Institutskolloquium des IPP 2016

Europe is pursuing an aggressive programme to increase its share of renewable energy source (RES). However, the integration of intermittent RES (wind and photovoltaic) in the electrical system requires either maintaining in operation thermoelectric backup systems or providing a substantial amount of electricity storage. We analyze the Italian data for the year 2013 provided by the transmission system operator TERNA. Intermittent RES power is scaled-up to a level at which it generates an amount of electricity equal to the annual demand. While a substantial reduction of the energy annually produced by backup systems (and the associated CO2 emission) with respect to the no-RES case is possible in many scenarios considered here, the backup power is generally only marginally reduced below the value in the absence of RES. The strategy proposed is based on the combination of a modest amount of storage (0.5-5TWh) and base-load power (6-15GW, to be used during the seasons of low RES production). In this way the non-RES installed power can be reduced from ~50GW to less than 15GW and could be covered by a combination of biomasses and nuclear energy without any CO2 emission. [mehr]

The axisymmetric helical field of a tokamak leads to closed unperturbed particle orbits, thus arising as one of the most viable concepts for a fusion reactor. Orbit perturbations due to either Coulomb collisions or electromagnetic potential fluctuations ultimately determine the energy and particle confinement times. Macroscopic temperature and density profiles result from the balance of external sources and of the internally produced fusion power with the transport processes due to the aforementioned mechanisms. Thereby, the numerical design of a commercially viable tokamak fusion reactor requires integration of physics tools that describe both the fast/small scale processes and the slow/macroscopic evolution of the plasma profiles and the plasma shape. To this end, nowadays, progress in the theoretical description of the transport processes allows the application of increasingly realistic theory-based models. This also implies that any modeling activity should be performed keeping into account the assumptions and potential limitations of the models that are employed. In this talk, first a description of the logical coupling of the tools is given, clarifying the underlying physics of each piece of the system, from the small to the large spatial/temporal scales. Practical applications are then shown. These are based on the ASTRA-SPIDER transport/equilibrium package developed at IPP and in collaboration with TUAP (St. Petersburg), with inclusion of additional modules for turbulence-driven transport fluxes (e.g. TGLF, from General Atomics), and impurity particle transport (STRAHL, developed at IPP). Finally, an outlook is given on the open challenges in this research activity. [mehr]

Sustainable energy generation by means of wind or from solar radiation through photovoltaics or concentrated solar power will be a significant part of the energy mix in 2025. Intermittency (due to e.g. day/night cycle) as well as regional variation of these energy sources requires means to store and transport energy on a large scale. A promising option is creating artificial solar fuels (or CO2 neutral fuels) with sustainable energy, which can easily be deployed within the present infrastructure for conventional fossil fuels. A candidate raw material would be CO2 itself (fitting in carbon capture and utilization, CCU, strategies). Presently, no efficient schemes are yet available for the conversion of CO2 into fuels. A plasma chemical approach potentially offers high energy efficiency (up to 90%) due to selectivity in the reaction processes that can be tailored via its inherently strong out-of-equilibrium processing conditions. At the same time, it is characterized by efficient and fast power switching, low investment costs, no scarce materials required, and high power density, which are all advantageous for addressing intermittency. In this presentation, the plasma chemical approach will be introduced and examples will be discussed of research carried out at the DIFFER to ultimately enable a scale up to industrial applications. In particular, a common microwave reactor approach is evaluated experimentally with Rayleigh scattering and Fourier transform infrared spectroscopy to assess gas temperatures (up to ~3000 K) and conversion degrees (up to 30%), respectively. The results are interpreted on basis of estimates of the plasma dynamics obtained with electron energy distribution functions calculated with a Boltzmann solver. It indicates that the intrinsic electron energies are higher than is favorable for preferential vibrational excitation due to dissociative excitation, which causes thermodynamic equilibrium chemistry still to dominate the initial experiments. Pulsing the power is shown to decrease gas temperatures and improve efficiency. Novel reactor approaches are proposed to tailor the plasma dynamics to achieve the non-equilibrium in which vibrational excitation is dominant. [mehr]