Investigation of the regulative operation of a Small Hydropower Plant with storage tank

In this Master's Thesis, with title "Investigation of the regulative operation of a Small Hydropower Plant with storage tank", the improvement of the performance of an existing Small Hydropower Plant (SHPP) under the addition of a storage tank was studied. The above research subject is of great interest as SHPs are plants that operate by exploiting the passing flow of the river, resulting to uncontrolled energy production. The only tank in which water is being collected temporally, before passing through the turbines, is the forebay tank, which purpose is to ensure under pressure conditions of the penstock’s operation. In other words, it is a "storage tank" that deals with transitional phenomena, without implying that it contributes to the controlled storage and passage of the supply discharge, through the turbines. As a result of operation rule of SHPPs, when the incoming flows of the river is less than the minimum, 𝑞𝑚𝑖𝑛, discharge that the turbines can operate, that amount goes unexploited, as for these values the turbines cannot produce energy. The same applies to incoming flows that are greater than the maximum discharge, 𝑞𝑚𝑎𝑥, that the turbines can produce, where the difference (𝑞𝑡 − 𝑞𝑚𝑎𝑥) cannot offer more power. On the contrary, if a storage tank with daily regulation, is added to the existing SHHP, the above ranges of incoming flows, that would otherwise be lost, can be stored and be exploited later. In this way, the flow passing through the turbines can be controlled in order to ensure the nominal flow rate for the longest possible time. Taking into account the above research proposal, by processing the historical daily flow data of the existing run-off-river Argiri Hydropower Plant, on the Platanias River (tributary of the Acheloos), a total of 11 scenarios of different volumes of storage tanks were formulated, each of which was expressed as a percentage of the average daily volume passing through the facilities of the Hydropower Plant. In each scenario, the regulatory rule for the operation of the SHPP with storage, was developed in a MATLAB language environment and applied, in order to calculate the new increased energy production. Specifically, the algorithm focused on the ranges of incoming flows that under the current operation of the SHPP are lost unused. That is, for inflows outside the operating range of the turbine. The regulatory rule of operation, in addition to the optimal utilization of the storage tank, also took into account the minimum operating times and non-operation times of the electromechanical equipment, in order for the new optimized operation to be simulating as realistically as possible. Then, according to the results obtained for each scenario, their techno-economic requirements were calculated. More specifically, each scenario was considered as a possible investment, taking into account their construction costs and the surplus in benefit from energy production due to the addition of storage. The aim was to find the economically and energy-optimal solution, among the examined scenarios, i.e., the solution that at the lowest possible cost gives the largest energy production and therefore profit. Key Performance Indicators which were used to characterize the most sustainable investment are the Net Present Value (NPV) and Internal Rate of Return (IRR).