More support for merit order effect | 28 comments (28 topical, editorial, 0 hidden)

Re: Speaking of costs (none / 0)

Uh, yes. This should not come as an unbearable surprise to anybody who is even casually acquainted with the physics involved.

- Jake

Friends come and go. Enemies accumulate.

by JakeS (JangoSierra 'at' gmail 'dot' com) on Thu Mar 3rd, 2011 at 12:09:42 PM EST
[ Parent ]

Re: Speaking of costs (none / 0)

Wow. Such an "obvious" knowledge? Please elaborate. Is the wind speed so much higher in a vacuum cleaner? I have seen pretty fast rotating wind mills. What about a gearbox? That would take out as much rotation speed as needed.

by kjr63 on Thu Mar 3rd, 2011 at 12:45:26 PM EST
[ Parent ]

Re: Speaking of costs (none / 0)

Is the wind speed so much higher in a vacuum cleaner?

The pressure gradient is a lot steeper (on the order of a tenth of an atmosphere per meter, while the pressure gradients generating winds are less than a hundredth of an atmosphere per kilometer). How that translates to wind speeds is a bit out of my field, but I guarantee you that you will not get a kW out of a vacuum cleaner fan if you stick it in even a gale-force wind.

What about a gearbox? That would take out as much rotation speed as needed.

Yeah. That's what windmills do. Large blades, big gearboxes. That's what makes them expensive. The generators themselves aren't, AFAIK, the main cost.

- Jake

Friends come and go. Enemies accumulate.

by JakeS (JangoSierra 'at' gmail 'dot' com) on Thu Mar 3rd, 2011 at 01:59:09 PM EST
[ Parent ]

Re: Speaking of costs (none / 0)

From wikipedia:
http://en.wikipedia.org/wiki/Airwatt

Airwatt
An airwatt or air watt is a unit of power very close to the watt which is used for various vacuum cleaning systems, such as vacuum cleaners. The airwatt is derived from English units. ASTM International defines the airwatt as 0.117354 * F * S, where F is the rate of air flow in ft3/m and S is the pressure in inches of water. This makes one airwatt equal to 0.9983 watts.
The airwatt is useful measurement of vacuum power, since the power carried by a fluid flow (in the case of a typical house vacuum the fluid is air) is equal to pressure times volumetric flow rate. This could be a more useful figure than the electrical power drawn by the vacuum system's motor, since the efficiency of motor and vacuum systems varies.

If i understand correctly, this means that electric power is directly related to air flow = air speed. So if, you put a relevant rotor in the vacuum cleaner, you get 2000W. Should not be too difficult.

That's what windmills do. Large blades, big gearboxes. That's what makes them expensive. The generators themselves aren't, AFAIK, the main cost.

Hard to believe. Can a rotor and couple of gears rise price from 3e/MW to 80e/MW? I believe generator manufacturers are being screwed.

by kjr63 on Thu Mar 3rd, 2011 at 02:30:01 PM EST
[ Parent ]

Re: Speaking of costs (none / 0)

If i understand correctly, this means that electric power is directly related to air flow = air speed. So if, you put a relevant rotor in the vacuum cleaner, you get 2000W. Should not be too difficult.

No you won't. With a pressure gradient on the order of tenths of atmosphere per meter, you get a considerable loss from friction. You'd be lucky to recover 200 W from a setup like that.

Hard to believe. Can a rotor and couple of gears rise price from 3e/MW to 80e/MW?

And a tower. And grid connection. And transformers. And installation. And output governors. And you're converting a pressure gradient into electricity, which is a lot harder than converting electricity into a pressure gradient.

- Jake

Friends come and go. Enemies accumulate.

by JakeS (JangoSierra 'at' gmail 'dot' com) on Thu Mar 3rd, 2011 at 04:11:19 PM EST
[ Parent ]

Re: Speaking of costs (none / 0)

Similarly, you assumed that your generator would survive 8600 hours of continuous operation. Assuming that your average household vacuum cleaner is used for three hours every week, that translates to a lifespan of something like fifty years.

- Jake

Friends come and go. Enemies accumulate.

by JakeS (JangoSierra 'at' gmail 'dot' com) on Thu Mar 3rd, 2011 at 04:16:55 PM EST
[ Parent ]

More support for merit order effect | 28 comments (28 topical, 0 editorial, 0 hidden)

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