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Wind Turbines

How does wind turbines function?

Wind turbines generate electricity from wind energy. The rotor’s rotation results in kinetic energy that is converted into electricity by a generator. The wind force measured in Beaufort (scale from 0 (calm) to 12 (hurricane)) determines the yield of electricity generated from wind power.

It should be noted that the wind force of a particular location can change significantly, affecting the power of the output, which can be variable. Electricity produced from wind energy can therefor only supplement the electricity mix. In addition, the power supply from wind energy depends strongly on the fluctuations of storage technologies.

Vertical Wind Turbines

Vertical wind turbines is a type of turbine in which a rotor shaft rotates around a vertical axis, in addition to the “classic horizontal wind turbines.

They are among the oldest windmills, known for their simple and robust construction. Back in the 7th century AD, the ancient Chinese and Persian cultures used these windmills, the so-called Persian windmills, long before the familiar horizontal axis.

Working Principle of Vertical Wind Turbines

Resistance Runner

These resistance runners operates on stream-resistance of a rotor. A dynamic pressure produced by wind constraints on the windward surface of the wing (=windward side) pushes the wing away from the wind (=lee). When the axis is vertical, a rotary motion occurs which the generator converts to electricity.

Buoyancy Runner

Buoyancy runners use the floating ability of a wing. The stream around a profiled wing creates a suction effect (negative pressure) on the front wing side and on the back slight overpressure. The pressure difference generates a driving force on the wing and depending on the wing profile, this pressure reaches its peak when in motion.

Hybrid Forms

Hybrid forms combine the advantages of resistance – and buoyancy runners at different wind speeds, making them more flexible in use. While they benefit from the low torque of a resistance rotor at low wind speeds, the high torque of the buoyancy rotor works in strong winds. These Hybrid rotors do not achieve the high performance like a classic rotor.

Types

Resistance Runners

Savonius Rotors
A resistance rotor, Savonius ‘s and LuvSide’s, never move faster than the current wind speed, as the rotor surface is practically pushed away by the wind.
Savonius rotors therefore have the lowest efficiency and achieve significantly lower power currents than other design types.

Further Resistance Runners:

  • Helix form
  • Shell rotor
  • Vertical axis wind turbine with individually rotatable wings
  • Durchström rotor with numerous blades on the circumference

Buoyancy Runner

Darrieus Rotors
Rotor blades of Darrieus rotors, in contrast to resistance rotors, are not quite perpendicular but slightly diagonal in the wind. The wind flowing on the rotor blade creates buoyancy – just like an airplane wing. The rotational speed of Darrieus rotors can thus be significantly faster than the current wind speed.

Other Lift Runners:

  • Helix form
  • O-shape (“whisk”)

Energy efficiency

The theoretical efficiency of wind turbines depends on the ability of the rotors to convert kinetic wind energy into power output. This so-called performance coefficient (or specific power yield) is a maximum of 59%. But due to losses in transmission and generator, the effective efficiency is lower.
The power coefficient of vertical wind turbines is significantly lower than horizontal turbines. Horizontal runners achieve according to the current design, a performance coefficient of about 50% whereas vertical runners a maximum of 40%. Horizontal runners are thus much more efficient.

Stromzähler

Electricity meter – save electricity

The decisive value for the profitability of a wind turbine is not just its power coefficient, but lies in the total cost of generating 1 kilowatt hour of electricity through wind energy. When the electricity production costs are cheaper than the electricity price of the energy supplier, you can save electricity costs.

The cost to generate electricity is often higher for vertical wind turbines than for horizontal runners. And it’s no coincidence that this design established itself amongst the massive multi-megawatt wind turbines.

Advantages and Disadvantages

Advantages

Disadvantages

Vertical runners, unlike horizontal rigs, can pick up wind from all directions (360 degrees). No wind tracking via a wind vane and a tracking system is necessary. Vertical wind turbines are low efficiencies and thus produces low power yields, especially in resistance rotors. Horizontal plants produce significantly more electricity.
Vertical runners are more suitable for locations with high air turbulence (eg, cities) as they are less sensitive to slanted currents, to frequent wind direction changes and to wind turbulence . Vertical wind turbines are still unfamiliar and unestablished in Germany due to the low market maturity of many products in the field. There is still no certification procedure for plants in Germany, adding to the lack on the certification process for Plants.
Vertical wind turbines require low maintenance due to their simple and robust design and their maintenance-intensive components such as the generator, are usually located closer to the ground. Vertical runners weighs more than horizontal runners.
Vertical wind turbines have reduced noise emissions and therefore are quieter than horizontal runners, which favors them for urban areas Due to their design, vertical systems are often subject to high vibrations and loads due to aerodynamic imbalances (fluctuating blades, pulsating torque, mast resonances). This leads to an increase on material stress of wear and tear.
Vertical runners, in contrast to horizontal systems, do not have an unpleasant shadow and work at lower speeds, which overall creates a calming effect for the observer. Attributable to the strong resonance behaviour of the mast and the vibrations, only limited mast heights are considered in vertical wind turbines. While low wind speeds prevail near the ground, horizontal wind turbines with higher masts reach higher air layers.
The threat to birds or bats emanating from electric wind turbines is less than that of horizontal turbines. The investment costs for vertical runners are usually higher than those of horizontal systems.
The rotor surfaces of vertical wind turbines are ideal as an advertising medium for logos, for example in the commercial sector. An auxiliary motor is required, as some rotor runners do not start by themselves.
To protect vertical wind turbines in storms, one cannot turn them against the wind.

A formula on the calculation of the performance of your potential wind turbine: P = 1/2 A ro cp v³

ro = 1.2041 kg / m³ (air pressure near the coast)
A = 2.8 m² (the area swept by the wind from the rotor)
Cp = efficiency / performance coefficient of the system
V = wind speed in m / s

Locations

For small wind turbines the location is usually given, for example on the property of the consumer. However, the concrete location of the installation of a small wind turbine is of central importance for the profitability in operations and cost-effectiveness. In contrast to photovoltaic systems, the site location for small wind turbines is much more demanding.
The (variable) wind potential in the region must be taken into account as well as the topographical characteristics of the respective terrain, which affect the stream-behavior of the wind (eg buildings, trees, hedges, etc.)

To estimate the quality of a potential location for a small wind turbine, the following questions about the current wind potential should be answered:

Wind Speed and Wind Conditions

At installation, the current wind speed plays a central factor for successful power generation and thus for the profitability of the plant.
It should be noted that the performance of the small wind turbine increases disproportionately with the increasing wind speed. Thus, the power at 6 meters per second is already three times higher than at 4 meters per second. The higher the distance of the small wind turbine from the ground, the higher the wind speed and the less annoying the air turbulence, which improves profitability as electricity currents/yields can rise significantly.

Wind Conditions According to Different Regions

West winds dominate in Germany. Generally the highest average prevail on the coasts and in lower mountain regions such as the Alpine foothills. These regions offer sufficient locations, with favourable altitudes that are suitable for the installation of small wind turbines.

The German Institute for Construction Engineering ( DIBt ) divides Germany into four wind-zones (DIN 1055-4) for better site and plant selection of wind turbines, according to its regional wind conditions. Based on this classification, the appropriate plant types can be selected: a distinction is made between wind zone I (low wind locations), wind zone II (typical inland locations), wind zone III (coastal locations) and wind zone IV (coastline).

Perform Your Own Wind Measurements

In order to assess the location quality of a potential wind facility, wind measurements should be executed. A wind sensor must be set up precisely at the location and height from where a future system is to be operated. This measurement should be carried out over a minimum period of 6 months to one year preferably. The recording of all four seasons offers a significant and comprehensive view on what to expect. Retailers for small wind turbines usually have “Leihmess” equipments, of which longterm wind measurements are taken.


Reproduced by permission of Bureau of Meteorology, © 2019 Commonwealth of Australia.

Reproduced by permission of Bureau of Meteorology, © 2019 Commonwealth of Australia.
 

Emissions Due to Shadows and Noise

The noise of a small wind turbine and their shadow are considered disturbing. Horizontal systems and their rotor rotation often cause disruptive flicker-effects whereas vertical systems are seldom affected by this problem. They operate at lower speeds, resulting in a quieter appearance for observers.

In terms of noise emissions, vertical systems are cheaper than horizontal systems. It is necessary to comply with the legal requirements of TA Lärm (technical instructions for protection against noise). Here one has access to corresponding information from the manufacturer of a small wind turbine. The greater the distance between the neighbours and the wind system, the lower the noise emissions.

It is imperative to converse with neighbours early and introduce your plans in advance to avoid potential conflict.

Economics

Approval

The practice of Approval is a critical factor in the expanding and processing of small wind turbines. In Germany, there is no conformity regulating the approval of small wind turbines at federal level. Such a procedure is subject to state building regulations, which differ between federal states. For example, small wind turbines above 10 meters must be approved in all federal states and exceptions apply only in some federal states for plants up to 10m.

Generally the permit situation for the construction of a small wind turbine in residential areas is likely more difficult than in industrial estates, mixed areas or in rural areas. Especially in congested areas, vertical wind turbines generally have better chances of success in obtaining a building permit than horizontal wind turbines (eg sound, optics, etc).

It is recommended arranging an interview with the respective building supervisory authority (Landratsamt) to seek clarification on the requirements of such an application and its implications before commencing with costly, time-consuming planning. This is especially true regarding the preservation of public interests:

The legal condition for the approval of small wind turbines in individual federal states is constantly changing and adapting. The influence of political control over wind power expansion and the framework conditions for small wind turbines, might see an adjustment in the medium term. In summary, it depends heavily on the people dealing with wind turbines on the ground. If the competent authority possess experience in the region, the approval of another plant becomes easier.

Cost of a Small Wind Turbine

Since the investment and operating costs of a small wind turbine compared to PV systems are relatively high, the economic operation of a preferred location should be clarified. Depending on the location and size of the plant, small wind turbines have electricity production costs between 15 and 30 ct / kWh.

kosten

For the investment costs the following points must be considered:

In addition to the investment costs, the following can incur during operation:

Market Prospects of Small Wind Turbines

Small wind turbines are still new in Germany, Austria and Switzerland. The report of the World Wind Energy Association (WWEA), states that around 74,000 small wind turbines were world-wide installed during 2011, an increase of 11% compared to the previous year. The total sum of small windmills installed increased by 730,000 units. In Germany, the number of previously installed KWE plants is between 10,000 and 15,000, the current data only allows for an estimate. The market analyses by the Federal Ministry of Economics foresee a demand in small wind turbines (KWEA) and in Germany an estimate of 10,000 units / year, along with a strong upward trend.

State support measures for small wind turbines are currently unavailable. In Germany, electricity feed into the public grid from wind turbines is currently remunerated at 9 cents per kWh. The feed-in is not worthwhile due to the non-cost-covering feed-in tariffs in Germany. By contrast, in countries such as Italy or Great Britain, the feed-in tariffs for small wind turbines are much higher. Instead, profitability can only be achieved through the self-consumption of the wind power produced. If this is cheaper than the electricity price of the energy supplier, you save electricity costs. Due to rising electricity prices, however, the profitability of small wind turbines will improve continuously in upcoming years. The more wind power you use, the more economical your own small wind turbine will become. With adequate site conditions in place, small wind turbines can economically operate in Germany today.

At various locations, the amortisation of a small wind turbine is moderate, especially for private consumers. With a lower power consumption (four-person household: 4,000 – 5,500 kWh) and lower installation of their facilities in populated areas with lower incomes. For farmers with high electricity consumption and a system in a most favourable position, however, the profitability of their small wind turbine is reached much faster.

In comparison to solar power systems, small wind turbines are currently still a niche-existence in Germany. An adjustment of state support and it’s framework – as experienced with photovoltaic systems a few years ago – would lead to an increased demand. The photovoltaic boom in Germany can be seen as a prime example of the successful expanding of energy technology.

The market for small wind turbines will continue evolving in the upcoming years. Firstly, self-produced electricity from wind power is becoming more and more economical due to increasing electricity rates. And secondly, the technology of small wind turbines continues to evolve and will be readily available for the market. By increasing efficiency, it is also possible to operate plants in locations that today still disallow cost-effectiveness.

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