-3MW turbine as their example.
• Page 3 of the Vestas brochure for that model gives a graph of power output for a given wind speed.
• If we just use the average wind speed, that translates into an average power of around 500Kw throughout the year. I think it's going to be higher than that, but my maths isn't up to it! If you look at figure 17 in the HKO document, 6.7 is the average, but as power is proportional to the square of the wind speed, we'll get a lot more electricity from the higher wind speeds. 
• So I'll make a rough guess that average power is 750KW through the year, or 25% of the stated maximum. For the whole wind farm, that would be 50MW.
• Over a year, the wind farm will generate 365*2*50 = 438,000MWh (Megawatt -hours).
• In 2008, Hong Kong consumed appx 147,000 terajoules of electricity, or 41,000,000 MWh. 
• So the wind farm will generate around 1% of the electricty we consume.

That feels like I've just done a maths exam, so feel free to pick holes in my calculations and assumptions.

Iowa

The Economist again: 'a farmer in Iowa who gives up a tenth of a hectare (a quarter of an acre) of land might earn $10,000 a year from it (about 3% of the value of the electricty it produces). Planted with maize, the same land would yield a mere $300-worth of bioethanol.'

Suction Caisssons

I think the document titled 'SUCTION CAISSON ANCHORS - A BETTER OPTION FOR DEEP WATER APPLICATIONS' might be a bit misleading. I don't read it as 'Suction caisson works better in deep than shallow'. From the content of the document, it is closer to 'suction caissons are better than piling in deepwater'. The document goes on to quote the difficulties of piling in deep water.

It's still true that suction caissons benefit from the increased pressure in deep water, but I don't see anything there that suggests they face problems in shallow water.

CLP has performed loading testing of a suction caisson at the proposed project location.

Thanks, MrB, for that comprehensive reply!

I had a look at the EIA section on the birds, and it's clear they've done a pretty comprensive job assessing the impact on pretty much all of the bird species in that area, so I agree this project seems acceptable on these grounds.

The capacity question still lingers, though, doesn't it? That is, places that use wind power have to find some way to meet peak demand without any contribution from the windmills, since they simply can't be counted on. So redundancy has to be built into the grid somewhere along the line, which isn't the most efficient scenario, but again to me seems acceptable if enough savings can be realized via the windmills.

I can also fully understand why many Iowa farmers find those yearly rental payments -- wait, I mean find those windmills -- downright handsome . . . .

OldTimer, I've seen it mentioned somewhere that the expected life span of windmills is 20-30 years. But I'm not sure if that refers to the rotors only, or to the whole setup, including the caissons. Has anyone else seen anything about this?

OldTimer, good to see you back again. There's also a mention on the website for this project:

Design Life: Typical turbine design is 20-25 years

Mr Tall, At this early stage, I don't think the varying output from the wind farm will cause much of a problem. Take a look at this graph of the demand for electricity in the UK over a 24-hour period. You'll see several times where there are changes of over 5% in a given hour, and the current system is able to cope with them.

If the wind farm goes from rest to full output, based on the earlier estimates the local grid will need to cope with around 4% extra power supplied. In terms of how the grid handles it, it doesn't seem it would be much different from the demand dropping by 4%. I'm not sure how quickly wind speeds vary, but in general I think it would take at least an hour to go from calm to a 15m/s wind?

It will become an issue if the installed capacity for wind climbs to say 20-30% of total demand. I figure that problem will take care of itself though - if the power companies see that 'free' electricity is being thrown away on a regular basis, I believe they'll have a strong incentive to find a make better use of it.

Thanks for all the questions, they've made me learn more about this.

Actually the main strength to support a suction caisson in water does not depend on the depth of water, but the lateral friction resistance between the boady of suction caisson and the seabed it stands. When wind blows the turbine, the suction caisson foundation holds itself resistantly because the great friction between body and its touched surface. So the geotechnial sea statistics will be quite essentially important to decide if suction caisson is OK or not. Even in a shallow water, if we let suction caisson goes deeper, where the touching surface is enough, the suction caisson can be OK.

Pls take a look at a field test in Denmark: a suction caisson foundation a 2.3MW turbine stands in a basin condition where water are much shallow.

Thanks for the comment Mr B. quote." I'm guessing the potential for self-generated power are limited." I am thinking not only of the many people who live in village houses in the New Territories (myself included), but even those in apartment blocks. Where there is a will there is a way! Surely the flat top roofs of apartment blocks would be an ideal site for individual or communal solar panels or wind generators. After all satellite dishes and TV antennas also go on roofs. It just needs owners and tenants to come to an agreement, and Government to encourage these facilities. With regard to power saving - What about insulation to prevent heat gain? Why does government not encourage insulated cladding to concrete walls and double glazing, as in most developed countries? As you say, some numbers to show the value of a moderate percentage saving in power consumption due to the combined effect of individual power generation and power saving through insulated buildings would be interesting. Mike

Alex, thanks for the link.

But the document says their solution is still under development:

Statistically, 1 of 3 prototypes have failed so far. This clearly underlines the vulnerability of the concept.

The monopod bucket foundation will not be commercialized before we are completely confident that we are able to handle all risks successfully!

It's not clear if their concerns apply to all suction caissons, or just to their own design. Any ideas?

Mike,

"Surely the flat top roofs of apartment blocks would be an ideal site for individual or communal solar panels or wind generators."

Solar heating. I've already seen solar water heating panels on NT houses (see government leaflet), so they're already an option.

Solar electricity. Possibly, though I'd still like to see some more numbers on what their potential contribution is if they are widely adopted, and then if the take-up rate is lower.

Wind. I don't see a good future for this. From what I've read of small turbines that would run on a 3-storey rooftop, the small turbine and low wind speed means the returns are not attractive. On top of a multi-storey does mean there's more wind power available, but I think safety concerns will make it unlikely we'll see many of these.

"With regard to power saving - What about insulation to prevent heat gain? Why does government not encourage insulated cladding to concrete walls and double glazing, as in most developed countries?"

This is an attractive solution. Build a more efficient building, and you use less electrcity regardless of the inhabitants behaviour. The magic word is OTTV, or "overall thermal transfer value", which describes how easy it is for heat to pass into a building. So a well-insulated building will have a lower OTTV.

New buildings in Hong Kong do have to meet a standard for OTTV. But the regulation applies to 'commercial buildings and hotels.' As I've grumbled elsewhere, a strange quirk in our regulations ecourages bay windows in residential buildings, which are a bad choice if you're trying to minimise the OTTV.

Worth further investigation.

MrB

Thanks Alex, I learn something new from this slide show.

When installed in the seabed supported by suitable material (local or additional), a suction caisson can stay in place plus supporting the windmill mounted on it.  I agree that the caisson will resist lateral (in the horizontal direction) movement, and skin friction with the seabed will also resist uplift movement of the caisson.

The term "suction caisson" is a bit misleading.  It refers a type of caisson which is driven into the seabed by suction action - removal of the air from inside the bucket thereby allowing the water pressure to press the bucket into the seabed.  Once the pumps are removed, the negative pressure inside the bucket will, over time, diminish when seawater seeps in from under to fill the void.  But we still call it a "suction" caisson.

It is interesting to note the buckling of the bucket skirt in the photo.  There are metal plates inside (roughtly every 30 degrees) so perhaps they might try to use more reinforcement.   I suggest the water pressure was not enough (not enough depth)  to drive the caisson downward and the negative air pressure exceeded the critical stage.

It appears then, that if the water is shallow and rocks may be present (about 40 feet in these examples), piling/hanmmering might be a better alternative.

I'm still a bit dubious about the long-term utility of wind farms, but this article suggests that their presence may even benefit the marine ecosystems in which they're placed. Interesting stuff!