Nuevas tendencias y enfoques de la Administración Pública moderna

In comes the vertical axis wind turbine. With vertical axis wind turbines the rotational axis of the turbine stands vertical or perpendicular to the ground. As mentioned above, vertical axis turbines are primarily used in small wind projects and residential applications.

This niche comes from the OEM‘s claims of a vertical axis turbines ability to produce well in tumultuous wind conditions. Vertical axis turbines are powered by wind coming from all 360 degrees, and even some turbines are powered when the wind blows from top to bottom. Because of this versatility, vertical axis wind turbines are thought to be ideal for installations where wind conditions are not consistent, or due to public ordinances the turbine cannot be placed high enough to benefit from steady wind.

Wind turbine power ouput variation with steady wind speed.

The figure below shows a sketch a how the power output from a wind turbine varies with steady wind speed.

39 Cut-in speed.

At very low wind speeds, there is insufficient torque exerted by the wind on the turbine blades to make them rotate. However, as the speed increases, the wind turbine will begin to rotate and generate electrical power. The speed at which the turbine first starts to rotate and generate power is called the cut-in speed and is typically between 3 and 4 metres per second.

Rated output power and rate output wind speed.

As the wind speed rises above the cut-in speed, the level of electrical ouput power rises rapidly as shown. However, typically somewhere between 12 and 17 metres per second, the power output reaches the limit that the electrical generator is capable of. This limit to the generator output is called the rated power output and the wind speed at which it is reached is called the rated output wind speed. At higher wind speeds, the design of the turbine is arranged to limit the power to this maximum level and there is no further rise in the output power. How this is done varies from design to design but typically with large turbines, it is done by adjusting the blade angles so as to to keep the power at the constant level.

40 Cut-out speed.

As the speed increases above the rate output wind speed, the forces on the turbine structure continue to rise and, at some point, there is a risk of damage to the rotor. As a result, a braking system is employed to bring the rotor to a standstill. This is called the cut-out speed and is usually around 25 metres per second.

Wind turbine efficiency or power coefficient.

The available power in a stream of wind of the same cross-sectional area as the wind turbine can easily be shown to be

If the wind speed U is in metres per second, the density ρ is in kilograms per cubic metre and the rotor diameter d is in metres then the available power is in watts. The efficiency, μ, or, as it is more commonly called, the power coefficient, cp, of the wind turbine is simply defined as the actual power delivered divided by the available power.

The Betz limit on wind turbine efficiency.

There is a theoretical limit on the amount of power that can be extracted by a wind turbine from an airstream. It is called the Betz limit .The limit is

μ=16/27≈ 59%

41 What is Betz Law?

We all feel the wind on us when we go for a ride on a motorcycle or on a windy day where you almost are swept off your feet. Wind can be very strong and we experience this power on windy days or storms. With all this wind energy flowing around us, scientists decided to put it to good use specially in these days with more emphasis on global warming there is a lot of pressure to use renewable sources of energy. Wind energy is flowing freely all around us and has not been utilized much. Well, with that in mind, wind farming is being tried and to some extent has been harnessed very successfully. Wind farming makes use of turbines which turn with the speed of the wind and create kinetic energy. This energy is converted to electricity by an electrical grid or generator.

Many experiments are being conducted to find the most cost effective and energy efficient solution. But one of the most important inventions was made way back in 1919 by a German physicist; Albert Betz demonstrating the limitations of wind turbines is worrying the scientists. Even today these findings known as Betz Law or Betz limit have been found to be true irrespective of man‘s effort to create different energy efficient wind turbines. Betz law is quite interesting and how a calculation made almost 100 years back holds true even today.

What is Betz Law or Betz Limits?

According to Betz law even when all the ideal conditions of energy generation are prevalent we can only derive 59% energy from wind turbines. 100% wind energy generation is simply not possible. Herein the capacity or ability of a generator to convert kinetic energy into electric energy is not under question. Rather the structure and mechanism of wind turbine has limitations in converting the wind energy into 100% kinetic energy owing to which we cannot take full benefit of wind energy.

42 Although we are always inclined to get 100% of everything, it‘s not always possible and most of the times nature has its genuine reasons for confining man from achieving his own will. Betz law although was invented in 1919 has been known unknowingly to mankind but in a simpler way. How? Well what happens when you extract 100% energy from any source? The energy becomes empty or dried out. Similarly, if we are successful in deriving 100% kinetic energy from wind energy will there be any air or wind left? No! And then what will rotate the wind turbine? So at least to keep the velocity enough so as to make the wind turbine rotate for energy generation it‘s important that 100% efficiency is not achieved.

What is the fundamental basis of Betz law?

Betz law basically talks about how a wind turbine cannot extract more than 59.3 % of Kinetic energy from the wind. Under Ideal conditions or theoretically the maximum energy that can be extracted from the wind is called the Power coefficient which is a ratio between the amounts of energy that can be extracted by a Wind turbine to the total energy in the Wind.

Power Coefficient (Beth's Coefficient) = Kinetic Energy that is extracted by a Wind turbine/Total energy in the Wind

What are the limitations for achieving high efficiency?

Usually the most important intention of energy generation is to achieve maximum efficiency within reasonable operational costs. So as to make the turbines cost effective, there would be a need to adapt design trade-offs but this can affect the overall efficiency of the system. So the idea is to get more power from stronger wind by sidelining the efficiency a bit. It has been found that less efficient rotor blades have been found to give more output. Moreover, the speed of wind is always a variable, while the turbines installed will always be of same efficiency and capacity. All these problems are currently being faced by the engineers and hence even today Betz law seems to be relevant.

43 CHAPTER 5)

BIOMASS

The term Bioconversion, also known as biotransformation refers to the use of live organisms often microorganisms to carry out a chemical reaction that is more costly or not feasible nonbi ologically. These organisms convert a substance to a chemically modified form. An example is the industrial production of cortisone. One step is the bioconversion of Progesterone to 11-alpha-Hydroxyprogesterone by Rhizopus nigricans. Another example of this is the conversion of organic materials, such as plant or animal waste, into usable products or energy sources by biological processes or agents, such as certain microorganisms, some Detritivores or enzymes.

The conversion of organic materials, such as plant or animal waste, into usable products or energy sources by biological processes or agents, such as certain microorganisms. The Bioconversion Science and Technology group performs multidisciplinary R&D for the Department of Energy's (DOE) relevant applications of bioprocessing, especially with biomass. Bioprocessing combines the disciplines of chemical engineering,

microbiology and biochemistry. The Group 's primary role is investigation of the use of microorganism, microbial consortia and microbial enzymes in bioenergy research. New cellulosic ethanol conversion processes have enabled the variety and volume of feedstock that can be bioconverted to expand rapidly. Feedstock now includes materials derived from plant or animal waste such as paper, auto-fluff, tires, fabric, construction materials, municipal solid waste (MSW), sludge, sewage, etc.