A wide literature review of recent advance on monitoring, diagnosis, and power forecasting for photovoltaic systems is presented in this paper. Research contributions are classified into the following five macroareas: (i) electrical methods, covering monitoring/diagnosis techniques based on the direct measurement of electrical parameters, carried out, respectively, at array level, single string level, and single panel level with special consideration to data transmission methods; (ii) data analysis based on artificial intelligence; (iii) power forecasting, intended as the ability to evaluate the producible power of solar systems, with emphasis on temporal horizons of specific applications; (iv) thermal analysis, mostly with reference to thermal images captured by means of unmanned aerial vehicles; (v) power converter reliability especially focused on residual lifetime estimation. The literature survey has been limited, with some exceptions, to papers published during the last five years to focus mainly on recent developments.

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This paper presents a novel bypass approach for photovoltaic panels relying on a bipolar transistor operated in saturation, the activation of which is handled automatically by a circuit comprising a pair of MOS transistors only. The functioning principle of the proposed system is explained and the improvements in terms of reliability of the bypassed subpanel and power produced by the string in comparison with a traditional diode-based scheme are quantified. The analysis is corroborated by dc/transient measurements and tailored PSPICE simulations.Index Terms-Active bypass, bypass diode, one-diode equivalent circuit, hot spot, photovoltaic (PV) panel, shading.