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ISIS Report 05/10/09
Wind Power Could Supply Global Electricity Needs 40 Times Over
Wind power could electrify the world or provide its energy needs many times
over, not necessarily with big turbines and wind farms Dr.
Mae-Wan Ho
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 The enormous potential of wind power
Wind
turbines on land could provide more than 40 times the world’s current electricity
consumption or over five times its total energy needs. That’s the latest assessment
using wind data from meteorological sources [1]. A network of 2.5-megawatt
(MW) turbines on land restricted to non-forested, ice-free, nonurban areas
operating at as little as 20 percent of their rated capacity would do the
trick; allowing for the fact that the wind does not blow constantly. To put
this into perspective, wind turbines installed in the US in 2004 and 2005
operate on average 36 percent of rated capacity.
For
the United States, the central plain states could accommodate enough wind
turbines to provide as much as16 times its total current demand for electricity.
Wind power is on a steep ascent. It accounted for 42 percent of all new electrical
capacity added to the US in 2008; but it is still only a tiny fraction of
the total capacity, 25.4 GW out of 1 075GW. The
Global Wind Energy Council projected a 17-fold increase in wind-powered generation
of electricity globally by 2030.
Simulating global wind fields based on state-of-the-art data
Xi
Lu and Michael McElroy at Harvard University, Cambridge Massachusetts in the
United States and Juha Kiviluoma at the Technical Research Centre of Finland
based their study on a simulation of global wind fields from version 5 of
the Goddard Earth Observing System Data
Assimilation
System (GEOS-5 DAS) that includes global meteorological data from a wide variety
of sources including surface and sounding measurements, measurements and observations
from aircraft, balloons, ships, buoys, dropsondes (radio probe dropped by
parachute) and satellites; the gamut of data that can provide the world with
the best possible meteorological forecasts enhanced by application of these
data in a retrospective analysis.
The
land-based turbines are assumed to have a rated capacity of 2.5 MW with somewhat
larger turbines, 3.6 MW, deployed offshore, to take account of the greater
cost of construction and the economic incentive to build larger turbines to
capture the higher wind speeds available there. In siting turbines on land,
the study excluded densely populated regions and areas occupied by forests
and environments distinguished by permanent snow and ice cover (notably Greenland
and Antarctica). Turbines located offshore were restricted to water depths
less than 200 m and to distances within 92.6 km off shore.
Optimal
spacing of the turbines in an individual wind farm involves a trade off between
various costs: turbines, site development, laying power cables, routine operations
and maintenance. Turbines must be spaced to minimize interference in airflow
and requires a compromise between maximizing power generation per turbine
and maximizing the number of turbines sited per unit area. For example, restricting
overall power loss to < 20 percent requires a downstream spacing >7
rotor diameters, and a cross-wind spacing of > 4 diameters.
The
power yield is assumed to be only a fraction (20 percent) of the maximum potential
to account for the variability of the wind over the course of a year.
In
this way, a world map of the annual wind power potential (W/m2)
is obtained; and the country by country potential for both on land and off
shore wind power also represented.
Wind power potential worldwide
The
total global potential power source for wind is estimated at 2 470 EJ (ExaJoule
= 1018J).
Table
1 gives the wind power potential of 10 countries identified as the largest
emitters of CO2 in 2005, though China has surpassed the US to be
the biggest emitter in 2006.
Table 1. Wind power potential for the 10 biggest CO2
emitting countries
As can be seen, wind power could supply close to 18 times the electricity
consumption for China, the bulk of which, 89 percent, could be derived from
land wind turbines. The potential in the US is 23 times the current electricity
consumption, the bulk 84 percent supplied on land. The UK’s wind potential
is 30 times its electricity consumption, with 41.5 percent derived from land.
In terms of wind power potential, Russia ranks number one, followed by Canada,
with US in third position. Much of the wind power potential in Russia and
Canada is located at large distances from population centres, however.
Wind power for the US
In
the US, demand for electricity peaks twice a year in summer and winter respectively
separated by minima in spring and fall. Demand is greatest in summer due to
air-conditioning, when it exceeds the minimum in spring/fall typically by
some 25 to 35 percent. There is a negative correlation between the monthly
averages of wind power production and electricity consumption. Very large
wind power can produce excess electricity during large parts of the year.
This allows the option of converting electricity into other energy forms.
For example, plug-in hybrid electric vehicles could take advantage of short-term
excesses in the electricity system, while energy-rich chemicals such as H2
– from electrolysis of water - could provide for longer term-storage [2] (Harvesting
Energy from Sunlight with Artificial Photosynthesis,
SiS 43)..
The annual onshore wind potential on a state-by-state basis shows a high concentration
in the central plains extending northward from Texas to the Dakotas, westward
to Montana and Wyoming, and eastward to Minnesota and Iowa. The resource in
this region could provide 16 times the total current demand in the US. As
resource is significantly larger than the local demand, it will require extending
the existing power transmission grid to exploit this resource. The Electric
Reliability Council of Texas, the operator responsible for the bulk of electricity
transmission in Texas, estimates that the extra cost of transmitting up to
4.6 GW of wind generated electricity is ~$180/kW, or about 10 percent of the
capital cost for installation of the wind-power generating equipment.
Micro-generation with small wind turbines
The
study convincingly shows that wind power can supply the world’s energy use
many times over; though it implies that big turbines and wind farms are necessary,
which is not the case. Like solar heating and photovoltaic, local micro-generation
of wind power is eminently feasible, and has been encouraged by the Ministry
of Agriculture, Food & Rural Affairs in Ontario, Canada, for several years
[3]. There it costs $2 000 to $8 000 per kilowatt to purchase a small wind
turbine; but that represents only 12 to 48 percent of the total costs of the
wind energy system, which includes inverters and batteries, sales tax, installation
charges and labour. The cost of energy produced by small (<10 kW) wind
turbine over its life time has been estimated to vary from $0.07/kWh, for
a low cost turbine in a high wind area to $0.96/kWh for a high cost turbine
in a low wind area.
In
the UK, micro wind electricity generation is increasingly popular for households
[4]. The average UK household uses around 4 000 kWh a year, which can be produced
with a 1.5 kW wind turbine. If a house is already linked to the national grid,
a wind turbine can supplement the mains supply. When the wind turbine is not
generating enough energy, mains electricity is used. When the turbine generates
more than is needed, the excess can be exported to the national grid. A 1.5
kW wind turbine costs around £3 000 to £ 5 000 (2007 prices). UK’s Department
for Business Enterprise and Regulatory Reform (BERR) runs a Low Carbon Buildings
Programme that provides grants for micro-generation technologies for householders
as well as public building [5]. The micro-generation technologies supported
include solar electricity, wind turbines, water turbines (small scale hydro),
solar hot water, ground source heat pumps, air source heat pumps, wood-fuelled
boilers (biomass), automatic pellet-feed wood burning stoves (biomass), renewable
combined heat and power, and fuel cells.
The
current cost of micro wind generation is still rather high, but it could come
down considerably. William Kamkwamba from a remote village in Malawi built
his first wind turbine from scrap when he was 14 years old, and Max Robson
in the UK has been inspired to produce an Envirocycle Scrap Wind Turbine prototype
at £20 budget, that he claims cost £2 000 on the market [6] (Harnessing
the Wind with Scrap, SiS 44). Such low cost micro generation options
are particularly appropriate for developing countries.
A cheap micro wind turbine at last?
In
another development, John Gregg, an international expert in spin electronics
and magnetic instrumentation at the University of Oxford has designed and
built a wind turbine prototype in his mother’s garden that uses a standard
induction motor as a generator [7].
In
an ordinary wind turbine, the rotor blades rotate in the wind and in doing
so, spin a shaft leading from the hub of the rotor to a generator. The generator
transforms the rotational energy into electricity. The simplest generator
works by electromagnetic induction to produce an electrical voltage – a difference
in electrical potential – that can drive an electric current through an external
circuit. Whenever an electrical conductor moves relative to a magnetic field,
voltage is induced in the conductor. If a coil is spinning in a magnetic field,
then the two sides of the coil moves in opposite directions, and the voltages
induced in each side add up to produce a direct current (DC) through the external
circuit. In order to fit in with the 60 cycles alternating current (AC) of
the domestic electricity supply, an inverter is needed to convert the DC into
60 Hertz AC, and this is complicated as the voltage produced depends on the
speed of the rotor, which in turn depends on the wind speed. The high costs
of wind turbines are due to custom-built generators, invertors, storage batteries
and complex circuitry.
Gregg
struck on the idea of using an electric (induction) motor as a generator as
the result of a question asked by a student: How can an induction motor work
as a generator?
An
electric motor uses electromagnetic induction to create motion, which is the
opposite of a generator. It consists of an electromagnet rotating in the field
of a permanent magnetic (or another electromagnet) on the simple principle
that like poles repel and opposite poles attract.
In
trying to answer the student’s question, Gregg spotted a novel and very cheap
way of using an induction motor as a generator, basically by running it backwards.
Induction motors can be found in everything from domestic appliances such
as washing machines to industrial machines.
The
electricity generated by using an AC inductor motor is not at constant voltage
or frequency. But, Gregg realises that hot-water tank heater elements don’t
mind variable voltages or frequencies. “That’s why we can make it cheaply
and why it performs well because we are not handcuffed by the necessity to
deliver 249V 50 Hz,” Gregg said.
Instead,
Gregg designed a patented electronic control method, drawing inspiration from
Swiss locomotives. Instead of a mechanical gearbox, the train changes gear
electrically as the field windings on the magnet on the motor are switched
to give maximum acceleration at all speeds. “Our generator works in a similar
fashion,” said Gregg. “Because the generator is configured as a constant power
source and acts effectively as a generator and a continuous variable electronic
gearbox, the turbine aerofoils operate on the peak of their performance curves
at all times, and all the power they deliver is harvested and channelled to
the load.”
The
wind turbine has a six-metre diameter blade and a standard 7.5 kW induction
motor used as a generator. Because of planning permission, it cannot be sited
high enough to catch the optimum amount of wind. Nevertheless, early results
show the equivalent of 1 kW continuous power. The turbine provides electricity
for a heat exchanger tank, which in turn feeds the domestic hot-water tank
and also feed surplus heat into the domestic central heating, so saving on
oil as well as electricity bill.
Five
years ago, when it all started, it would have cost £33 000 to install an equivalent
commercially available turbine.
With
co-inventor Mazhar Bari, Gregg is now proposing a spinout company, Renewox,
though Isis Innovation, the technology transfer company of Oxford University.
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There are 4 comments on this article so far. Add your comment
| Liz Chafer Comment left 5th October 2009 22:10:16
All the wind turbines installed in Germany have had little impact on Co2 emissions in that country due to the intermittency of wind . The same is the case for Denmark cf. the CEPOS report sept 2009 In many countries including USA Canada France and the UK there is immense pressure to install industrial wind turbines often within a mile of houses affecting the health of those living in the vicinity. Even where I live the load factor will only be 15% but lack of wind doesn't seem to present a problem to the wind industry promoters.
Intermittency is a serious problem until there is a means of stocking the energy produced.There are other forms of renewable energy that should be developed in preference to that of wind - wave power for example. | Mark Russell Comment left 23rd October 2009 18:06:38
Those are big, sweeping statements about nuclear ... "the nuclear black hole in terms of cost, safety and sustainability." All (except maybe sustainability in the grand scheme) are nothing more than populist fears, and not based on fact or reality. Wind power is positively medival by comparison no matter how you dress it up. Once the planet is out of all other forms of energy wind power may make sense (and by implication it is last on my list of desirable technologies). By that time the place will look like "planet of the apes" anyway so wind power will fit right in. | Mae-Wan Ho Comment left 22nd October 2009 22:10:49
All you people against wind and pro-nuclear really want to come down to earth and look at the nuclear black hole in terms of cost, safety and unsustainability. We are not for big wind farms. Cheap affordable small wind turbines are here! Read our complete report and get a full picture. Join the dots and join the future. | Mark Russell Comment left 22nd October 2009 22:10:18
Once the "storage solution" is worked out, why would you fill that storage with energy produced by industrial wind turbines when you could fill it with energy produced by nuclear power at a fraction of the cost, and without the massive eyesore that are wind farms?
A storage solution notwithstanding, the cost of wind power in general will cause countries that have committed to wind power losing almost all of their manufacturing base to countries that can supply cheap, reliable energy, whether clean or dirty (manufacturers don't really care). |
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