I have no idea if that is true. However, they are generally reported based on the maximum capacity of the associated generator. That is misleading as that level of power is rarely generated. Most turbines require a wind of 14 m/s to reach rated power. One of the few caseswhere wind in meters per second is used, because it doesn't sound so bad. In other ways of expressing it, a steady wind of at least 30 mph is required, a Beaufort scale force wind, or a near gale. In the US, small craft warnings are posted when numerous gusts exceed 25 mph. As wind power is proportional to the cube of speed, output falls rapidly with lower winds. 25 to 33% of rated power is often estimated as an annual average, but many installations fall short of this, and numbers of 20% and lower occur at many installations. This requires much larger capacity than the local area's electric consumption, and there will still be lulls in the wind which must be met by spinning reserves at fossil power plants. By definition, spinning reserve is consuming fuel (but less than if it were actually generating at full power).. The spinning reserve fuel requirement should be added to the manufacturing energy (or customers should be taught to go without power when the wind dies). Installation decisions should be based on the average annual power delivered, not rated power, and the promises made beforehand reviewed after completion.
--- On Sat, 9/5/09, John Frewen-Lord <[email protected]> wrote: From: John Frewen-Lord <[email protected]> Subject: [USMA:45737] Re: [Fwd: Energy and power] To: "U.S. Metric Association" <[email protected]> Date: Saturday, September 5, 2009, 2:18 AM I was once told by a very experienced engineer, involved in wind turbine design, that the energy used to manufacture all these devices can actually exceed the energy they will produce over their lifetimes. I haven't worked any numbers out for myself, but it would be interesting to see if he is right or not. John F-L ----- Original Message ----- From: "James R. Frysinger" <[email protected]> To: "U.S. Metric Association" <[email protected]> Sent: Saturday, September 05, 2009 1:27 AM Subject: [USMA:45736] Re: [Fwd: Energy and power] > > Right you are, John! I had the conversion factor for watt hour in my head and > forgot to apply the value for the prefix. > > Ah, well, if Rich Leventhal picks up on that we'll know that he's done some > studying. And if he replies, I'll give him that correction. > > The hype on this device is what you say and more. This is what drives me nuts > about the wind and solar energy crowd. They love to quote peak values with no > mention of the calm spells and night hours. If the difficulties of > integrating such sporadic sources into the distribution grid are addressed at > all, they are mentioned only in passing. By the time one looks at storage > needs to smooth out the "wrinkles", the capital costs rise many times over > the advertised capitalization figures for the raw devices. > > As Kermit said, "It's not easy being green." > > Jim > > John M. Steele wrote: >> Jim, >> You missed a factor of 1000 somewhere. 1 kWh is 1000 W for 3600 s, hence >>3.6 MJ. >> In a drivethru application, this might hit 2 kW instantaneous power, but >>the window will have a significant transaction time severely limiting the >>average power. >> He, of course, may have slightly different numbers, but my estimates are an >>average vehicle with mass 2.5 t, driver accelerates to 2 m/s in a stop-and-go >>line and needs to stop at the window, where he will have a 60 s transaction >>to receive his food, pay, receive change >> Kinetic energy, (½mv²) is >> 0.5* 2500 kg * (2 m/s)² = 5000 J >> If the car stops in 2 s, 2500 W would be generated during that period. >> However, with a 60 s transaction at the window, the average power is 5000 >> J/60 s = 80 W more or less. Even this (useless) level of power assumes 100% >> efficiency, so real world results will be lower. >> Assuming a line of cars awaiting their turn at the window, perhaps one >>device for each waiting position in line could improve this somewhat. I >>don't see it making a lot of power. Especially if anyone is stopped in the >>wrong place and everybody has to use their real brakes. >> >> --- On *Fri, 9/4/09, James R. Frysinger /<[email protected]>/* wrote: >> >> >> From: James R. Frysinger <[email protected]> >> Subject: [USMA:45733] [Fwd: Energy and power] >> To: "U.S. Metric Association" <[email protected]> >> Date: Friday, September 4, 2009, 2:44 PM >> >> >> I recently posted this email to Rick Leventhal at FoxNews.com. >> >> Jim >> >> Dear Mr. Leventhal, >> >> I have just finished reading your online article >> N.J. Burger King Testing Energy-Producing Speed Bump >> http://www.foxnews.com/story/0,2933,546512,00.html >> posted on FoxNews.com. >> >> In this article you have made an error that detracts significantly from >> your report. You apparently confused the two distinctly different >> quantities energy and power. Power is the rate at which energy is >> produced, used, or transferred. Think "power equals energy divided by >> time". Conversely, "energy equals power times time". >> >> In your article you state, "That force turns gears inside, generating >> 2000 watts of electricity instantaneously, according to the engineers >> who designed it." The implication is that some amount of electrical >> energy is produced in a short period of time. But energy is measured in >> joules (J), not in watts (W). In the electrical utility industry, they >> often use kilowatt hours to measure energy; a kilowatt hour is equal to >> 3600 joules, or 3.6 kilojoules (kJ). >> >> The watt (W) is used to measure power. It is defined to be 1 J/s. Let's >> assume that object 1 transfers 1000 joules (1000 J) of energy over the >> time span of 1 second (1 s) to object 2 and this generates electricity >> with 100 % efficiency. The power of this generation event would then be >> 1000 J divided by 1 s or 1000 W. If instead the transfer of energy and >> energy production took 0.5 seconds, the power level would be 2000 W. Or >> if the transfer and generation took 2 seconds, the power level would be >> 500 W. All of these would of course be the average power levels during >> the time span of the interaction; between interactions the power level >> would be zero. >> >> The way you should have worded your sentence would be of the form, "That >> force turns gears inside, generating an average of 2000 watts of >> electrical power during the time span of the energy transfer, according >> to the engineers who designed it." >> >> The website for New Energy Technology states: >> "All vehicles in motion possess kinetic energy. The amount of >> kinetic >> energy a vehicle possesses is based upon the vehicle’s speed and weight. >> The faster the vehicle is moving and the more it weighs, the more >> kinetic energy it possesses." >> It would have been more informative if you had given us a typical value >> for interaction time and the power produced during that span of time OR >> a typical value for the amount of kinetic energy delivered and the >> amount of electrical energy produced for some typical car and speed >> circumstance. >> >> I encourage you to study the difference between energy and power, and >> the units used to report them, before writing anything else that uses >> them in the discussion. >> >> regards, >> /s/ >> >> -- James R. Frysinger >> 632 Stony Point Mountain Road >> Doyle, TN 38559-3030 >> >> (C) 931.212.0267 >> (H) 931.657.3107 >> (F) 931.657.3108 >> >> >> >> >> >> -- James R. Frysinger >> 632 Stony Point Mountain Road >> Doyle, TN 38559-3030 >> >> (C) 931.212.0267 >> (H) 931.657.3107 >> (F) 931.657.3108 >> > > -- James R. Frysinger > 632 Stony Point Mountain Road > Doyle, TN 38559-3030 > > (C) 931.212.0267 > (H) 931.657.3107 > (F) 931.657.3108 >
