Small hydropower plant enhanced with minimal storage capacity: Investigation of its techno-economic feasibility with intra-day regulation

In recent years, the penetration of Renewable Energy Sources (RESs) into the EU energy market has become increasingly significant. The perpetual availability of RESs, has given them the leverage of enabling rapid and growing implementation. Propelled by the above, this research examines how one of the most well-known and widely adopted renewable energy sources, namely run-of river hydropower plants, can be optimized to reduce their uncertainty and thus facilitate their integration into the grid. In particular, it is assessed how a Small Hydropower Plant (SHPP), operating as a typical run-of river scheme, can benefit from the addition of a small storage tank. In this vein, a novel operation rule of the SHPP with storage tank is proposed on a daily basis with hourly step, to ensure the best exploitation of the passing inflows. To evaluate the possible augmentation of the SHPP's efficiency, different scenarios are investigated regarding the size of the storage tank based on a percentage of the mean daily water supply. The results are rated after conducting a techno-economic assessment for each scenario, also considering their construction costs and the surplus from energy production due to storage. Key Performance Indicators are the Net Present Value (NPV), the Internal Rate of Return (IRR) and the Benefit-Cost ratio (B/C). Additionally, a sensitivity analysis is performed regarding the electricity sales prices, total investment cost, economic lifespan and discount rate. From the results for the small hydropower plant of nominal power 6.9 MW, net head 300 m, maximum inflow 2.40 m3/s, at the Argyri area of river Platanias, Greece, which is being studied, it is found that tanks with a capacity of up to 5 % of the mean daily water supply are technically and economically viable. The optimal result is achieved for a capacity corresponding to 1 % of the mean daily water supply, with an active volume of 620 m3, basic cost of 120 k€, with a Net Present Value equal to 436 k€, Internal Rate of Return equal to 40.83 % and Benefit-Cost ratio equal to 3.99, for an economic lifespan of 20 years and a discount rate of 6 %.