The challenges of local pumped storage hydropower: modelling the equipment of the pumping-turbining cycle to improve the flexibility and efficiency of the plant.

摘要

Pumped Storage Plants (PSP) are key assets to facilitate the integration of Intermittent Renewable Energy Sources (IRES). However, most of these plants are above 100MW and connected to the transmission grid, while the growth and the geographic diversity of the IRES inevitably cause increased stress on the distribution grids. Distributed smaller and highly flexible PSP may provide qualitative enhancement, notably through ancillary services. Without the economy of scale factor, it is absolutely imperative to act and find new sources of profit. This is achieved through the smart control of a virtual power plant where IRES provide energy and a PSP provides flexibility. The plant output and ancillary services1 are optimized by computer, on the basis of the forecast and the monitoring of both IRES production and electric markets' prices. Increasing the value of this concept requires to optimize the efficiency and the operating range of the PSP. A separate losses method has been developed to calculate the losses of all elements in the pumping-turbining cycle: hydraulic and electrical machines, bearings, runner turning in air, Variable Frequency Drive (VFD), transformer, etc. The connection to the distribution grid bounds the power range to 5-20MW, which allows the use of full VFD for starting and control the speed of the pumps. Thus pumps do not require a synchronous speed. Cooling losses are not included in the usual VFD losses and have to be introduced in the global efficiency calculation. Variation of water levels in the upstream and downstream reservoirs have an influence on the head, modifies the efficiency of the hydraulic machines, and reduces the operating range of the pump in order to fulfill the cavitation criteria. A reliable modelling of the PSP efficiency is required to: Optimize the design and the choice of the electro-mechanical equipment of the PSP. Simulate all the possible scenarios of PSP cycle in relation with the various energy and ancillary services of the energy market.