N. A. Sadchikov

Progress In Developing HCPV Modules Of SMALFOC-Design

This work presents a module generation which has been named as “SMALFOC module design”. The abbreviation reflects the main features of the modules: Small-size concentrators; Multi-junction cells; “All-glass” structure; Lamination technology; Fresnel Optics for Concentration. Investigated modules have revealed a quite low over-heating temperature of cells in the MPP regime of operation and a real way for increasing the PV efficiency, if the rear glass base is supplied with an antireflection coating. Outdoor and high/low temperature tests have shown a good potential for long-term operation of such a type of modules.

Thermal Regimes of Fresnel Lenses and Cells in “All‐Glass” HCPV Modules

We report on research carried out at the Ioffe Physical Technical Institute in the field of operational conditions of the high‐concentration photovoltaic (HCPV) module components. The subject of investigations are thermal regimes of the primary Fresnel lenses and multijunction solar cells. Two main issues governing the design of a solar concentrator module with III–V triple‐junction solar cells (SCs) are considered: the effective concentration of radiation using Fresnel lenses, and effective heat removal from SCs. By theoretical and experimental simulating these processes, the design parameters of modules’ elements have been found. A test batch of sub‐modules (HCPV modules based on individual Fresnel lenses) has been fabricated and tested. The influence of different operation temperatures on the optical efficiency of Fresnel lenses and conversion efficiency of solar cells have been estimated.

Evaluation of the PV Cell Operation Temperature in the Process of Fast Switching to Open-Circuit Mode

A procedure for measuring the overheating temperature (ΔT ) of a p-n junction area in the structure of photovoltaic (PV) cells converting laser or solar radiations relative to the ambient temperature has been proposed for the conditions of connecting to an electric load. The basis of the procedure is the measurement of the open-circuit voltage (VOC ) during the initial time period after the fast disconnection of the external resistive load. The simultaneous temperature control on an external heated part of a PV module gives the means for determining the value of VOC at ambient temperature. Comparing it with that measured after switching OFF the load makes the calculation of ΔT possible. Calibration data on the VOC = f(T ) dependences for single-junction AlGaAs/GaAs and triple-junction InGaP/GaAs/Ge PV cells are presented. The temperature dynamics in the PV cells has been determined under flash illumination and during fast commutation of the load. Temperature measurements were taken in two cases: converting continuous laser power by single-junction cells and converting solar power by triple-junction cells operating in the concentrator modules.

CPV Modules Based on Lens Panels

A work on development of the high concentration photovoltaic (HCPV) modules with Fresnel lens panels and III-V multijunction cells is presented. A composite structure of the small-aperture area 40x40 (or 60x60) mm2 Fresnel lenses, united in a panel, was realized. A silicate glass sheet (front side of a module) serves as a superstrate for transparent microprisms formed in silicone. Small averaged thickness of the prisms ensures low IR absorption of sunlight in comparison with acrylic Fresnel lenses. Temperature dependences of the optical properties in such a type of the solar concentrators and PV properties of the cells in passive heat dissipation conditions are under consideration. The solar cells are the triple-junction InGaP/(In)GaAs/Ge cells with designated illumination area 1.7-2.3 mm in diameter. A HCPV module consists of the 144 (or 64) sub-modules in 12x12 (or 8x8) configuration. Solar cells are protected from environment in different ways: by side walls of a module body, or by a rear glass sheet at integrated sealing the cells in a back-side module panel. Module design includes refractive smooth-surface secondary lenses. The cell strings are glued to the rear glass surface of the module body using lamination process. Proper quality of the solar cells in a multistage module assembling procedure is ensured owing to specially developed contactless test method, based on analyzing the electroluminescent signals at local photoexitation. For arrangement of the HCPV modules in a solar installation, a number of the solar trackers have been developed and realized for 1-3-5 kWp of the installed power.

HCPV Modules With Primary And Secondary Minilens Panels

We report on research activities at the Ioffe Physical Technical Institute in the field of secondary lenses for HCPV modules based on primary Fresnel lenses and multijunction cells of 12×12 or 8×8 configuration. For this, the smooth‐surface secondary lenses, each about 12 mm in diameter, are integrated into a secondary minilens panel placed in front of the solar cells. For both panels the glass sheets 4 mm thick serve as the common base plates. The cells with passive copper heat spreaders are placed on the outer side of the secondary minilens panel, so that this panel is a common protective cover glass for cells integrated in the module. Significant increase in the local sun concentration ratio and in the module acceptance angle have been measured both indoors and outdoors.

HCPV modules of SMALFOC design in versions for PV and PV/T operation

The recently developed HCPV modules of SMALFOC design (Small lenses, Multijunction cells, All from glass, Lamination, Fresnel, Optics, Concentration) are characterized by structural and technological similarities with flat plate modules. In the paper, two variants of module usage are considered: (i) version for an “ordinary” generation of electricity; (ii) version for operation as a hybrid system, where a combined PV/Thermal approach is realized for producing both electricity and heated water. Water as a heat removing fluid is made to flow through a flat structure applied to the laminated back side of a HCPV module. PV and PV/T performances of the modules at different operation conditions are presented.

Influence of Heat Dissipation Conditions on the Characteristics of Concentrator Photoelectric Modules

The results of studying the effect of various conditions of heat dissipation on heating and temperature distribution in components of concentrator photovoltaic modules are reported. The modules based on Fresnel lenses and triple-junction solar cells InGaP/GaAs/Ge mounted on copper and steel heat sinks are studied. In order to determine the thermal characteristics, we use a method, which makes it possible to measure the temperature of the p–n junctions in the solar cells under laboratory conditions upon the simulation of thermal processes arising in the course of operation of the module under typical conditions. Further, the above temperature is used to calculate the value of the thermal resistance for a system consisting of a solar cell and the surrounding medium. The thermal processes in the module are simulated by transferring current through the solar cells in the forward-bias direction. The value of heating of the solar cells is determined by comparing the forward-voltage drops measured at the time of its rapid application or switching-off under various conditions of heat removal. The conditions of heat removal are varied using the generator’s air flow.