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On the technical side, how are the measurement campaigns set up when the masts should be offshore? Do you build a platform just of the mast offshore or do you trust data points in the vicinity (lighthouses?)?

Rien n'est gratuit en ce bas monde. Tout s'expie, le bien comme le mal, se paie tot ou tard. Le bien c'est beaucoup plus cher, forcement. Celine
by UnEstranAvecVueSurMer (holopherne ahem gmail) on Thu Jul 19th, 2012 at 02:57:49 PM EST
[ Parent ]
You don't actually need onsite data offshore - correlation with met data from not-too-distant sources is good enough - offshore wind is predictable over long distances and you can use mesoscale studies (modelisation done using NOAA data for instance).

The one tricky issue offshore is wake effect (i.e. the impact of one row of turbines on the production of the row "behind" them) as it can be quite significant (10-30% for individual rows) in some wind directions - both from the wind fair itself as from neighboring ones.

Wind power

by Jerome a Paris (etg@eurotrib.com) on Thu Jul 19th, 2012 at 04:12:28 PM EST
[ Parent ]
Thanks. Some further questions if you have the time...

Do you use raw NOAA data or GFS + validation using other meteorological models? GFS afaik underestimates wind speeds, especially for higher speeds, so I would be curious to see how one corrects for that.

As far as wake losses are concerned, I suppose your regular 2.5/5 diameter rule does not apply... but why is that? Is it because wake effects do not move linearily with rated power?

Rien n'est gratuit en ce bas monde. Tout s'expie, le bien comme le mal, se paie tot ou tard. Le bien c'est beaucoup plus cher, forcement. Celine

by UnEstranAvecVueSurMer (holopherne ahem gmail) on Thu Jul 19th, 2012 at 04:27:25 PM EST
[ Parent ]
What 2.5/5 diameter rule?

Spacing is determined by the energy-weighted wind rose.  But it takes anywhere from 12 to >20 diameters before upwind turbulence has decayed and boundary layer mixing has replenished the energy taken out by the upwind row.

No project developer uses such spacing today, which puts extra load cycles on the downwind turbines in any direction.. There should be a happy medium, with well understood tradeoffs between energy capture and excessive load avoidance. But proper spacing greatly increases cable costs as well, so... it's often not under major consideration.

We'll have to wait for more operational data from the low rpm greater diameter WTs to see how great the problem is before there's a chance of establishing a rule of thumb. This can also be an underestimated problem between projects, when they are clustered with a narrow shipping lane between.

The science is obtained incrementally.

"Life shrinks or expands in proportion to one's courage." - Ana´s Nin

by Crazy Horse on Fri Jul 20th, 2012 at 08:06:20 AM EST
[ Parent ]
Offshore these days is typically spaced 7 diameters apart in the prevailing wind direction and 5 in the other direction.

Wind power
by Jerome a Paris (etg@eurotrib.com) on Fri Jul 20th, 2012 at 12:16:24 PM EST
[ Parent ]
You do get higher correlation by having a mast to use as a base station. The most expensive ones are complete research stations, which can be used for wave and current measurement and environmental issues. They can run over €3M, which can be shared between projects. Germany has built two in the North Sea and one in the Baltic. FINO 1 was operational since 2003, and FINO 3 since 2009.

You can visit FINO 1, 2, and 3 on the web, starting in english HERE.  You can get live speed data and images. FINO 3 cost €12M which includes years of research and measurement projects. It measures to 105m, with a 15m lightning rod taking it to 120m.

There are less expensive versions primarily aimed and wind and wave measurement. The technology of floating stations is gradually gaining acceptance as well, or at least entering the market, usually LIDAR or SODAR based. Here's a test of one model:

I believe many of the larger projects will need to have a station, because there is no substitute for onsite data. This can help with power curve verification as well as wake analysis, so should prove cost effective, especially if shared.

"Life shrinks or expands in proportion to one's courage." - Ana´s Nin

by Crazy Horse on Thu Jul 19th, 2012 at 05:03:19 PM EST
[ Parent ]
yes - which means you don't need wind masts at every project location, which is what I meant.

Wind power
by Jerome a Paris (etg@eurotrib.com) on Fri Jul 20th, 2012 at 12:19:01 PM EST
[ Parent ]
Yup. And the FINO masts are a perfect example of valid government funded infrastructure (which you comment on often), which provides significant value to project financing. The German masts were funded by the government, the EU, and private research groups on the studies.

When such base stations are established, then short-term floating LIDAR and turbine sited measurements can be very well-correlated.

"Life shrinks or expands in proportion to one's courage." - Ana´s Nin

by Crazy Horse on Fri Jul 20th, 2012 at 01:01:49 PM EST
[ Parent ]

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