Nibs-I'm pretty ancient-- 5 push-ups might be more appropriate. I don't think I can build a Vawt to be more efficient than a Hawt altho based purely on instinct I 'm not sure its impossible given the technical ingenuity of some of the newer designs , and some of the down to earth ingenuity of those guys on the backshed web site. All I'm hoping is that it will be possible to narrow the gap to the point where the other advantages of vawts make them worthwhile. Was n't aware of sail switches but not fond of the idea of giving back hard won electron flow to motor the rotor up to speed. Reminds me of those poor people who invested in lousy hawts and vawts only to find they generated negative amounts of electricity-there are loads of those stories on the web !! Thanks your offer to peer over my shoulder-I really need help with the aerodynamics , the mechanics and electrics I'm probably OK on. For next 3 months or so I will be logging wind speeds -I ain't building a watermill until I've checked I've got a river !!-so expect a period of hibernation. Rgds.

This page has some good info on VAWTs: Darrieus wind turbine analysis - Home

Why all the interest in exotic materials for the foils? It is really hard to beat wood, except for abrasion resistance. When I made wooden aircraft props, we used to offer a self adhesive (peel off backing) thin stainless steel leading edge cover, took care of much of the abrasion problem.
You can laminate wood into any curved shape & carve the foil using hand tools. Wood in tension is almost indestructible, and will flex to within 90% of its modulus of elasticity an infinite number of times, I do not think there is another material which can make that claim. We used to laminate 1/8" maple for our aircraft props and use a solid piece of 1/4 sawn fir for our wind blades, both worked very well.
Cheers, Tony

Nibs -I don't know if you've read the Daox post on the jet turbine windmill but from that article I see the germ of an idea to save me push-ups. That is if I can get a " series B funding of $25M " It also occurs to me ,again from that post that maybe I'm more of a disrupting Ecorenovator than a lurking one. Come to think of it I'm not sure I 've had my series A funding yet-no wonder I'm always doing push-ups !!
Suppose you'll claim the jet turbine job as a horizontal as even a persistent b----d like me can't see a way of making it work vertically. (hey wait a minute -isn't that pole its on vertical )
Take the point on wood, I tend to have enthusiasm at the build stage and less for the maintenance stage and ally seemed a better prospect but I'll look at wood again.

Now I see that the first post has shown up, I will leave this one because it is a bit different.
MOD feel free to delete if you think it redundant.
Darn, a couple of nights ago I wrote a few paras on this but must not have pushed the post button.
The main thrust of my unsent post was - Why all the interest in exotic blade materials?
Wood with the exception of abrasion resistance is an almost perfect material. Wind turbine and wooden aircraft blades will obviously withstand wind speeds of hurricane force, they can be laminated into desired shapes and carved with hand tools. We used to sell a thin self adhesive stainless steel leading edge cover for our aircraft props, but abrasion was never a problem for our turbine blades.
Buckminster Fuller claimed that wood can be flexed to within 90% of its modulus of elasticity an infinite number of times without failing. There may be another material that equals this, I do not know of it. Wood is tremendously strong in tension, the fastening usually breaks before the wood fails. The greatest amount of stress on high speed turbine blades is radial. The big guys are different, they are not spinning fast so their main load is wind pressure.

Vertical axis blades pass through the wind shadow of the other blades and of the axis column, as they rotate, so I think the downwind argument is a bit thin. I have read that a downwind horizontal machine can set up harmonic vibrations as the blades pass the tower, under some conditions. I have no experience with downwind machines, so cannot comment.

It is late I must go and get rested up in case (not likely) for the pushups Al thinks he will win.

Al, if you get round one financing, I shall expect a handsome retainer and consulting contract, as the expert from afar.

Of course , Provided I've enough strength left from push-ups to write a cheque. I have some hope now that Flodesign have received $35M they will ,in the spirit of true ecorenovators , pass on the spare $10M to me for the ongoing development of my Megawatt Vawt in a shoebox.
A short technical input-I've been interested to observe that sod's law which states among other things " any newly erected turbine will immediately suffer no wind conditions " also applies to anenometers . My newly erested wind monitoring power predictor is just sitting looking at me.Al.

Hey Big Al, I was driving in Jacksonville today when I saw these 3 VAWTs at the side of the road. I thought they were just eye-catchers to get people to come into the nearby car dealership, but a Google search found the linked article saying they are real power generators. They were spinning like crazy and I would say the wind was about 10 mph. Wind: Eye-Catching Alternative Energy on Atlantic Blvd | Firstcoastnews.com | Top Stories Video: http://www.firstcoastnews.com/video/...id=51741642001

Patrick. Was aware of these windspires but many thanks for input. For some reason they and Mariah power have a bad reputation. One of the gurus Paul Gipe, wrote a very sarky article about them. Looking at them my only comment would be they look a bit flimsy. Unless the central axis is pretty strong I would n't see them standing up to strong winds. If they were spinning fast in 10mph wind they ought to be reasonable generators given a good design and I don't entirely understand why Gipe was so critical unless torque is very poor, altho this would n't alter the "flimsy" argument.
I'm hoping my several MegaW Vawt in a shoe box will be so efficient that it can be totally enclosed in the shoe box except for one (or at most two ) pinhole (s) on each side to allow limited amounts of wind through. In which case Nibs will have to do so many push-ups we won't need turbines. We'll just wire him up to generate a significant portion of the worlds' energy needs. Big Al

Well supposedly it costs about $10,000 per turbine and the output is about 2000 kWh/yr. At my rate of 12.6 cents/kWr that's a savings of $252/yr. 10,000/252 = 40 years for them to pay for themselves. So maybe that's Gipe's complaint. But it's not cost-effective for me cuz I won't be here in 40 years.