[A-List] The Energy Challenge 2004 - Wind

[Bill Totten <shimogamo@xxxxxxxxxxxxx>]

by Murray Duffin

[Although the technical level in the section on "intermittency" of the following
article might seem daunting, I am posting the article anyway because wind energy
is important in the overall discussion of the Energy Challenge.  Bill Totten]

The Energy Challenge 2004 - Wind

by Murray Duffin

http://www.energypulse.net (October 13 2004)


In addressing the declining availability of fossil fuels, and with nuclear
energy less than popular, the remaining choices are energy efficiency and
renewables. Fortunately, they are complementary choices and have the added
virtue of being carbon free. Renewables include hydro, wind, solar, bio-fuels,
geo-thermal, wave, and tidal energy. Of these, wind, solar, geo-thermal, and
wave/tidal are abundant, but only wind is currently economical and easy to
harness.

Whatever you think you know about wind, especially the negatives, if it was
based on data and analysis prior to 2000 you can be pretty sure it's wrong.
Wind has made enormous strides in the last fifteen years. In 1992 the average
size of installed wind turbine was 200 kilowatts. In 2002 it was 1.4 megawatts.
Now almost all units being installed are over 2 megawatts. Total world installed
wind energy in 1992 was 2.5 gigawatts. By 2003 it had reached 40 gigawatts,
a compound annual growth rate of 30% per year.


How Much Energy

Probably the best early data on the total USA wind resource is the 1993 report
found at www.nrel.gov/wind/potential.html. This report estimated total potential
for 25% efficient turbines, with 25% losses, and average 50 meter hub heights,
and made exclusions for environmental, urban, and agricultural purposes. The
result was that about 15 quads of equivalent fossil fuel energy could be
replaced by class 5 to 7 winds. Adding class 4 winds, which were marginal
at that time, raised the potential to greater than 60 quads. Most recent
Texas wind farms are in class 4 areas.

This report was based on 1991/92 technology, when the largest envisioned
turbines were 300 kilowatt and blade rotation speeds were such that considerable
areas were excluded for environmental reasons, such as bird kill. Best wind
speeds were 15-25 miles per hour and it was also assumed that only 20% of the
actual wind energy per square kilometer could be converted to electricity.

Now for 1.5 megawatt turbines with hub heights near 80 meters, Archer and
Jacobson <1> find class 3 winds are economic, and are available for about 20% of
the lower 48 land area. ["Lower 48" means the United States excluding Alaska and
Hawaii.] They also have found that near shore coastal areas with suitable winds
cover more than twice the shoreline of the 1993 paper. Today turbines being
installed are up to 3 megawatts, and up to 5 megawatts are in development. Blade
rotation is much slower. Efficiencies are now above 30% and losses below 15%.
Productive wind speeds are now in the class 3 range. Conservatively, total lower
48 available wind energy with 2004 technology is in the order of 150 quads,
fossil fuel equivalent, or 50% more than total USA current primary energy demand.
We are unlikely to want to harness more than 1/4th of that between now and 2050.


Intermittency

The primary problem usually raised by wind opponents is intermittent
availability with significant daily, monthly, and seasonal variations.
Probably the first person to address this issue systematically was Gregor
Czisch for Western Europe. He analyzed 3 hour interval recorded wind speed
(at ten meter average height above ground) for all areas that could provide
1500 or more full load hours per year, that is, minimum 17% full load factor.
His analysis shows that:

 5 minute correlation is near zero at 20 kilometers
12 hour correlation is near zero at less than 1000 kilometers
24 hour correlation is near zero at 1800 kilometers
monthly correlation is near zero at 2500 kilometers.

Of course at the eighty meter hub height of a 1.5 megawatt turbine the full load
hours and correlation distances would improve significantly. Archer and Jacobson
(A&J) <1,2>  found that for a small area only 500 by 700 kilometers centered in
Kansas, averaged over eight wind-farm locations, the incidence of zero power
wind was zero.

One turbine might be expected to produce 30% of rated kilowatt hour during a
year. Using the 8 wind farm curve of average windspeed vs percent of time
available, and assuming the ratings of the NEG/Micon NM82/150 turbine (nominal
windspeed of 12 meters per second, cut in windspeed of 3 meters per second and
cut out windspeed of 18 meters per second) the eight wind-farms produce 85.5%
of nominal annual output and operate at or above nominal 38% of the time.

However this estimate understates probable performance for three reasons:

1. A&J used measured wind speed increase from ten meters to eighty meters
on a few sites, generated a formula to be applied to all other sites where
measurements at eighty meters were not available, and generated their curve
using the estimated eighty meter windspeed. Because wind speed increase is not
linear with height, and because power is proportional to the cube of windspeed,
the upper half of the swept circle has more weight than the lower half.
The "virtual" windspeed at the hub is higher than the estimated.

2. Turbine manufacturers specify performance parameters conservatively.

3. Measured upper level wind speeds tend to be slightly higher then estimated.

Therefore, as a conservative adjustment, to better reflect expected performance,
the A&J <8> wind-farm curve was shifted right by one meter per second and
performance recalculated. With this adjustment, for the selected turbines, the
eight wind-farms can be expected to produce 111% of nominal energy in a year,
and would be at more than 100% of nominal output 48% of the time. With wind
turbine costs now at about $0.90 per watt installed, and amortization over
thirty years at 6% the direct cost of electricity at nominal output would be
1.91 cents per kilowatt hour. If we increased the number of turbines by 33% the
cost of electricity at nominal output would go to 2.54 cents per kilowatt hour,
we would be at more than nominal output 58% of the time and we would generate
147% of nominal output energy per year.

If we added hydrogen fueled gas turbine backup at 40% of nominal power at a
capital cost of $.60 per watt financed at 6% for thirty years we would be at
more than nominal output 75% of the time and nominal electricity would go up
to 3.14 cents per kilowatt hour. Total output would go to 157% of nominal. If
the surplus energy is used to generate and store hydrogen at 75% efficiency
(feasible with existing electrolysis and compression equipment), and the backup
burns hydrogen to generate electricity at only 40% efficiency (greater than 50%
should be possible with a CCGT), there would be at least 70% more hydrogen than
needed to run the backup generator. The cost of the hydrolysis, compression and
storage might push the direct cost for total nominal electricity to 3.5 cents
per kilowatt hour. This cost is better than coal or natural gas at 2004 prices.

Now extend this approach to even more efficient 3 megawatt turbines and perhaps
three times as many wind-farms spread over say 500 by 2000 kilometers and
nominal power will be available close to 100% of the time, so the problem of
intermittence can readily be overcome. However, to get there utility management
would have to think in whole system terms and would have to cooperate over a
large interstate geographic area, a couple of things they are not accustomed to
doing.


A Possible Surprise

If it will scale up an even more exciting potential has been illustrated by
a ninth grade Canadian girl. <6>  A dual rotor turbine has the potential to
harness lighter winds, lowering cut-in and cut-out speeds, and greatly
increasing the harnessable wind resource. Alternatively the two-rotor approach
could enable significantly smaller rotors for the same wind regime. The
two-rotor approach might also lower turbine cost by enabling a more balanced
design. There is some possibility that three rotors would provide additional
improvements, but perhaps not enough to be cost effective.

Certainly this possibility calls for immediate analysis by the wind industry,
even if the source might prove to be a bit embarrassing.


Operation

To make such a system work effectively we need three additional elements, good
hourly to daily wind forecasting, computerized dispatching and load matching,
and a well-integrated transmission network. The keys to smooth operation that
have been listed by various experts are:

<>  variable speed and power factor turbines
<>  modern control systems with remote sensing and control
<>  regional wind forecasting up to two days ahead
<>  local wind forecasting up to two hours ahead
<>  minimum start and stop transients
<>  good smoothing of individual turbine outputs in wind-farm outputs
<>  wind-farm policy integrated into regional utility policy.

All of these are common sense, manageable requirements.

Wind antagonists raise cost issues of connections to the grid, and the costs
of ancillary services due to wind variability. In many cases the output from
wind-farms can serve local communities, thus reducing load on regional grids.
However large scale development of wind power will require upgrades of regional
and national grids. Any energy policy must strongly address upgrading and
development of the transmission infrastructure. Wind should be central to such
planning and execution. This is simply not a wind specific issue. Several
studies <3> have been done to cost the ancillary services with resulting
estimates from 0.2 to 0.6 cents per kilowatt hour with wind from 5% to 20% of
the local total energy supply. The worst case includes day ahead forecast errors
of 50%. With a well integrated network of wind-farms as described in 3) above,
these already very small costs would decline


Cost

In a 1995 disinformation effort, the coal industry sponsored a report developed
by Resource Data International and published by the Center for Energy and
Economic Development, projecting wind energy costs of 6.8 cents per kilowatt
hour in 1995, remaining unchanged until 2010. <1> In a rebuttal, NREL estimated
5.3 cents per kilowatt hour in 1995, going to 3.5 cents in 2010. <1>  The Lake
Benton Wind Farm in Minnesota, now in production, produces electricity at 4
cents per kilowatt hour unsubsidized, using one megawatt turbines. With larger
turbines the cost would be lower. Of course the cost will vary with wind class
and siting issues, but for developments we are likely to see by 2010, the NREL
estimate is looking good. We can expect average costs in the future to be
cheaper than coal fired plants, with none of coal's environmental issues.


Objections <5>

The usual objections presented by wind skeptics are:

<>  Bird kill
<>  Unsightliness
<>  Land area
<>  Noise
<>  Low energy returned on energy invested
<>  Future like the past

In response to these objections one can state:

Bird kill - The only place that has posed a real problem was the Altamont pass
in the 1980s, with small fast rotating turbines. There is no evidence that new
large turbines, with slowly rotating blades, kill even as many birds as power
lines do. <4>

Unsightliness - Surveys in Palm Springs (US) and Wales (UK) show that neighbors
grow to like wind farms and find them attractive. Most wind farms in the USA
will be sighted in areas that vary from rural to empty, where the issue is
unlikely to arise.

Land area - Class 4 and higher wind areas available for wind development are 6%
of total lower 48 land area. Of this area, less than 5% would be occupied by
turbines, equipment, and access roads. Cultivation can be carried out almost to
the base of the turbines, and livestock like the wind shadow.

Noise - Modern turbines have noise levels below 50 dbm (like a summer breeze in
the trees) at distances of about 250 yards.

Low EROEI - A recent study at the University of Wisconsin-Madison finds that
wind farms generate between 17 and 39 times as much energy as is required for
their construction and operation. The Danish wind energy association comes up
with an energy payback time of less than six months, or a return of over 60
for a thirty year life.

Future like past - Saying that wind will never happen, because it never has is
like saying a one-year-old will never walk because he never has.


Benefits

Perhaps the major benefits are environmental. There is one well documented and
quantified example to support this advantage: In 2001, Ontario Canada's five
coal fired power plants were responsible for 20% of all greenhouse gases
released in the province, 23% of all sulphur dioxide emissions, 14% of nitrogen
emissions and 23% of mercury emissions. These plants are scheduled for closure
by 2007.

More specifically, one can say for wind that:

<>  It's not a source of nuclear waste.
<>  It's does not despoil the land like strip mining for coal.
<>  It does not damage fragile habitats, like drilling for coal bed methane.
<>  It does not threaten the Arctic National Wildlife Refuge.
<>  It's not a source global warming greenhouse gases.
<>  It's not a source of fish-contaminating mercury.
<>  It's not a source of acid rain.

Apart from clean, inexpensive power, the surprise benefits to the economy can be
a drop in farm subsidies. Minnesota farmers earn less than $30 per acre with
livestock, and $250 per acre with crops, but can earn $1,000 per acre from land
rental for wind farms, and still have the livestock or crop.

The big benefit to operators is freedom from fuel price risk, and that benefit
will only grow from an already very attractive level in 2004.


The Challenge

Several states have goal of getting 10% of their electricity from wind by 2015
or 20% by 2020. With declining availability of natural gas and oil, we will have
to do much better than that on a national basis. The real goal should be to get
perhaps 20% of our total energy (albeit a declining total) by 2030 or 2040.

A two megawatt wind turbine with a 30% duty cycle and 95% availability will
generate 5.8 million kilowatts hour per year. Fifteen quads of wind power by
2030 would require 750,000 turbines, or 30,000 per year starting now. That is
five times present world production capacity, but is probably a worst-case
estimate. At three megawatts, 35% duty cycle and 15 quads we would need only
450,000. Building 15,000 to 30,000 turbines per year is no big deal for an
economy that can build seventeen million cars, trucks, and busses per year,
but still, we had better get cranking. It can't wait until after 2020.

Could the two-rotor design mentioned above reduce dramatically the number of
installations needed? The wind industry needs to address this question urgently.

References:
1. http://www.stanford.edu/group/efmh/winds/winds_jgr.pdf

2. http://fluid.stanford.edu/~lozej/winds/winds.html

3. http://www.nrel.gov/wind/pdfs/grid_integration_studies_draft.pdf

4. http://www.awea.org/faq/sagrillo/swbirds.html

5. http://www.eere.energy.gov/windpoweringamerica/

6. http://www.alumni.ca/~walk4d0/sf11.html

Copyright 2004 CyberTech, Inc.

http://www.energypulse.net/centers/article/article_display.cfm?a_id=843


Bill Totten     http://www.ashisuto.co.jp/english/