Outdoor testing of PV module temperature and performance under different mounting and operational conditions Jurij Kurnik n , Marko Jankovec, Kristijan Brecl, Marko Topic University of Ljubljana, Faculty of Electrical Engineering, Trzaska 25, 1000 Ljubljana, Slovenia article info Article history: Received 5 November 2009 Received in revised form 15 February 2010 Accepted 14 April 2010 Available online 28 April 2010 Keywords: PV module temperature Energy balance model PV module mounting and operational conditions abstract Outdoor performance of photovoltaic (PV) modules primarily depends on the instantaneous plane-of- array irradiance (G poa ) and PV module temperature (T pv ). T pv can be estimated from the ambient temperature (T amb ) and the G poa as T pv ¼T amb +k T G poa . The coefficient k T depends strongly on the way the PV module is mounted (open rack, ventilated or unventilated roof mounting, etc.), wind speed and also on the module type. In the presented paper, open rack mounted and unventilated roof integrated cases of PV module installation are experimentally and theoretically examined. Linear relationship with k T is upgraded with a nonlinear one based on the energy balance model and measured data. Nevertheless, T pv is also affected by the module’s regime of operation. The T pv dependency on different regime of operation (open-circuit and maximum power point tracking) for two types of PV modules in two regimes is reported. Differences are discussed in light of energy balance equation within thermal management, where impact of the PV module conversion efficiency on T pv is also shown. & 2010 Elsevier B.V. All rights reserved. 1. Introduction Performance of photovoltaic (PV) modules is usually specified under standard test conditions (STC), but the performance of the modules under real field conditions differs from the expectations derived from the results under standard test conditions due to variety of continuously changing conditions. Therefore it is important to monitor the behaviour of PV modules under real field conditions. For this reason automated computer-controlled monitoring systems [1] are used to measure the I–V curves, total and diffused solar irradiance, module temperature and other meteorological parameters. Under steady-state (or slowly changing) conditions the instantaneous performance primarily depends on the instanta- neous plane-of-array irradiance (G poa ) and PV module tempera- ture (T pv ). The T pv can be estimated from the ambient temperature (T amb ) and the G poa as T pv ¼ T amb +k T G poa . The coefficient k T depends strongly on the way the PV module is mounted (open rack, ventilated or unventilated roof mounting, etc.), wind speed (v) and also on the module type. In the presented paper, open rack mounted and unventilated roof integrated cases of installation are examined. Linear relation- ship with k T is upgraded with an energy balance model. Never- theless, T pv is also affected by the module’s regime of operation. The module temperature dependency on different regimes of operation (open-circuit and maximum power point track- ing—MPP) is reported. We have monitored open rack mounted and roof integrated flexible a-Si VHF modules (Sunslick 7 W, P max ¼ 6.75 W, S pv ¼ 0.24 m 2 , flexible front sheet–back sheet back membrane encapsulation) in open-circuit conditions and also open rack mounted Sanyo HIT modules (HIP-210NHE1, P max ¼ 210 W, S pv ¼ 1.26 m 2 , front glass-backsheet encapsulation) in the two regimes (open-circuit and maximum power point tracking) in parallel and differences are discussed in light of energy balance equation within thermal management. 2. Outdoor PV module monitoring site At our outdoor PV module monitoring site, located on the roof of the faculty of electrical engineering in Ljubljana (Slovenia), we continuously monitor different PV modules from 1st of January 2007. The outdoor monitoring site has been presented in detail elsewhere [2]. The monitored modules at the test site are either open rack mounted or integrated onto a metal roof element and are oriented south with an inclination angle of 301 (optimal inclination angle for Ljubljana). The monitoring facility offers real- time measurement of PV modules’ I–V characteristics together with the measurement of the total and diffused irradiances on the horizontal plane and additionally with measurements of the total irradiance on the inclined plane of the PV modules (301). We also monitor the ambient temperature T amb and temperatures of each module T pv by digital temperature sensors glued on the back sheet Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/solmat Solar Energy Materials & Solar Cells 0927-0248/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.solmat.2010.04.022 n Corresponding author. E-mail address: jurij.kurnik@fe.uni-lj.si (J. Kurnik). Solar Energy Materials & Solar Cells 95 (2011) 373–376