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[VAWT] Plausible improvements of the Savonius windmill

Cut a barrel in half, mount it on a shaft and you have a windturbine. If the barrel is used, then what else probably would end up on a scrap heap is instead used for converting renewable energy.

Simplicity and low cost makes this an attractive option especially for societies with limited economy and a malfunctioning or non existing electric grid. Small off-grid electrical networks can be built and people who perhaps most needs electricity get that. Isn't that neat?

Savonius (from

An overlooked potential?
The Savonius though has a widespread reputation of having low effiency and is often dismissed as a credible option around forums and in formal litterature. However, when looking at the graph below from a publication Wortman did 1983, the effiency can be realtively high provided that the TSR(Tip-to-Wind-Speed-Ratio) is held at a correct value and the windmill should work quite nicely. In practice this could probably be done by controlling the generators braking torque by controlling it's output current.

As far as I could see nobody else had published info regarding how the effiency of the Savonius could be improved by controlling the TSR. I therefore sent this in as a proposal for a Bachelors Thesis at Chalmers and we're now a group working on how or if this could be achieved.

Preliminary calculations
My part in the project so far has mostly been to determine analytical expressions and doing calculations. The preliminary results were most interesting. They are not yet mature for publicing, but anyway showed that if the generator isn't carefully matched just rotor effiency only easily can drop to on average 5-10%  in the operating wind range.

Today I derived a preliminary analytic expression, with some simplifications, for average diode losses in a step-up converter connected to the generator. These also grow significantly high if the all system parameters aren't carefully choosed.

A Savonius mill that is built without considering theoretical implications could thus get a total effiency of just a few percents. And even if these parameters are carefully choosen, parameter variations still could have a huge impact on the total effiency. These could be reasons why the Savonius concept as a whole perhaps has got a worse reputation than it deserves.

First prototype
Rapid prototyping is great whenever possible I believe. The other day we created this quick-and-dirty model of a Savonius. It's made of used cable drums and melting glue and hooked up to a small BLDC motor.

This was spinned by bursting some pressurized air on it.
We already learned some from this first prototype, among other things that the generator picks up quite a lot of electrical noise from the sorroundings.

From now on I choose to tag my posts so that they can be separated more easily. This project is tagged [VAWT], standing for Vertical Axis Wind Turbine.


Populära inlägg i den här bloggen

[VAWT] Affordable wind measurements

The shop Clas Ohlsson in Sweden sells a spare anemometer for the  WH-1080 weather station for a hobbyist friendly price around 15 euros. This anemometer can probably be found in other countries too.

The WH-1080 spare anemometer

Here  you can read about how to use this anemometer together with an Arduino or any other embedded system.  As we couldn't find any data on the characteristics of this sensor, we did our own calibration in a wind tunnel and the results are presented in the report above. This anemometer was used in a Bachelors Thesis project related to the devlopment of optimization of the Savonius Turbine, here tagged [VAWT].

[RR] Automated rescue boat

We have a project course at our  master program System, Control and Mechatronics, were we could apply to one of around 30 projects available. I was really happy that I got my first choice, which is a project carried out as a joint effort between SSRS (Swedish Sea Rescue Society) and Chalmers. The goal is to develop  autonomous or/and semi-autonomous vehicles that can help out in rescue missions. The current vehicle, a large water scooter named Rescue Runner, is able to follow a larger leader boat.

However, the people involved want some better tracking capabilities and stability of the control system. We are currently a team of three persons hoping to achieve this. Stay tuned, more information will be posted when we finish. Or well, not if we sink though. Then I'll try to cover it up, and hope for dedicated readers to spam me with comments ;)

Here you can read some in Swedish about the project: