Hello dear friends!Wind turbines rotate at low angular velocity
because their blades are huge, around R=100m these days. Though, generators prefer a high azimuthal speed that increases the voltage hence power at identical current and ohmic losses. Two solutions have competed for decades:
- A gear increases the angular velocity for a fast, small, cheap and efficient generator. But the gear for huge torque is costly and needs maintenance.
- A wide short thin generator, like D=10m, rotates at the turbine's speed. Less maintenance, but the generator is costly and it can waste 10% of the harvested power.
Vestas makes some fuss presently by announcing a superconducting generator. Logic: accept small voltages because high currents have no drawback.
This option differs so much, with a small but costly generator of unknown reliability and maintenance, that comparisons are difficult.
I should like to remind the electrostatic machines
I described over a decade ago. One may try the wayback machine: http://www.physforum.com/index.php?showtopic=26432 https://lofi.physforum.com/Electrostatic-Alternator_26432.html https://saposjoint.net/Forum/viewtopic.php?f=66&t=1684
Their are powerful according to my figures, nothing intuitive nor banal for electrostatic devices. They have essentially no ohmic losses, so they accept a slow rotation with excellent efficiency.
Now, I suggest induction machines with chilled metal conductors
as one more alternative. Copper and aluminium resistivity drops /10 around 80K and /100 around 45K, so do the ohmic losses. https://nvlpubs.nist.gov/nistpubs/Legacy/TN/nbstechnicalnote365.pdf
[5MB] pages 40 and 20
That is, instead of dissipating at 300K 10% of the harvested power, the conductors would dissipate 1% at 80K or 0.1% at 45K. Carnot limits the cooler's efficiency to 1/3.8 and 1/6.7. If the cooler is no worse than 1/2.6 or 1/15 of Carnot's limit, chilled metal brings a net power advantage. The power advantage can then be traded for size reduction.
The machine is more complicated than at room temperature, but far less than at superconductor temperature. Big superconducting devices, for colliders or NMR, still operate at 4K presently: the brittleness of 77K superconductors must stop the designers.Other applications
need slow machines and considered superconductors, for instance orientable propulsion pods for boats. Chilled metal seems an alternative for them.
Marc Schaefer, aka Enthalpy
[I will need your help for liquids with high permittivity that insulate very well, more to come.]