Savonius Picoturbine 'ish

[Mark Parsons]

In my quest to fly a HAWT and a VAWT of similar swept area I found very good plans on the website:
http://www.picoturbine.com/

Since I spent some time this past weekend starting final assembly I wanted to start this thread and solicit any constructive comments. I haven't yet figured out how to caption or insert text between the photos.

I deviated from the Picoturbine site on blade design. They promote the Benesh version of half circles with overlap. I like the elegant design of a Lissajous waveform. This waveform is plotted by multiplying sin and cosin values together through 180 degrees. This shape is easily recognizable as the ancient Ying-Yang shape in Chinese lore. The trailing edge joins the rotation arc very nicely.

The blade material is 0.10" HDPE (called Puck Board in Canada). A 4 x 8' sheet is cut into 4 -2' x 4' rectangles. The blade forms are UHMW (Ultra High Molecular Weight plastic). The dish plates are 3/4" plywood. The axle is 1" Ridgid Aluminum conduit. A cradle made from 2x6 pressure treated lumber will contain the flange bearings and the Ametek DC motor mount.

Picoturbine classes this size as 250 Watt. Swept area is 17" (radius) x 96" high for a total of 1632 sq.in. A 6:1 pulley ratio will increase the Ametek RPM for 12.5V cut-in wind speed of 3.5 MPH.

Hopefully, I will have this flying after another weekend of construction. Then I can start to compare the power output to a previously built 48" diameter HAWT - swept area 1809 sq.in.

[Jay Miller]

Mark,
Nice work. I am considering a project similar to yours.

If you don't mind could you please tell me what kind of bearing assembly and size your are planning on using to mount your blade. This would be quite helpful to me if you have the time.

I look forward to see your finished project and also to see the results.

Thanks

[Mark Parsons]

Greetings Jay,

I went to the local bearing store and bought 2 - NTN flange type eccentric lock bearings, and a 12" and a 2" type B V-belt pulleys. Since 1" ridgid aluminum conduit measures about 1.315" OD it takes a few minutes with some emery cloth to get it into the 1-5/16" (1.313") bearings and pulley taper lock. A nice tight fit.

The photos below should help to show the mounting cradle and generator mount with V-belt in place. Used a hinge, gear clamps, a scrap piece of aluminum extrusion and a screen door spring to tension the belt. I used a 51" type 'A' belt. It rides very deep in the pulley grooves to help offset any mis-alignment. An 'A' belt is still rated for a few horsepower so lots of capacity for this project. The unit spins the Ametek 50VDC generator up to 6 volts with 2 shop fans blowing at it. I have a short 3 second mpg showing it rotating but can't get it to upload.

I flew it outside horizontal as shown for a few minutes yesterday. She really spun up when a gust hit it from the right direction. I decided to bring it back in. I will need to recuit some help to get it vertical and outside for a proper test. It weighs about 120 pounds. Not that much but quite awkward without help since it is 12' long and the cradle spins on bearings.

I'm sure the group would love to see and learn more about your project.

Mark

[Mario De Castris]

Hello Mark,

I have been following your progress with a lot of interest because I believe that a project like you are working on can be used in many different applications. Do you think it would work under water? Please keep up the good work and keep posting lots of pictures.

Regards, Mario

[Jay Miller]

Thanks Mark for your response.

Looks good. I hope you get if flying soon.

My project is just in the planning stage now but I hope to get it started in the next few weeks. I will post to share the details and results.

Keep up the good work.

Jay

[Mark Parsons]

Greetings Mario,

A very good question. Would the Savonius design shape as above work under water? A set of Savonius blades running horizontal to the water, and half-in, half-out, is an undershot water wheel - or flowing through the center, is called a Banki-Mitchell turbine. I built both. The Banki provides a few watts 24/7 for my cottage and the undershot is integrated with a sling pump to provide pressurized water.

I don't have the water depth in the creek that flows beside my cottage for a vertical Savonius. I do have good depth in the river that flows beside my home.

A quick Google search doesn't reveal any other attempts at this. Perhaps I will consider this for a future experiment.

The river beside my home is classed as navigable and I hesitated to test my paddlewheel pump system here for fear of traffic interference. However, I did test it upstream where the flow is much faster and less navigable.

Of course, the rub (there is always at least one). Even if a Savonius is a reasonable kinetic energy harvesting device for water flow, the output RPM would be very low. Lots of losses in the power transmission system just to get it up into dual rotor axial flux alternator range.

Mark

[Mario De Castris]

Hello Mark,

As usual with my zero engineering knowledge I've been thinking about some device that would result in a fairly slow r.p.m. but high torque to shore to be connected to what ever. I have the same problem as you, the waterway in front of my place is navigable and during the fishing season I have sports fisherman casting right under the dock looking for bass as well dragging fishlines close to shore for walleye.

Mario

[Mark Parsons]

Greetings Mario,

Check out my MicroHydro thread on Paddlewheel Power. The machine harvests river flow energy and scoops water each turn and pumps it and compressed air out with high pressure. This high pressure water and compressed air can spin turbines and alternators efficiently. If you have docks intruding onto the water way you can probably place one of these machines between to keep out of the navigable section. It floats, so should not fall under scrutiny of MNR or DFO.

I have a design aid spreadsheet that models the physics and can provide you expectations based on your site parameters - i.e. river velocity and depth and available width for the machine.

Regards,
Mark

[Mark Parsons]

Another weekend is gone without flying the Savonius. It's been a calm period here. Hopefully, in the next week or two the winds will pick up long enough for me to put the unit outside and record some power values and see if all of it is up to the challenge.

Will update this post with details.

Mark

[Mario De Castris]

Hello Mark,

At the risk of getting in trouble with Rob I decided to answer your last post. Too bad you are so far way because I would lend you my wind tunnel to test your turbine. Mario

It is after all April 1st ( I will remove it later ) :o

[Rob Beckers]

LOL! :p
Got to get me one of those....

-Rob-

[Mark Parsons]

Not having even brief access to Mario's wind tunnel, I had to wait. Finally yesterday some wind.

Got the machine vertical and outside. Spins up in the lightest of breezes. Loaded it up with some resistive cartridge heaters. Used 2 in parrallel for a net 22 ohm load. Saw some 40W gusts. No ill effects other than a small bearing squeak in the Ametek. 30V from the Ametek is equal to about 800RPM. That means the Savonius spun up to about 130RPM in yesterday's observed gusts. At a loaded TSR of 0.75 that would be a gust of about 17MPH. I need to get an annemometer.

[Mark Parsons]

Another thought has occurred to me. I get these once in a while. ;)

Further mental consideration about motors recalls that torque in a motor (generator) is proportional to applied current. In reverse, this would mean that applied torque to a generator is proportional to its output current. This fact is easily observable in commercial synchronous wind turbines. They don't change speed regardless of wind speed. They pitch the blades to keep AoA correct to extract energy from the wind at a fixed rotational speed. This pitch change converts torque from the blade into current (power) to pump into the grid.

My point. For a battery based system, the voltage is clamped by the battery. This voltage clamp essentially holds the generator close to a fixed RPM similar to the synchronous AC machines. To speed the generator up faster than the voltage clamped RPM, requires torque. This torque slightly increases the RPM to create the small added voltage needed to cause charging current to flow through the low internal resistance of the generator windings and hence to the battery. To obtain this torque efficiently in a HAWT at a clamped RPM requires variable pitch to maintain a lift torque AoA at all wind speeds with fixed RPM. I now understand why MPPT is a significant advantage for battery charging systems using variable speed horizontal turbines.

The Savonius is a mostly drag machine. It converts wind speed directly into torque. As it rotates slower than the wind speed due to voltage clamping, the wind applies more torque to its blades. I'm wondering if it is inherently a better battery charging machine due to its ability to convert wind speed to torque (charging current) without the need for a MPPT controller to maintain the AoA across the range of natural winds.

Comments?

Mark

[Mario De Castris]

Hi Mark,

I know how handy ananometers are. I bought a hand held one before I started my wind system to determine what wind speed I had on the ground. I guess it`s a navigation unit that sailors use, it's also very handy to set the r.p.m. on my wind tunnel before I test a turbine. I am trying my best to follow your post but I got a bit lost with your short terms such as TSR and AoA, also I have a question about the Ametek you are using, is it a PM or a regular motor.

Thanks Mario

[Mark Parsons]

Hi Mario,

I apologize for the jargon. I've been getting caught up in wind energy physics and acronyms. I still have a long ways to go to get my head around all the airfoil complexities.

TSR = Tip Speed Ratio. This ratio is an indicator of the lift component of an airfoil blade. It is the ratio of Blade Tip Speed to Wind Speed. Airfoils usually run faster than the wind. To my knowledge, typical small HAWT blades run in the 3 - 7 range. You are flying one or two commercially available units. I'm sure they must list this design spec in their documentation. A Savonius is typically a much lower TSR. There normally isn't much lift force from a barrel cut in half, and half the unit is always turning directly into the wind.

AoA = Angle of Attack. This is another airfoil term. To keep an airfoil producing a high lift force component the angle of attack is an important aspect. It is related to the apparent wind angle created by the rotational velocity of the blade and the oncoming wind. Twist in a HAWT blade is required to maintain a constant AoA over the length of the blade due to rotational velocity changes from root to tip.

The Ametek I bought on e-bay for $40. It is a 50VDC model. It is a PM DC motor with brushes. I measured the voltage constant at 38VDC per 1000RPM. It is allegedly capable of about 500W continuous power. I am barely working it with 40 - 80W peaks. BTW - These peak power measurements taken yesterday and today are right in line with the test results of my HAWT of similar swept area.

I flew the Savonius again for a few hours this afternoon. Another blustery wind day. Winds were mostly from the east 10 - 30 km/hr and very turbulent, especially near the ground behind my shop. I'm impressed with the fact that the machine did not stop rotating all afternoon. In the observations I made it was above cut-in speed (12V) probably over 80% of the time. The HAWT I tested behind the shop would stop rotating frequently and seek the new wind direction created from the turbulence. So far no bolts or nuts have loosened off (contrary to the HAWT). The machine is holding up nicely. Even the bearing squeak stopped today. I added more resistive load today to bring the loaded RPM down to make the motor force more torque from the machine. Now running into a 14 ohm load. It seemed to help with total power capture to some extent.

I am looking forward to side by side comparison with the HAWT when this machine heads north later in the spring.

Regards,
Mark

[Paul Bailey]

Mark : I'm not sure why I'm inrtigued by that thing but I just am. Clean low speed power at ground level. How much torque/power are you estimating this will have /What are the capabilities or are we to early to tell.????:)

[Mark Parsons]

Hi Paul,

The jury is still out on this Savonius' capabilities. It needs more quantification. Bear in mind this unit is sized only slightly larger than a toy and not intended to power a home. PicoTurbine list it as a 250W unit. With its swept area of 1,670 square inches, 250W harvest would require more than a 22MPH breeze. It was made with a swept area very close to my 48" diameter (1,800 sq.in) horizontal 3 blade unit.

I spent the (cold) Easter weekend at the cottage. I saw my horizontal unit spinning a total of 3 times. None of which even met cut-in RPM. My new weather station says the winds were almost exclusively under 10km/hr. I couldn't help thinking that the Savonius would have spun a bunch more.

My cottage is located at the bottom of a river valley surrounded by 1,000 foot high hills and gobs of 60-80 foot tall pine trees. Wind resource is very poor. What wind there is, is very turbulent due to the hills and trees. The Savonius is an attempt to capture some of these very turbulent and low power winds.

The planned acid test of the Savonius is strapping it to the side of the same pole as the horizontal machine later this month and then logging power output of both machines over a period of time. This will take me some time since I'm only at the cottage intermittently. (even less during blackfly season)

Upon data analysis, I plan to build a larger version of the winning concept. One that will be sized to provide a significant fraction of the cottage's electricity requirements.

Mark

[Mark Parsons]

Got the VAWT and HAWT on their test pole this weekend. An alternate use for a Balsam tree. No, I didn't climb the tree to mount these things. A friend with a bucket truck is a valuable asset... ;)

Hub height on the HAWT is about 35 feet. Center height of VAWT is about 15 feet.

Now all I need is more vacation time to spend observing and logging the results.

Mark

[Mark Parsons]

Posted this video on youtube.
YouTube - Turbine tree

No data results yet. Need some time to observe with the shunt resistors and meters in place to get a feel for power output from both devices. I did see wind gust power harvest of over 80 watts from the units combined on the weekend. I don't know how much of this total is attributed to VAWT vs HAWT.

More info to come.

[George Craft]

Hi Mark, I love your wind generator. I've seen this style built from used 50 gallon plastic drums. People cut them in half vertically, then shift the two halves and attach them to metal brackets. The DC motors that you are using as a generator are found in the old tape drive systems, used for mainframe backups. I find them quite often while visiting the metal recycling yards. You are doing a great job and I really like the photos. They are worth a thousand words.

[Mark Parsons]

Thank you George for the kind words.

I'm having a blast thinking of ways and building devices to power and provide services to my off-grid cottage without incurring any utility company bills.

Hopefully, next trip up I can get some data on VAWT vs. HAWT power output. My original intent was to gather data to determine the concept for a single larger machine. I'm now thinking irregardless, I will build a larger HAWT machine anyway. If the VAWT wins the power output test, maybe I'll build a larger VAWT too. Can't imagine having too much power. Should be able to find uses for it. I'm anticipating some could be used to charge a vehicle in a year or two when plug-ins become available.

Regards,
Mark

[George Craft]

I've thought of some interesting ways of using up the extra power when the wind generator starts producing more power than you require. How about using heating elements in water tanks? On a cold winter day, when the wind is just howling, you could actually be assisting in keeping the place warm by heating up water and circulating it around the room via pipe radiators.

[Ralph Day]

Hi George

Or for simplicity's sake do like me and rig to run small electric heaters, dehumidifier or shame! shame! a little a/c!

You can't go by me tho, i cut my lawn with a reel push mower and cordless trimmer, no more stink, noise and frustration of starting ICEs. Get a workout too!:D

ralph

[George Craft]

Hi Ralph,

I never had much trouble starting ICEs. I always carry a small can of QuickStart ether. A couple of shots of this stuff down the carb and it usually starts on the first pull. You are right about the stink though, gas fumes give me a headache...

PS: One of my latest projects is a bicycle that sits on two pontoons.
Reference: http://www.boatdesign.net/gallery/showphoto.php/photo/5497

[Mark Parsons]

I was able to connect the shunt resistors to both VAWT and HAWT today and watch 2 digital meters for about 1-1/2 hours with some light winds. Was able to relax in a chair in the shade and enjoy a couple of beverages while observing the meters. Life is great.

The HAWT won. Not by much. It did provide more battery charging energy and spent more time above cut-in RPM than the VAWT.

Of course, the HAWT has a slightly higher swept area (8%), is mounted at twice the elevation and has much reduced mass relative to the VAWT, hence much lower inertia.

The VAWT wasn't very far behind. If given an entirely equal playing field I would peg the 2 options pretty close. Given a steadier breeze in my turbulent location the results may also have been different.

I will repeat the procedure at least twice more in varied conditions to ensure no anomolies. A great way to kill a couple of hours at the cottage anyway.

Mark

[Kricnit Not]

I was just curious why you choose to remove the gap between the two blades? I think the reason it was design in was to permit partial backflow thrust to counter act the front side of the upflow blade resistance.

Kricnit Not

[Mark Parsons]

Greetings Kricnit,

The overlap you refer to was published as an improvement by Benesh. This improvement was further tested at Sandia for overlap gap and range. It was observed that not much overlap and gap provided the small peak percentage gain of this configuration. Then I read this white paper that claims even better efficiency without overlap and gap. http://www.energy.ca.gov/2005publications/CEC-500-2005-084/CEC-500-2005-084.PDF

If you look close at my pictures you can see that the blade material bows between attachments and this creates a overlap condition and the airflow can pass between blades as in your sketch.

Part of the problem was getting the biggest swept area from a 4' x 8' sheet of puck board material.

This machine has been flying since April. It has survived a couple of big wind gust events with no damage.

Are you planning on building one of these? Got any pictures, plans or ideas to share?

Regards,
Mark