Cheap Electricity from Offshore Wind:

Further offshore has the best wind.  The water is deep there, so the wind turbines must be floating.  It is reliably asserted that floating offshore wind could power the whole world - many times over.  The only way to realize that huge potential is to make it cheap.  Here are several ideas that could bring the cost down.

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Mass has a stabilizing effect.  The heavier our foundation, the more inertia to resist movement.  A rowboat in a storm is tossed about;  an aircraft carrier much less so.  Big heavy foundations can resist oscillation better than lighter foundations.  We might naturally think of concrete.  It is heavy, cheap, and readily available most everywhere. 

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Generally, as turbine size increases, electrical output increases per dollar of investment.  Bigger turbines make cheaper electricity. 

An idea as to scale:  The International Energy Agency has designed the “IEA 15 MW Reference Wind Turbine”.  The turbine blades would be 117 meters (384 feet) long.  The steel tower would be 6 to 10 meters (32 feet) in diameter and 150 meters (492 feet) in height.  Weight would be about 2,000 metric tons. 

On land, trucking of the giant components for the largest turbines can be prohibitive.  Transporting components by ship scales more easily.  At sea, entire foundations can be towed out, floating.  Our candidate concrete foundation would be a platform with an array of five or six hollow concrete cylinders providing flotation (see attached 6 Cell Floating Foundation sketch).  Depending on its dimensions it would weigh approximately 10,000 to 20,000 metric tons.  

 

How could this be cheap?

1. It is made at an aggregate plant located on the coast.  With the aggregate sourced onsite, and mixed with ship delivered cement, we would have the cheapest concrete anywhere.  Cement could be supplied from the "greenest" source worldwide.

2. The foundation would be built on a flat casting bed. Once semi-cured, the round  top would be post-stressed.  This large one-piece foundation would be jacked off the casting bed into the adjacent deep water.  Many complete foundations could be stored, floating nearby.   To minimize logistics, it would seem most economical to tow each manufactured foundation directly to its final permanent location.  Once there it would be permanently tied in place to pre-positioned anchorages.

3. There are not many waterside rock quarries.  And those few probably do not have ample dock and storage space to receive shiploads of components.  Assembling the turbines would be most efficient at large specialized facilities.

4. The wind turbine components would be arriving by ship from around the world.  For maximum economy, the turbines would best be completely assembled in established harbors where dock space, storage space, and skilled workers are available.

5. Transporting a 200+ meter (650+ feet) high wind turbine in the upright position would be slow and hazardous.  It would be safer not to catch too much wind until anchored.  Also, some suitable harbors have limiting bridges (Golden Gate Bridge).  Generally, vertical transport seems impracticable.

6. For both convenience of assembly, and subsequent ease of transport, the turbines could be assembled in the horizontal position onto special transport vessels .  Those vessels would transport the turbines in the horizontal position directly to their permanent locations.

7. At the final location, with a series of simple moves, the turbines could be connected to the already anchored in-place foundation, then pivoted to the vertical, and bolted into final position (see Wind Turbine Erection at Sea sketch).  No at-sea turbine assembly and no giant seagoing crane would be required.

 

Economical Dockside Assembly:

The wind turbine tower would be assembled whole at dockside.  A dockside crane would place the assembled tower onto a padded cradle on the transport vessel (see sketch).  Next, the female half of a temporary hinge (Temporary Hinge) would be bolted to the tower base.  (The male half will be bolted to the foundation once at the final location at sea).  Next the nacelle, with its axis near vertical, would be bolted onto the tower.  The blades would be bolted onto the nacelle with the tower horizontal at dockside. These operations would be accomplished much easier at dockside than high in the air by a floating crane-ship at sea.

 

Transport:

The transport vessel takes the completed turbine, in the horizontal position, to its permanent location in the wind turbine array.  Considerations of wind, waves, and current determine the optimal relative orientation of the floating foundation and the turbine transport vessel.  For example, a 36 bolt circle of temporary anchor bolts presents 36 possible orientations of the foundation and transport vessel. 

To make tower erection manageable we propose to lock the transport vessel to the foundation for roll.  We need to eliminate relative movement between the floating foundation and the floating transport vessel for roll.   (Total lock together would be nice, but, let us, for now, rule that out as impractical.)  When we eliminate roll we must deal with relative movement between these two large heavy objects on just the pitch axis.

Key to tower installation is a clamping and axle assembly carried at the front of the transport vessel.  A small crane has the clamping assembly ready to install. 

First, to ease locating and mounting of the clamping assembly, two guidance cones are swung aboard and screwed to two of the temporary bolts.  Then the clamp and axle assembly is craned aboard the foundation and, guided by the cones, is bolted down at the desired orientation (Clamp and Axle Assembly on Foundation).  Next the two clamp halves are activated.  They grip the foundation powerfully. 

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For the erection process to go smoothly it is important that the pitch axis between the foundation and the transport vessel, and the axis of the erection hinge are aligned.  The erection axis is integral with the clamping assembly and is bolted down to the base plate. Since these are all machined parts the erection axis is located accurately.  But the clamp halves are gripping the foundation's concrete rim.  That might be so accurate.  So, the two clamp halves have hydraulic adjustment to effectively lock both clamps to the same axle that is the erection axis.  Then, both the erection axis and the pitch axis are co-axial.  Two giant arms, the "Huge Clamps", with integral pitch bearings grab onto the ends of the axle.

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Lock Together:

The lock-together process has several stages.  First, the transport vessel nudges up close to the floating foundation.  Using its two "Huge Clamps" the vessel at first just lightly grabs the axle ends.  By differentially adjusting the two "Huge Clamps" the vessel adjusts itself right or left until the centerlines of the axle and the vessel are  closely perpendicular.  Then the transport vessel powerfully closes its grip on the foundation.  They are locked together for roll.  Thus, we eliminate relative movement between the floating foundation and the floating transport vessel except to just the pitch axis.

 

Preparation for Erection:

The lift cylinder is released and it swings down to vertical.  It is extended a little.  Because of the counterweight in the cradle, the tower pivots on the rear support.  The slide in the cradle feeds the female hinge half at the base of the tower into alignment with the male hinge-half (the axle) bolted to the foundation.  Once the two female hinge halves engage with the landing strips on the axle, the rear cradle support drops away. The hydraulically activated female hinge halves close on the axle and slowly lock the connection.

 

Erection Sequence:

The sea water powered, telescopic, trunnion mounted erection cylinder is released. It swings down to the vertical.  The cylinder is extended rotating the cradle holding the turbine to a near-erect position.  On the opposite side from the hinge, cushioned "catcher cylinders" engage with the base of the tower.  With the tower grabbed by the "catcher cylinders", the vessel's tower support cradle pulls back. (see Tower Erection). The "catcher cylinders" lower the tower into final position.  The tower is bolted down.  Installation complete, the vessel's Huge Clamps release the foundation, the axle assembly releases its grip and is unbolted.  The axle assembly is picked up and stowed aboard.  The lift cylinder is retracted, rotated up, and stowed.  The transport vessel heads back to port.  

 

Economical Seabed Anchorages

Another important element of cost is anchoring the foundation's guy lines to the seabed.  Piling and giant steel anchors are commonly used.  But most economical would be steel rods cemented deep into the seabed.  A self-propelled autonomous underwater drill rig could drill high strength steel rods over 100 feet long into the seabed (see Underwater Drill Rig sketches).  They would be cemented deep into the underlying strata.  In this way, it is the weight of the seabed that holds the wind turbines in place.

Another, more simple option, is to manufacture heavy concrete buckets at the same facility that manufactures the foundations.  The bottom of the anchor bucket would be customized to the seabed (see Anchorage Bucket sketch).  The buckets would be sunk at the vertices of the turbine array, and then filled with rock.  Each riprap bucket could restrain four anchor lines.  The piles of riprap would probably constitute desirable habitat.

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Windmill Stores

With the Climate Crisis looming, electricity supply agencies around the world want Green Energy Now.  But, as it stands today, the timing of permissions is frustratingly indeterminant.  When permission finally comes the pent-up need then still requires more waiting for manufacture.  There is entirely too much waiting. An alternative to such waiting is Windmill Stores. 

 

Synopsis: Some far-seeing and well financed wind development organization commences the mass production of large floating wind turbines. They build a stock of giant foundations floating them in storage.  They order and stock all the components lined up within crane reach of dockside.  These turbines would be ready-to-go.  This might be financed by philanthropies, hedge funds, pension funds, sovereign wealth funds, or any other shrewd deep pockets.  The most visionary of the oil majors might be likely. 

 

Windmill Stores, by offering immediate availability, might corner the market.  Most importantly, they would help abate the Climate Crisis.  After struggling through permitting, financing, and all the other delaying hindrances, what organization, we ask rhetorically, wants to additionally wait through turbine ordering and fabrication?  Perhaps none, not when the Windmill Store offers immediate delivery.

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In electricity starved regions around the world, in regions considering diesel, gas, or (still) coal, offshore green power, immediately available, might swing their choice.  Just call the Windmill Store and, in a few days, your very own Giant Wind Turbines will be headed straight to your offshore location.

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Immediate availability could incentivize orders.  Lots of orders would require mass production.  Mass production facilitates low prices.  The Model-T got cheaper every year as Henry Ford got rich.  The country that pioneers Windmill Stores might become the Saudi Arabia of wind.