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 <[email protected]> wrote:
From: James R. Frysinger <[email protected]>
Subject: [USMA:45741] Re: [Fwd: Energy and power]
To: "U.S. Metric Association" <[email protected]>
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"
<[email protected]>
> To: "U.S. Metric Association" <[email protected]>
> 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"
<[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
>>>
>>
>
>
>
>
-- James R. Frysinger
632 Stony Point Mountain Road
Doyle, TN 38559-3030
(C) 931.212.0267
(H) 931.657.3107
(F) 931.657.3108
