Abstract
High-efficiency solar cells and modules exhibit strong capacitive character resulting in limited speed of transient responses. A too fastI-Vcurve measurement can thus introduce a significant error due to its internal capacitances. This paper analyses theI-Vcurve error of a measured solar cell or module in light of scan time and irradiance level. It rests on a two-diode solar cell model extended by two bias-dependent capacitances, modelling the junction, and the diffusion capacitance. A method for determination of all extended model parameters from a quasistaticI-Vcurve and open-circuit voltage decay measurement is presented and validated. Applicability of the extended model and the developed parameter extraction method to PV modules is demonstrated and confirmed. SPICE simulations of the extended model are used to obtain theI-Vcurve error versus scan time dependence and theI-Vcurve hysteresis. Determination of the optimal scan time is addressed, and finally the influence of the irradiance level on theI-Vcurve scan time and error is revealed. The method is applied but is not limited to three different wafer-based silicon solar cell types.
Highlights
The I-V curve measurement is an essential performance characterization technique for solar cells and modules as two-terminal DC generators
It is the static I-V curve matching that is essential for good open circuit voltage decay (OCVD) simulation agreement
A method of optimal I-V curve scan time determination of solar cells and modules based on the extended two-diode model was presented
Summary
The I-V curve measurement is an essential performance characterization technique for solar cells and modules as two-terminal DC generators. Either in dark or under illumination, the measurement concept is simple: during the sweep of the terminals of the device under test (DUT) from open circuit to short circuit or vice versa, voltage and current should be measured in quasi static conditions. It can be mistakenly assumed that PV generators exhibit negligible internal capacitance. The last generation thin film solar cells (SCs) and high-efficiency crystalline silicon SCs exhibit extremely high internal capacitances [1]. The internal capacitance together with the series, parallel, and diode differential resistance form an RC circuit that introduces a transient time constant into the measurement process. The time constant determines the quasi static condition. Its magnitude depends on various parameters such as the operating point (voltage and current), temperature, irradiance level, minority carrier lifetime, and other semiconductor parameters only to mention the most important ones
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