Énergie

In the wake of the COP21 conference in Paris, the transition to a low-carbon energy supply remains a central issue on the political agenda. The deployment of renewable energies is often challenged by multiple issues (e.g., public acceptance, landscape protection, and so forth). Political actors try to overcome such challenges with various measures; however, the policy instruments used vary greatly in their strength. This article questions what factors lead to the adoption of strong policy instruments promoting hydroelectricity. Explanatory factors are derived from Kingdon's multiple streams framework and are analyzed with fuzzy-set qualitative comparative analysis within the Swiss cantons. The findings show that the strength of policy promoting hydroelectricity depends on the conjunction of mainly two factors: ambitious climate targets and an already well-established hydroelectricity sector that generates large tax revenues for the cantons. Depending on the context, the strength of left-wing and green parties as well as the current level of exploitation play an important role with the aforementioned factors.

We monitored CH₄ emissions during the ice-free period of an Alpine hydropower reservoir in the Swiss Alps, Lake Klöntal, to investigate mechanisms responsible for CH₄ variability and to estimate overall emissions to the atmosphere. A floating eddy-covariance platform yielded total CH₄ and CO₂ emission rates at high temporal resolution, while hydroacoustic surveys provided no indication of CH₄ ebullition. Higher CH₄ fluxes (2.9 ± 0.1 mg CH₄ per m² per day) occurred during the day when surface water temperatures were warmer and wind speeds higher than at night. Piston velocity estimates (k₆₀₀) showed an upper limit at high wind speeds that may be more generally valid also for other lakes and reservoirs with limited CH₄ dissolved in the water body: above 2.0 m s⁻¹ a further increase in wind speed did not lead to higher CH₄ fluxes, because under such conditions it is not the turbulent mixing and transport that limits effluxes, but the resupply of CH₄ to the lake surface. Increasing CH₄ fluxes during the warm season showed a clear spatial gradient once the reservoir started to fill up and flood additional surface area. The warm period contributed 27% of the total CH₄ emissions (2.6 t CH₄ per year) estimated for the full year and CH₄ accounted for 63% of carbonic greenhouse gas emissions. Overall, the average CH₄ emissions (1.7 to 2.2 mg CH₄ per m² per day determined independently from surface water samplings and eddy covariance, respectively) were small compared to most tropical and some temperate reservoirs. The resulting greenhouse gas (GHG) emissions in CO²-equivalents revealed that electricity produced in the Lake Klöntal power plant was relatively climate-friendly with a low GHG-to-power output ratio of 1.24 kg CO_2,eq per MW h compared to 6.5 and 8.1 kg CO_2,eq per MW h associated with the operation of solar photovoltaics and wind energy, respectively, or about 980 kg CO_2,eq per MW h for coal-fired power plants.

Hydropower plants are an important source of renewable energy. In the near future, high-head storage hydropower plants will gain further importance as a key element of large-scale electricity production systems. However, these power plants can cause hydropeaking which is characterized by intense unnatural discharge fluctuations in downstream river reaches. Consequences on environmental conditions in these sections are diverse and include changes to the hydrology, hydraulics and sediment regime on very short time scales. These altered conditions affect river ecosystems and biota, for instance due to drift and stranding of fishes and invertebrates. Several structural and operational measures exist to mitigate hydropeaking and the adverse effects on ecosystems, but estimating and predicting their ecological benefit remains challenging. We developed a conceptual framework to support the ecological evaluation of hydropeaking mitigation measures based on current mitigation projects in Switzerland and the scientific literature. We refined this framework with an international panel of hydropeaking experts. The framework is based on a set of indicators, which covers all hydrological phases of hydropeaking and the most important affected abiotic and biotic processes. Effects of mitigation measures on these indicators can be predicted quantitatively using prediction tools such as discharge scenarios and numerical habitat models. Our framework allows a comparison of hydropeaking effects among alternative mitigation measures, to the pre-mitigation situation, and to reference river sections. We further identified key issues that should be addressed to increase the efficiency of current and future projects. They include the spatial and temporal context of mitigation projects, the interactions of river morphology with hydropeaking effects, and the role of appropriate monitoring to evaluate the success of mitigation projects.

This study presents the first quantitative meta-analysis of the non-market valuation literature on the external effects associated with wind power production. A data set of 60 observations drawn from 32 studies is constructed. The relative economic values of different types of externalities as well as the impact of various methodological and sample characteristics on welfare estimates are examined. The results indicate a significant effect of visual externalities on welfare estimates in both directions, i.e., a positive effect of visual improvements and a negative effect of deteriorations. This finding corresponds to predictions of the importance of visual impacts in the social science literature. External effects of wind power on biodiversity (mainly birds) do not affect welfare estimates. Indirect externalities caused by conventional sources of electricity that can be avoided by wind power, such as a the reduction of air pollution, do neither have a significant impact on welfare measures. Methodologically, we find substantial but inelastic income effects and, for choice experiments, clear evidence of sensitivity to scope. From a policy point of view, our results suggest that a policy mix combining a promotion of wind turbines with another green policy facilitates expansion of wind energy.

Two different aeration regimes were studied in a low pressure gravity driven membrane bioreactor without any flushing or (back-) washing. In one reactor, the aeration was positioned below the membrane module, thus exposing the membranes to aeration shear stress. A second reactor was operated at low shear stress by placing the aerator in a different compartment. Flux stabilization at 2.0 L/(m² h) occurred in the reactor with low shear stress while no flux stabilization was observed in the reactor with aeration shear stress, resulting in a flux of 0.5 L/(m² h) after 120 days. The thickness of the bio-fouling layer in the reactor with aeration shear was smaller (129 vs. 344 µm), which implies that shear stress resulted in a thinner, denser and less permeable bio-fouling layer. The results can be explained by differences in (1) the morphology of the bio-fouling layer and (2) the EPS contents (proteins and polysaccharides) in the bio-fouling layer. The low-shear system provides a suitable solution for decentralized grey water treatment, or other conditions where maintenance and energy consumption should be minimized. Furthermore, the results can contribute to decrease the energy consumption in MBR systems.