How to Spot a Psychopath

Regarding the widely reported "new discovery" of "WiTricity", wireless electricity transmission, as mentioned in Austenite's comment the other day:

Bollocks.

The people at MIT who came up with this "new invention" would be the first to tell you that the basic technology involved in it isn't new at all. It's just an electrical transformer with a large air gap between the primary and secondary coils. This, inescapably, means its efficiency gets worse the further away the receiving device moves, and it wastes energy heating up conductive things in the area.

I'm sure that the MIT research is doing clever things with the control and detection systems; it may even result in real useful products some time quite soon. It's quite possible that at some point in the future we will indeed have charging pads we can put various devices on to be inductively recharged. The same goes for the bigger versions envisaged by the WiTricity idea, where a laptop will work without a power connection anywhere in a room; to make that work, you'll probably have to build your primary coils into the very walls of the room.

It's not even out of the question that such an arrangement could be used to power transportation systems, though we'd need to start making our cars out of plastic before it'd be workable.

The reason for this is tied to the main problem with these sorts of systems, which are proposed about twice a year by some crank who thinks he's the one who can do what Tesla didn't. The problem is that if you put a conductive loop in the field, like a wristwatch with a metal band, it'll eat most of the power output and get hotter and hotter. It's that problem which I presume the MIT researchers are working on, though it's hard to figure that out from the press coverage.

That big problem, plus the crippling loss of efficiency as your secondary coil(s) get further away from the primary, is why inductive/magnetic "wireless electricity" for powering normal appliances, streetlights and most other straightforward everyday things still seems to be a complete non-starter.

(As usually happens when a subject that's covered in first-year Electrical Engineering comes to the attention of the masses, there's a decent Slashdot thread about all this. I've also written about inductive chargers before, here and here.)

I'm looking forward to some really dumb mutations of this idea over the next few weeks. Given the well-established inability of the "electrosensitive" crowd to tell the difference between milliwatt radio waves and ionising radiation, the notion of "electricity beams" popping up all over the place should make them go absolutely spare.

If we can't make these idiots see sense, we should at least attempt to gain as much amusement from them as we can.

Using a roof ventilator as a wind turbine (I think this is the home site of the video creators) is a neat idea. It'd really work, and make a great science fair project - just hook up a little brush motor to the rotor, connect an LED (or several) to it, and see how much wind you need before your LED pops.

This design will not, however, really give the advertised "cheap" power on a dollars per watt basis, since I doubt you could put more than a few watts of generator braking on one of those roof turbines without stalling it in anything short of a gale.

A roof-ventilator turbine could still be useful for charging a battery to run minor stuff occasionally, like a radio and a small light in a shed somewhere where the wind blows but the sun doesn't shine much. Or as a supplemental charger for a system that has a solar panel as well. Plus, you could still use it as a roof ventilator.

There's a reason why you don't see a lot of vertical turbines, though. Yes, they're simple - most importantly, you don't need a mechanism to make them face into the wind, and power take-off is very easy when you've got a simple vertical shaft to work with - but they just don't work very well. This is not just because they don't suck as much energy out of the air as a propeller-type turbine does (see also: Paddle-Wheels, And Why We Don't Use A Lot Of Them Any More), but also because they usually don't turn fast enough.

Slow-turning turbines can be good if you want to direct-drive a pump or something, but generators usually want more RPM, and gearing up a wind turbine is a great way to make it stall.

There are other vertical turbine designs that're very quick to make and have a lot more blade area for the wind to push on. The "Savonius" versions made from oil drums cut in half (technically, roof ventilators are a multi-bladed Savonius turbine) are the price/performance winners for small jobs, I think. But the world is not short of other ideas.

There are also commercial vertical turbine designs, the domestic-sized versions of which have a tendency to be scams.