question: why are wind turbines shaped like that? Would having wider blades or more than three blades give them more energy conversion for a given wind?
comment: It's about energy per unit cost. More blades extract more energy, but weigh more, so the energy is mostly spent making the big object rotate, not making electricity. It makes more sense where the momentum of the big wheel also helps deal with load changes, like a water pump. The load in a power generator is controlled and constant. Bigger structures also disrupt the wind. Thin structures slice through the air, and the time from blade #1 to blade #2 lets the wind stabilize. That way you can have rows without them fouling each other's airflow. One blade would be the best, but that leads to balance problems. Two blades have lots of harmonic interactions that cause wear in bearings. Three is the best compromise.
passages: Section::::Applications.
  
  Section::::Applications.:Wind turbines.
  
  Wind turbines are a potential application of cyclorotors. They are named in this case variable-pitch vertical axis wind turbines, with large benefits with respect to traditional VAWTs. This kind of turbine is stated to overcome most of the traditional limitations of traditional Darrieus VAWTs.
  
  Section::::Applications.:Ship propulsion and control.
   In addition to aerodynamic design of the blades, design of a complete wind power system must also address design of the hub, controls, generator, supporting structure and foundation. Further design questions arise when integrating wind turbines into electrical power grids.
  
  Section::::Aerodynamics.
  
  The shape and dimensions of the blades of the wind turbine are determined by the aerodynamic performance required to efficiently extract energy from the wind, and by the strength required to resist the forces on the blade. 
   On most horizontal wind turbine farms, a spacing of about 6–10 times the rotor diameter is often upheld. However, for large wind farms distances of about 15 rotor diameters should be more economical, taking into account typical wind turbine and land costs. This conclusion has been reached by research conducted by Charles Meneveau of the Johns Hopkins University, and Johan Meyers of Leuven University in Belgium, based on computer simulations that take into account the detailed interactions among wind turbines (wakes) as well as with the entire turbulent atmospheric boundary layer.
   As the normal wind turbine does, the wind lens harnesses the energy of the wind but has a few modifications in order to increase efficiency as well as the impact on the environment.
  
  Section::::Design.:Efficiency of power production.
  
  Studies have shown that the Wind Lens can have between two and five times more output of power compared to the wind turbine due to the way it harnesses more wind.
   Section::::Applications.
  
  Section::::Applications.:Rooftop.
  
  Wind-turbines can be installed on building roofs. Examples include Marthalen Landi-Silo in Switzerland, Council House 2 in Melbourne, Australia. Ridgeblade in the UK is a vertical wind turbine on its side mounted on the apex of a pitched roof. Another example installed in France is the Aeolta AeroCube. Discovery Tower is an office building in Houston, Texas, that incorporates 10 wind turbines.
   A Turgo runner looks like a Pelton runner split in half. For the same power, the Turgo runner is one half the diameter of the Pelton runner, and so twice the specific speed. The Turgo can handle a greater water flow than the Pelton because exiting water doesn't interfere with adjacent buckets.
   Section::::Types.:Vertical axis.:Giromill.
  
  A subtype of Darrieus turbine with straight, as opposed to curved, blades. The cycloturbine variety has variable pitch to reduce the torque pulsation and is self-starting. The advantages of variable pitch are: high starting torque; a wide, relatively flat torque curve; a higher coefficient of performance; more efficient operation in turbulent winds; and a lower blade speed ratio which lowers blade bending stresses. Straight, V, or curved blades may be used.
  
  Section::::Types.:Vertical axis.:Savonius wind turbine.
   Leading edge tubercles are up and coming in the manufacturing area. Wind turbine performances rely on blade aerodynamics where similar flow characteristics are observed (source # 9) modern turbines have twisted blades to account for the angle of attack at specific design conditions. However, in practical application, turbines often operate at off-design conditions where stall occurs, causing a decrease in performance and efficiency. In order to look for possible improvement of the energy efficiency of turbine, the influence of leading edge tubercles must be investigated in more depth.
   New wind turbine designs push power generation from the single megawatt range to upwards of 10 megawatts using larger and larger blades. A larger area effectively increases the tip-speed ratio of a turbine at a given wind speed, thus increasing its energy extraction.
  
  Computer-aided engineering software such as HyperSizer (originally developed for spacecraft design) can be used to improve blade design.
   Wind turbines can be used to generate electricity in areas with strong, steady winds, sometimes offshore. Many different designs have been used in the past, but almost all modern turbines being produced today use a three-bladed, upwind design. Grid-connected wind turbines now being built are much larger than the units installed during the 1970s. They thus produce power more cheaply and reliably than earlier models. With larger turbines (on the order of one megawatt), the blades move more slowly than older, smaller, units, which makes them less visually distracting and safer for birds.
  
  Section::::Power from renewable energy.:Marine.
   BULLET::::- Largest vertical-axis: Le Nordais wind farm in Cap-Chat, Quebec, has a vertical axis wind turbine (VAWT) named Éole, which is the world's largest at 110 m. It has a nameplate capacity of 3.8 MW.
  
  BULLET::::- Largest 1-bladed turbine: The largest single-bladed wind turbine design to be put into complete operation is the MBB Messerschmitt Monopteros M50, with a total power output of no less than 640kW at full capacity. As far as the number of units is concerned, only three ever have been installed at an actual wind park, of which all went to the Jade Wind Park.
   Unconventional wind turbines
  
  Unconventional wind turbines are those that differ significantly from the most common types in use. 
  
  , the most common type of wind turbine is the three-bladed upwind horizontal-axis wind turbine (HAWT), where the turbine rotor is at the front of the nacelle and facing the wind upstream of its supporting turbine tower. A second major unit type is the vertical-axis wind turbine (VAWT), with blades extending upwards, supported by a rotating framework.
   Vortex generators may be used to control the lift characteristics of the blade. The VGs are placed on the airfoil to enhance the lift if they are placed on the lower (flatter) surface or limit the maximum lift if placed on the upper (higher camber) surface.
  
  Section::::Power control.:Furling.
   Section::::Horizontal axis.:Counter-rotating horizontal-axis.
   Wind turbine design
  
  Wind turbine design is the process of defining the form and specifications of a wind turbine to extract energy from the wind.
  
  This article covers the design of horizontal axis wind turbines (HAWT) since the majority of commercial turbines use this design.
   In onshore turbines the most common type of foundation is a gravity foundation, where a large mass of concrete spread out over a large area is used to resist the turbine loads. Wind turbine size & type, wind conditions and soil conditions at the site are all determining factors in the design of the foundation.
  
  Section::::Costs.
   This type is efficient at full gate, but at partial gate some Francis turbine designs are more efficient. The usual orientation of the wheel was horizontal and the first devices were even alternatively named as "horizontal water wheels". However, some sources mention turbines with both vertical and horizontal shafts.
  
  N.F. Burnham, an American turbine manufacturer, patented numerous improved designs in the second half of 19th century. His turbines had greater efficiency than the Jonval, especially at partial gate, and fewer maintenance problems.
   How closely to space the turbines together is a major factor in wind farm design. The closer the turbines are together the more the upwind turbines block wind from their neighbors. However spacing turbines far apart increases the costs of roads and cables, and raises the amount of land needed to install a specific capacity of turbines. As a result of these factors, turbine spacing varies by site. Generally speaking manufacturers require 3.5 times the rotor diameter of the turbine between turbines as a minimum. Closer spacing is possible depending on the turbine model, the conditions at the site, and how the site will be operated.
   In 2006, Wind Harvest International began design work on a series of Windstar turbine models to take advantage of the properties demonstrated in the 530G LAVTS prototype: Model 636, 1500 and 3000 turbines. The Model 636 is a direct evolution of the 530G, with an increase in blade length, in order to increase swept area, and including a modified bearing design. The 1500 and 3000 turbine models stand high with a rotor and 50-75 kW generators. The Windstar 1500 is wide and is designed for higher wind speed locations. The Windstar 3000 will be wide to operate better in lower wind speed locations (14-16 mph). Model 636 continues to use extruded aluminum blades, similar to the 530G. Models 1500 and 3000 use pultruded fiberglass blades.
   Section::::Horizontal axis.:Downwind rotor.
  
  Nearly all wind turbines place the rotor in front of the nacelle when the wind is blowing (upwind design). Some turbines place the rotor behind the nacelle (downwind design). This design has the advantage that the turbine can be made to passively align itself with the wind, reducing cost. The main drawback is that the load on the blades changes as they pass behind the tower, increasing fatigue loading, and potentially exciting resonances in other turbine structures.
  
  Section::::Horizontal axis.:Ducted rotor.
   The 845-megawatt Shepherds Flat Wind Farm in Oregon is the first windpark in the United States to utilize this model as its primary wind turbine.
  
  The Fantanele-Cogealac wind farm in Romania, constructed in 2008, uses 240 GE 2.5xl wind turbines capable of generating a total of 600 MW, powering a million Romanian households each year.
  
  The offshore GE 3.6 SL model was installed at the Arklow Bank Wind Park.
   Section::::Design.
  
  Smaller scale turbines for residential scale use are available. Their blades are usually in diameter and produce 1-10 kW of electricity at their optimal wind speed. Some units have been designed to be very lightweight in their construction, e.g. 16 kilograms (35 lb), allowing sensitivity to minor wind movements and a rapid response to wind gusts typically found in urban settings and easy mounting much like a television antenna. It is claimed, and a few are certified, as being inaudible even a few feet (about a metre) under the turbine.
   Larger, more costly turbines generally have geared power trains, alternating current output, and flaps, and are actively pointed into the wind. Direct drive generators and aeroelastic blades for large wind turbines are being researched.
  
  Section::::Wind turbine spacing.
   Wood is being investigated as a material for wind turbine towers, and a 100 metre tall tower supporting a 1.5 MW turbine has been erected in Germany. The wood tower shares the same transportation benefits of the segmented steel shell tower, but without the steel resource consumption.
  
  Section::::Connection to the electric grid.
  
  All grid-connected wind turbines, from the first one in 1939 until the development of variable-speed grid-connected wind turbines in the 1970s, were fixed-speed wind turbines.
   The generators for small wind turbines usually are three-phase alternating current generators and the trend is to use the induction type. They are options for direct current output for battery charging and power inverters to convert the power back to AC but at constant frequency for grid connectivity. Some models utilize single-phase generators.
  
  Some small wind turbines can be designed to work at low wind speeds, but in general small wind turbines require a minimum wind speed of .
  
raw_presuppositions: More than 3 blades would give more energy conversion to wind turbines.
raw_corrections: More than 3 blades would weigh more, so the energy would be mostly spent making the blades rotate.