I was struck by the following statements in a GristMill article the other day:
Archer and Jacobson, perhaps the world's leading experts on wind potential, estimate that wind energy at 80 meters in commercially developable sites alone could supply five times the world's current energy demand ...
Is it power variability that worries experts? Jacobson and Archer have documented that connection via long distance transmission can reduce that variability.
Both of these statements run against the grain of what I understood to be the common sense notions (myths?) about the fallibility of wind power. Intrigued, I decided to look in more detail at what Archer and Jacobson had done to arrive at these conclusions.
The first of the two articles cited, an "Evaluation of global wind power"1, contains a detailed estimate of wind power availability from over 8000 measurement stations all over the world. Among these stations Archer and Jacobson found that 13% had an annual average wind speed greater than 6.9 m/s at a height of 80 m, meaning that these sites have a wind power class of 3 or greater2 as preferred for low-cost wind power generation. Areas of great wind power potential are found all over the world, and tend to be clustered along the coastlines of the continents. Interestingly, many of the most promising sites (of wind power class 7) are found on the east and west coasts, and in the Great Lakes region of Canada.
To calculate the global wind power availability Archer and Jacobson assume that global wind distribution is well mapped by the 8000+ measurement stations in their study, and hence that 13% of the earth's land area of 130 million square kilometres would have a wind power class of 3 or greater. They further assume that this land area could be covered by wind turbines at a density of 6 per square kilometre, with each turbine generating 720 kW of power (on average, as calculated from the wind speed data). Based on these numbers, they find that the global economically available wind power is approximately 72 TW (or 54 000 Mtoe3 per year). To put this in context, the global demand for electrical power in 2001 was in the range of 1.6-1.8 TW (14 - 15 x 1012 kWh per year) and the global demand for energy for all purposes for the year 2001 was 7-10 000 Mtoe. Cheap, readily available wind power alone could thus meet 40 times the 2001 global electricity use, and over five times the total energy use for all purposes.
Meeting global energy needs from wind power alone would require the installation of 20 million wind turbines over 16 million square kilometres (2.5% of the earth's land area), generating 15 TW of electrical power. To put this in context, the total installed wind capacity for the world was 94 GW in 2007 4, and it has been increasing by ~20 GW/year. In order to meet the global energy demand by the year 2050 through wind alone, approximately 370 GW or roughly 500 000 new wind turbines would need to be installed every year for the next forty years. It's time to get moving, but then we already knew that, didn't we.
One of the commonly expressed concerns with wind power is that the variability of wind makes it unreliable as a primary source of electrical power. In a 2007 article5, Archer and Jacobson examine one possible method for reducing the variability in the power generated: the interconnection of networks of wind farms over a large area. Because some wind turbines can be turning on one farm, even while they might not be on another some distance away, a network of wind farms is able to average out the peaks and troughs and deliver some level of stable power. By examining a network of 19 wind farms in the American mid-west, over an area spanning 850 km, Archer and Jacobson found that the interconnected wind farms could deliver guaranteed power of 222 kW/turbine at the same level of performance as a coal-powered generating station6. This means that as much as one-third of the total available wind power in the network could be used to supply reliable baseload electrical power, while the remaining, intermittent, two-thirds of the power could be used to, for example, charge batteries or generate hydrogen gas.
Taken together, these two articles strongly suggest that wind power alone could meet global electricity and energy needs, with room to spare. And that is reason for hope.
- Cristina L. Archer and Mark Z. Jacobson, J. Geophys. Res. 110, D12110 (2005).↩
- Wind power classes are linearly related to the power density of the wind at different wind speeds. See the AWEA Wind Energy FAQ for more information.↩
- Mtoe: Millon tonnes of oil equivalent.↩
- From the Wikipedia entry on Wind Power.↩
- Cristina L. Archer and Mark Z. Jacobson, J. Appl. Meteor. and Clim. 46, 1701 (2007).↩
- Interestingly, Archer and Jacobson also find that interconnecting the wind farms can allow for a reduction in the size of long-distance transmission lines carrying the electricity from the network to a city. Because some farms will have low wind speeds at any given point in time, the total capacity of the lines can be reduced without losing energy. This reduction would allow for the cheaper construction of long-distance transmission lines, thus making wind power even more economical.↩