High wind power is an idea of great interest to my brother Dan. Each time we discuss it, I give this rather radical idea further thought. This essay from Power Electronics Technology provides a nice overview.
We’re Still Searching for the Best Alternative Energy Source – ARE WE THERE YET?
That could very well be the question that has to be answered when it comes to the optimum new energy source. So far, I’ve described photovoltaic systems Electronic Design, February 2011), ocean energy (Power Electronics Technology, September 2010), wind power (PET, April 2011), electric aircraft (PET, October 2010), and electric vehicles (PET, May 2011). In each of these examples, we could not tell for sure whether we have a solution for an optimum energy source for the electric grid or for vehicles. In its August 2011 issue, Power Electronics Technology we describe yet another potential energy source that might alleviate our dependence on fossil fuel-based energy sources.
According to Sky WindPower (Oroville, CA), when you consider all costs, including the true costs of nuclear fission and the external costs of fossil fuel energy sources, airborne wind energy could be the world’s cheapest energy source. (Possible exceptions are limited hydro sources and limited situations where surface-based wind turbines may be the most economic for supplying relatively local needs.) High energy winds are at altitudes high above us, not just at a few hundred feet where they can be tapped by turbine rotors on towers. Airborne wind energy (AWE) technologies will employ tethered wind energy capture devices that iflyi to altitudes where wind power is much stronger than it is at ground level. For example, Sky WindPower’s Flying Electric Generators (PEGs), located at rural locations not very far from urban centers, in connection with electrical grids can serve man needs.
Compared with tower-based turbines, much smaller rotors are necessary per megawatt captured in the higher velocity altitude winds. Rated capacities of an FEG will initially be about 1 MW. Their generators produce a high voltage at relatively low current to allow use of small diameter, lightweight tether cable. At least eight U.S. companies are developing AWE systems, which will be handled in manners similar to photovoltaic and other wind power systems that tie in to the electric utility grid. They will require an inverter and a means for synchronizing the generated voltage when connecting to the grid. In turn, this will require efficient power semiconductors, such as GaN or SiC devices.
An important solution required for a viable high altitude FEG is an appropriate tether cable that can survive the environment and also the high voltage flowing through it. If my calculations are correct, a 1 MW (1×10 6 W) system would require generation of 10,000V at 100A. Obviously, this would be difficult to achieve in a tethered system that could be a few thousands of feet long. The people at Sky WindPower would not disclose their approach, because this technology is also being developed by its competitors. Here, we require a solution that minimizes the voltage drop on the tethered cable. This technology would involve innovations in tether design and possibly material science.
Also, technology solutions have not been found yet for electric vehicles and electric aircraft. This solution hinges on the ability of creating a portable energy source that exceeds the present capability of lithium-ion batteries. The industry is waiting for a “magical” approach that extends the range of these vehicles. And, oh yes, the solution must be cost effective. Perhaps one solution is to use fuel cells to power vehicles, which would require a recharging infrastructure for the fuel cells. FEGs would produce electricity at night when more is not always needed, and this excess could be used for hydrogen production. It would make present gas stations obsolete, replacing them with fuel cell recharging systems. Power production throughout the night could provide plenty of cheap electricity to support EV charging, too. Although it would be admirable to develop technologies to replace our existing energy source system with a new technology, we aren’t there yet. However, it does open up the possibility for power electronic engineers to work on new and exciting technologies. And, keeping working is a good thing, particularly now.
0 SAM DAVIS, Editor-in-Chief POWER ELECTRON1Cs TECHNOLOGY July 2011 http://www.powerelectroncs.com