21 replies to this topic

[DaveMac]

grumpyhack, on Jul 1 2009, 05:40 PM, said:

Surely methane power generation must be an option with all the sh*t that 180,000 people produce.

I'm sure each longdrop could power its individual cubicle lighting / fresh air fan !

[mikeb]

kerplunk, on Jul 1 2009, 03:47 PM, said:

uh ok I'll have to think about that one

If you're old enough to remember dynamos for lighting on bikes: riding the bike with the lights turned off required little extra effort but turn the lights on and you need lots more grunt. The input power needed is always going to be the output power demanded plus all losses such as friction, copper loss, mechanical/gearbox losses and so on. The overall design efficiency will obviously be as high as practicable so the losses should be relatively small when compared to the maximum output power and therefore providing the output power demanded is near-zero, the input power to turn the thing will be minimised.

Having said that, it also depends how it was being done. In principle a motor and generator are the same machine of course however each is obviously optimised for the relevant task. Simply applying power to the generator and effectively using it as a motor to turn the rotor may well be possible providing the gearbox can be back-driven but it would certainly be *very* inefficient compared to normal use. However, if it was just a mock-up (and the more I think about it, the more I don't think it was actually big enough to be the real thing and it also seemed to be turning at a near-constant speed regardless of apparent wind speed) then the chances are it was a small motor (rather than the normal mechanics that would be expected at the head of the tower) just turning the rotor and nothing else. The power required to do this would therefore be very small indeed I reckon and could no doubt easily be sourced from a solar panel together with backup batteries if expected to run 24/7. Any wind would also assist turning the rotor as well of course especially so if there was no other significant mechanics or load to consider.  If it wasn't for the fact that I think there were periods when there was no apparent wind but it was still spinning, I would have suggested it was perhaps simply a tower with a rotor on top acting like a kiddies windmill ... and doing nothing much else.

Edited by mikeb, 01 July 2009 - 11:52 PM.