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.  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”.