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SI - Site Forums : Silicon Investor - Legacy Interface Discussion (2004-2011) -- Ignore unavailable to you. Want to Upgrade?

To: Biomaven who wrote (2660)	11/24/2004 7:30:06 PM
From: Sam Citron	Respond to of 6035

Peter, You may be right. I dunno. It reminded me of a conversation I had last month with a guy who installs PV systems. He said that the payback period of a typical install in CA had recently gone from 15 years to 20 years lately as a result of tight silicon fab capacity and the phase-out of certain production tax credits. He was looking for business to pick up next year with new fab capacity coming on stream and new legislation, which is less likely to happen now that Bush has been reelected. He mentioned that if things did not pick up soon in solar, he was thinking of joining a company that specialized in helping companies generate energy from small turbines fixed inside of pipes. It sounded pretty interesting. Sam

To: Biomaven who wrote (2660)	11/24/2004 8:15:45 PM
From: SI Bob	Read Replies (1) \| Respond to of 6035

So if I replaced the tailgate on my truck with basically a pair of box fans that when put together have the same size and shape as the tailgate, there would be more drag than there would be from the tailgate itself? It seems to me that the drag would be, at most, the same amount of drag you get with the tailgate itself. And then only if the total swept area were the same as the surface area of the tailgate, and the fans are pulling hard as they can against a generator. I have no idea about the math involved, but would guess that if a 403 wind genny can make 400 watts in a 28-mph wind, a set of fans driving a generator could do at least that much in the 70-mph wind they'll get on the highway. 400 watts isn't much (my truck's alternator does 1400), but if it can be gotten with no increase in drag, it's not exactly a free lunch, but a discounted one. As for harnessing wind power at the front of the vehicle, my premise for it may be completely flawed. The premise is something I read a while back that said a really efficient 3-blade windmill has so little wind movement behind the blades that you can light a match behind the windmill in a 50 mph wind. Which leads me to think that the vehicle behind the windmill I'm describing will be running in a partial vacuum. The windmill/turbine/whatever itself will be creating drag, but I would think it'd be possible to design it such that it creates no more drag than the vehicle itself would. Try pushing a model airplane rapidly through the air with and without its propeller and you'll quickly see what I mean. That part makes sense because the frontal area of the prop is enormous. And because if the prop is stationary, air that hits it will also have to hit the plane behind it. It's why motorcycles, with their far more efficient engines and very little weight, don't fare much better than economy cars in mpg. Much more drag for a bike and rider than a car. I'm gonna have to try my tailgate fan idea just to test it and because it's comparatively easy to build. Wish I could wind-tunnel test it to confirm that the drag doesn't increase, but it seems intuitive that if the swept area of the fans is equal to the surface area of the tailgate, then the drag would be the same and any power you can extract from the fans would be free. I seriously doubt a pair of converted box fans could push a pair of 100-amp alternators at full load, but even if they make 10 amps, it's a gain. Well, a reduced loss.