It is vitally important for the future of humanity to push forward for better sources of energy, sources which are safer, more efficient, less harmful for the environment, and renewable, or at least with plentiful reserves. Saphon Energy, a Tunisian start-up company, is touting a new wind power generator which will revolutionize wind energy harvesting. Their claims are bold. Let’s take a look at this new technology after the break.
I became aware of Saphon Energy via an article by Adam Williams for Gizmag. You can read Adam’s article here. The piece seems to mostly restate the company’s press information uncritically, alas, but it did intrigue me enough to take a further look.
You can read Saphon’s claims and their information on their website here: www.saphonenergy.com. In essence, they have created a conical sail which flutters in the wind, much like a boat sail will flap. This fluttering motion, apparently, drives linear pistons which move a hydraulic fluid. This moving fluid can be used to spin a hydraulic motor (for power generation or other work) or stored via a hydraulic accumulator (a pressurized storage tank which can store hydraulic fluid in a manner which retains the energy of pressurization). You can see a short video of prototypes in use here: http://youtu.be/H2IeCJiddQg. It all sounds pretty awesome. There are, however, some items which raised a few flags with me.
The big claim that hit my buttons was that their device exceeds the Betz limit. Their claim:
“By replacing the blades’ rotor by a compact sail-shaped body (curved) that enjoys high aerodynamic coefficients (Cl and Cd), the Saphonian has set itself free from the insurmountable Betz limit. “ Source: http://www.saphonenergy.com/index.php?option=com_content&view=article&id=84&Itemid=95
The Betz limit (Betz law) is a calculated maximum power which can be extracted from wind. [1][2] The calculation is based upon the maximum amount of kinetic energy which can be extracted from moving air. As the energy is removed, by the wind power device, the air necessarily slows. If all the energy is extracted, the air stops moving. This causes the device to slow and eventually stop due to the air piling up (since it’s not moving anymore). The theoretical maximum amount of energy one can reasonably expect to extract is 59.3%. In practice, turbines approach this limit asymptotically. When a device claims to exceed calculated efficiencies, a bit more skeptical examination is required.
I took a look at their international patent application for a few more clues. You can take a look here: http://patentscope.wipo.int/search/en/detail.jsf?docId=WO2012039688&recNum=1&tab=PCTDocuments&maxRec=1&office=&prevFilter=&sortOption=&queryString=WO%2F2012%2F039688
I notice with some surprise that the patented product has a bladed ring in addition to the cone/sail. This doesn’t match the prototype in the video very well either.
A bit of internet searching turned up this bit of criticism: http://www.quora.com/Wind-Power/Are-stationary-circular-sails-the-future-of-wind-power
Of course, this is a lay-person’s analysis (no better than my own) and he provides no citations or references, but his skeptical senses are clearly tingling as well.
I don’t know if this is an awesome new wind power device or a scam to get more investment dollars. They seem to actually have a product that does something, unlike many scams. I’d like to see better, more efficient wind power. Is Saphon legit? Maybe. Is their product legit? Maybe. Does it violate the Betz limit? Probably not, but some of the assumptions used to calculate the limit for their device may be off. I’m skeptical that the device will scale up well and I have concerns about the efficiencies of converting the hydraulic power into usable power.
For some amusement, check out the comments on the initial Adam Williams article. There are several skeptical commenters with good information followed by a real gem of a comment by Kevin Schmidt which characterizes the skeptical commenters as being under the influence of the “evil Koch brothers”.
[1] http://en.wikipedia.org/wiki/Betz%27_law
[2] http://c21.phas.ubc.ca/article/wind-turbines-betz-law-explained
Very interesting take on this technology. The company’s media materials call to mind a few of the red flags of pseudoscience, and I wasn’t able to find an explanation of the technology that satisfied me. It’s a cool idea and it would be great if it works, but I need more convincing.
I hope there is something useful in this technology/approach. All we can say so far is that most of the claims are unlikely or wrong. It’s symptomatic of their inconsistent logic, that the Saphon and Hassine Labaied fault the wind turbine as being archaic, based on 400 year old technology. Later they extoll the efficiency of the sail, a technology more than 2000 years old. They present the time-tested reliability of the sail as evidence of its advantages. Hence, they have no hesitation to argue both sides of the time question.
They don’t comment on the fact that the sail is an airfoil, and has a significant amount in common with the airfoils of a wind turbine. Nor do they mention that sailors and sail designers realize that a fluttering sail is inefficient, and therefore try to avoid flutter in the sail as much as possible. Finally, they compare their device to a sail, but ignore the fact that a sail does not address the wind at anything like the angles used in their device.
Saphon says that a sail can extract all of the energy of the wind, but they offer no reason why this should be so. Sail designers know that their sails don’t extract all of the energy of the wind. They know that a fluttering sail produces a large amount of turbulence (and this massive turbulence can be used in sailboat racing to decrease the sailing efficiency of downwind boats). Anyone who has seen flow diagrams around an object similar in shape to the Saphon device can attest to the turbulence. Just standing near an metal sign oscillating in the wind gives an easy sensation of the turbulence produced and the amount of energy wasted.
Saphon harps on the importance of efficiency in extracting the energy from the wind. This is obviously important, but that too is presented in a misleading way. If this device is ever independently tested, it will be interesting to see what the efficiency looks like.
Funny enough sails are more efficient when they act like wings (e.g. wind turbine blades) than as wind blockers. I couldn’t read thru all of Saphon’s boilerplate as that kind of thing makes my head hurt.
I wonder if the Betz limit would even apply to a machine like this. One of the assumptions of the Betz limit calculation is that work is being done on the turbine blades as a mass of fluid passes through them. Because no air mass passes through this “turbine”, how can you talk about the work done by that passing air? It seems like a more logical calculation would be to find the energy imparted to the disk through collisions with the wind.
@Anonymous. The applicability of the Betz limit to Saphon’s device doesn’t interest me, until they get some independent efficiency figures. Suppose, just for the sake of argument, that this device tests out at an efficiency of 3%. In this case, the Betz limit is irrelevant. I’d say the same if a reliable test showed an efficiency of 20%. The Betz limit only becomes interesting, if their is evidence that this device can get near it, or exceed it. We have no evidence of that, just an unsupported assertion.
Sorry for the typos. I wish we could correct a posted reply.