More alternative-energy innumeracy
As an engineer, I hate to see bad engineering treated like a good idea.
I've written recently about questionable proposals for human power generation, electric vehicle recharging and fuel cells. In some cases, there's nothing really wrong with the underlying technology, but it's being implemented and promoted using bad math and misleading promises.
The latest example of innumeracy comes from Shawn Frayne, an independent inventor here in Silicon Valley. Frayne's Windbelt is a low-cost wind-power generator that uses a fluttering membrane instead of rotating blades to convert wind power into mechanical motion; a simple linear generator turns the motion into electricity.
The Windbelt idea won a "Breakthrough Award" in the November issue of Popular Mechanics, but not because Windbelt is actually useful or innovative. It looks like the magazine was a bit too eager to jump on the alternative-energy bandwagon, so nobody bothered to run through the numbers.
The numbers are awful. According to Frayne's estimates, for "a few dollars" you could make a version of the Windbelt capable of generating 40 milliwatts of power in a 10-mph wind. In a 5-mph wind, if the things works at all, it'll produce less than 5 milliwatts.
In a stronger wind, it's liable to break entirely, since the power of wind varies as the cube of the wind speed. In a 40-mph wind, the Windbelt could potentially extract more than 2.5 watts...but in practice, the membrane would simply tear. This failure is exactly what caused the famous 1940 failure of the Tacoma Narrows bridge in Washington.
Frayne wants the Windbelt to power LED lighting, replacing kerosene lamps in Haitian homes, but that's not going to happen. I did some simple research through Google--the kind of research the staff of Popular Mechanics should have done--and the numbers just don't work out. It would take at least 5 watts of power to produce enough LED light to replace a kerosene lamp. Generating that much power would require 125 of Frayne's small Windbelt generators.
Current Windbelt prototypes are small, so one might suppose they can simply scale up to produce more power. Unfortunately, they can't scale very far because of limits to how strong the membrane can be. There's an inherent conflict between making the membrane thin to maximize flutter and making it strong so it can tolerate more fluttering.
Conventional propeller-bladed wind turbines are not commonly made with outputs below about 50 watts, but there's no reason that can't be done. It isn't done because it isn't worthwhile. For low-power applications--especially in sunny places like Haiti--the appropriate technology is solar power. Solar panels have no moving parts, require little maintenance and when properly protected, are pretty much immune to high wind.
And there's nothing to be developed for this situation. Home Depot sells truckloads of solar-powered lighting equipment. I checked the company's Web site just now, and for a mere $26.97, you can get a solar-powered LED floodlight that includes the solar panel, a battery and a three-LED lamp. Such a product would require some repackaging for the home-lighting market, but all the parts are there.
I suspect someone's already done that work, but I didn't turn up any commercial products intended for this kind of use in my brief search. If you're aware of such products, add a comment! Thanks.
Peter N. Glaskowsky is a computer architect in Silicon Valley and a technology analyst for the Envisioneering Group. He has designed chip- and board-level products in the defense and computer industries, managed design teams, and served as editor in chief of the industry newsletter "Microprocessor Report." He is a member of the CNET Blog Network and is not an employee of CNET. Disclosure. 
I know you from Jerry's site. I'm "Phil". You asked about cameras a while back. I've been using the EOS20D for 3 years. I've got little ones and the DSLR's capture those "moments" that the point and shoots can't. Canon just released a new pair of pro and pro-sumer DSLR's. The EOS 1D Mark III and the EOS40D respectively. You can get EOS 1D Mark II's on Ebay for about 2300.00. If you look carefully, you can find another avid amateur trying to sell up to the Mark III who has a low shutter use Mark II for sell. You should be able to find one with 10K shutter actuations or so verses the Pro's selling up with 100K actuations. I did. After receiving my Mark II, I can tell you that it is what you want. Fast and built like a tank.
On lenses. Get Canon L glass. The 24-105 F4 L is a great start.
My 3.14 cents worth.
Phil
. png
- by secretvid March 24, 2008 1:20 PM PDT
- Without arguing the specific merits of the windbelt idea, Peter's dismissal of the technology is a bit misleading... he says that "It would take at least 5 watts of power to produce enough LED light to replace a kerosene lamp". While this may be true, the fact is that all that power doesn't have to be produced at the same time. Just as Peter recommends solar cells, which collect power throughout the day to be used at night, the windbelt (or any other wind powered micro-generation unit ) only has to collect enough energy to be used for the few hours before the family goes to bed. And if the wind continues blowing at night, then all the better! Also, a single kerosene lamp is not a particularly efficient light source in the sense that it's light coverage is indiscriminate and single-source. Rechargable LED headlamps for each member of the family would consume LESS power than the kerosene lamp since all the light produced would go toward lighting each individuals specific needs..
- Like this Reply to this comment
-
(4 Comments)