Energia Eolica Savonius.pdf

My Savonius Rotor - Making Electricity

Table of Contents

Composition Revised March 30, 2007

Opening

Enough Wind? Should you build?

Good Air

Performance of the Savonius Wind Turbine

History of the Windmill

Earliest Known Design – VAWT, 500AD

More than you want to know about alternators

Magnets and wires

Left Hand Rule

Picking a phase for the alternator

Taking what I learned to start my project

VAWTs are very high torque

A fresh look at the VAWT, my breakthrough

1 st step

Finding the center of a circle

Steps 2 through 6 basic rotor construction

7 th Starting to construct the alternator on the rotor

Over simplified diagram of completed unit

Steps 8 through 10 the alternator and winding coils

The “Flux Capacitor”

Rectifier

Full Bridge circuit

Rotor Alternator “Y” circuit

Most basic unregulated charge circuit

Deep Cycle batteries

Understanding AMP hours

Common battery codes

Inverters

Transfer switch

Tools and Materials

Glossary

Alternator as a separate project

A new spin on an old twist. My take on the Savonius rotor, a Vertical Axis Wind Turbine

or VAWT. Here I will share the information that I used to develop my wind power

generating unit. I hope the information is of value to you.

Today, (February 2007), I read in the ABC news that wind is being seriously considered

for off shore power generation. “ Offshore wind turbines could produce enough electricity to

power nine states, plus the District of Columbia, with a surplus of 50 percent for future growth,

according to the study. At the same time, carbon dioxide emissions would be reduced by 68

percent, and all greenhouse gases would be reduced by 57 percent, according to the study,

published in the Jan. 24 issue of Geophysical Research Letters.” Imagine if everyone in this

country in a good wind area put up a home size wind generator system, we could have a

positive impact on the environment while saving lots of money in the long run. There is no

reason to put off a project of this type.

Before you begin, you will want to make sure you are in an area that has enough wind to

make this a worthy endeavor. Here is a wind map of the U.S. It was obtained from the

following website address: http://en.wikipedia.org/wiki/Wind_power

Since the chart is not really legible, let me just say that if you are in a white zone, this may

not be a project for you. The darker the color, the more steady wind and at higher average

speed is recorded for the area. If you appear to be in a white zone, you can always buy an

anemometer to measure wind speed and keep a log over time to know if you live in an area

that is an exception. This map is very general. You can also research average wind speed

with your local weather service. Another more detailed website on wind speed is as

follows:

http://www.eere.energy.gov/windandhydro/windpoweringamerica/wind_maps.asp

According to my reading, the “good air” is about 20 feet or higher above the ground. This

is also something to consider. You want air flow to hit your windmill without a lot of

turbulence from structures. Local city and or community ordinance may not allow you to

have anything above a certain height other than a tree.

Another thing to consider is wind gusts, wind energy potential increases very rapidly with

increasing wind speed. In fact, if wind speed doubles, the energy content goes up by a

factor of eight. So even if you have relatively calm wind with regular gusts, you may want

to “catch” some of that energy. Remember, the savonius rotor doesn’t mind gusts or even

what direction they come from. This unique attitude of the savonius rotor allows you to

take full advantage of varying and gusty winds.

From: “The Journal of Solar Energy Engineering” – Feb 1989 Vol 111/71

On the Performance of the Savonius Wind Turbine

An extensive wind tunnel test program is described which assesses the relative

influence of system parameters on the Savonius rotor performance. The

parametric study leads to an optimum configuration with an increase in efficiency

by around 100 percent compared to the reported efficiency of ≈ 12-15 percent.

Of particular interest is the blockage correction procedure which is vital for

application of the wind tunnel results to a prototype design, and facilitates

comparison of data obtained by other investigators. Next, using the concept of a

central vortex, substantiated by a flow visualization study, a semi empirical

approach to predict the rotor performance using measured stationary blade

pressure data is developed. The simple approach promises to be quite effective

in predicting the rotor performance, even in the presence of blockage, and

should prove useful at least in the preliminary design stages.

Introduction

The Savonius rotor concept never became popular, until recently, probably

because of its low efficiency. However, it has the following advantages over the

other conventional wind turbines:

- simple and cheap construction;

- acceptance of wind from any direction thus eliminating the need for

reorientation;

- high starting torque;

- relatively low operating speed (rpm).

The above advantages may not outweigh its low efficiency and make it an ideal

economical source to meet small scale power requirements, especially in the

rural parts of developing countries. ----- The concept of the Savonius rotor was

based on the principle developed by Flettner. Savonius used a rotor which was

formed by cutting the Flettner cylinder into two halves along the central plane

and then moving the two semicylindrical surfaces sideways along the cutting

plane so that the cross-section resembled the letter “S.” -----

The following are some rules for construction of a Savonius rotor.

a. The size of the end plates, to which are mounted the buckets, should

be about 5% larger than the diameter of the rotor.

b. The central shaft should be mounted to the end plates only, and not

through the buckets. By keeping the shaft to the end plates, the air

space is not blocked. For example, a central shaft of about 20% of the

rotor diameter reduces the power coefficient by about 8%.

c. The aspect ratio, height to diameter, 6 to 8 gives a better performance.

However, an aspect ratio of about 2 is desirable from the economic

point of view.

d. Use only two buckets, as a higher number reduces the efficiency.

e. The use of augmentation devices such as concentrators or diffusers or

combination of the two result in increased power coefficient. Again,

the increased costs of such devices should be weighed against the

increased capital cost and complexities.

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