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Due to high power demand photovoltaic regulators are being switched at high frequency. The solar cell capacitance increases the ripple voltage of the switching regulators at higher switching frequencies. Increased ripple due to array capacitance is calculated and its effect in limiting the maximum design switching frequency is studied. An experimental switching regulator is designed and used to confirm the theoretical considerations. This study has identified a method of solar cell capacitance measurement that is relevant to the design of a switching voltage regulator.

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An experimental setup has been developed to measure the solar cell ac parameters using an impedance spectroscopy technique. It consists of an electrochemical interface to set the dc bias voltage and to apply the signal voltage across the solar cell and a frequency response analyzer to generate the excitation signal with varying frequency and analyze the result. The setup is calibrated with a standard RC network and measured an error of ±4% (maximum). Solar cell capacitance, parallel resistance and series resistance are calculated from the measured data.

Type II Ge clathrate (Na x Ge 136 ) films containing a small amount of Na were successfully synthesized on a sapphire substrate by thermal annealing of precursor NaGe composite films. A new technique for Na removal from Na x Ge 136 was developed by applying the electric field in an Ar environment at 275 °C. Rietveld refinement analysis of Na x Ge 136 films showed an almost guest free nature (Na contents x ∼ 0) using this new technique. In addition, absorbance spectra obtained from Na x Ge 136 films showed a decrease in the absorbance intensity in the lower photon energy (<0.5 eV) with annealing. It suggests the decrease in free carrier absorption by the removal of Na atoms in Na x Ge 136 .