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Friday, February 14, 2014

WHAT IS THE FUTURE OF WIND FARMS?

On Monday I reported on the largest wind energy conversion systems (WECS), all of them horizontal axis  (HAWT) propellers.  One of them is taller than two football fields.  John Dabiri (left) of Caltech and his colleagues suggest that the field is going in the wrong direction.  They believe that much shorter vertical-axis turbines in a tight array with each turning in an opposite direction to its neighbors can be at least 10 times as efficient for any given area.  If true, this will totally change the nature of wind farms.

While there is a whole range of vertical axis wind turbine systems (VAWTs), Georges Jean Marie Darrieus of France, who obtained a U.S. patent for his VAWT in 1931, might have the most promising design, looking like an eggbeater (there are three here, but two-bladed systems became commercial):


It was nearly a third of century ago that I visited FloWind's 300 kW VAWTs in the State of Washington.  I liked what I saw and actually considered investing some money.  I didn't, but FloWind went on to install 500 or so of its turbines in California's Altamont and Tehachapi (right) Passes.  By 1985, their installed capacity was 95 MW, and in 1987 they were supplying electricity for 20,000 households.  

Paul Gipe (left) has an excellent summary of what went wrong:  cataclysmic collapses, degradation of extruded aluminum, joint failures, overstated performance and outlandish power rating (their average capacity factor was 12% and less). However, their two marketed models were just second generation devices, so materials development (perhaps carbon fiber composites), more substantive joint connections and honest performance numbers could well place the Darrieus systems back in the game.

Three major pluses for HAWTs are the fact that they are into an advanced generation where the kinks have been engineered out--while nothing much has been done with the VAWT since FloWind crashed--wind speeds are higher at elevation and they are cheaper.   But, there are some advantages to the VAWT over the HAWT:
  • More easily maintained, as everything is virtually at ground level.
  • Omnidirectional:  but you need to be able to start it, and, by all means, have a good brake.
  • Much quieter:  ten meters from the tower, a VAWT is at 38 dB, a whispered conversation, while a HAWT reaches 98 dB, passing traffic on a busy highway measured from the road shoulder.
  • VAWTs can be packed close to each other, whereas HAWTs need to be separated by a space ten times the diameter of the propeller.
The Caltech study is, thus, largely based on this latter advantage of closer placement:


Watch this 40 minute presentation by Professor Dabiri.

There is a 4 MW Darrieus VAWT turning in Quebec:


Just a generation or two, then, to a quieter, lower and more efficient wind farm of 8 MW VAWTs, perhaps, maybe even a community supportable effort on Molokai or Lanai???

But if not, what about placing wind farms on floating platforms at sea?  One problem is that while typical wind farms today produce electricity at around 9 cents/kWh, offshore wind energy now averages out at 22 cents/kWh.  Yet, Hywind of Scotland is already doing this, and hopes to have five 6 MW HAWTs off the coast of Aberdeenshire 100 meters offshore:


But would these Darrieus turbines reduce the cost?  There actually is a company, Floating Windfarms Corporation, based in Houston with China connections already active:


The future of windfarms?  VAWTs at sea?  In Hawaii, local activists have killed, for now, Big Wind on land.  The best wind regimes are actually between the islands where the flow is also laminar. A series of Darrieus wind farms on floating platforms in a gyre or controlled region where electricity can be sent through undersea cables, or, someday, even transmitted wirelessly, would be worthy of exploration.  Another option if there is a commercial option would be the production of hydrogen.

Oh yes, Snoopy sends a Happy Valentine greeting:


The Sochi 2014 Winter Olympics
Medal standings
        COUNTRY                 GOLD             SILVER                  BRONZE
1
Germany
7
2
1
10
2
Switzerland
5
1
1
7
3
Canada
4
5
2
11
4
Norway
4
3
6
13
4
United States
4
3
6
13
6
Netherlands
4
3
5
12
7
Belarus
3
0
1
4

Norway and the USA are tied with 13 medals.

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