Work on site study of the proposed 2000-megawatt (MW) Rs.7,000-crore Sillahalla pumped storage hydro-electric project in the Nilgiris and Coimbatore districts will begin next month.
Around the middle of May, the Tamil Nadu Generation and Distribution Corporation (Tangedco) will float bids, inviting proposals from survey agencies to carry out the study.
It is on completion of the study that the authorities will know precisely the extent of land requirement and details regarding ownership and nature of use of lands to be acquired, according to an official. Four months will be earmarked for the study.
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A few days ago, Chief Minister Jayalalithaa announced in the Assembly that her government decided to take up the project, which would take eight to 10 years to complete.
Explaining the salient features of the project, the official says that the project has been envisaged to impound the Sillahalla river, which comes under the Kundah river basin in the Nilgiris district.
The project seeks not only to dam the Sillahalla but also to interconnect the proposed dam with the Avalanche-Emerald reservoir, which is also located at the same level. It includes the construction of both a surface storage point and an underground power house.
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Approximately, 4.2 thousand million cubic feet (TMC) of water is to be impounded by the proposed dam in a year. The inter-connecting tunnel will have a provision for two-way flow.
As being done in the case of the 400-MW Kadamparai pumped storage plant in Coimbatore district, the authorities are planning to operate the Sillahalla power plant for catering to peak hour demand.
The Sillahalla dam can act as a balancing reservoir between the Avalanche-Emerald dam and the downstream Pillur dam.
The project is called so because water from Pillur will be pumped up to the proposed Sillahalla reservoir, normally between midnight and 6 a.m., when power is available at cheaper rate. During morning or evening peak hours (6 a.m./6 p.m. to 9 a.m./10 p.m.), water will be released from the reservoir to the underground power house, which will generate electricity that can be sold at higher rates.
Higher capacity
Asked how the capacity of 2,000 MW has been arrived at, the official says that it is because of the availability of the hydraulic head (difference between level of Avalanche-Emerald-Sillahalla dams and that of Pillur reservoir) of 1500 metres.
Asked whether the estimated cost of the project has been realistically prepared, the official replies in the affirmative and adds that that cost is inversely proportional to capacity.
The project has been conceived to derive several benefits. The proposed dam along with the existing Avalanche-Emerald reservoir will ensure sustained power generation by four hydro-electric (HE) plants of Kundah with 515 MW. Additionally, 178 million units of energy will be produced, which, in terms of monetary value, will come to about Rs. 100 crore per annum.
Apart from meeting higher demand during peak hours, the proposed plant will provide flexibility to the State grid for operation.
It can be used as a conventional HE plant too in times of surplus flows. As most of the Kundah units were commissioned in the 1960s and their life cannot be extended beyond a point, the Sillahalla will be an effective replacement.