Student Projects

The energy transition to non-fossil energy sources and carriers calls for a massive expansion of renewable energy sources such as photovoltaic (PV) systems or wind turbines. These systems provide electrical energy in a highly intermittent fashion. This is challenging both in terms of the grid balance (matching of supply and demand) and in terms of power peaks, especially during the day, when the solar irradiation is most intense. An obvious solution to this challenge is the introduction of energy storage systems. There are several possibilities for short-term energy storage systems. They differ in terms of energy storage density, round-trip efficiencies, power-to-capacity ratio, and cost. In this thesis, we focus on thermal energy storage. In this process, excess electrical energy is converted into heat, which is then stored. When electricity demand arises, the stored heat is converted back into electrical energy. Typically, such a conversion chain incurs significant losses. However, a new concept applies the well-known thermodynamic cycle from gas turbines to a piston-based engine, achieving a round-trip efficiency of over 70%. This efficiency is comparable to that of battery solutions and is outstanding for thermal storage systems. This concept is made possible by fully variable valve actuation developed by etavalve.

The aim is to find an optimal design and controller of such a thermal energy storage system as described above. The system shall be setup in simulation and optimal designs shall be evaluated for different use cases using the optimization framework DEnOBS from the IDSC. The ultimate goal is to evaluate the economic potential of such an energy storage system in various environments and configurations.

Dr. Theo Auckenthaler, ML H40, 071 511 61 99, tauckenth@ethz.ch; Dr. Andyn Omanovic, etavalve, ML H40, 079 524 39 89, andyn.omanovic@etavalve.com

Heavy industries generate waste heat as a byproduct. In Europe alone, the energy dissipated annually into the atmosphere amounts to 918 TWh. If all of it were converted to electricity, it could power 72 million homes. However, current heat-to-power conversion solutions are turbine-based and unsuitable for most waste heat sources. Turbines cannot handle fluctuations in heat supply and power demand, and small-scale applications in the single- digit megawatt range, as well as temperature levels below 900°C, decrease efficiency and render the system economically non-viable. At etavalve, we are developing a novel category of engines to convert industrial waste heat at 400°C or more into electricity with an anticipated conversion efficiency of 35% to 45% - an outstanding value for waste heat recovery systems. Our innovation lies in applying the well- known gas turbine cycle to a piston-based engine, enabled by our patented variable valve actuators. These actuators allow the handling of fluctuations and maintain high efficiency even in part-load operation.

In this thesis, we focus on developing a zero-dimensional model that captures the fast dynamics of a piston engine and the slow thermal inertia of the heat exchanger. The model will be fitted with data from Simcenter Amesim, an industrial 1D simulation tool, and later with measurement data from the test bench. The aim is to obtain an accurate yet computationally lean model, which will then be subjected to optimization methods. With the established framework, a controller will be designed to ensure the optimal startup of the engine and robust disturbance rejection caused by fluctuations in heat supply and power demand.

Dr. Andyn Omanovic, etavalve, ML H40, 079 524 39 89, andyn.omanovic@etavalve.com Giona Fieni, ML K39, gfieni@idsc.mavt.ethz.ch To apply for this project, please send me your CV and your transcript of records.