Sustainable hydropower in a renewableenergy system, fluctuating climateand with environmental constraints

Background

Major issues for hydropower are due to the transition towards a renewable energy system in combination with climate driven fluctuations in the energy availability in such renewables. Figure 1 shows a quantification of the average energy levels of terrestrial hydrology in Sweden based on half-a-century of hydro-climatic data. Such variations in the technological conditions and energy availability affect not only the management strategy for hydropower storage in water reservoirs (Fig. 2), but also many aspects regarding the long-term safety of embankment dams, internal erosion, design floods for dams, spillway design and multi-purpose management of water use for energy, irrigation and municipal water supply. Such technical services need also to take into account long-term climate fluctuations and environmental concerns for the aquatic environment (Fig. 3). Further, the shift towards renewable energy, in particular hydropower, is associated with human impacts on the hydrological regime, which could affect frequency and magnitude of flood events. At the same time, though, dams and reservoirs for hydropower production can play a role in attenuating flood events, thus reducing adverse consequences of flooding. 

Aims
Important aims of this research include the development of management models for hydropower production with account taken to new challenges due to climate change, change of the energy systems towards more renewable energy sources, new environmental requirements and resource constraints. Globally, there is enough renewable energy, but a major problem is to balance the production over time using relatively limited hydropower and bioenergy, which is why it is important to develop management models for ensuring reliable energy supply on regional to global level. Two useful applications are a) production management models that can directly enhance production effectiveness and b) strategic planning of renewable energy systems with account to environmental and climatic constraints. As a basis for such model development it is essential to provide temporal statistics and spatial mapping of hydropower potential and the associated large-scale groundwater renewal.  

Approaches
Hydro-climatic processes induce significant fluctuation in the availability of renewable energy, which can be expressed in terms of power spectral diagrams (Fig. 4). Such representation separates the variance in a time-series on different time periods or frequencies and, in this case (Fig. 4), shows that there is – not surprisingly – a high seasonal variance in hydropower availability (PTot). The diagram also shows major bi-annual and long-term variations that may impose significant problems for a reliable energy supply by regulating the energy production over time by the use of hydropower. Our group is developing a spectral analytical method that links the basic physics of hydrological processes to the statistics of the forcing and resulting time-series; this means for example that it is possible to statistically link climate-driven variation in renewable energy availability (forcing time-series) to the power production demand spectrum (resulting time-series) through mathematical models of the regulatory behavior of as well as regulation strategy for the hydrological system with its water reservoirs. Particularly, the method makes it possible to predict thresholds of the regulatory capacity of the hydropower system or, conversely, the need for expanding the capacity to accommodate a higher degree of renewable energy production. Unlike previous statistical approaches for reservoir design this method formally separates climate drivers for bio-, wind-, solar and hydropower from the physical dynamics of the regulation system, thereby, facilitates a more reliable water reservoir design under variable conditions.  

Links
Wörman, A., Lindström, G., Riml, J., 2017. “The Power of Runoff”, J. Hydrology, 548(2017): 784-793, dx.doi.org/10.1016/j.jhydrol.2017.03.041 

Zmijewski, N., Bottacin-Busolin, A., Wörman, A., 2015. “Incorporating hydrologic routing into reservoir operation models: Implications for hydropower production planning”. Water Resources Management, December 2016, 30(2):623–640, DOI: 10.1007/s11269-015-1181-x 

Zmijewski, N., Wörman, A., 2016.  “Hydrograph variances over different time-scales in hydropower production networks”, Water Resources Research, 52(8):5829-5846, 10.1002/2015WR017775 

Åkesson, A., Wörman, A., Riml., J., Seibert, J., 2016. “Change in streamflow response in unregulated catchments in Sweden over the last century”, Water Resources Research, 52(8): 5847-5867doi/10.1002/2015WR018116 

Project leader & Other project members

Prof. Anders Wörman*  

Assoc. Prof. Luigia Brandimarte* 

Ass. Prof. Joakim Riml* 

Doctoral Student Shuang Hao 

*Division of River Engineering