Selsam Multi-Rotor Wind Turbine Still Spinning
by Lloyd Alter, Toronto on 05.14.08
When we first wrote about Doug Selsam's multi-rotor wind turbines three years ago, it attracted some nasty and dismissive comments. When Jetson Green and Engadget posted (very old) pictures we went back and had a look at Selsam's website we found that while the site design is stuck in 2004, the contents are not.
Beside the fact that his turbines are out of prototype and actually for sale, which should take some of the wind out of the sails of the complainers three years back, Doug presents some grand new visions, like his 2,000 foot city-within-a-city tower that is a "net exporter of power, and desalinates its own fresh water."
Another fascinating idea is his offshore Superturbine. Unlike conventional turbines, it does not have to be engineered to stand straight in the face of the wind, but can bend with the wind. This "lowers costs by eliminating all unnecessary components that do not directly contribute to power generation. Flotation near the surface forms a fulcrum, with the weight of the rotors and driveshaft balanced by a downward force from mooring below. The result, combined with the force of the wind, defining the projecting angle of the shaft. The rotors can be staggered, spiral, or in line."
Here is an offshore turbine that even Ted Kennedy could love; the "minimalist structure offers minimal visual impact"
Congratulations to Doug Selsam for continuing dream such big dreams, and persevering in the face of criticism from so many "experts." ::Selsam Innovations in Alternative Energy
2 kwH at 30mph? And 80-270 at 10-15mph? That's one heck of a ramp up, but for average wind turbines it's...well...average power at best (talking about the dual turbine actually for sale). The main problem is in the extremely low power for your average windspeed, which in the US is 12mph. Most generators can get 500 wH out of that which is double what they get out of it at 270. I expect it has something to do with the way the tower handles the duel rotors and the directional stability of the blades, basically they lose energy until they get a "stable" current of pretty strong wind. Not a bad price if you live in an area where you can take advantage of those winds though at $2k to $4k.
The beef people had with the original post was not so much with the design idea, rather the logic used to state that there was proof of concept. So there is no need to take anything personal by saying "I told you so."
Me personally, I think the designs are fine and would rather see information on his site about proof of concept by stating, "Here is what happened when this idea was implemented..." Which leads me to my next point, his site is one of the worst I have seen in a while and I would say is late 90s in style. It's too bad, because he has a great idea.
There are so many problems with the Superturbine design it is hard to know where to begin. I love the idea, but there is too much wishful thinking in his current design.
1. Structure. It is one thing to make a flexible shaft like the 15' long prototype Superturbine has, but structures do not simply scale. A piece of paper is very stiff in the mm range, flexible in the cm range and floppy as a dachshund's ear in the meter range. Likewise for his main shaft/support column. When it becomes actual size, it will be excessively flaccid.
2. What keeps the Superturbine vertical? As you get taller, you need to get wider, or stiffer, or else you fall over, as in guy wires on TV transmitter towers. Tall structures do not behave like CB antennas. His drawings show a kite attached to the top of the column to keep it afloat. What happens when the wind dies?
3. I didn't see any dimensions, but from all the computer renderings, the towers look at least several hundred feet tall. What is it fabricated from?
4. Compression and expansion energy loss/material fatigue. Assuming you could get the string of propellers to stay afloat, each revolution of the main shaft (which must be very stiff to support the turbines) will undergo compression on the underside of the shaft and the tension on the top of the shaft, which contribute to wasted energy, but more important, material fatigue. All structural systems try to avoid all material fatigue/cycling as it accelerates cracking and failure. His system depends upon it.
5. There exists no structure ever built (and still standing) that has as much material stressing inherent to the design. Trees flex in the wind, but as living systems, they can repair the induced stress damage.
6. Shaft balancing, wave movement, high wind speed damage, harmonic vibrations,... and so on.
The 2000 ft tower is DOA practically. How do you service the rotors? How do you ensure that a broken rotor does not fly off and cause havoc? Why make it desalinate water? Why not have it crack water into hydrogen and oxygen for potable power? Water cheap, Hydrogen expensive.
I also object to the "told you so" nature of the article. This design has not proved anything yet. Overall, it looks like it uses more material to generate the same amount of power as "normal" turbines.
Also, they don't look any better than normal turbines(even weirder) so Ted Kennedy's NIMBYism is unlikely to change.
Another flaw in the plan is that the Rotors are the hardest part of the wind turbine to make and the biggest reason for back log in production of Wind turbines. Now you are looking at multiplying the number of blades per turbine. Production schedule cannot look good for this. Otherwise, I think it looks like a good idea IF it can be pulled off. Looks like a bucket after a visit from a shotgun after some of the above postings.
I am no expert but here are some responses to the previous comments:
About it being a big ramp up in power at 30mph, it is important to remember that the power available in the wind goes up as the cube of the wind speed.
About the floppyness of the long shaft, spinning the shaft stabilizes the shape. On the site the photos of the largest prototype with 7' blades has a shaft that looks about 60' long and it does not seem to have any problem with stability.
The floating turbines are held vertically by the leverage of the float pulling against the cables anchoring the turbine to the sea bottom. Also because the angle of the rotors is always tilted toward the wind, there is probably a significant amount of lift coming from them like a kite or autogyro rotor.
Regarding materials fatigue, all conventional large windmills have their blades and shaft continuously flexed and the number of failures has been pretty low. Granted this design has a high frequency flexing, but carbon fiber is tremendously resistant to fatigue.
"5. There exists no structure ever built (and still standing) that has as much material stressing inherent to the design."
Two words: Suspension Bridge
Two More: Aircraft Wings
Rotors in this design are the cheap part since they are so small and they do not have to be very strong. This is a huge advantage over conventional designs that are very heavy and difficult to handle.
about that flexible tower...
think of a flexible desk lamp stabalized by tension cables. nothing really flexes, there are just a lot of movable joints in series.
PS: those things hardly ever break.