The Technical and Economic Potential of Airborne Wind Energy
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In this thesis, a methodology is developed, to assess the feasibility of airborne wind energy. A particular concept called pumping kite generator (PKGs), is analyzed. Previous works on this topic suggest that the cost of energy of such systems can be far lower than for conventional wind energy, mainly because higher altitudes can be reached and material can be saved. The cost of energy of pumping kite generator designs in the 1 to 2 MW range is calculated. For this purpose, power curves are calculated by using a simple and quick performance simulation. The power curves are then used to calculate the annual energy production based on either a Rayleigh distribution or wind data from a weather model. For each component of the pumping kite generator, two cost functions are developed: A lower and a higher limit for the expected cost. Assuming a normal distribution of component costs, the probability density function for the total cost or total annual cost can be calculated as a function of several design parameters. The levelized cost of energy of a baseline design is determined and its sensitivity to changes of various design parameters, the site specific wind conditions and the operating altitude is evaluated. It is shown that the basic design parameters – kite area, nominal generator power and nominal tether force – of the baseline design, are within a robust optimum range for the chosen baseline wind conditions. The kite properties, especially its lifetime and coefficient of lift are shown to be the most important factors for the feasibility of the pumping kite concept. A comparison to a large onshore wind farm with 1.5 MW horizontal axis wind turbines (HAWTs) shows that PKGs can be cost competitive in this sector. The technology can be economical under current subsidy schemes and at good sites even without government support. However, the comparison also suggests, that the cost of airborne wind energy will stay in a similar range as conventional wind energy in the mid-term. It is concluded that addressing niche energy markets in remote areas or with complex terrain, where PKGs have great advantages, can play an important role when introducing the technology. Low wind sites and deep offshore projects look the most promising for the long term. In addition the possibility of increasing the capacity factor of a PKG at low extra cost can be a crucial factor when competing with conventional wind turbines in a free market, without feed-in tariffs in a grid with high wind power penetration.