Abstract - A monitoring circuit for individual photo- voltaic (PV) panels in grid-connected systems is proposed, which exhibits a number of features devised to simplify and reduce cost of diagnostics and maintenance of the PV plant. In particular, the system is provided with an effective energy harvesting supply stage, which eliminates the requirement for external supply or batteries; furthermore, no cables are needed for data transfer due to the adoption of a rugged wireless connectivity. Index Terms - Energy harvesting, monitoring system, photovoltaic panel, supercapacitor I. INTRODUCTION Monitoring of PV plants to quantify the energy yield and detect failures has assumed a relevant role in recent years. Various monitoring solutions have been indeed presented in literature in order to identify the reasons leading to efficiency losses. In [1], some environmental variables and the I–V curves of the PV plant are evaluated; in [2], the energy conversion is maximized by means of a PV panel incorporating a DC-DC converter with an integrated maximum power point tracker (MPPT). However, the proposed circuits are quite complex and often require a cumbersome installation: in [1], additional cables are needed for data transmission and supply distribution over the PV plant; in [2], every panel is provided with a power stage (boost converter) and power line communications (PLC), which reduce the system performance in terms of reliability and working life. Satellite-based monitoring systems have been also developed to identify power outages [3]. However, their application is unavoidably limited to satellite-observed PV plants. Unfortunately, none of the above solutions allow the monitoring of individual panels embedded in grid-connected PV systems, which – accordingly to recent studies [4] – contribute to 15% of the failure cases. In this paper, a novel system allowing for a single- panel-granularity monitoring is proposed as an attempt to tackle and solve the above shortcomings. The circuit is equipped by a suitable energy harvesting supply stage relying on supercapacitors, which makes the whole system self-powered. For the first time, cabling is avoided by exploiting a rugged wireless communication to transfer the data measured on the individual panel. II. THE MONITORING CIRCUIT The proposed monitoring circuit, whose schematic block diagram and PCB prototype are illustrated in Figs. 1 and 2, respectively, can be described as follows. A. The supply stage The supply is provided by the monitored panel through an energy harvesting stage, which generates the requested voltages (i.e., 3.3 V for the logic unit and 12 V for the measurement circuit). The supply strategy is based on the adoption of supercapacitors, which are typically preferred to electrochemical batteries in energy harvesting applications (as in e.g., wireless sensors [5], [6]) due to the longer working life [7], [8] (i.e., number of discharge/charge cycles), lower cost and size, higher efficiency, and faster/simpler charging. In the developed prototype, two supercapacitors are employed to operate as back-up energy storage elements (a) during the measurement stage and (b) in low-light hours (i.e., in low solar irradiation conditions). The supply circuit involves two sub-networks, which can be addressed as follows. The first one is devised to charge the supercapacitors by deriving current from the panel. In previous works [5], [6], [9], this portion is realized through a custom DC-DC converter with a dedicated MPPT to adjust the operating point of the panel accordingly to the energy requirements of the overall circuit. Unfortunately, such a strategy is not suited for energy production applications, in which the operating point must not be affected by the supply circuit. In order to tackle this issue, we conceived and designed an ad hoc charge network, which relies on a “feedback” monitoring action on the voltage drop across the super- capacitors (in particular, such a network automatically starts charging the capacitor as the voltage drop is lower than a threshold value). This strategy – differently from the approach employed in [5], [6], [9] – prevents modifying the operating point of the panel due to the relatively small amount of current derived. In particular, the charge network absorbs 60 mA only during the start- up phase (i.e., when the circuit is installed) and, more in general, at each dawn, in order to guarantee a fast circuit switching on, while deriving about 20 mA during the standard behavior. The charge network is fully deactivated by the control logic during the measurement A Novel Wireless Self-powered Microcontroller-based Monitoring Circuit for Photovoltaic Panels in Grid-connected Systems M. Gargiulo*, P. Guerriero*, S. Daliento*, A. Irace*, V. d’Alessandro*, M. Crisci**, A. Smarrelli**, and M. Smarrelli** * Department of Biomedical, Electronics, and Telecommunications Engineering (DIBET), University of Naples Federico II, via Claudio 21, 80125 Naples, Italy. Phone: +39-081-7683122; fax: +39-081-5934448; e-mail: daliento@unina.it ** ISET Energia – Divisione di ISET (Industria Sistemi Elettronici) S.r.l., via Votta Consorzio ARCHO, 81020 Valle di Maddaloni, Italy. 978-1-4244-7919-1/10/$25.00 ©2010 IEEE SPEEDAM 2010 International Symposium on Power Electronics, Electrical Drives, Automation and Motion 164