Potential increase in energy storage capacity in the Swiss Alps to support the massive development of renewables: Case study of the Grande Dixence hydropower scheme

Only 42 % of the mean annual production of large hydropower plants in the Swiss Alps is stored in their reservoirs. Once the reservoirs are full at the end of the summer semester, plants are operated as run-on-the-river in order to avoid spilling. A significant part of the hydropower resources are thus sold at discount prices and cannot be transferred to the winter semester. It is precisely in the winter semester that Switzerland imports large volumes of electricity from its neighbours. In order to support the nuclear power phase-out planned in the Swiss Energy Strategy 2050, hydropower must not only maintain its 2012 production level but mainly step-up its role in the grid and improve its remuneration. Following this strategy, the present production of the nuclear plants will be mainly replaced by renewables and the total electricity storage capacity must therefore be increased by 10 to 30%. Hydropower schemes face two challenges: to reduce the lack of electricity production in the winter semester and to lay a suitable foundation for the increased storage demand of intermittent renewables such as wind and solar. In this work, we propose a methodology to evaluate the potential increase in energy storage capacity of a portfolio of large reservoirs in Alpine regions, considering future climate scenarios and future reservoir operation scenarios corresponding to different economic conditions (e.g. more/less PV and wind production) and reservoir management time scales (seasonal, multiannual). In addition to exploring the performance of existing reservoirs in different future conditions, we assess the possibility to link reservoirs (mutualising the use of storage) and/or to raise dams (increasing storage and annual runoff regulation). In fact, several large dams provide the structural capacity to be heightened by at least 10% of their height. Additionally, there are strategic locations that could be used to create new large reservoirs. This methodology is applied to a test site located on the left bank of the Rhône River in Switzerland. Our method uses both recent and future hydrology, as well as operational data to determine the optimal reservoir live storage capacity for a hydropower scheme. In addition to intra-annual energy and water transfer, we also consider the transfer in between years to account for adverse climate conditions. In order to apply this methodology to the Grande Dixence hydropower scheme, we show two opportunities to increase the seasonal storage capacity: heightening of the main dam and the creation of a new upstream reservoir. Our study shows that the largest Swiss reservoir with 400 hm3 can provide more seasonal storage in all climate scenarios, however a full heightening of 10% may not be optimal regarding the different intra-annual operation modes investigated. However, should the operator wish to guarantee production in extreme dry years the reservoir heightening would also provide the possibility of establishing a pluriannual reserve or extra room for pumped storage.

The Facilitation of Mini and Small Hydropower in Switzerland

Nicolas Crettenand

The electricity sector in Switzerland is undergoing important changes following the liberalisation process and the facilitation of renewable energy technologies. Furthermore, the phasing out of nuclear power will increase the demand for new domestic electricity generation. According to the Federal Energy Strategy 2050, additional generation will have to come from hydropower (currently 57% of Swiss electricity production), including small hydropower (currently 6%, i.e. 3.8 TWh). The small hydropower technology, with an installed capacity between 100 kW and 10 MW (whereby 100 kW till 1 MW is considered to be mini hydropower), is a renewable energy technology (RET) which is well developed. However, the technology still requires further innovation to improve its environmental integration and reduce costs. Small hydropower (SHP) provides electricity with a high energy payback ratio and, generally, with lower production costs than other RETs, aside from large hydropower. SHP can be combined within multipurpose infrastructures such as drinking water and irrigation networks. The institutional framework of SHP is conditioned by multi-level (i.e., Federal, Cantonal and Communal) and cross-sectorial institutions (e.g., within the electricity and water sectors, spatial planning). SHP still has significant potential in Switzerland with the possibility of increasing the production of 2010 by 40-50% by 2050. However, SHP requires appropriate policy instruments for its development within a liberalised electricity market as it is, on average, not yet cost-competitive. In 2009, for example, a Federal feed-in remuneration scheme was introduced. To further develop the SHP potential, the institutional framework has still to evolve. This research was aimed at identifying changes in the institutional framework in Switzerland which can contribute towards developing SHP and increasing the alignment between the technology and its institutions. To this end, the literature on co-evolution and the framework of coherence between institutions and technologies in the case of network industries, such as electricity, were used for the analysis. This thesis contributes towards further development of the coherence framework. Policy instruments are identified that can support the development of SHP. Measures to simplify and harmonise administrative procedures are evaluated, even though their implementation remains difficult. A promising endeavour, however, is to reduce opposition, thus duration of procedures, by developing regional master plans and/or multi-criteria evaluations of projects at the very early project development phase. This enables the pursuit of projects for which all stakeholders are favourable to their realisation. Another required measure is guaranteeing the technical quality of plants which receive the feed-in remuneration by introducing a global efficiency criterion. Finally, other policy instruments are analysed such as green certificates, the feed-in remuneration scheme, and CO2 credits, which will become necessary following the opening of new gas-fired plants. The current institutional facilitation of RETs generating electricity focuses solely on quantity, i.e. kWh. It does not consider the need for flexible production and energy storage to deal with the intermittent generation of some RETs and to align the electricity demand and supply. This is not coherent. The institutional facilitation should take into account flexible production and energy storage, and thus specifically support technologies such as storage and pumped-storage SHP. This research investigated, using an explorative and bottom-up approach, the technical potential of small storage and pumped-storage plants by focusing on existing and planned reservoirs in order to reduce investment costs and environmental opposition. Eleven projects were identified in the Canton of Valais. The potential in Switzerland is evaluated at roughly 200-300 MW for storage SHP plants (today 106 MW is used) and 70-150 MW for pumped-storage SHP plants (today 15 MW is used). In order to further develop this potential, which is complementary to the large storage and pumped-storage hydropower potential, some remuneration instruments are identified. The instruments include adapting the feed-in remuneration scheme to facilitate not only run-of-river plants, introducing requirements for ancillary services from RETs (in addition to large hydropower), and CO2 credits and green certificates depending on the production profile (e.g., peak and off-peak). The identified instruments lead to policy recommendations which would further facilitate the development of SHP in Switzerland, including storage and pumped-storage plants. In summary, the main findings of this research are four-fold: The institutional framework has to further evolve to be aligned with the small hydropower technology. The institutional facilitation of renewable energy technologies must not only focus on the quantity of energy, i.e. kWh, but also on the "quality", such as flexible production and energy storage. Storage and pumped-storage small hydropower could play an important role in producing distributed peak and balancing electricity and in contributing to distributed energy storage. Its technical potential in Switzerland is significant enough to shape the institutional framework adequately. The coherence framework offers a very useful lens to analyse technological and institutional changes in the network industries. However, it still needs to be improved to become more robust and less conceptual.

EPFL2012

The complex winds of the Alps: an unseen asset for the energy transition

Jérôme François Sylvain Dujardin

Wind energy has played a major role in the development of our society since 5000 BC when the first sail boats traveled the Nile River. Wind technology continued to advance with the invention of wind-powered pumps and mills in China and the Middle East as early as 200 BC, and by the late 19th century the first electricity-generating wind turbines were built. Today the effects of human driven climate change are pushing the world to transition from a fossil fuel dominated energy diet to a menu composed of a variety of technologies powered by renewable energies, including wind power. Our consumption habits and the historical design of our electricity grids were based on relatively few, centralized, and controllable power plants that use various fossil or nuclear fuels to generate power on demand to match real time use. The weather driven nature and low energy density of renewable sources like solar, wind and hydro lead to a more distributed and fluctuating electricity generation, which results in multiple problems: In Switzerland, under the foreseen future where photovoltaic (PV) panels are predominantly installed in urban areas, the nuclear phase-out will cause large deficits of electricity in winter. This thesis contributes to the solution of these important challenges in two ways: first by presenting a model that combines a variety of renewable energy sources to form a reliable and efficient electrical system, and secondly by improving the assessment of wind power potential in the Alps. The first two parts of this thesis are concerned with the simulation and optimization of the Swiss electrical system, in which the nuclear reactors are replaced by a combination of solar and wind energy sources. A spatially explicit approach is required to consider the spatio-temporal variability in renewable sources. Storage hydropower is a remarkable asset for the energy transition, and thus occupies a central role in the manner the system is modeled and operated (Part I). A novel algorithm explores how the whole system reacts under various combinations of PV and wind energies (Part II). By simultaneously optimizing the generation mix and location of PV panels and wind turbines, while considering the electrical grid and land use, this algorithm showed that a large number of carefully located wind turbines and a small number of PV panels located in the Alps can provide a much more balanced system than the conventional, urban PV scenario. Part III of this thesis addresses the difficulty of wind power potential assessment in mountainous terrain. On such terrain, high horizontal resolution is required in the numerical models that simulate the air flows. This constraint, and the need for long time series, prohibit the simulation of large domains and thus the identification of the best locations for wind turbines in the entire Swiss Alps. Downscaling models for wind are often used to obtain high resolution and long time series, but perform poorly on such terrain. In order to improve these models, a new method based on deep learning is presented. It downscales the outputs of the operational numerical model COSMO-1 used for the Swiss weather forecast, which has a resolution of 1.1 km, to a 50-meter resolution. The validation at 60 measurement stations shows that wind speeds and directions are more accurate than COSMO-1 and present many of the expected orographic effects like deflection, sheltering and ridge acceleration.

EPFL2021

Interplay between photovoltaic, wind energy and storage hydropower in a fully renewable Switzerland

Stuart John Bartlett, Jérôme François Sylvain Dujardin, Annelen Kahl, Michael Lehning

As part of its ambitious long term energy strategy, Switzerland plans to phase out nuclear power production and replace most or all of its significant share of national electricity production (40%) by renewables, in particular by photovoltaics (PV) and wind energy. The existing large fraction of hydropower and significant pumped-storage hydro capacity in the mountainous regions of the country will potentially provide valuable balancing and ancillary services for the management of intermittent production from PV and wind. We present a set of calculations based on data from the current Swiss electricity system, which investigate the effect of different PV-wind mixing ratio scenarios on required import and export from foreign neighbors. It is shown that the current hydropower is a good basis to deal with intermittent energy sources and to keep import rates of electricity at current levels in a fully renewable Switzerland as long as the PV-wind ratio is small. For higher PV-shares, forced export and import will increase but appear acceptable if PV-contribution stays below 0.6. Enlargement of reservoir capacity or oversizing of intermittent renewables can further reduce required import effectively. These findings are quantitatively specific for Switzerland but qualitatively transferable to similar mountainous environments with abundant hydropower resources.