The demand for accurate solar irradiance nowcast increases together with the rapidly growing share of solar energy within our electricity grids. Intra-hour variabilities, mainly caused by clouds, have a significant impact on solar power plant dispatch and thus on electricity grids. All sky imager (ASI) based nowcasting systems, with a high temporal and spatial resolution, can overall mean-absolute deviation (MAD) and root-mean-square deviation (RMSD) are 0.11 and 0.16 respectively for transmittance. The deviations are significantly lower for optically thick or thin clouds and larger for clouds with moderate transmittance between 0.18 and 0.585. Furthermore we validated the overall DNI forecast quality of the entire nowcasting system, using this transmittance estimation method, over the same data set with three spatially distributed pyrheliometers. Overall deviations of 13% and 21% are reached for the relative MAD and RMSD with a lead time of 10 minutes. The effects of the chosen data set on the validation results are demonstrated by means of the skill score.

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The current study allows the recognition of the most optimal combination of excitation frequency, kind of orifice, and synthetic jet-to-surface spacing in order to obtain the fastest cooling time using a Taguchi experimental design. To this end, the heat transfer and synthetic jet velocity behavior using different kinds of orifices are obtained experimentally. A piezoelectric diaphragm has been selected as a vibrating actuator. Four kinds of orifices have been studied: circular, rectangular, triangular, and square. First, the study consists of recognizing the excitation frequency in which each orifice produces the highest flow velocity. A hotwire anemometer has been used in order to measure the synthetic jet velocity. Additionally, a steel plate has been heated and then cooled using the synthetic jet set at the excitation frequency in which the jet velocity was the largest for each orifice. For the statistical analysis, the input study variables are the type of orifice and jet-to-surface spacing. The output variable has been the cooling time. The results show that using a combination of a rectangle orifice, 20 mm of jet-to-surface spacing and an excitation frequency of 2000 Hz, it is obtained the fastest cooling time. In addition, using these parameters, a mean heat transfer coefficient of 11.05 (W/m2K) with a coefficient of performance (COP) of 49.21 has been obtained. Finally, for each kind of orifice, there is the presence of two resonant frequencies, the Helmholtz (acoustic resonance) frequency and piezoelectric diaphragm natural frequency.

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