4 ms·

Rotors are tiny compared to conventional wind turbines. Even with six of them, just no comparison. Sure they harvest the wind much higher and it flys in circles

by borism 16y ago

Rotors are tiny compared to conventional wind turbines. Even with six of them, just no comparison. Sure they harvest the wind much higher and it flys in circles quite fast, but I'm not quite sure how they'll be able to generate 1MW with on of those production things. It has the wingspan of B737! It's a neat idea, but do benefits outweigh problems?

krakensden 16y ago
I was under the impression that most of the reason conventional wind turbines are so huge is so they can have the blades move slowly, to be more hospitable to local birds.
- jacquesm 16y ago
  That impression is completely wrong. The tip speed is what counts, the key governing factor is called the 'tip-speed-ratio', the apparent wind speed (as seen by the tips of the rotor) versus the real wind speed (as seen by an observer relative to the ground). Almost all windmills that want to be efficient have design TSRs somewhere between 6 and 8, and consequently, in a given wind they all travel about as fast at the tips. The design constraints are the speed of sound and the forces on the blade root as well as the tendency of the blade to start fluttering. It has absolutely nothing to do with birds. Birds will fly in to a stationary building just as easily as they'll fly in to windmills, it's rare but it does happen every now and then. The larger a windmill, the slower the blades will rotate. The reason why they are so large is because the power harvested by a windmill goes up with the square of the rotor diameter, many small windmills are more costly to maintain and operate than a single larger one. Right now the sweet spot is somewhere around 2MW and 80 meter rotors for best $/W.
  - erikpukinskis 16y ago
    The reason why they are so large is because the power harvested by a windmill goes up with the square of the rotor diameter Doesn't the Makani wings get around this issue by equivalent to a turbine with a massive wingspan and a wingtip that generates power, but without the rest of the structure?
    - jacquesm 16y ago
      The outer third of the blades account for roughly 60% of the total power generated by a windmill, the 'massive wingspan' would have to be normal to the direction of the wind, in order to say more about what Makani does or does not do there would have to be a lot more design data available than there is now. Windmills with 'just the tips' have been proposed and constructed, there are some good reasons to include the blade all the way to the root. Part of that is to stem vibration, also to help with rotor start-up and low wind conditions.
      - erikpukinskis 16y ago
        It is normal to the wind direction, that's clear on the site. From the way you're talking it doesn't sound like you bothered to even look at what they're doing.

by borism 16y ago

krakensden 16y ago

I was under the impression that most of the reason conventional wind turbines are so huge is so they can have the blades move slowly, to be more hospitable to local birds.

jacquesm 16y ago
That impression is completely wrong. The tip speed is what counts, the key governing factor is called the 'tip-speed-ratio', the apparent wind speed (as seen by the tips of the rotor) versus the real wind speed (as seen by an observer relative to the ground). Almost all windmills that want to be efficient have design TSRs somewhere between 6 and 8, and consequently, in a given wind they all travel about as fast at the tips. The design constraints are the speed of sound and the forces on the blade root as well as the tendency of the blade to start fluttering. It has absolutely nothing to do with birds. Birds will fly in to a stationary building just as easily as they'll fly in to windmills, it's rare but it does happen every now and then. The larger a windmill, the slower the blades will rotate. The reason why they are so large is because the power harvested by a windmill goes up with the square of the rotor diameter, many small windmills are more costly to maintain and operate than a single larger one. Right now the sweet spot is somewhere around 2MW and 80 meter rotors for best $/W.
- erikpukinskis 16y ago
  The reason why they are so large is because the power harvested by a windmill goes up with the square of the rotor diameter Doesn't the Makani wings get around this issue by equivalent to a turbine with a massive wingspan and a wingtip that generates power, but without the rest of the structure?
  - jacquesm 16y ago
    The outer third of the blades account for roughly 60% of the total power generated by a windmill, the 'massive wingspan' would have to be normal to the direction of the wind, in order to say more about what Makani does or does not do there would have to be a lot more design data available than there is now. Windmills with 'just the tips' have been proposed and constructed, there are some good reasons to include the blade all the way to the root. Part of that is to stem vibration, also to help with rotor start-up and low wind conditions.
    - erikpukinskis 16y ago
      It is normal to the wind direction, that's clear on the site. From the way you're talking it doesn't sound like you bothered to even look at what they're doing.