Retrofitting, district heating and energy storage: neighborhood energy planning

We compare simulated energy retrofitting of individual buildings with energy refurbishments optimized at the scale of the neighborhood. For the neighborhood case, buildings can also be connected together through a heat network. We use a detailed three-dimensional model to estimate heating needs (CitySim) and a mixed-integer linear optimizer to analyze different options for energy refurbishment, including various heating technologies. According to our simulations, planning at the neighborhood scale results in slightly lower costs (about -5%) and lower C02 emissions (about -60%) than planning energy refurbishment at the building scale, showing that integrated planning of energy refurbishment is beneficial from both environmental and economical points of view.

ENERGY STORAGE: LIQUID CH4 AND CO2 NETWORK INTEGRATION

Charles-Thomas Stern

In this project, we will study the energy storage with liquid methane linked to a CO2 network that provides heat for district heating. The generated methane enters an hybrid cycle composed of a solid oxide fuel cell and turbines to generate electricity. The goal of this project is to determine the global eciency of the system but also to optimize it with the help of softwares like Belsim Vali and Osmose. In addition, we determine its cost. At the end, we compare the global system with an equivalent one without the CO2 network integration.

2014

Urban Energy System Design from the Heat Perspective using mathematical Programming including thermal Storage

Jakob Moritz Fabian Rager

Energy planning recently received more attention in Switzerland through the new strategy phasing out nuclear energy by 2034. Often however the energy planning is only done from the electrical side. This work takes a different angel and helps communities and energy utilities planning tomorrows energy system from a heat based perspective. After the data collection and structuring, the methodology presented here designs an energy system. Based on the quality of the collected data, the approach to define the energy demand should be chosen. In order to reduce calculation time, a data reduction approach is developed to reduce the input data without loosing significant information and precision. In particular, the methodology focuses on the integration of a stochastic resource, in this case solar thermal heat production, in combination with thermal energy storage. The thermal energy storage can be used as a short or long term thermal energy storage. The framework compares design solutions for the two storage types considering either a total cost approach or a life cycle assessment approach using the cumulative exergy demand (CExD). The proposed mathematical programming framework is based on a mixed integer linear programming (MILP) approach, that can work on different levels of detail between building to community or city level. The optimization problem can also be further simplified to a linear problem, increasing the size of problem that can be solved while reducing or keeping a constant computation time. The discussed cases show an interest in further investigating storage solution using both, the short and long term storage at once, because they allow to reduce the system's overall costs or CExD significantly. The framework is then extended to consider buildings as an energy storage. The building's internal temperature can be raised from 20 \degree C up to 23 \degree C, giving a comfort temperature range that can be used for storing heat. The integrating of both storage types, the thermal energy storage and the building as an energy storage, show no significant impact on the energy system design. However, costs or CExD can be reduced. In addition, the heat demand can be modified through the decision of optimal energy retrofitting strategy for a group of buildings. The framework decides which of the building to refurbish based the overall CExD including CExD used for retrofitting the building. Finally, a method is proposed to integrate uncertainty of the model's input parameters into the system design. A global sensitivity analysis evaluates the impact of each uncertain parameter onto the system, allowing to focusing on the outputs of interest. Robust optimization is applied with a simulation-based approach, the additional costs for a robust design are calculated, as well as the different unit sizes. The low complexity of the developed models allows for an easy integration of new data collected during the development of a project, which is often the case in urban energy planning applications.

EPFL2015

Swiss Potential for Hydropower Generation and Storage - Synthesis report

François Avellan, Paolo Burlando, Pedro Filipe De Almeida Manso, David Felix, Martin Schmid

Hydropower (HP) is the backbone of the Swiss electricity system providing around 60 % (36 TWh/a) of the total electricity generated on a yearly average. With the planned phase-out of nuclear power plants, HP and other Renewable Energy Sources (RES) will need to fill the substantial gap in domestic electricity generation, particularly in the winter season. Because of the intermittent nature of RES generation (mainly solar photovoltaics and wind) and their typically lower production in winter, the need for storage up to the seasonal time scale increases. Such large-scale storage is offered mainly by storage HP. However, maintaining the HP infrastructure will pose significant challenges, mainly due to market and legal conditions. For the latter, partly diverging interests according to the Swiss legislation will need to be fulfilled at the same time. On the one hand, HP is supposed to be extended in the scope of the Energy Strategy (ES) 2050 and to keep climate goals by reducing greenhouse gas emissions. On the other hand, current negative effects of mainly older HP infrastructure on aquatic ecology will need to be remediated according to the Swiss Waters Protection Act to fulfill biodiversity goals. Meeting all these goals will require to systematically refurbish the existing Swiss HP fleet, to extend it in a smart way with prioritization on large storage HP to foster electricity generation in the critical winter season and to construct new HP schemes, again with a focus on electricity generation in winter. As to new HP facilities, the retreating glaciers open new opportunities for high-altitude storage plants that, besides generating quasi CO2-free electricity, have also other benefits like protection from natural haz- ards and water supply for irrigation. Extending existing storage lakes by heightening of their dams is a complementary option to create additional storage with generally low environmental impact and possibly higher public acceptance. Both the environmental legislation and economic and market conditions currently hinder investment in HP infrastructure. Regarding legal conditions, certain energy infrastructure has been declared to be of "national interest" in the Swiss Energy Act. However, wetlands of national importance are excluded from this weighing of interest, limiting hence the HP development potential at retreating glaciers that feature such protected wetlands in their forefields. Regarding market environments and general framework conditions, the major uncertainties during typical concession periods of 80 years in combination with long planning and approval procedures do not foster investments in HP. The target values of the ES 2050 in terms of annual generation by HP can be met only in an upper-bound scenario, which would require more favourable framework conditions for HP than today. Otherwise, a intermediate scenario is more realistic, according to which the annual generation is expected to increase by 0.5 TWh/a until 2050, which is well below the target of 2.6 TWh/a. A lower-bound scenario predicts a decrease by -3.0 TWh/a, mainly due to mitigation measures to fulfill the Waters Protection Act, with reductions in generation primarily from increased residual flow requirements. In terms of energy storage, an effective increase of 1.2 TWh by 2050 is forecast in the intermediate scenario including dam heightening and a few new periglacial storage HP plants. Such an increase would correspond to almost 20 % of today’s energy storage capacity of the Swiss HP reservoirs. It is expected that the increase of storage capacity of 2 TWh by 2040 envisaged in the recently revised draft version of the Electricity Supply Act cannot be implemented by HP within this rather short time frame. However, setting such targets is important. All in all, significant efforts are required to maintain the electricity generation from HP around its current level. Potential increases are very limited because a high share of the Swiss HP generation potential is already exploited. In contrast to generation, the storage capabilities of HP shall be significantly expanded because more large-scale seasonal storage is an essential prerequisite for the efficient integration of a higher share of RES into the electricity supply system.