Electrolytic hydrogen offers a promising alternative for long-term energy storage of renewable energy (RE). A stand-alone RE system based on energy storage as hydrogen has been developed and installed at the Hydrogen Research Institute, and successfully tested for autonomous operation with developed control system and power conditioning devices. The excess energy produced, with respect to the load requirement, has been sent to the electrolyzer for hydrogen production. When energy produced from the RE sources became insufficient, with respect to the load requirement, the stored hydrogen was fed to a fuel cell to produce electricity. The RE system components have substantially different voltage-current characteristics and they are integrated through power conditioning devices on a dc bus for autonomous operation by using a developed control system. The developed control system has been successfully tested for autonomous operation and energy management of the system. The experimental results clearly indicate that a stand-alone RE system based on hydrogen production is safe and reliable. Index Terms-Electrolyzer, energy storage, fuel cell, hydrogen, photovoltaic (PV), wind energy. NOMENCLATUREEnergy efficiency of the electrolyzer. Current efficiency of the electrolyzer. Current efficiency of the fuel cell system. Efficiency of the fuel cell system. Energy efficiency of the fuel cell system. Boost converter efficiency. Efficiency of the energy storage as hydrogen. Conversion constant. Input current to the electrolyzer. Output current of the fuel cell system. Number of cells in the electrolyzer. Number of cells of the fuel cell stack. Heat loss in the fuel cell system. Power available at the electrolyzer for storage. Fuel cell system power output. Hydrogen production rate. Hydrogen consumption rate of the fuel cell system. Time. Reversible voltage of the electrolysis reaction.

No abstract

No abstract

No abstract

The compact, rugged, re-entrant radio-frequency resonator [A. R. H. Goodwin, J. B. Mehl, and M. R. Moldover, Rev Sci. Instrum. 67, 4294 (1996)] was modified for accurate measurements of the zero-frequency dielectric constant (relative electric permittivity) εr of moderately conducting liquids such as impure water. The modified resonator has two modes with frequencies near 216/εr MHz and 566/εr MHz. The results for εr at both frequencies were consistent within 0.0002εr, verifying that the low-frequency limit had been attained with water samples with conductivities in the range 100–2500 μS/m. The results for water and for the insulating liquid cyclohexane were within 0.0005εr of literature values. The present analysis is based on a simplified equivalent circuit that accounts for the loading of the resonator by the external instrumentation. This circuit can easily be generalized for a resonator with three or more modes. The present resonator has a thick gold plating on its interior surfaces. With the plating, the quality factors Q of the resonances varied in a predictable way with frequency and temperature. Predictable Qs were essential for obtaining accurate values of εr.