School of Earth Sciences - Theses
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ItemThe Flying Electric Generator: evaluating the claims of a largely ignored proposal for generating electricity from high-altitude winds( 2015)This thesis concerns the Flying Electric Generator (FEG), a technology proposed to generate electricity from winds several kilometres high in the sky. Airborne Wind Energy (the generation of electricity from high altitude winds) is an emerging field of research, with several technological approaches under development. High altitude winds are attractive for this purpose because they are generally much faster than surface level winds, and because power is a cubic function of wind velocity. Winds are fastest within the subtropical jet stream, located about 25–30 degrees north and south of the equator, at an altitude of 10–12 km. The FEG is a device consisting of multiple rotors attached to a frame, which is tethered to the ground. The rotors work as autogyros to provide lift; additional energy extracted from the wind is converted to electricity and conducted to the ground via the tether. The FEG would operate kilometres high in the atmosphere, up to jet stream levels. Papers about the FEG were first published in 1979, and in 2002 a company was founded to commercialise the FEG. So far, this has not happened, and many details of how the technology would operate remain uncertain, despite three decades of research literature. Only small test craft (rotors of up to 24 feet in diameter) have flown at low altitudes (up to 100 feet). Many of the claims in the literature, which are optimistic about the FEGs performance at high altitude, are experimentally untested. FEGs have never operated at the altitudes described in the corresponding literature, and the project has not been commercialised or attracted much if any recent research funding. Other, newer entrants to the Airborne Wind Energy field have seen success in research funding and commercialisation. This thesis addresses two problems: first, it tests some of the claims in the FEG literature and second, it attempts to fill in details not provided. The particular claims concern the power density available in high altitude winds over Australia and its seasonal variation, the amount of time a hypothetical FEG setup would be "grounded" due to insufficient wind speeds to keep it aloft, and expected capacity factors of a hypothetical FEG setup. Claims about the magnitude of the wind power resource were tested using reanalysis data (the ERA-40 dataset was used, and was validated against Bureau of Meteorology upper air statistics). Power density and wind speeds at different altitudes above Australia were calculated and analysed. The reanalysis wind data in conjunction with a model of FEG operation (based on lifting rotor theory detailed in the FEG literature) were used to calculate downtime and capacity factors. The results showed a clear seasonal variation in power density over Australia, which was most pronounced at 30 degrees south of the equator (although winds above Tasmania showed much less variation). Winter had the strongest winds, and summer the weakest. The highly skewed distribution of power density meant that median power densities (unreported in the FEG literature) were more appropriate than means. Downtime calculations showed that a particular FEG setup rated at 240 kW operating at a pressure level of 600 hPa would be landed for at least 20% of the year at all locations in Australia, and for at least 40% of the year north of 20°S. Annual capacity factors for the same FEG setup were calculated to vary between 0.1–0.4 over Australia, no different from conventional ground-based wind turbines. Capacity factors for the summer months were substantially lower than the annual values. These results support the main contention of the thesis, that the FEG is far more limited in its potential as source of energy from the wind than the literature claims.