ORIGINAL PAPER Comparative study of lead-acid batteries for photovoltaic stand- alone lighting systems B. Hariprakash Æ S. K. Martha Æ S. Ambalavanan Æ S. A. Gaffoor Æ A. K. Shukla Received: 18 April 2007 / Revised: 13 August 2007 / Accepted: 22 August 2007 / Published online: 14 September 2007 Ó Springer Science+Business Media B.V. 2007 Abstract The lead-acid battery is often the weakest link in photovoltaic (PV) installations. Accordingly, various versions of lead-acid batteries, namely flooded, gelled, absorbent glass-mat and hybrid, have been assembled and performance tested for a PV stand-alone lighting system. The study suggests the hybrid VRLA batteries, which exhibit both the high power density of absorbent glass-mat design and the improved thermal properties of the gel design, to be appropriate for such an application. Among the VRLA-type batteries studied here water loss for the hybrid VRLA batteries is minimal and charge-acceptance during the service at high temperatures is better in relation to their AGM counterparts. Keywords AGM-VRLA battery Á Flooded-electrolyte lead-acid battery Á Gelled-electrolyte VRLA battery Á Hybrid VRLA battery Á Photovoltaic lighting 1 Introduction It is estimated that earth constantly receives 96 billion kW of power [1]. If this colossal and unlimited energy could be more fully utilized, our dependence on the fast dwindling fossil fuel cache will be drastically reduced. Solar energy is available in various forms such as direct solar radiation, wind, wave, rain (in the form of hydropower), photosyn- thesis and ocean thermal gradients [2]. Among these, the direct generation of electricity from solar radiation through solar cells is clean and attractive [3]. However, due to the intermittent nature of solar radiation, efficient and economic management of electrical energy requires its storage. The storage and retrieval of electrical energy is most conveniently accomplished at present with storage batteries. There are several types of storage batteries, but it is the lead- acid battery, which predominates when the requirement is for stored energy of more than a few 100 W-h because no other battery is yet able to compete on cost grounds [4, 5]. How- ever, in photovoltaic (PV) installations, the lead-acid battery is often the weakest link owing to its limited cycle-life and hence its premature replacement [6–17]. This communication describes a study conducted on the performance of hybrid VRLA, absorbent-glass-mat (AGM) VRLA, gelled-electrolyte VRLA, and flooded-electrolyte versions of lead-acid batteries for a PV application, namely stand-alone solar-lighting during February 2005 and June 2006. The study suggests the hybrid VRLA batteries to be most appropriate among all the aforesaid battery types. 2 Experimental details 2.1 Preparation of plates Both positive and negative plates for the batteries were prepared using Pb–Ca–Sn–Al alloy (0.1% of Ca, 1.2% of Sn and 0.03% of Al) grids. The batteries were assembled in ABS containers using 1.25 specific gravity aq. H 2 SO 4 as B. Hariprakash Á S. K. Martha Á A. K. Shukla Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560 012, India S. Ambalavanan Á A. K. Shukla (&) Central Electrochemical Research Institute, Karaikudi 630 006, India e-mail: shukla@sscu.iisc.ernet.in S. A. Gaffoor NED Energy Ltd, 6-3-1109/1 Navbharat Chambers, Raj Bhavan Road, Hyderabad 500 082, India 123 J Appl Electrochem (2008) 38:77–82 DOI 10.1007/s10800-007-9403-4