Comments by "seneca983" (@seneca983) on "Engineering with Rosie" channel.

  1.  @charlesbeaudry3263  "you need to consider the additional capital cost of doing this vs just staying on the grid, which entails no additional CAPEX" Yes, but the cost of PV has come down a lot. I think the return on investment is good enough in many (sufficiently sunny) places.
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  2.  @charlesbeaudry3263  "The bigger issue with renewables for them to become say 75% of the grid power is that it cannot be sustained." It might not be worth to invest in, say, PV that much but a lower percentage probably makes economic sense (in sunny places). If storage becomes more common, it makes a higher percentage make more sense.
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  3.  @charlesbeaudry3263  "You seem to think that it binary, either we go only renewables or we no renewables." Not at all. Whatever gave you that idea.
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  4. I think he understands it now even if he didn't before.
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  5. Is it possible to control the blade pitch passively? I mean, could the member that the blade is connected to be flexible such that it would bend with the wind and rotation to produce a closer to optimal pitch? Or would the wind tend to bend the blade to the wrong direction?
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  6.  @karora  Directly downwind with a static sail cannot produce a speed in excess of wind speed.
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  7. "For the car to move faster, its kinetic energy K2 MUST be greater than the kinetic energy K1 that it receives from that moving "mass of air"." No, it doesn't. It just needs to receive kinetic energy from a sufficiently large mass of air.
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  8. What do you mean? Interest has to be taken into account.
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  9.  @johnborton4522  If it were a turbine it could exceed windspeed if it were travelling against the wind. However, travelling downwind faster than the wind indeed requires a propeller as you said.
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  10.  @matthijsklomp  "No wind powered vehicle can travel upwind faster than the windspeed, only downwind." They can by the same logic as this cart can. It just works in reverse with wheels being powered by a turbine rather than the reverse.
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  11.  @matthijsklomp  "Explain to me what powers the cart if the blades were powered by the wheels." The propeller pushes the cart forward and that allows the wheels to power the propeller. The wheels powering the propeller does cause a decelerating force but that can be less than the accelerating force from the propeller because of the movement of the air relative to the ground.
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  12.  @matthijsklomp  "You can simply view this vehicle as wind turbine on wheels with the turbine driving the wheels" No, it's the other way around. The wheels have to power the propeller/turbine when going downwind. You can even see in the videos that the turbine spins the opposite way from what it would be if the wind was turning it. However, a turbine powering the wheels would work if the vehicle was were going against the wind.
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  13.  @julianjenkins5553  "so that it is not traveling directly downwind" But note that this cart could exceed the wind speed while travelling directly downwind. A boat using a static sail cannot do that.
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  14. I was going to mention this but didn't have to.
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  15.  @shainshoesmith8840  The pressure difference alone wouldn't cause air to move because the pressure gradient simply matches gravity. Having bigger or smaller opening won't change this.
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  16.  @deadeye_john  I don't think you can just inject glue inside solid material.
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  17.  @deadeye_john  Yes both, at least to my knowledge.
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  18.  @deadeye_john  Surely it can't prevent cracks from forming. A (cured) glue is a material like any other. It's not magically immune to cracking.
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  19. The maximum speed depends on friction and air resistance so it's not simple to calculate.
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  20.  @Bennyboy-dog  Waste treatment is probably not any different than for more traditional reactors. Same procedures can be applied.
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  21.  @Bennyboy-dog  How has waste been badly managed. I'm not aware of problems (at least not in high-income countries).
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  22.  @Bennyboy-dog  I have heard of the plastic waste in oceans (though it's not a literal island) but I meant that specifically nuclear waste is to my knowledge generally well managed (excluding in poorer countries like Russia). The volume of waste, or at least spent fuel, is pretty low compared to the amount of power generated. The low volume makes it easier to manage than other waste types which have much higher volumes.
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  23.  @Bennyboy-dog  "Radioactive waste is cumulative over time time" Even with cumulation the volume is really small. You can e.g. search for image labelled "45 years worth of Swiss nuclear waste is not enough to fill a single room". The difference to other forms of waste is enormous. Even one day worth of plastic waste (in Switzerland or elsewhere) far surpasses the amount seen in that picture.
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  24. It's taking kinetic energy from the wind and therefore the laws of thermodynamics aren't being violated.
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  25.  @duncangroenewald  My point was that the first law of thermodynamics, i.e. the conservation of energy, is not being violated because the energy is extracted from the wind.
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  26.  @duketoby0  "how the conservation of energy is respected here" The propeller decelerates air (relative to the ground). Therefore the air is losing kinetic energy and the cart is gaining some.
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  27. "yet the propeller proceeds to accelerate" To me it looks like the propeller isn't accelerating but rather the earlier frames in the video are just slowed down.
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  28. It's not because it extracts energy from the wind.
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  29.  @PranavSinganapalli  It's not a perpetual motion machine.
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  30. Stirling engine works on a temperature difference which is a bit different.
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  31. "One thing that confuses me is talking about wheel speed relative to the ground." It's just the speed of the wheels' axis of rotation relative to ground. It implies how fast the wheels rotate assuming a good grip.
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  32.  @toddmoore9841  "Once the car reaches windspeed, the only energy it has to turn the wheels is the kinetic energy from the vehicle itself." No, the propeller is decelerating the wind (relative to the ground) so the cart is still getting kinetic energy from the wind.
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  33. "Sure, I would like rooftop solar PV, but utility scale is better in terms of LCOE." I'm not so sure about that. One advantage of PV is that it doesn't come much more expensive per unit in smaller installations. Also, rooftops don't have much other high value usage whereas large solar farms have to pay for the land that they use and therefore only make sense where low-value land is available. Also, in addition to avoiding transmission losses rooftop solar can be helpful during a power outage.
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  34. It's not a closed loop because the propeller decelerates air (relative to the ground).
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  35. No.
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  36. "Trained technicians can burn hydrogen for electricity and heat" I don't think that makes sense. Why not just burn the natural gas directly for electricity and/or heat?
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  37.  @Ikbeneengeit  Pipelines are cheaper than ships, at least for sufficiently large volumes. There's a reason why they're used. The more expensive option of using ships makes hydrogen from North Africa seem even less viable. Just building more electric transmission capacity seems a much simpler option (though it's not clear to me whether North Africa even has a sufficiently big advantage in electricity generation). The 30% round-trip efficiency of hydrogen is pretty dismal when compared to just using electricity directly when possible.
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  38. "yes there was base load and in the U.K. anyway, that was nuclear which is inflexible. Coal, hydro and gas are flexible" Many coal plants are slow to ramp up and down. They can easily take hours or more to make a cold start. "it is robbing Peter to pay Paul" No, it's not. It's a genuine benefit to shift demand to the times when there's more supply.
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  39.  @ronalddump4061  That's not true. Wind relative to ground is crucial for it to work.
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  40. It's taking kinetic from the wind so no laws of thermodynamics are being violated.
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  41.  @user-fx2oo3bi9c  "kinetic energy from wind 🌬️🍃 and travel faster than wind" Yes. That doesn't violate the laws of thermodynamics.
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  42.  @user-fx2oo3bi9c  But 100% efficiency isn't required here. It's enough that dissipative losses are smaller than the amount of energy extracted from the wind.
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  43.  @user-fx2oo3bi9c  This vehicle doesn't break any such limitations. It just takes energy from the wind, that's all.
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  44. "Does it mean a solar sail can travel faster than light?" No, that would mean going backwards in time in some inertial frame. Also, reaching the speed of light would require an infinite amount of energy.
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  45.  @rcmrcm3370  "my bet would be noise, as they would be using DC which had to be inverted" That cannot be the reason because "normal" wind turbines have their output converted to DC and then inverted back to AC.
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  46.  @EngineeringwithRosie  OK, I guess that makes sense. I was thinking of e.g. the turbines at 2:45. I thought the blades were actually shaped like that.
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  47. I don't think it does. Rosie mentioned that as turbines get bigger the rotational speed gets lower meaning the velocity of the tips of the blades doesn't increase.
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  48. Why are the tips of the turbine blades bent backwards in the more modern turbines?
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  49. If the wind stops it will also come to a halt after a while.
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  50. Here's one way to think about it. From the cart's perspective both the ground and the air are moving backwards (once wind speed has been exceeded). However, because of the wind the air is moving backwards slower than the ground (from the cart's perspective). This is crucial and allows the forward force generated by the propeller to be greater than the backward force from the grip of the wheels.
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