So, whatever form of blade shape for a wind turbine would create the most energy? Flat blades are the oldest blade style and have been used on windmills for thousands of years, however they are becoming less popular than other blade designs. The wind pushes against the flat blades, and the blades push against the wind.
Because the blades that rotate back on the up stroke after generating power are in opposition to the power production, the resulting rotation is very sluggish. The phrase drag-based rotor blades comes from the fact that the blades act like large paddles going in the wrong direction, pushing against the wind.
Is it possible to build wind turbines on a vertical axis?
The main rotor shaft of vertical axis wind turbines (or VAWTs) is positioned vertically. The turbine does not need to be aimed into the wind to be functional, which is one of the main benefits of this setup. On areas where the wind direction is highly varied, this is a benefit.
What are some of the drawbacks of vertical wind turbines?
Vertical axis wind turbines feature seven distinct characteristics that make them ideal for small-scale power generation in windy environments. They do, however, have some downsides. In fact, as engineers seek to meet the challenges, the design of this type of turbine remains popular.
We’ve also discovered and addressed various challenges and improvements with vertical axis wind turbines during the course of 5 years of research and development.
1. Rotation Efficiency Is Low
Wind turbines with a vertical axis have a lower rotation efficiency. This contributes to the reduced efficiency of vertical axis wind turbines.
The blades on the vertical axis rotor do not all receive incoming wind at the same time due to the rotor design. In actuality, only the blades facing the wind are turned by the wind, while the others merely follow. Vertical axis rotors experience increased drag or aerodynamic resistance on the blades during rotation.
Because Savonius wind turbines have broader blade surfaces, this is especially evident.
2. Reduced Wind Speed Available
Because vertical axis wind turbines are normally erected on the ground, they are unable to capture the higher wind speeds encountered at higher elevations. As a result, ground-level vertical axis wind turbines have less wind energy available. Installing the turbine on the roof of a building is a frequent solution.
We altered the rotor design to allow it to be positioned on top of a mast to solve this difficulty. Our vertical axis wind turbine’s rotor and mast combined tower to a height of 10 meters, with the generator and power electronics positioned at a 4-meter height.
What is the ideal wind turbine blade angle?
The angle is adjustable in radians, and it appears to have a maximum value of about 0.62 radians, or 35.5 degrees. This leads to a maximum of 38.5 percent of wind power being converted to rotational motion. To get the most energy out of flat blade windmills, the blades should be slanted at an angle of around 35.5 degrees from the oncoming air stream.
This blade angle was the subject of a computational fluid dynamic (CFD) analysis to investigate the pressure distribution and airflow as it passed through the blades. Unfortunately, the Fluent CFD software license has run out. Below is a meshed model of the blade design created with the program Gambit.
Should the blades of wind turbines be heavy or light?
A wind turbine, also known as a wind energy converter, is a mechanical device that transforms wind kinetic energy into electrical energy. Wind turbines operate on the simple premise of wind turning the propeller-like blades of a turbine around its rotor, powering a generator to generate electricity.
Wind turbine blades should be light since lighter blades are more efficient. It improves the performance of wind turbines by making them easier to assemble and disassemble as well as turn. While lightweight, high-material-strength systems are preferable, lowering bulk may raise the danger of structural collapse.
The balance of criteria of strength versus weight for overall performance is common in mechanical systems. This article will look at whether lighter or heavier blades help wind turbines operate better, as well as how wind turbines work and the mechanical systems that go into their construction.
Which vertical wind turbine design is the most efficient?
Since the 1980s, there has been a significant consolidation of design, however new types of electrical generators have added to the diversity.
The advantages of omni-directionality and having gears and generating equipment at the tower base were studied for vertical axis designs.
They are, however, intrinsically inefficient (because of the variation in aerodynamic torque with wide range in angle of attack over a rotation of the rotor).
Furthermore, due to the weight and cost of the transmission shaft, it was determined that having the gearbox of big vertical axis turbines at ground level was not viable.
Taking into account cross arms in the H type design, the vertical axis design also entails a lot of structure per unit of capacity (Figure 3.2).
The Darreius design (Figure 3.3) is more structurally efficient.
The blade is shaped like a troposkein curve and is only loaded in tension by the forces generated when the rotor spins, not in bending.
However, much of the blade surface is visible to be near to the axis.
The blade parts closest to the axis rotate more slowly, resulting in a reduction in aerodynamic efficiency.
Darrieus rotors with the famous ‘egg-beater’ design had a number of major technical issues, including metal fatigue-related failures of the curved rotor blades.
Because of these drawbacks, the vertical axis design path has been phased out of the major commercial sector.
Over a decade ago, FlowWind, the leading commercial supplier of vertical axis turbines, stopped making them.
Despite the lack of significant market penetration, there has recently been a notable resurgence of innovative VAWT designs in the category of small systems for a variety of applications, particularly on building roof tops, as well as a few future innovative designs for large-scale offshore applications.
Water pumping is still done with multi-bladed turbines on a small scale.
They have a low aerodynamic efficiency but can give a strong beginning torque due to their huge blade area (turning force).
This allows the rotor to turn even in mild breezes, which is ideal for water pumping.
Although one and two-bladed wind turbine designs were attempted to market in the 1980s and early 1990s, most modern wind turbines have three blades.
Because it has the largest blade section dimensions and all of the installed blade surface area in a single beam, the single-bladed design (Figure 3.4) is the most structurally efficient for the rotor blade.
Wind turbines are typically shut down (parked) in high winds to safeguard them from damage.
This is because if they continued to function, they would be subjected to substantially higher blade and tower loads.
The one-bladed design allows for innovative parking methods, with the one blade functioning as a wind vane or downwind behind the tower, potentially reducing storm loading.
There are, however, a number of drawbacks.
There is less aerodynamic efficiency and complex dynamics with a counterweight to balance the rotor statically, necessitating the use of a blade hinge to relieve loads.
From an acoustic standpoint, the designs of Riva Calzoni, MAN, Messerschmidt, and others had too fast a tip speed to be acceptable in the present European market.
The two-bladed rotor (Figure 3.5) is technically equivalent to the traditional three-bladed rotor.
Either more cyclic loads must be absorbed or the complication of a teeter hinge must be added for the benefit of a potentially simpler and more efficient rotor construction with more possibilities for rotor and nacelle erection.
The teeter hinge permits the rotor’s two blades to travel as a single beam during an out-of-plane revolution of around 7.
Allowing this little motion can greatly reduce loads in the wind turbine system, albeit when the teeter motion approaches its limits, some essential loads return.
A two-bladed rotor is slightly less aerodynamically efficient than a three-bladed rotor.
In general, increasing the number of blades on a rotor has minor advantages.
This has to do with cutting down on losses at the blade tips.
In the aggregate, these losses are lower for a large number of narrow blade tips than for a few wide blade tips.
When designing a rotor, the working speed or speed range is usually chosen first, taking into account factors like as acoustic noise emission.
With the selected speed, the entire blade area for maximum rotor efficiency must be determined.
The number of blades is theoretically unlimited, but with the fixed (optimal) total blade area, more blades imply more slender blades.
This is a summary of the basic principles that influence blade numbers.
It’s also worth noting that assuming that doubling the number of blades will double the rotor’s power is a pure myth.
Instead, if the rotor was well-designed in the first place, it would reduce power.
It’s difficult to see the difference between a two-bladed and a three-bladed design in terms of overall cost savings.
It is a common misconception that saving the cost of one of three blades in a two-bladed rotor design, because two blades of a two-bladed rotor do not equivalent to two blades of a three-bladed rotor.
Most older designs would have noise issues since two-bladed rotors have a far higher tip speed than three-bladed rotors.
However, there is no fundamental explanation for the faster tip speed, and it should be ignored in a technical comparison of the merits of two versus three blades.
As a result, the one-bladed rotor may be more technically challenging, but the two-bladed rotor is essentially acceptable.
Visual effect was the deciding element in eliminating one-blade rotor designs from the commercial market, and almost eliminating two-bladed designs.
The blade(s)’ apparent unstable passage through a cycle of rotation has frequently been deemed to be undesirable.
Stall regulation and pitch regulation are the two main methods for regulating rotor output in high operational wind speeds.
The section The technical problem of a unique technology introduced Stall. Stall-regulated machines require speed regulation and a torque speed characteristic that is built into the rotor’s aerodynamic design. If the rotor speed is kept constant, the flow angles over the blade sections steepen as the wind speed increases. Without any extra active control, the blades get increasingly stopped, limiting power to acceptable levels. The electric generator is connected to the grid under stall control to maintain an essentially constant speed. In this way, the grid acts like a big flywheel, keeping the turbine’s speed relatively constant despite changes in wind speed.
Stall control is a complex process that is difficult to explain clearly and adequately, both aerodynamically and electrically.
Without going into technical details, a stall regulated wind turbine will run at a nearly constant speed in high wind without producing excessive power, and it will do so without modifying the rotor shape.
Pitch regulation is the most common option to stall regulation.
To adjust the power collected by the rotor, the wind turbine blades are rotated along their long axis (pitched).
Pitch regulation, unlike stall regulation, necessitates changing the rotor geometry by pitching the blades.
This is accomplished by an active control system that detects blade position, measures output power, and commands necessary blade pitch modifications.
Pitch regulation has a similar goal as stall regulation: it controls output power at high operational wind speeds.
‘Active stall regulation,’ another approach, using full-span pitching blades.
They are, however, pitched into stall in the opposite direction of fine pitching, in which the leading edge of the aerofoil sections is twisted into the wind direction.
This design, like the traditional fine pitch method, makes use of the pitch system as a primary safety mechanism, but it also takes advantage of stall regulation characteristics to achieve significantly lower pitch activity for power limiting.
Initially, most wind turbines produced power at a constant speed.
In a start-up sequence, the rotor may be parked (kept still) and then propelled by the wind once the brakes were released until the needed fixed speed was reached.
A connection to the energy grid would be created at this stage, and the grid (via the generator) would maintain the speed.
When the wind speed exceeded the level at which rated power could be generated, power would be managed in one of two ways: by stalling or pitching the blades.
Variable speed operation was introduced later.
This allowed the rotor and wind speed to be matched, allowing the rotor to maintain the most efficient flow geometry.
In very light winds, the rotor could be connected to the grid at low rates and would accelerate up in proportion to the wind speed.
The rotor would revert to virtually constant speed operation when rated power was approached, and certainly once rated power was produced, with the blades pitched as needed to regulate power.
Variable speed operation, as used in modern large wind turbines, differs from traditional fixed speed operation in the following ways:
- Variable speed operation at lower than rated power can help you catch more energy.
- Variable speed capability over rated power (even over a limited speed range) can relieve loads, reduce pitch system workload, and minimize output power fluctuation significantly.
Pitch versus stall and the degree of rotor speed variation are clearly linked design challenges.
The classic Danish three-bladed, fixed-speed, stall-regulated design was popular in the 1980s.
The idea of employing stall was shocking to aerodynamicists outside of the wind industry (such as for helicopters and gas turbines).
However, due of the progressive nature of stall over the rotor of a wind turbine, it has proven to be a highly feasible method of running a wind turbine and utilizing, rather than avoiding, stall.
It is one of the most distinctive features of wind technology.
The control mechanism in which the blades pitch along their axis like propeller blades is known as active pitch control.
This approach appeared to offer better control than stall regulation on the surface, but experience has shown that pitch control of a fixed-speed wind turbine in high operational wind speeds above rated wind speed (the minimum steady wind speed at which the turbine can produce its rated output power) can be difficult.
The causes are complicated, but it is difficult to maintain adjusting pitch to the most appropriate angle and high loads in turbulent (constantly changing) wind conditions, and significant power variations can ensue when the control system is ‘caught out’ with the blades in the wrong position.
Pitch control combined with a tightly controlled speed became characterized as a “tough” combination due to such challenges, which were especially evident in high operational wind speeds (say 15 m/s to 25 m/s).
Vestas initially addressed this issue by inventing the OptiSlip system (a degree of variable speed active with pitch control in power limiting operation, which allows about 10 percent speed variation using a high slip induction generator).
Suzlon currently uses a comparable technique called Flexslip, which allows for a maximum slip of 17%.
Variable speed helps to manage power and lessens the need for quick pitch movement.
Variable speed offers several advantages, but it also has some drawbacks in terms of cost and reliability.
With predicted cost reductions and performance improvements in variable speed drive technology, it was considered as a way of the future.
This has been realized to some extent.
Small energy advantages were compensated by extra expenditures and also additional losses in the variable speed drive, therefore there was never a clear justification for variable speed on economic grounds.
The current push for variable speed in new large wind turbines stems from a desire for more operational flexibility as well as concerns about the power quality of classic stall-regulated wind turbines.
During the 1980s and 1990s, two-speed systems arose as a compromise for enhancing energy capture and noise emission characteristics of stall-regulated wind turbines.
The stall-regulated design is still possible, but variable-speed technology provides higher grid output power quality, thus it is now driving the design of the largest machines. Variable speed and stall regulation have been used in several trials, although variable speed naturally combines with pitch regulation. An electrical variable speed system permits pitch control to be successful and not hyperactive for reasons linked to power control approaches.
The agreement by certification authorities that this permits the rotor to be treated as having two distinct braking systems acting on the low speed shaft is another key incentive for the application of pitch control, and specifically pitch control with independent pitching of each blade.
As a result, only a parking brake is necessary for the machine’s overall safety.
Pitch control was introduced to wind turbine technology largely as a technique of power regulation, avoiding stall when stall was viewed as problematic, if not disastrous, in industries other than wind.
It does, however, offer unique characteristics to restrict loads and fatigue in the wind turbine system when combined with variable speed and advanced control systems, and it is virtually universally used in new large wind turbine designs.
The pitch system’s load limiting capability enhances the wind turbine system’s power to weight ratio and efficiently compensates for the costs and reliability consequences of having a pitch system.
Is it possible to power a home with a modest wind turbine?
Micro-wind or small-wind turbine systems, which harness the power of wind to generate electricity, can provide more than enough energy to power the lights and electrical appliances in a standard home when placed in an exposed position.
Is it true that HAWTs are more efficient than VAWTs?
VAWTs have a number of benefits. They are omnidirectional, which means they do not alter orientation to meet the direction of the wind, as HAWTs must. As a result, the number of pieces is reduced. A direct drive is found in almost all VAWTs (they require no gearbox between the rotor and the generator). This lowers running expenses while also improving durability and reliability. VAWTs are said to be much more efficient in turbulence, allowing for rooftop and urban installations, and they turn at a lower RPM, resulting in less vibration and noise. Most VAWT manufacturers claim noise levels of less than 40 decibels at a distance of less than 20 feet/6 meters, whereas the few HAWT manufacturers who provide such measurements frequently indicate noise levels of 50 to 60 decibels or higher at far greater distances. VAWTs are typically smaller and operate at lower altitudes, making them less noticeable.
VAWTs, on the other hand, may have challenges with reliable self-start in low wind speeds, as well as less efficient power generation than HAWTs, according to some (the low rotation speeds are quiet but not necessarily efficient). Jacken Chen, the creator and general manager of Hi-VAWT Technology Corp., a Taiwan-based manufacturer of a combination Savonius/Darrieus VAWT, addresses this issue in a study. The Savonius unit has a more dependable self-start, while the Darrieus components are more power efficient. Other sources say that just altering Darrieus designs with better turbine sizing and higher-performance blade shapes will achieve the same results.
Is it possible to use a car alternator as a wind turbine?
If you’re new to the idea of making a wind generator out of repurposed parts, you’ve undoubtedly asked yourself a few questions like these:
- Why are automobile alternators suitable for wind energy?
- What adjustments are required to convert an automobile alternator into a functional wind generator?
- What is it about Delco-style alternators that makes them so popular?
- Which WindyNation blades work best with Delco-style PMA wind generators?
Perhaps we asked that last question ourselves! In any case, if you’ve ever wondered about repurposing automobile alternators, now’s your chance to learn everything you need to know.
Wind power enthusiasts are increasingly common around the world, taking advantage of excess supplies of alternators or motors that were originally intended for purposes other than generating electricity from the wind. Fisher & Paykel washing machine motors are quite popular in Australia and New Zealand, as these machines utilise big permanent magnet motors. Ametek, Inc. is best known in North America for their tape drive motors, which were once readily available and immensely popular for constructing wind generators.
However, when it comes to DIY modest wind power, the Delco brand of permanent magnet alternators is likely the most popular.
Why are Delco-style Alternators So Popular?
The Delco moniker is derived from Dayton Engineering Laboratories Co, a long-time supplier to General Motors. Delco had a long and illustrious history, which included the invention of the first practical battery ignition system. Hundreds of key components for American-made autos were manufactured by the enterprise, which was absorbed into a variety of larger mega-corporations. GM still uses the Delco brand name, especially for its ACDelco components division, but the corporation has come a long way since its early pioneering days.
Since the early 1980s, the American auto industry has had a lot of excess production capacity, which has often gone into generating a lot of components that don’t always wind up in automobiles. Even though these alternators didn’t find a place under a hood, they found a way to be useful. Delco has experienced a rebirth among wind power aficionados. For usage in small wind generators, repurposed vehicle alternators have become exceedingly popular and relatively cost-effective.
Most ACDelco generators that are sold specifically for use as a wind generator have been repurposed or rebuilt. The reason for this is that when a Delco automobile alternator is employed in a wind turbine, it operates under different conditions than a permanent magnet alternator.