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Photovoltaic (PV) systems can generate less energy than expected owing to inefficiency of the inverter, deterioration of the PV modules or conditions of partial shading and soiling. The monitoring and diagnosis techniques of PV systems are therefore quite important to recognize the causes of the performances reduction and optimize the PV energy production. For a more in-depth diagnostic capability, it would be necessary to know the short-circuit current (Isc) and the open-circuit voltage (Voc) of the PV system. These quantities are indeed useful to recognize non-uniform operating conditions of the PV modules (partial shadings, malfunctions, generic electro-optical mismatch conditions), estimate the PV module junction temperature and the voltage temperature coefficient. However, so far, these quantities cannot be measured by the inverter in operative conditions. With this contribution we propose and test a new electronic interface for a more advanced diagnostics of the PV system to be easily installed between the PV string and the inverter, able to measure the values of Isc and Voc as well as the inverter voltage, current and power working points, avoiding any downtime of the PV system and minimizing the power losses during the diagnosis activity.

A new theoretical approach is proposed for the performance simulation of multijunction (MJ) solar cells, starting from the weakness and strength of the Hovel model and of the transfer matrix method for describing the propagation of electromagnetic waves inside the solar cell structure. It is based on the scattering matrix method (SMM) and on a simplified generation function that allow describing with good accuracy the propagation of electromagnetic waves in the solar cell device, preserving, at the same time, the possibility of getting simple analytical solutions of the continuity equations. The numerical stability of the new theoretical approach is first demonstrated on triple junction InGaP/InGaAs/Ge solar cells, in which the Ge substrate is considered as the last layer (layer N) and then as the N‐1 layer. Further, the new theoretical approach is applied to simulate the performance of thin quadruple junction (QJ) InGaP/InGaAs/SiGeSn/Ge solar cells, in two‐ and three‐terminal configurations. Efficiency values of up to 45.1% and 44.9%, respectively, have been simulated at 1000× concentration, by considering the MJ limited by the InGaAs subcell. Finally, it is estimated that the QJ InGaP/InGaAs/SiGeSn/Ge solar cell has the potential to reach efficiencies over 50% by assuming proper antireflective coatings. [ABSTRACT FROM AUTHOR]

This paper describes the results of an intercomparison of spectroradiometers for measuring global normal incidence and direct normal incidence spectral irradiance in the visible and in the near infrared, together with an assessment of the impact these results may have on the calibration of the short circuit current ( Isc) of triple-junction photovoltaic devices and on the relevant spectral mismatch calculation. The intercomparison was conducted by six European scientific laboratories and a Japanese industrial partner. Seven spectroradiometer systems, for a total of 13 different instruments/channels using two different technologies and made by four different manufacturers were involved. This group of systems represents a good cross section of the instrumentation for solar spectrum measurements available to date. The instruments were calibrated by each partner prior to the intercomparison following their usual procedure and traceability route in order to verify the entire measurement and traceability chain. The difference in measured spectral irradiance showed to have an impact on the calibration of a set of Iso-Type cells varying from ±2% to ±14% for middle and bottom cell, respectively. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We have deposited Ge, SiGe, SiGeSn, AlAs, GaAs, InGaP and InGaAs based structures in the same metalorganic vapor phase epitaxy (MOVPE) growth chamber, in order to study the effect of the cross influence between groups IV and III-V elements on the growth rate, background doping and morphology. It is shown that by adopting an innovative design of the MOVPE growth chamber and proper growth condition, the IV elements growth rate penalization due to As "carry over" can be eliminated and the background doping level in both IV and III-V semiconductors can be drastically reduced. In the temperature range 748–888 K, Ge and SiGe morphologies do not degrade when the semiconductors are grown in a III-V-contaminated MOVPE growth chamber. Critical morphology aspects have been identified for SiGeSn and III-Vs, when the MOVPE deposition takes place, respectively, in a As or Sn-contaminated MOVPE growth chamber. III-Vs morphologies are influenced by substrate type and orientation. The results are promising in view of the monolithic integration of group-IV with III-V compounds in multi-junction solar cells. [ABSTRACT FROM AUTHOR]