First large renewable energy project in India using geomembrane systems

Pumped storage schemes are increasing in number worldwide to facilitate the transition to clean energy. The repeated loading and unloading conditions, created by the water in motion, place demanding loads on the storage containment structures. To avoid water loss, the reservoirs must be designed to maintain watertightness in the long term. In new reservoirs, mostly created by continuous or discontinuous embankments, critical issues are the resistance to settlements, and to differential displacements that can occur at boundaries with concrete appurtenances. Geomembranes, and in particular thermoplastic geomembranes, have demonstrated to be capable of coping with such challenges, due to their tensile and endurance properties. Geomembranes have been used in pumped storage schemes since the 1990s; their scope then was to restore watertightness at one of the dams forming the reservoirs. In the last two decades, with increasing applications in new embankment dams, ingenious design alternatives have been developed, and since the middle of the 2010s thermoplastic geomembranes have started being adopted for new pumped storage reservoirs, instead of concrete/bituminous concrete facings. At present, there are several cases around the world where an exposed geomembrane system is the only barrier preventing water loss, which is an important issue for pumped storage facilities, to ensure safety (avoiding uncontrolled water presence in the embankments) and financial profitability (water loss implies energy loss). The paper focuses on the case history of Pinnapuram, the first renewable energy project in India adopting an exposed geomembrane system as the only water barrier; to be completed in 2024, it is part of the Pinnapuram Integrated Renewable Energy pumped storage project, which includes 1000 MW solar, 550 MW wind and 1680 MW of standalone pumped storage capacity. The scheme is the first pumped storage project developed by Greenko, an independent power producer in India. The upper reservoir features a 6.5 km long rockfill dam, forming a continuous embankment with a nearly rectangular shape in plan, and maximum height of about 40 m. The lower reservoir is formed by three separate rockfill dams connecting existing natural slopes, with total crest length of about 3.3 km and maximum height of about 46 m. The paper discusses the value engineering involved in the study and design of the exposed geomembrane liner for all the dams and for the tail race channel from the tail pool to the lower reservoir, approximately 1.6 km long and where the exposed geomembrane substituted a multilayer bituminous concrete facing originally planned. Some installation aspects will also be discussed. The paper also presents some information on Murdhari 36 m high rockfill dam in Albania, where the original asphalt core design was modified, when the project had already started, to a Geomembrane Face Rockfill Dam (GFRD) to make the dam safer, faster, and easier to build, and less expensive. Murdhari, completed in 2013, has a geomembrane design conceptually similar to that of Pinnapuram dams; the leakage data available after 10 years of operation show a remarkable performance.