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Author: search.filters.author.Nowak, WolfgangSubject: search.filters.subject.333.7

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    Optimal design of experiments to improve the characterisation of atrazine degradation pathways in soil
    (2021) Chavez Rodriguez, Luciana; González‐Nicolás, Ana; Ingalls, Brian; Streck, Thilo; Nowak, Wolfgang; Xiao, Sinan; Pagel, Holger
    Contamination of soils with pesticides and their metabolites is a global environmental threat. Deciphering the complex process chains involved in pesticide degradation is a prerequisite for finding effective solution strategies. This study applies prospective optimal design (OD) of experiments to identify laboratory sampling strategies that allow model‐based discrimination of atrazine (AT) degradation pathways. We simulated virtual AT degradation experiments with a first‐order model that reflects a simple reaction chain of complete AT degradation. We added a set of Monod‐based model variants that consider more complex AT degradation pathways. Then, we applied an extended constraint‐based parameter search algorithm that produces Monte‐Carlo ensembles of realistic model outputs, in line with published experimental data. Differences between‐model ensembles were quantified with Bayesian model analysis using an energy distance metric. AT degradation pathways following first‐order reaction chains could be clearly distinguished from those predicted with Monod‐based models. As expected, including measurements of specific bacterial guilds improved model discrimination further. However, experimental designs considering measurements of AT metabolites were most informative, highlighting that environmental fate studies should prioritise measuring metabolites for elucidating active AT degradation pathways in soils. Our results suggest that applying model‐based prospective OD will maximise knowledge gains on soil systems from laboratory and field experiments.
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    The role of fast frequency response of energy storage systems and renewables for ensuring frequency stability in future low-inertia power systems
    (2021) González-Inostroza, Pablo; Rahmann, Claudia; Álvarez, Ricardo; Haas, Jannik; Nowak, Wolfgang; Rehtanz, Christian
    Renewable generation technologies are rapidly penetrating electrical power systems, which challenge frequency stability, especially in power systems with low inertia. To prevent future instabilities, this issue should already be addressed in the planning stage of the power systems. With this purpose, this paper presents a generation expansion planning tool that incorporates a set of frequency stability constraints along with the capability of renewable technologies and batteries to support system frequency stability during major power imbalances. We study how the investment decisions change depending on (i) which technology - batteries, renewable or conventional generation - support system frequency stability, (ii) the available levels of system inertia, and (iii) the modeling detail of reserve allocation (system-wide versus zone-specific). Our results for a case study of Chile’s system in the year 2050 show that including fast frequency response from converter-based technologies will be mandatory to achieve a secure operation in power systems dominated by renewable generation. When batteries offer the service, the total investment sizes are only slightly impacted. More precise spatial modeling of the reserves primarily affects the location of the investments as well as the reserve provider. These findings are relevant to energy policy makers, energy planners, and energy companies.