A Study Of Wind Powered Turbine Generation

ADVANTAGES OF VAWT
1)        Easier to maintain because most of their moving part are located near the ground.
2)    As the rotor blades are vertical, a yaw drive is not needed, reducing the need for the bearing and its cost.
3)    Low height useful where laws do not permit structures to be placed high.
4)    Usually have a lower tip-speed ratio so less likely to break in high winds.
5)    Does not need a free standing tower so is much less expensive and stronger in high winds that are close to the ground.
6)    In place like hilltops, ridgelines etc. we can get higher than and more powerful winds near the ground than up high because of the speed effect of the winds moving up a slope or funneling into a pass combining with the winds moving directly into the site. In these places, VAWTS placed close to the ground can produce more power than HAWTS placed higher up.
DISADVANTAGES OF VAWT
1)    Most VAWTS need to be installed on relatively flat piece of land and some sites could be too steep for them but are still usable by HAWTS.
2)    A VAWT that uses guyed wires to hold it in place put stress on the bottom bearing as all the weight of the rotor is on the bearing. Guyed wires attached to the top bearing increase downward thrust in wind gusts solving this problem requires a superstructure to hold top bearing in place to eliminate the downward thrusts of great events in guyed wired models.
3)    Most VAWTS are low starting torque.
3.3    POWER IN THE WIND
The power in the wind can be extracted by allowing it to blow past a moving wing that exerts torque on a rotor. The amount of power transferred is directly proportional to the density of the air, the area swept out by the rotor, and the cube of the wind speed.
The power available in the wind is giving by P = 1/2 PÏ€ R2V3 .The mass flow of air
that travels through the swept area of a wind turbine varies with the wind speed and air density. The kinetic energy of a given mass varies with the square of its velocity. Because the mass flow increases linearly with the wind speed, the wind available to a wind turbine increase as the cube of the wind speed.
As the wind turbines extracts the energy from the air flow, the air is slowed down, which causes it to spread out and diverts it around the wind turbine to some extent. Windiness varies and an average value for a location does not alone indicate the amount of energy a wind turbine could produce there. To assess the climatology of wind speed at a particular location, a probability distribution function is often fit to the observe data. Different locations will have different wind distribution.
Because so much power is generated by higher wind speed, much of the average power available to a windmill canes in short bursts. Half of the energy generated arrived in just 15% of the operating time. The consequent is that wind energy does not have a consistent output as fuel-fired power plants.
Additional output can only be made to compensate for load increase by utilizing advanced wind storing technologies (e.g. giant compressed air storage tank facilities).
Since wind speed is not constant, a wind generator annual energy production is never as much as its nameplate rating multiplied by the total hours in a year. The ratio of actual productivity in a year to the theoretical maximum is called the capacity factor. A well-sited wind generator will have a capacity factor of about 35%. This compares to typical capacity factors of 90% for nuclear plants, 70% for coal plants, and 30% for oil plants.
When comparing the size of wind turbine plants to fuel power plants, it is important to note that 1000km of wind turbine potential power would be expected to produce as much energy in a year as approximately 500km of coal-fired generation.
Though the short term output of a wind-plant is not completely predictable. The annual output of energy tends to vary only a few percent points between years.
The drag type rotor, such as Savonius rotor and American Multi blade, have lower tip to speed ratio and power coefficient compared to the lift type propeller HAWT. The curve from the propeller type rotor (RAWT) indicates that the rotor is able to maintain high efficiency over a long range of rotor rpm while the sharp curve from Darreus rotor experience drop drastically when the rotor rpm movies away from the narrow optimum range, the Darreus rotor with low power coefficient at low tsr range indicates a weak self-starting ability thus when the Darrius type VAWT is coupled with a low efficiency Savonius rotor its initial stating torque is developed and also on the alternative an induction machine could be coupled with the perils rotor to improve its starting characteristics.
3.4    MATCHING WIND TURBINE TO LOAD
The rotor efficiency alone will not determine the efficiency of wind energy system as the coupling of the rotor load like generators will further reduce the overall efficiency. The power output curve for a system consisting of a rotor and generator depends not only on the individual efficiency of both components but also how well they were matched. The plot/curve below shows a torque of rotor at different speed.