Can never be 100% efficient. or else you would be left with still air behind the blades, thus blocking the incoming. Usually significantly less the 50% efficeincy to allow the air after the blades to have some energy left to carry it away.
around 1-5% actually.
If you take the actual kinetic energy of teh whole wind mass up[ to the blade tip hight over the windfarm area.
If it were 50% the windmills downwind would stop turning.
In message , Grimly Curmudgeon writes
my coat has left without me ...
I don't believe the Darius rotor is more efficient, but the multi-directionality is an advantage. Another attraction is that in principle it could be cheaper to build. Numerous attempts have been made to design a practical Darius rotor, but none has taken off (so to speak). One major problem with the design is that the blades experience oscillating loads as they rotate - on half the cycle to force is towards the axis, on the other half it is away from it. This tends to cause fatigue failures in the blades. (I speak with feeling: I am still a shareholder in a more-or-less defunct company that was started with the aim of developing a commercially viable Darius rotor.)
Hopeless efficiency. Extracting energy from the wind requires use of airfoils and very careful attention to aerodynamics.
Or even energy. B-)
I doubt 6kW (which is no doubt the maximum rated output) would be enough to keep half the lights on in a Tesco. They'd save *far* *Far* more energy by not having the so called 24hrs shopping. I say "so called" 'cause the one time I did want to shop late at night I went to one of these 24hr Tescos and it was shut...
They would still have the lights on for the shelf stackers though...
I doubt it takes all night to restack the shelves, it appears to be a non-stop process when the store is open. Shelf stackers don't need the lighting level that is there for the customers either, say 75% would still be ample. I can't imagine that any of these 24hr stores get many customers past midnight to say 0600, probably depends on location though but that comes down to opening when there are customers about, like early or late to fit with shift changes at a large local employer or nearby market.
I used to not infrequently end up in Tescos in Canley about the middle of that time bracket. Granted, its not going to be as busy as 11 o'clock on a Saturday morning, but I certainly wasn't shopping alone.
The Tescos near my parents was originally 24-hours when it opened, but went to "normal" opening hours after a while due to lack of late-night custom (which doesn't surprise me where my parents live). So they don't keep them open on some sort of principle - those that open 24-hours do so because it's economically worth it.
Pete
Some 24 hour supermarkets in Germany (I think?) had 'singles nights' where you could shop for food and friends at the same time...
Sounds like you could go out to buy some Jam Tarts and end up with a fruity one.
G.Harman .
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.