Energy 32 (2007) 755–759 An investigation of mismatch losses in solar photovoltaic cell networks N.D. Kaushika a,Ã , Anil K. Rai b a Bharati Vidyapeeth School of Multidisciplinary Research, B.V. College of Engineering, A-4 Paschim Vihar, New Delhi 110063, India b Centre for Energy Studies, Indian Institute of Technology Delhi, Hauz-Khas, New Delhi 110016, India Received 12 August 2005 Abstract Solar photovoltaic (PV) arrays in field conditions deliver lower power than the array rating. In this paper, the sensitivity of solar cell parameters in the variation of available power from the array is investigated. The parameters characteristic of aging and fresh cells used in prototype field systems have been used for computation of reduction in the available power. It is found that in series string the fractional power loss would increase from 2% to 12% with aging of solar cells. However, this fractional power loss may be reduced to 0.4–2.4% by an appropriate series-paralleling. r 2006 Elsevier Ltd. All rights reserved. Keywords: Solar photovoltaic; Cell characteristics; Mismatch power loss 1. Introduction In solar photovoltaic (PV) arrays solar cells are connected in series and parallel in the network to match the required voltage and current requirements. An un- desirable and important feature of the solar PV arrays that has emerged from the field experience is that their output power ratings based on name plate rating of modules are universally higher than those observed in field conditions even when the operating conditions were close to standard test conditions (STC) [1]. The feature of delivering power lower than the array ratings in the field conditions is often referred to as mismatch loss. Several authors (e.g., [2–5]) have investigated the lowering of available power in solar PV arrays and found it to be due to small variations in cell characteristics. In this paper, we investigate the effect of aging of solar cells on the reduction in available power. This investigation is based on real-life data of ensemble of fresh and aging solar cells and is intended to enable the sizing of solar PV system in such a way that it can deliver power to the given load without failure for longer duration [6–8]. 2. Mismatch losses in solar PV arrays The mismatch losses in solar PV arrays can be due to a variety of reasons as follows [9–11]. 2.1. Manufacturer’s tolerances in cell characteristics Physical differences between cells or cell-processing material may arise during normal processing and different cells may have slightly different characteristic parameters. Consequently, in an array the output power of the combination is less than the sum of maximum output power of constituents. This power loss may tend to enhance with time due to degradations resulting from aging. 2.2. Environmental stresses The environmental stresses in solar PV array include the partial or full opening of a string due to cell cracking (provoked by hail impact) or otherwise. This not only gives rise to mismatch loss but also could result in excessive heating of the regions of power dissipation, which in turn can lead to solder melting and damage the encapsulant. ARTICLE IN PRESS www.elsevier.com/locate/energy 0360-5442/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2006.06.017 Ã Corresponding author. Tel.: +9111 25278444; fax: +91 11 25275436. E-mail address: ndkaushika@yahoo.com (N.D. Kaushika).