Optimization of number of collectors for integrated PV/T hybrid active solar still M.K. Gaur * , G.N. Tiwari Centre for Energy Studies, Indian Institute of Technology, Hauz Khas, New Delhi 110 016, India article info Article history: Received 6 May 2009 Received in revised form 11 September 2009 Accepted 21 October 2009 Available online 30 November 2009 Keywords: Optimization PV/T collector Hybrid active solar still Exergy abstract The aim of this paper is to optimize the number of collectors for PV/T hybrid active solar still. The number of PV/T collectors connected in series has been integrated with the basin of solar still. The optimization of number of collectors for different heat capacity of water has been carried out on the basis of energy and exergy. Expressions of inner glass, outer glass and water temperature have been derived for the hybrid active solar system. For the numerical computations data of a summer day (May 22, 2008) for Delhi cli- matic condition have been used. It has been observed that with increase of the mass of water in the basin increases the optimum number of collector. However the daily and exergy efficiency decreases linearly and nonlinearly with increase of water mass. It has been observed that the maximum yield occurs at N = 4 for 50 kg of water mass on the basis of exergy efficiency. The thermal model has also been exper- imentally validated. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Desalination is a process to produce the distilled water from brackish/saline water for the use of medical, drinking and charging of the batteries, etc. purposes by using solar energy called solar still. The solar distillation systems are mainly classified as passive and active solar still. In passive solar still, the water in basin is heated directly by solar radiation i.e., without feeding an external energy but in the active solar an additional thermal energy is fed into the basin of passive solar still to increase basin water temper- ature. Daily yield of the solar still can be increases either by chang- ing the design [1–6] (passive solar still) or by increasing the temperature of basin water by external mode (active solar still) [7–11]. Rai and Tiwari [7] have investigated performance of the solar still connected with flat-plate collector. They have observed that with the use of flat-plate collector yield production is increased by 24%. Later on Tiwari and Lawrence [8] have studied thermal analysis of a double effect distillation unit in active operation, tak- ing into account the system as well as climatic parameters. On the basis of numerical computation they have observed an increase of 20% and 30% in efficiency of a solar distillation unit working under active and passive modes, respectively. Kumar and Tiwari [9] have optimized number of collectors and basin area for higher yield for a given depth of active solar still. Kumar et al. [10] have concluded that the annual yield of active solar still is optimum when collector is inclined at 20° and still glass cover is inclined at 15°. Monthly performances of the passive and active solar stills have been eval- uated by Singh and Tiwari [11] for different Indian climatic condi- tions. They have concluded that an annual yield depends on water depth, condensing cover inclination and collector area. They have reported the maximum annual yield at 28.35° inclination of con- densing cover, which is latitude of New Delhi (India). Hermann et al. [12] developed a corrosion-free solar collector for sea water desalination. Kalogirou [13] designed a parabolic trough solar en- ergy collector for enhancing the solar still productivity. The new concept in the field of active solar still is integration of photovoltaic panel with the flat-plate collectors [14]. Hybrid pho- tovoltaic and thermal (PV/T) collectors are introduced to generate electricity and thermal power simultaneously [15]. The rationales behind the hybrid concept is to make the system are self sustain- able so that it can be used in the rural area where the electricity is a major problem. For the performance improvement, many researchers con- nected the various types of solar stills such as double-roof stills, diffusion stills, wetted wick stills to the external assisting systems (flat-plate collectors, concentrators, heat pipes and waste-heat sources) and have been investigated the performance. An increase of electric efficiency by 2% and the thermal efficiency of 60% at 0.01 kg/s flow rate of water for the PV/T water collector with single glazing consisting of tubes in contact with the flat plate, in tran- sient conditions, has reported by Chow [16]. Further a study on the unglazed hybrid (PV/T) system with suitable thermal contact between the PV module and the collector has done by Zak- harchenko et al. [17]. They have reported that the area of module and collector in the PV/T system need not to be equal for higher overall efficiency. A rigorous study has been carried by Kumar and Tiwari [14] on hybrid (PV/T) active solar still. They have re- ported that daily yield obtained is 3.5 times of the passive solar 0306-2619/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2009.10.019 * Corresponding author. Tel.: +91 9953041248; fax: +91 11 26591251. E-mail address: gmanojkumar@rediffmail.com (M.K. Gaur). Applied Energy 87 (2010) 1763–1772 Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy