As fossil fuel energy sources fall into disfavor due to climate-warming greenhouse gas emissions and other pollution associated with their use, renewable sources of energy are expected to make up an increasing role in the world’s energy portfolio. Wind energy is one of the cheapest and fastest growing renewable energy sources available; however, conventional wind farms are often criticized for their intermittence and lack of overall power. Harnessing wind power from higher altitudes (500–12,000 m) could mitigate both of these problems by making use of the jet streams’ abundant and relatively persistent wind energy (Archer and Caldeira 2009). Unfortunately, even the jet streams suffer from variations, and high-altitude wind power systems will still require large energy storage capabilities if they are to become reliable sources of electricity. —Noah Proser
Archer, C., Caldeira, K., 2009. Global assessment of high-altitude wind power. Energies 2, 307–319.
Archer and Caldeira assessed the availability of high-altitude wind power using data collected from the National Centers for Environmental Prediction and the Department of Energy from 1979 to 2006. They focused on wind speed and density in order to determine the optimal elevations and geographic regions for high-altitude wind power. Wind power densities were then divided into percentiles representing the density that was exceeded 50, 68, and 95% of the time as a measure of dependability. For the purposes of this assessment, they considered two means of high-altitude wind power. The first system, KiteGen, uses kites connected to generators on the ground that create electricity when the kites are pulled by the wind. KiteGen is designed for altitudes of 1,000 m and can produce 620 kW per unit. Alternatively, Flying Electric Generators produced by Sky Windpower use rotors to generate electricity, which is transmitted back to the ground. These generators are designed to fly at 10,000 m and produce 40 MW each.
Archer and Caldeira found that cities like Tokyo, Seoul, and New York, which are affected by polar jet streams, could harvest more than 10 kW/m2 at high altitudes (8,000 m) at least 50% of the time. Furthermore, since wind speed increases with altitude, most regions considering wind power would be greatly benefitted by using high-altitude generators rather than conventional turbines. Ideally, these high-altitude generators would be able to adjust their altitudes as winds shift with weather conditions.
Even with all of the advantages of high-altitude wind power, intermittency can still be a problem. To deal with this problem, wind farms can store energy in batteries, pumped hydroelectric, and other forms during non-peak hours. This stored energy can then be supplied to the grid when the wind farm is not at optimal production. Another way to deal with the intermittency of wind power is to have several farms in different locations. When the wind isn’t blowing in one area, farms in other areas can still provide electricity to the grid.
It is still unclear whether wind can provide reliable baseload power for our growing energy demands; however, high-altitude wind power seems like a serious contender among renewable energies. At high altitudes reliability and overall power production are greatly increased. Furthermore, high-altitude wind power is available where ground-level wind power may not be feasible. Nonetheless, before widespread wind power can become a reality, improvements must be made in energy storage technologies, as well as large-scale transmission grids. —Noah Proser