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In this work the uncertainty of wind power predictions is investigated with a special focus on the important role of the nonlinear power curve. Based on numerical predictions and measured data from six onshore wind farms the overall prediction accuracy is assessed and it is shown that due to the power curve the relative forecast error increases by a factor of 1.8–2.6 compared to the wind speed forecast. This factor can be considered as an effective nonlinearity factor. A decomposition of the commonly known root mean square error is beneficially used to distinguish different error sources related to either on-site conditions or global properties of the numerical weather prediction system. The statistical distribution of the wind speed prediction error is found to be Gaussian in contrast to the the one of power prediction error. Using the power curve and conditional probability density functions of the wind speed the unsymmetric distribution of the power prediction error can be explained and modeled such that it can be estimated even if no measurement data is available.

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In this work the thermodynamics of thermochemical fuel production using a CeO 2 redox cycle are studied. The need to reduce the oxygen partial pressure in order to improve efficiency is investigated, with both sweep gas and vacuum pumping considered as methods of achieving this. At ambient pressure the cycles can be maximized with respect to the temperature swing, the minimum oxygen partial pressure, and the extent of the oxidation reaction. For reduction at 1500°C the maximum efficiency was found to be 4.5%, which is significantly lower than the values found in previous studies. In addition isothermal operation had very low efficiency (less than 2%) under all of the conditions considered. If the system is operated at lower than ambient pressure, the pumping efficiency will depend on the pressure. From an investigation of commercially available pumps the pressure dependence was given an analytical expression. The results showed the cycles have an optimal operating pressure and that using sweep gas, as well as pumping, only reduced the overall efficiency. The efficiency was maximized with respect to the temperature swing, the reduction pressure, and the extent of oxidation, giving a peak efficiency of 7.5% for a reduction temperature of 1500°C. Reducing the pressure during reduction could also be beneficial due to improved reaction kinetics at lower pressure and an increased yield due to lower oxygen partial pressures. Recovering heat from both the high temperature ceria and the oxidation reaction, and using it as process heat, was also considered. With 60% of this heat being recovered, the peak efficiency for the 1500°C pumped cycle increased to 11%. Finally the practicality of the cycles, in terms of the quantity of ceria required to maintain continuous operation, are considered, and some suggestions for improving the cycle are given.

A materials screening of perovskites for oxygen storage applications yielding two promising materials, SrFe0.95Cu0.05O3−δ and Ca0.8Sr0.2MnO3−δ with outstanding performance.