Floating Wind Power
Floating wind turbines will be located where the wind is best. Manufacture of the towers, nacelles, and blades is international and highly competitive. But there is room for innovation in making the floating foundations. Concrete is cheap and provides welcome inertia in tossing seas. Large concrete foundations manufactured at waterside rock quarries could be made economically and would provide the desired stability. We explore that idea here.
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.
A rowboat in a storm is tossed about; an aircraft carrier much less so. Mass has a stabilizing effect. The heavier our foundation, the more inertia to resist movement. Conclusion: 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.
Let’s get 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.
Generally, as turbine size increases, electrical output increases per dollar of investment. Bigger turbines make cheaper electricity. On land, trucking of the giant components for the largest turbines can be prohibitive. But, transporting components by ships scales more easily. And entire foundations can be towed out, floating. Our candidate concrete foundation would be an hexagonal platform with an array of six hollow cylinders providing flotation (6 Cell Floating Foundation sketch below). Depending on its dimensions it would weigh approximately 10,000 to 20,000 metric tons.
How could this be cheap?
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.
The foundation would be built on a flat casting bed. Once semi-cured, it would be post-stressed and 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.
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 will require large specialized facilities.
The wind turbine components would be arriving by ship from around the world. For maximum economy, the turbines would be assembled complete in established harbors where dock space, storage space, and skilled workers are available.
Transporting a 200+ meter (650+ feet) high wind turbine in the upright position would be 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.
For both convenience of assembly, and subsequent ease of transport, the turbines could be assembled in the horizontal position onto special transport vessels (Transport Vessel). Those vessels would transport the turbines in the horizontal position directly to their permanent locations.
At the final location, with a series of simple moves, the turbines could be connected to the already in-place foundation, pivoted to the vertical, and bolted into final position. 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 male half of a temporary hinge (Temporary Hinge) would be bolted to the tower base. (The female half will be bolted to the foundation only at the final location). Next the nacelle, with its axis near vertical, would be bolted onto the tower. The blades would be bolted on semi-horizontally. The low assembly elevation and stable dockside location makes these operations much easier than with a crane-ship at sea.
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. The transport vessel grips the foundation in order to reduce relative movement to just the pitch axis (Transport Vessel with Grippers). At the desired radial location, the female hinge-half is bolted to the foundation (Female Hinge-Half on Foundation).
The transport vessel feeds the male hinge half at the base of the tower into the female hinge half on the foundation. Immediately, hydraulically activated clamps on the female hinge-half lock the connection and the tower-rest on the vessel drops away. Using its large sea-water hydraulic cylinder, the transport vessel rotates the turbine to a near-erect position. Cushioned "catcher cylinders" engage with the base of the tower and lower the tower into final position as the vessel's tower support cradle pulls back. (see Tower Erection). The tower is bolted down. Installation complete, the hinge halves are removed and stowed aboard. The transport vessel releases its grip on the foundation and 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 ship’s anchors are commonly used. But more 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 (Underwater Drill Rig). 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 bins at the same facility that manufactures the foundations. The bottom of the anchor bin would be customized to the seabed (Anchorage Rock Bin). The bins would be sunk at the vertices of the turbine array, and then filled with rock. Each rock bin could restrain four anchor lines. The piles of rock would probably constitute desirable habitat.
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 and float 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.
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.
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 could become the Saudi Arabia of wind.