Effects of Lake–Reservoir Pumped-Storage Operations on Temperature and Water Quality

Ulrike Kobler,Martin Schmid,Alfred Wüest

doi:10.3390/su10061968

Abstract

Pumped-storage (PS) hydropower plants are expected to make an important contribution to energy storage in the next decades with growing market shares of new renewable electricity. PS operations affect the water quality of the connected water bodies by exchanging water between them but also by deep water withdrawal from the upper water body. Here, we assess the importance of these two processes in the context of recommissioning a PS hydropower plant by simulating different scenarios with the numerical hydrodynamic and water quality model CE-QUAL-W2. For extended PS operations, the results show significant impacts of the water exchange between the two water bodies on the seasonal dynamics of temperatures, stratification, nutrients, and ice cover, especially in the smaller upper reservoir. Deep water withdrawal was shown to strongly decrease the strength of summer stratification in the upper reservoir, shortening its duration by ~1.5 months, consequently improving oxygen availability, and reducing the accumulation of nutrients in the hypolimnion. These findings highlight the importance of assessing the effects of different options for water withdrawal depths in the design of PS hydropower plants, as well as the relevance of defining a reference state when a PS facility is to be recommissioned.

Highlights

The share of “new renewables”, such as photovoltaic and wind power plants, to the electricity production is increasing globally as a consequence of political decisions to reduce greenhouse gas emissions [1,2]
This study aimed to assess the impacts on temperature, stratification as well as water quality in a natural lake and a reservoir connected by a PS hydropower plant
The results shown for Sihlsee were generated at model segment 38 (SEG38), and those for Upper Lake Zurich at model segment 90 (SEG90) (Figure 1)

Summary

Introduction

The share of “new renewables”, such as photovoltaic and wind power plants, to the electricity production is increasing globally as a consequence of political decisions to reduce greenhouse gas emissions [1,2]. At the end of 2016, 2017 GW of renewable power capacity were installed globally [3], with parts of ~300 GW and ~490 GW from photovoltaic and wind power, respectively. The integration of these “new renewables” to the electrical grid is challenging due to their intermittency [4] and entails network load stability problems resulting from decentralized production [5]. The most efficient technologies for storing electric energy are still pumped-storage (PS) hydropower plants, which provide ancillary services such as voltage support and various forms of reserve capacity to fine-tune the matching of supply and demand and to ensure reliability [3]. Within the last few years, PS operations regained attention, and overviews of proposed PS hydropower plants have been presented in various studies [1,7]

Objectives

Methods

Results

Discussion

Conclusion