Akio Takeoka

Development and application of see-through a-Si solar cells

Abstract A new type of translucent amorphous silicon (a-Si) solar cell, called the see-through a-Si solar cell, is developed. It has multiple microscopic holes within its effective area to transmit light and it generates electric power. A series of technical data on the fabrication processing with various patterning and photovoltaic performance are presented. Some examples of application systems such as car sunroof and home interior are introduced and discussed on a wide variety of new areas of PV applications. The see-through a-Si solar cell was mounted on a car sunroof to drive the cars ventilating system or to charge its battery. The ventilating system reduced the interior temperature of the car from 61 to 47°C during daytime parking.

Advanced photovoltaic technologies and residential applications

Expectations for solar cells have grown with deepening concern over global environmental and energy problems. This paper reviews the development history of solar cells and their current status. Applications of solar cells are also described, especially residential applications, such as a solar-powered air conditioner and grid connected photovoltaic power generating systems.

Microwave Detector Using Granular-Type YBCO Superconductors

A highly sensitive microwave detector has been developed for the first time by granular-type bulk YBCO superconductors with fine particles. Particles with a size of about 1 µm, having a SNS-like grain boundary, were controlled by a coprecipitation method, followed by a sintering process. A new fabrication method for bulk superconductors was also developed to produce a precise microbridge-type structure. Sensitivity to microwave power below -40 dBm was obtained, and a direct mixing effect was obtained at a frequency of 8.6 GHz at the temperature of 77 K. It was confirmed that the Josephson effect of the detector at the SNS grain boundary formed in the sintering process for ceramics is the most responsive for microwave detection.

Development of an ultralight, flexible a-Si solar cell submodule

Abstract An ultralight, flexible a-Si solar cell fabricated on a polyimide film substrate has been developed. It was found that prebaking the polyimide film substrate improved the output performance of the cell by reducing the amount of H 2 0 and polymers released from the substrate. Also, using an i-layer fabricated at high temperature (250°C) and a p-layer fabricated at low temperature (80°C) improved the cells output performance to a level of over 10%. A maximum output of 782.4 mW and a power-to-weight ratio of 340 mW/g were obtained for an integrated-type flexible a-Si solar cell submodule with a size of 113 mm × 120 mm.

Residential photovoltaic power generating system connected to utility line

Abstract We successfully developed a utility grid interconnected photovoltaic (PV) power generating system with reverse power flow capability and installed it in an occupied private residence for the first time in Japan. The system, which consists of a 1.8-kW PV array, a 3-kVA inverter, and an interconnection protection device, has been operating satisfactorily since July 31, 1992. On a clear day, about 77% of the PV generated power was reversed to the utility between 10:00 AM and 2:00 PM. For a one-month period in May, 1993, the system generated 180 kWh of power, and fed 61% of this generated power back to the utility line. A 3-kW PV array could be installed on the roof of an ordinary Japanese house, which would supply almost all of the power required for household consumption and alleviate peak power demand.

Heterodyne Detection of Microwaves Using Granular-Type Y1Ba2Cu3O7-x Superconductors

A heterodyne mixing experiment of microwaves at about 20 GHz was performed using a microwave detector made from granular-type Y1Ba2Cu3O7-x (YBCO) superconductors. Although the bridge included many boundaries, voltage steps corresponding to the Josephson frequency and step height dependence for microwave power similar to those of a single weak-link bridge were clearly observed. The IF signal showed peak amplitudes corresponding to the peak dynamic resistantance due to nonlinearity resulting from the Josephson effect. It was confirmed for the first time that this detector operates stably for the heterodyne mixer at 60 K or below and has a potential for high sensitivity due to its large dynamic resistance.

Hysteresis-like Characteristics of Ring-Shaped Ceramic Superconductors

We investigated the residual magnetic field characteristics of ring-shaped ceramic superconductors in a Y–Ba–Cu–O system with high-Tc. The residual magnetic field of a superconducting ring to which external fields were applied showed hysteresis-like characteristics. The induced persistent current in the saturated ring corresponded to the critical current of the ring. The residual magnetic field of a ring with asymmetric current paths, supplied by external currents, was zero while one of the branch currents remained below the critical current; but a residual magnetic field appeared at currents above the critical current as a result of a difference between the inductances of the paths. It became saturated and showed hysteresis-like characteristic when both branch currents exceeded the critical current. Saturated magnetic fields are thus subject to critical current of the ring.

Fundamental Design for Meissner Motor

We have developed a new superconducting motor, called the “Meissner Motor”, using high-Tc ceramic superconductors. The output of this motor depends on the repulsive force caused by the Meissner effect and the heat flow rate from superconductors to liquid nitrogen. The motor output has been estimated by computer simulations in view of the Meissner effect and the heat flow rate. The maximum output of the motor with a radius of 30 mm is simulated at about 0.03 W. It is a fairly low output compared with commercial motors. Superconductors with a higher Meissner effect are required to improve the motor output.

Fundamental Properties of a New Superconducting Motor

We developed a brand new superconducting motor using high-Tc ceramic superconductors for the first time. This motor, named the “Meissner Motor” , utilizes the repulsive force caused by the Meissner effect, which appears below Tc and disappears above that. The motor rotated at a maximum speed of 40 rpm and generated a torque below 0.66 gf-cm. Though the repulsive force to drive the motor increased with the decrease of temperature or the increase of the gradient magnetic field, it was only about 1.1 gf/g at 77 K in 3500 G/cm and differs a little with the processes’ of magnetization. The rotating speed of the motor is limited by heating ability and the torque is limited by cooling ability.