Experimental investigation of the optimum photovoltaic panels’ tilt angle during the summer period John Kaldellis * , Dimitrios Zafirakis Lab of Soft Energy Applications & Environmental Protection, TEI of Piraeus, P.O. Box 41046, Athens 12201, Greece article info Article history: Received 1 August 2011 Received in revised form 27 November 2011 Accepted 29 November 2011 Available online 23 December 2011 Keywords: Solar energy Experimental measurements Greece abstract The photovoltaic (PV) technology has made considerable progress during the recent years in both grid connected and stand-alone applications, especially in areas of high local solar potential. In this context, the interest recently demonstrated in the Greek region concerning PVs encourages the investigation of optimum operation conditions for such systems. At the same time, summer-only applications, being rather common in Greece, require maximum exploitation of the local solar potential during the specific period of the year. For this purpose, an experimental study is currently carried out in the area of Athens, in order to evaluate the performance of different PV panel tilt angles during the summer period. According to the experimental results obtained, the angle of 15  (2.5  ) is designated as optimum for almost the entire summer period, while conclusions drawn are accordingly theoretically validated by means of established solar geometry equations. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Remarkable increase of installed capacity worldwide [1] and constantly decreasing costs [2] of the photovoltaic (PV) technology have turned PV applications into one of the most interesting energy alternatives, especially in areas of high quality solar potential. In this context, analogous interest is noted during the recent years in the Greek region as well [3,4], where the favorable local solar potential (annual solar energy at horizontal plane even exceeding 1650 kWh/m 2 [5], Fig. 1) encourages operation of such systems. Installed capacity of PVs in Greece (Fig. 2) exceeds 200 MW (end of 2010) [6], i.e. almost four times the respective of the previous year (55 MW), while at the same time a promising local PV industry seems to emerge (Fig. 3). Furthermore, considerable remuneration of energy produced by grid connected rooftop PV systems under a feed-in-tariff of 550 V/ MWh [7] has attracted numerous applicants in the category of <10 kW p (Fig. 4). At the same time, experience gained in the field [8] (7% of installed capacity corresponds to systems below 10 kW p and 17% to systems below 20 kW p ) largely applies to the sector of small scale stand-alone systems as well. Actually, owed to the fact that there are numerous remote consumers across the Greek region [9,10] that cannot appreciate connection to a solid electricity grid, PV stand-alone applications gradually gain interest on the basis of experience obtained by the operation of small to medium scale grid connected systems. What should be noted is that a large share of these remote consumers concern summer use only (e.g. summer houses, summer hotel units), while in many of these cases, extreme water needs (especially in semi arid areas of the Aegean islands) should also be stressed. As a result, use of PV systems in such summer-only applications (when the local available solar potential maximizes) is thought to be an interesting solution that needs to be examined for the satisfaction of both electrification and irrigation needs [11e 14]. At the same time, efficient operation of PV installations depends on many factors, among which is also the tilt angle of panels. Acknowledging the need to ensure maximization of energy production during the summer months of the year for the appli- cations previously discussed, a systematic effort is currently undertaken to obtain the optimum summer tilt angle of a PV installation located in the area of Athens, central Greece. For this purpose, conduction of experimental measurements during the entire summer season is carried out in the specific study, so as to designate the optimum panels’ tilt angle during the specific period of the year. At this point, it should be noted that investigation on the optimum panel installation angle started in the early 80’s. At that time, Felske [15] investigated the optimum tilt angle in relation to * Corresponding author. Tel.: þ30 210 5381237; fax: þ30 210 5381467. E-mail address: jkald@teipir.gr (J. Kaldellis). URL: http://www.sealab.gr/ Contents lists available at SciVerse ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy 0360-5442/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2011.11.058 Energy 38 (2012) 305e314