TECHNO-ECONOMIC STUDY OF AN EXISITNG PUMPED STORAGE PLANT

Abstract

The growing economy with corresponding increase in power demand causes more challenges in power sector of developing countries. In India, the increase in peak power demand necessitates energy storage schemes over and above the storage - hydro, oil and gas based peak power plants to ensure power system stability. In utility energy storage schemes, the Pumped-hydro energy storage schemes (PHES) attract more attention even in the developed countries due to their unique operational flexibility over other energy storage systems. In India, PHES are developed for improving the net efficiency of the base load thermal power plants. The availability of suitable topographies, hydro-thermal ratio imbalance in various regions, optimal storage capacity for flexible power system operation, requirement of spinning reserve, increased generation from renewable energy sources gives a thought for the planers and executors to implement these schemes to meet peak demand. Under these circumstances, this research initially addresses the present operating conditions of the existing PHES of the country, their operational constraints, historical performance and future prospects. In the beginning, these schemes were operated only at times of peak and major power plant outages due to less cycle efficiency. The analysis of the existing schemes reveal that the major reason for less output from the PHES in India than that envisaged in the planning stage is deficit off-peak power available for pumping almost in all the regional power grids except the north-eastern grid. But gradual increase in efficiency has been realized from PHES operation after the introduction of the availability based tariff (ABT) in 2003. Further, a performance evaluation has been carried out for the 26 year-old Kadamparai pumped storage plant (4x100 MW) located in the state of Tamil Nadu, India since it is the first successful pumped storage plant of the country by operation. Detailed analysis of the plant have been mainly focused on i) reservoir regulation, ii) introduction of variable speed technology of pumped storage and iii) the economic aspects of pumped storage plant. Reservoirs are the major part of a hydro power plant especially for a pumped storage plant since recycling process of water is essential. Hence the reservoir regulation of the Kadamparai pumped storage plant has been analyzed. For this purpose, a water regulation model has been developed based on hydrological mass balance with the ii objectives of energy maximization and spill minimization. Monthly reservoir storage curve and operating policies have also been derived and presented for future operation of the plant efficiently. Variable speed operation is a new area of study in pumped storage operation. The newly planned pumped storage schemes are mostly equipped with this technology worldwide. But, in India no such schemes are existing now and the first variable speed pumped storage scheme of the country (Tehri) is under construction. Hence a variable speed analysis has been conducted to check the feasibility of variable speed drives installation in the Kadamparai pumped storage plant during renovation and modernization due in next few years. The efficiency difference between fixed and variable speed operation has been analyzed and the results have been presented. Further, the efficiencies and the discharges derived from the efficiencies have been analyzed with existing five years (2006-2010) reservoir data and the pumping benefits have also been worked out to determine the additional energy likely to be generated. The analysis reveals that the results are encouraging and hence variable speed machines have been recommended for the plant during renovation and modernization. In addition with the above technological analysis, an economic analysis has also been carried out in this research. Preliminarily, various costs involved in pumped storage operation of the country have been analyzed which will be useful for the planners and policy makers for future planning of pumped storage schemes. Regarding Kadamparai, an economic analysis has been carried out with pumping energy cost to check the economic status of the plant in the state grid. The analysis reveals that the considerable economic benefits obtained by the PHES in the state grid after 2003 i.e. after the introduction of ABT and the cost of generation from the pumped storage plant is comparatively less than that of other peaking plants such as gas and diesel peaking power plants of the state. The research reveals that the installation of pumped storage plants is essential for the flexible operation of Indian power system and to optimally utilize the vast renewable energy sources of the country. Regarding Kadamparai analysis, the derived reservoir storage curves, operating guidelines and the variable speed analysis are certainly helpful to increase the plant performance.