Wind Farm Feasibility Study and Site Layout Design
Aerotek JSCo entering the wind energy market by developing a portfolio of wind farms. Through a strategic search Aerotek JSCo identified a series of sites for potential wind farm development in Bulgaria and several neighbour countries.

For increasing of wind power production of big wind farm is proposed jet blade VAWT s  fixed on small towers between the bigger HAWT turbine. As an example of JET BLADE   VAWT see the video here.

Aerotek JSCo provides technical and environmental services to progress the priority sites, including a feasibility study for a large site in mountainous and coastal regions. The viability of the site was known to be dependent on the realisticcapacity of the wind farm, due to amajor cost anticipated in relation to the required Aerotek JSCo provided an initial estimate of potential wind farm capacity at the site, followed by an in-depth study, whichdetermined the feasible number and location of turbines. This was achieved by investigating the technical and environmental constraints experienced at the site and by developing an appropriate wind farm design in response to thespecific features of this site and surroundings.

Our team gave consideration to priority issues, including:

• Selection of suitable wind turbine type
• Researching site constraints including protected designations, dwellings planned land use and infrastructure such as gas pipelines and microwave links
• Optimisation of energy production based on wind data from a local Meteorological Station and 3 dimensional wind speed analysis
• Respecting local properties by assessing likely noise levels and currence of shadow flicker at occupied dwellings
• Understanding visual impact of the proposed project incorporating advice from our landscape architects regarding sensitive local viewpoints and landscape-related designations noted from the adopted Local Plan.
The project demonstrated our breadth of understanding of key issues at the early stage of a wind farm design and development:
• Appreciation that a proposed wind farm size and shape should be basedon a realistically constrained scenario; this pragmatism was particularly
important for actively negotiating the lease agreement for the site, using our work as a guide to the available income from the site
• Given that visual impact is a crucial planning consideration for wind farms, we understand the benefit of input and advice from landscape architects at project inception. Aerotek JSCo incorporated aesthetic criteria when positioningturbines at the site, including the use of curved rows of turbines, thus avoiding straight unattractive grids
• The ability to balance technical and environmental concerns whenproposing the feasible capacity of a wind farm site.
• Identification of priority further work including peat probing, vehicle access
study, consultation with signal operators (Radiocommunications operators), and landscape led design study.

Aerotek JSCo’s report presented findings and recommendations for the development of a realistically sized wind farm, which would provide high income.

State stimulus for wind power plants in Bulgaria

Power engineering is the fastest progressing branch of the world energetics in the last years, and it is due to a lot of reasons. Most important of them are; rise in the price of energy in general; increasing of the global warming and ecological problems with thermoelectric end atomic power stations, which dominate in the world energetics, increasing of the capacity of wind power generators, and not at the last place – reduction of the prices of the wind power generators on a world scale, toward their level ten years ago. On the background of the described global tendency, the energy policy of our government is completely in unison with the european tendencies for economy and administrative stimulations of energy production from renewable energy sources (RES). The preferential purchase price, for example, of the electricity from RES, in particular from wind, defined from The Commission of energy and water regulation, raised from 6 eurocents per kilowatt-hour in 2003 to nearly 9 eurocents per kilowatt-hour in 2006. Namely the permanent and methodical examination of the euro-energy policy guarantee, that in our state, energy productions from RES will progress ahead of time.

At these profitable preferential legal and economic conditions, the wind climate in more regions in Bulgaria already allows building of effective wind power stations, which are profitable, and at the same time provide not long term of recovery of the investments.

In the colloquial language, and in the meteorology as well, the velocity of the wind is accepted as parallel vectors to each other, square to the terrain, which vectors has changeable at all azimuths direction. But in the reality such wind doesn’t exist; furthermore at the frontier layer of air.

Differential wind energy audit
Generally said, the vector of the wind is not horizontal. Its horizontal ingredient is this one, which has the energy importance for the operation of wind generators. But it is part of the wind speed, which has components along the other two axes of the three-dimensional Cartesian (3-D) space as well, and these components hinder more or less the work of the wind turbines.

The results of this measurement are being analyzed individually as components, and in common.
First goal is sifting out the important energy ingredients of wind from the other – not useful, which the turbines drug along, and evaluation of the damages. These damages do not depend only on the not horizontal compounds but on the amplitude fluctuations of the wind at all directions, called turbulence, as well.

Designing of wind power plants
At the wind power stations, the primary energy resource (the wind) is variable at its velocity and its direction. Therefore the designing of wind power stations always divides into two consecutive phases. The first one is the wind energy audit, and the second one is the designing itself. Both phases are even important. First phase is decisive for the choice of transformation technology of the wind energy into electricity, which has important meaning for the optimal choice between competitive wind power generators.
At the second phase are being chosen alternative variants (alternatives) of wind power generators, on the base of analysis of their technical parameters of energy and their best correspondence with the specific wind climate conditions of the audited place.
The project concludes with a technical and economical analysis, investments and ecological evaluations of the projected alternative versions.

Detailed plan within three steps, of preliminary engineering, is presented below:

Stage 1

WIND ENERGY AUDIT OF TERRAINS
1. Calculation of energy density of the wind currents
1.1. Identification of the terrains
1.2. Profile of the landscape
1.3 . Influences of wind climate over the operation of the wind power aggregates
1.3.1. Influences of the climate specifics
1.3.2. Influences of the wind dynamic on the work of the wind turbines
1.3.3. Analysis of the results of 3D-measurements
1.3.3.1. Analysis of the turbulence
1.3.3.2. Differential analysis of the wind energy, used for driving wind aggregate
1.3.3.3. Transformation of the important wind energy into electricity, according to the parameters of wind aggregates
1.3.3.3.1. Aerodynamic losses of wind energy
1.3.3.3.2. Mechanical and electromagnetic losses
1.4. Diagrams of speed frequencies of the wind at directions for the chosen places
1.5. Wind-dynamic and analytic modeling
1.5.1. Initial parameters for wind-dynamic modeling
1.5.1.1. Authentic year of measurement
1.5.1.2. Correlating wind-dynamic modeling
1.5.1.4. Correlated wind statistic
1.6. Results of the mean density of the wind energy stream
1.6.1. Calculating method.
1.6.2. Results of the density of the wind energy stream
1.6.3. Results of the density with energy importance, of the wind energy stream
1.6.4. Expected deviations of the measurements and the results

Conclusions

Stage 2

CHOOSING OF OPTIMAL WIND AGGREGATES FOR THE TERRAINS, ACCORDING TO THE ENERGO-TECHNICAL CRITERIA

2. Determination of the technical parameters of the wind power generators, in accordance with the results of wind energy audit
2.1. Fixing the places of foundation of the wind power generators
2.2. Aerodynamic specifics
2.3. Alternatives for the height of the supporting post
2.4. Alternatives for rotors
2.5. Alternatives for transmission and electro generation
2.5.1. Transmissions
2.5.2. Generations and supporting of standard parameters of the electricity
2.5.3. Connecting
2.5.4. Innovative fundamental points
2.5.5. Offer for proper alternatives for the concrete project
2.6. Pessimistic, optimistic and realistic evaluation of the annual production of electricity for the chosen alternatives of generators
2.6.1. Absolute potential of the annual production of electricity
2.6.1.1. Determination of the average annual operating hours of the wind aggregates
2.6.1.2. Determination of the actual prevailing wind velocity
2.6.2. Actual annual production of electricity
2.7. Graphic analysis of the capacity and the efficiency of the wind aggregates
2.8. Parallel between the capacity and the efficiency of the chosen wind aggregates

Conclusions

Stage 3
TECHICAL AND ECONOMICAL ANALYSIS OF THE INVESTMENT EVALUATION OF THE CHOSEN ALTERNATIVE PROJECTS
3. Investment and economical evaluations of the appropriate versions
3.1. Size of investment
3.2. Financial incomings
3.3. Risks and discount percent
3.4. Operational expenses
3.5. Investment cycle
3.6. Period of recovering of the investment
3.7. Net present value of the investment
3.8. Internal norm of profitableness
3.9. Correlation incomes/expenses
3.10. Cost price of the electricity production
3.11. Comparison of the alternatives
3.12. Results of ecological investigation
3.12.1. Ecological evaluation
3.12.2. Ecologically-economical evaluation
3.12.3. Conclusion of the investigation
Final conclusions and recommendations

Not techncal criteria of wind power farm design
In principle, each project has energy-technical and economical part. Here we will mark formal and economical criteria, which have essential place in the complete engineering. It is inexpediently for these questions to be considered in details in one book, because each detailed analysis is concrete. Such analyses are being made individually for each wind energy project.
We should mind at firs place, that the choice of over all dimensions and consequently the capacity of the turbines depends on the terrain and on the way of using it. There are two formal restrictions, in accordance with special regulation, where the distances between the turbines and between them and the urbanized territories, are defined (they exist in project as well). Distances between 5 to 7 turbine rotors at the direction of the prevailing wind for the concrete terrain are standardized and 3 to 5 diameters – square to this direction. This is criterion, which provides relatively good work of a group of turbines, but it doesn’t guarantee neither their optimal production of electricity, nor their optimal reliability and durability. For evaluation of these characteristics, it is necessary to be made configurational project, which is subject of the second part of this book, whose first edition was published in 2005.

The second formal criterion is the sanitary norm that is determined in a minimum -600 meter from the frontiers of the urbanized territories. Without making detailed comment, we should note that the closeness to transmission line with proper tension and free capacity to export generated electricity from the wind power station also has importance at the engineering stage. If there isn't existing proper electric infrastructure, the time for putting the project into operation will be shortest.

Prices of power generated by wind turbines  

Since the beginning of 2007, there are two stage preferential tariff for buying up of the electricity, generated by new wind turbines,

• For wind generators with 2250 (more than 0.257 capacity factor ) and more full effective operational hours annually -  80 euros / MWh

• For wind generators with less than 2250 (below 0.257 capacity factor ) full effective operational hours annually - 90 euros / MWh

The above tariffs are without VAT. As new wind generators are considered turbines, produced later than 01.01.2006. Wind generators, produced before this date, are considered as old, no matter if they are exploited or not.

From the table we can see that the differences are quite big and they will have significant influence over the investment indexes, as well as on the size of the needed opening stock.

Even without making such analyses, one can see that it is economically profitable the turbines to work less than 2250 hours, in comparison with the case, when they would have worked a little bit more than this hour limit This refers to new machines. If they are not big, their transport and their montage will be not expensive and in the long run it could be turned out that they are economically more effective over terrains, where the wind conditions are more unfavorabl. But If the machines are cheap (second hand) and proper aggregates are being mounted on windy places the, than their economical efficiency could be better in comparison with the new machines, no matter that the buying up tariff is considerably lower.

This brief analysis gives us the possibility to understand, that universal proper choice of aggregates doesn’t exist. They can be small or big; new or old; horizontally-axial or vertically-axial; individually working, or a few in a big group – wind park; or in few smaller groups etc. All reciprocally excluding alternatives mentioned here, can be combined in different ways. But providing for the height of the generators over the terrain and their initial expenses, the problem appears with ambiguitive solution.

The tariffs above will be subject of increase, because according to the Energy Law, they may not be lower than 70% of the end price of electricity for the home consumers.

Designing of innovative wind turbines

In large numbers one can see the propeller wind turbines. They work optimally, when the horizontal component of the complex vector of the wind is parallel to their rotor shaft. That’s why these turbines are being frequently called horizontally axial HAWT. The basic disadvantage of HAWT is that their rotor always revolves not only around its horizontal shaft, but it also moves at 360 angular degrees at the azimuth. This necessity complicates the structure of the entire turbine, and make it more expensive, furthermore if considering that the rotor is posed high above the terrain and the mechanical forces from the pressure of the wind as well as the bending moments they create, are considerable, which impose the rotors to be mounted on solid and massive supporting towers and respectively fundaments. All these problems can be avoided, if the wind turbines are constructed in such way, that is not necessary the revolving of the rotors around two mutually perpendicular axles, but only around one – the axle of their rotor shaft. Such machines are constructed, most frequently, with vertical rotor shafts and their blades turn around vertical axle. They are being called vertically axial machines or VAWT.VAWT are relatively simple in their structure and have significant advantage, that their center of gravity is low, close to the terrain, in contrast to the center of gravity of HAWT. For that reason the forces and the bending moments over their supporting construction, are vastly reduced. After all said till now, naturally appears the question why the horizontal axial propeller machines are much more distributed in practice than the vertical axial turbines.

The answer of the question, in brief, comes from the fact that the blades of propeller machines are loaded only from one side – the side of the wind pressure direction, and that’s because the rotor always revolves so, that the wind is parallel to its shaft. From mechanical, dynamical and kinematical point of view, the unilateral load over the blades is more advantageous, and therefore the rotors of HAWT are much more lighter and can rotate with higher revolutions, because the centrifugal forces in them are smaller. For each revolution of the vertical axial machine, its blades pass through two positions, in which they are loaded bilaterally consecutively. Such librating load over the blades for each revolution is a reason for them to be made robust, respectively heavy, the centrifugal forces are being got big and the rotors, as a whole, revolve unstable, particularly at high revolutions. And the energy effectiveness at transformation of the kinetic energy of the wind into useful work, when revolving the shaft of the turbine, strongly increases with the rise of the revolutions. Therefore, even if in principle, two prime kinds of turbines have a nearly even theoretical effectiveness, the limitation of the rise of revolutions of the vertical axial turbines, make their real energy effectiveness lower.
However, in contradiction from the horizontally axial turbines, which are unstable in not horizontal and turbulent wind flows, the vertically axial turbines are slightly sensitive in not horizontal and turbulent wind flows; furthermore they are considerably more noiseless. The last two characteristics make them applicable also for populated places, where the wind flows are turbulent, and where the noise during their operation time is unallowable.

That’s why our efforts are concentrated on designing of innovative vertically axial turbines, which are discussed in these pages. And the optimal engineering and constructing of the blades, rotors, transmissions and generators of the vertically axial machines, we make on the base of detailed study of the not laminar character of the wind flows. This study we carry out with equipment for 3-dimensional measurement of the characteristics of air currents, which we briefly call differential 3D wind audit.

Cybernetic system for wind farm control -  Patent pending

Vertical and horizontal wind shears, yaw misalignment and/or turbulence act together to produce asymmetric loading across a wind turbine rotor. The resultant load produces bending moments in the blades that are reacted through the blades, hub and low-speed shaft. The amount of blade’s deflection is measured using one or more sensors placed on the turbine tower. The output signals from the sensors are used to determine the magnitude of the resultant rotor load. This information is used to effect the blade pitch change needed to reduce the load and thereby reduce fatigue and loading on various turbine components.

Full title of the invention is: “Method and control system for blades load of the turbines and turbulence minimization in a wind farm based on blades deflection and turbulence of turbine wake flow” according to our pending patent. The mentioned method is applicable after low cost and very simple wind turbine upgrade.

Autor and inventor: George Tonchev, Ph.D.

F A Q,s

How reliable are wind turbines?
Modern wind turbines can be extremely reliable — the percentage of times many systems are available to produce power often nears 99 percent.
Another perspective is provided by comparisons with helicopters. The rotor blades must often be replaced after several hundred hours, while wind turbine blades commonly last 10 to 20 years or more. Because the wind turbines at the MEAN Wind Project at Kimball were manufactured with modern, durable, high-quality materials, their estimated life span is more than 20 years.

Wind turbine life and reliability
Driving your car an average of 50 mph would require 2,000 hours of engine run time to go 100,000 miles.
At an average in-town speed, which may actually be much lower than 50 mph, the engine may get 3,000 hours. During that time, you would need to change the oil 20 times, tune-up perhaps 10 times, change the timing belt once or twice and replace two sets of tires. Reduced to engine hours, that is about 27,000 hours of use.
At a U.S. Department of Agriculture test site in Bushland, Tex., a 40-kilowatt turbine runs about 60 percent of the time (when the wind is high enough to make power). Running 60 percent of the time with 8,760 hours in a year, 3,000 hours of operation takes about seven months. The turbine is still running after 15 years of almost continuous operation. —Contributed by Eric Eggleston

How do wind turbines work?
Aerodynamic operating principles of wind turbines According to the basic aerodynamic operating principles of a horizontal-axis wind turbine, wind passes over both surfaces of the airfoil-shaped blade. It passes more rapidly over the longer (upper) side of the airfoil, creating a lower-pressure area above the airfoil. The pressure differential between top and bottom surfaces results in a force, called aerodynamic lift. In an aircraft wing, this force causes the airfoil to rise, lifting the aircraft off the ground. Because the blades of a wind turbine are constrained to move in a plane with the hub as its center, the lift force causes rotation around the hub. In addition to lift force, a "drag" force, perpendicular to the lift force, impedes rotor rotation. A prime objective in wind turbine design is for the blade to have a relatively high lift-to-drag ratio. This ratio can be varied along the length of the blade to optimize the turbine's energy output at various wind speeds.

Basic principles of wind turbine power production
The output of a wind turbine varies with the wind's speed through the rotor. The "rated wind speed" is the wind speed at which the "rated power" is achieved and generally corresponds to the point at which the conversion efficiency is near its maximum. In many systems, the power output above the rated wind speed is mechanically or electrically maintained at a constant level, allowing more stable system control.
At lower wind speeds, the power output drops off sharply. This is explained by the Cubic Power Law, which states that power available in the wind increases eight times for every doubling of wind speed (and decreases eight times for every halving of wind speed).
Using the power curve, it is possible to determine roughly how much power will be produced at the average or mean wind speed prevalent at a site. In the example above, the turbine would produce about 20 percent of its rated power at an average wind speed of 15 miles per hour (or 20 kilowatts if the turbine was rated at 100 kilowatts). This is somewhat lower than most modern wind turbines.

What are the factors in the cost of electricity from wind turbines?
The cost of electricity from utility-scale wind systems has dropped by more than 80 percent in the last 20 years.
In the early 1980s, when the first utility-scale wind turbines were installed, wind-generated electricity cost as much as 30 cents per kilowatt-hour. Now, state-of-the-art wind power plants at excellent sites generate electricity at less than 5 cents per kilowatt-hour. Costs are continuing to decline as more, larger plants are built and advanced technology is introduced.
Aside from actual cost, wind energy offers the following additional economic benefits, which make it even more competitive in the long term:

* Greater fuel diversity and less dependence on fossil fuels, which are often subject to rapid price fluctuations and supply problems. This is a significant issue around the world today, with many countries rushing to install gas-fired electric generating capacity because of its low capital cost. As world gas demand increases, the prospect of supply interruptions and fluctuations will grow, making further reliance on it unwise and increasing the value of diversity.

* Greatly reduced environmental impacts per unit of energy produced, compared with conventional power plants. Environmental costs are becoming an increasingly important factor in utility resource planning decisions.

* Long-term income to ranchers and farmers who own the land on which wind farms are built.

Selection of a suitable site is key to the economics of wind energy. The power available from the wind is a function of the CUBE of the wind speed, which means, all other things being equal, a turbine at a site with 5-meters-per-second (m/s) (11 mph) winds will produce nearly twice as much power as a turbine at a location where the wind averages 4 m/s (9 mph). In the electric power business, where technology options often hinge on very small economic differences, good wind resource assessment and siting is critical.
In general, winds exceeding 5 m/s (11 mph) are required for cost-effective application of small grid-connected wind machines, while wind farms require wind speeds of 6 m/s (13 mph). For applications that are not grid-connected, of course, these requirements may vary, depending on the other power alternatives available and their costs.

Wind turbine glossary

Anemometer Measures the wind speed and transmits wind speed data to the controller.

Blades Most turbines have two or three blades. Wind blowing over the blades causes them to "lift" and rotate.

Brake A disc brake that can be applied mechanically, electrically or hydraulically to stop the rotor in emergencies.

Controller Starts up the machine at wind speeds of about 8 to 16 miles per hour (mph) and shuts off the machine at about 65 mph. Turbines cannot operate at wind speeds above 65 mph because their generators could overheat.

Gear box Gears connect the low-speed shaft to the high-speed shaft and increase the rotational speeds from about 30 to 60 rotations per minute (rpm) to about 1,200 to
1,500 rpm — the rotational speed required by most generators to produce electricity. The gear box is a costly (and heavy) part of the wind turbine and engineers are exploring "direct-drive" generators that operate at lower rotational speeds and don't need gear boxes.

Generator Usually an off-the-shelf induction generator that produces 60-cycle AC electricity.

High-speed shaft Drives the generator.

Low-speed shaft The rotor turns the low-speed shaft at about 30 to 60 rotations per minute.

Nacelle The rotor attaches to the nacelle, which sits atop the tower and includes the gear box, low- and high-speed shafts, generator, controller and brake. A cover protects the components inside the nacelle. Some nacelles are large enough for a technician to stand inside while working.

Pitch Blades are turned, or pitched, out of the wind to keep the rotor from turning in winds that are too high or too low to produce electricity.

Rotor The blades and the hub together are called the rotor.

Tower Towers can be made from tubular steel or steel lattice. Because wind speed increases with height, taller towers enable turbines to capture more energy and generate more electricity.

Wind direction "Upwind" turbines are designed to operate facing into the wind. Other turbines are designed to run "downwind," facing away from the wind.

Wind vane Measures wind direction and communicates with the yaw drive to orient the turbine properly with respect to the wind.

Yaw drive Keeps the rotor of upwind turbines facing into the wind as the wind direction changes. Downwind turbines don't require a yaw drive because the wind blows the rotor downwind.

Yaw motor Powers the yaw drive.

Source: U.S. Department of Energy

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