Taken out of context, it was not clear that the W/m² refers to the land. It is meant to be reflective of the section of the Earth's surface that is occupied by the towers to the max practical density. The larger the propeller, the larger the radial and axial distance between adjacent towers. Thus the 1 W/m² is universal and it comes from wind farms in operations, not prognosis. Big difference.
The 1 W/m² is the measured, NET output of the sites that had operated long enough (several years, preferably) to provide annual averages. The largest number I ever saw was 1.25 - the best location. Many more sites must be yielding less than 1 W/m² The paper is about the land area for a watt of power form various sources. And although the land occupied by the wind farm can potentially be used for growing something (not cities, though) that is a different subject. Stan . ----- Original Message ----- From: John M. Steele To: U.S. Metric Association Sent: 09 Sep 05, Saturday 18:46 Subject: [USMA:45742] Re: [Fwd: Energy and power] I am having trouble relating to Stan's figure of 1 W/m². However, the usual development of the equations looks at the swept area of the rotor. The machine can only extract a fraction of the wind power, 30% overall being GOOD.. This page gives a reasonable development of the equations: http://www.awea.org/faq/windpower.html The government has maps of the total power available in the wind (NOT the extractable fraction). The wind distribution is usually approximated as a Rayleigh function which gives a first order model of variability, based on just average speed. There are better models with additional parameters. Maps: http://zebu.uoregon.edu/ph162/images/wpower1.gif Obviously, it is important to put turbines where the winds are, possibly overriding aesthetic and environmental concerns. If you put them where the wind ISN'T, the power ISN'T either. In a good location, they may or may not make economic sense; in a bad location, they clearly don't. --- On Sat, 9/5/09, James R. Frysinger <j...@metricmethods.com> wrote: From: James R. Frysinger <j...@metricmethods.com> Subject: [USMA:45741] Re: [Fwd: Energy and power] To: "U.S. Metric Association" <usma@colostate.edu> Date: Saturday, September 5, 2009, 4:43 PM Stan, You provide a figure of 1 W/m2 for a quality site. Is that area in the denominator the land area, the blade surface area, or the blade-swept area? You've raised many valid points which one will not see discussed much, if at all, by green-wind aficionados. Jim Stan Jakuba wrote: > > Of course they will never pay for themselves (otherwise they would have been all over the place paid for by private money). Their electricity also will not get relatively cheaper when oil prices go up. Nor will wind mills reduce "foreign oil" consumption. Electricity production is unrelated to oil in the U.S. But oil prices impact greatly the cost of the mills production, their transportation and erection. Here is a pertinent section from my paper: > > Below is a balance sheet of an EU town’s wind farm. The town installed two wind mills, 600 kW name plate each, and ran them long enough to assess their potential. Unlike the usual optimistic projections one reads in “green” magazines, this is a record from a user, and it was obtained after the plant was in routine operation. > > > > Installed power (name plate) 1200 kW > > Power actually measured over a year 116 kW > > Utilization (capacity) factor 9.7 % > > Useful life of the structure 20 years > > Electricity produced in that life span 75.7 TJ > > Sale of that electricity 56,760,000 > > Note: Supported by government subsidies, the town’s kWh rate was higher than the market price. > > Purchasing price 60,000,000 > > Note: This cost was subsidized per standard practice. The town records list only the paid amount. > > Net gain (loss) at the end of the useful life (9.5) % > > That percentage is based on the assumption that the repair and maintenance cost was zero, taxpayers’ subsidies will last, and taxes forgiven. > > > > Notice that if the town had invested the purchase amount at a reasonable interest, say 5.5 %, it would have had 180,000,000 by that 20th year. Instead, in addition to the pain of the loss, the town will be facing the pain of financing the cost of dismantling and disposal of the mills. Fortunately, the metallic parts should bring scrap money. And the massive foundations may potentially be left in place and support new mills should the town decide to continue selling electricity. > > Source: Town Hall records of Jindrichovice pod Smrkem. > > > > The tabled capacity factor is less than 1/2 the more recently encountered numbers. This does not mean that the two turbine/generators were inefficient. The factor provides an indication of how the propeller power is matched to the generator power. If the generator is sized for the maximum (and rarely occurring) wind speed the capacity factor will be low. And vice versa, a mill with an “undersized” generator will yield a high capacity factor. But the 24/7 average amount of electricity may actually be lower with the latter for the generator’s inability to utilize the high velocity winds. Most wind mills have about the same efficiency, and it is close to the theoretical limit for both the blades and the generator. The amount of electricity generated is simply a function of the size of the mill, time, and the wind velocity. A wind farm on a “quality” site yields about 1 W/m² net output and that number is essentially independent of the size of the machinery. A site with highly fluctuating wind will produce less than 1 W/m² for it may be shut down at high winds, and, at low winds, its output drops with the 3rd power such as to just 1/8 if wind velocity drops to 1/2. > > > > Stan > > > > > ----- Original Message ----- From: "John Frewen-Lord" <j...@frewston.plus.com> > To: "U.S. Metric Association" <usma@colostate.edu> > Sent: 09 Sep 05, Saturday 02:18 > Subject: [USMA:45737] Re: [Fwd: Energy and power] > > >> >> 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" <j...@metricmethods.com> >> To: "U.S. Metric Association" <usma@colostate.edu> >> 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 /<j...@metricmethods.com>/* wrote: >>>> >>>> >>>> From: James R. Frysinger <j...@metricmethods.com> >>>> Subject: [USMA:45733] [Fwd: Energy and power] >>>> To: "U.S. Metric Association" <usma@colostate.edu> >>>> 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 >>> >> > > > > -- James R. Frysinger 632 Stony Point Mountain Road Doyle, TN 38559-3030 (C) 931.212.0267 (H) 931.657.3107 (F) 931.657.3108