This paper describes a theoretical approach to evaluate the performance of a hybrid solar system made with photovoltaic cells and thermoelectric (TE) modules. After a brief treatment of the integrated system, energy conversion and performance parameters are evaluated through numerical simulations depending on the global radiation and temperature distribution obtained by the Joint Research Center of the European Commission and of the National Renewable Energy Laboratory. The contribution of TE module to total energy seems significant in southern European towns and less substantial when the locations considered are very distant from the equator and show the possibility of using TE devices for energy production.

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Feasibility of a Photovoltaic–Thermoelectric Generator: Performance Analysis and Simulation Results

The thin-film multijunction thermal converter (PMJTC) developed in cooperation between Physikalisch-Technische Bundesanstalt (PTB) and Institut fur Physikalische Hochtechnologie e.V. (IPHT) is today's most sensitive and accurate standard for the precise measurement of electrical AC quantities in the frequency range of 10 Hz-1 MHz. Thin-film technology and micromechanics in silicon were essential for this success. The thin-film heater and bismuth/antimony thermocouples with high Seebeck effect deposited on a thin membrane of low heat conductance result in the attractively high sensitivity of the PMJTC which allows voltage measurements down to 100 mV to be performed. The statistics of the mass production of the PMJTCs show that PMJTCs built into a housing with an N-connector at the input can be reproducebly manufactured with an AC-DC voltage transfer difference smaller than 0.1 /spl mu/V/V at 1 kHz, 8 /spl mu/V/V up to 100 kHz, and below 40 /spl mu/V/V up to 1 MHz for a heater resistance of 90 /spl Omega/. A compensation circuit has been added on the chip which results in low-frequency PMJTCs (LF-PMJTCs) with AC-DC transfer differences below 0.3 /spl mu/V/V at 10 Hz.

Development of thin-film multijunction thermal converters at PTB/IPHT

This paper describes a new ac-dc current-shunt calibration system with a current range of 1 mA-100 A and a frequency range from 10 Hz to 100 kHz. The new system consists of an ac-dc comparator controlled via a universal serial bus and a set of reference coaxial shunts with dedicated thermal voltage converters. The design of the custom-built shunts has been optimized through a theoretical modeling. The results of the calibrations of the reference coaxial shunts are presented.

AC-DC current shunts and system for extended current and frequency ranges

A micro-machined thermal flow sensor to measure a minute amount of gas flow rate is developed, and tested to quantify the flow measuring characteristics over the variation of flow rate. A bifilar-Evanohm-R alloy heater and chromel-constantan thermopiles were formed on a sandwich membrane, Si3N4/SiO2/Si3N4, which consist a core part of the sensor. In performance test of the sensor, range of gas flow rate was regulated from 0.2 to 1.0 slm and the heater power was variated from 0.72 to 5.63 mW. In the present experiment, the Reynolds number based on the diameter of a flow passage was ranged from 81 to 408. It is confirmed from the experiment that the sensitivity (S = ∂ΔV/∂Q; ΔV, voltage difference between thermopiles; Q, flow rate) of the sensor is enhanced with increasing the heater power and decreasing the measuring flow rate range. Also, the sensor response time required to a stable state is reduced with increasing the flow rate range.

Sensitivity enhancement of a silicon micro-machined thermal flow sensor

We have measured the thermoelectric transfer difference of two thermal voltage converters using a Josephson source and compared the results to similar measurements made with a conventional semiconductor source. Both sources use the fast reversed DC method. The Josephson source is an array of 16 384 superconductor-normal-superconductor Josephson junctions that is rapidly switched between voltage states of +0.5 V, 0 V, and -0.5 V. A marginally significant difference is detected between measurements with the two different sources.

/pdf/thermoelectric-transfer-difference-of-thermal-converters-59dq6vt1mx.pdf

Thermoelectric transfer difference of thermal converters measured with a Josephson source

The AC-DC transfer differences of thermal converters due to thermoelectric effects in the heater circuit are directly measured with a fast reversed DC to an uncertainty of a few parts in 10/sup 7/. This new and independent method allows former theoretical methods for evaluating thermoelectric effects in thermal converters to be checked. >

Measuring thermoelectric effects in thermal converters with a fast reversed DC

Thermoelectric effects in a single-junction thermal converter (SJTC) are responsible for an AC-DC transfer difference of the order of a few parts in 10/sup 6/. Different thermoelectric effects are found in SJTCs. These are characterized by different time-constants that reflect the characteristic scales of the thermoelectric effects and, hence, may give us a clue for identifying the location and the cause of the thermoelectric effects. A numerical simulation for a fast-reversed DC (FRDC) measurement was performed for the SJTC to determine the relationship between the characteristic scale of the thermoelectric effect and the characteristic time-constants associated with it. The relationship was in good agreement with a simple formula proposed for a one-dimensional thermal system.

https://staff.aist.go.jp/hitoshi-sasaki/FRDC/paper/frdcHS6.pdf

A numerical simulation of thermoelectric effects in single-junction thermal converters

The thermoelectric transfer difference of Thermal Converters (TCs) can be evaluated in both current mode and voltage mode, using a fast-reversed dc (FRDC) source. Some types of TCs show differences in the thermoelectric transfer difference between voltage and current mode as large as some parts in 10/sup 6/. In order to investigate the origin of the discrepancy, the change of the thermoelectric transfer difference with the value of a resistor in series with the thermal converter has been measured. The result was in good agreement with an assumption that the Seebeck effect in the heater/heater support junction is the main source of the voltage transfer difference.

https://staff.aist.go.jp/hitoshi-sasaki/FRDC/paper/frdcKT6.pdf

AC-DC voltage transfer difference due to Seebeck effect in thermal converters

A formula for determining the time-constants of thermoelectric effects in thermal converters from the FRDC-dc transfer difference measurements in relation to the reversing frequency is derived. The error due to higher-frequency harmonics in the FRDC-waveform is calculated for shunt capacitances and dielectric losses in the heater/range-resistor combination.

Determination of the time-constants of thermoelectric effects in thermal converters using a fast-reversed DC

The improved design of the fast reversed DC source allows the measurement of thermoelectric effects in thermal converters of all designs and serves as a basic tool to control reference standards for ac-dc transfer. Residual effects in thermal converters are measured which are explained by nonuniformities in the heater material.

H. Sasaki

Papers

Measuring thermoelectric effects in thermal converters with a fast reversed DC

A numerical simulation of thermoelectric effects in single-junction thermal converters

AC-DC voltage transfer difference due to Seebeck effect in thermal converters

Determination of the time-constants of thermoelectric effects in thermal converters using a fast-reversed DC

Fast reversed dc: basic reference for ac-dc transfer