Jan Frederick Unnewehr

2021

• Unnewehr JF, Jalbout E, Jung C, Schindler D, Weidlich A
  Getting more with less? Why repowering onshore wind farms does not always lead to more wind power generation – A German case study
  2021 Renewable Energy, Band: 180, Seiten: 245 - 257
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  Kurzfassung

  The best wind locations are nowadays often occupied by old, less efficient and relatively small wind turbines. Many of them will soon reach the end of their operating lifetime, or lose financial support. Therefore, repowering comes to the fore. However, social acceptance and land use restrictions have been under constant change since the initial expansions, which makes less area available for new turbines, even on existing sites. For the example of Germany, this study assesses the repowering potential for onshore wind energy in high detail, on the basis of regionally differentiated land eligibility criteria. The results show that under the given regional criteria, repowering will decrease both operating capacity and annual energy yield by roughly 40% compared to the status quo. This is because around half of the wind turbines are currently located in restricted areas, given newly enacted exclusion criteria. Sensitivity analyses on the exclusion criteria show that the minimum distance to discontinuous urban fabric is the most sensitive criterion in determining the number of turbines that can be repowered. As regulations on this can vary substantially across different regions, the location-specific methodology chosen here can assess the repowering potential more realistically than existing approaches.
  
  
   
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2020

• Unnewehr J
  Tracking CO2 emissions from power generation in high spatial and temporal resolution – Case study for the German electricity system
  2020 Energy Informatics, Band: 3
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  Kurzfassung

  Until today it is not possible to allocate the CO2 emissions in the German electricity system to a specific region and its corresponding electricity demand that caused them. This paper presents a new energy system model and uses established methods for answering this question. A detailed bottom-up model of the German electricity system is built to represent a highly spatial and temporal representation of the Germany electricity system in 2019. In combination with a customized input-output analysis, the individual emissions from the producer to the caused consumer can be traced. The analysis demonstrates the importance of considering spatial and temporal effects as well as electricity exchanges between regions in estimating emissions footprints.
• Unnewehr J F, Waldl H-P, Pahlke T, Weidlich A
  Reducing Operational Costs of Offshore HVDC Energy Export Systems Through Optimized Maintenance
  2020 Energies, Band: 13, Nummer: 1146, Seiten: 1 - 20
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  Kurzfassung

  For the grid connection of offshore wind farms today, in many cases a high-voltage direct current (HVDC) connection to the shore is implemented. The scheduled maintenance of the offshore and onshore HVDC stations makes up a significant part of the operational costs of the connected wind farms. The main factor for the maintenance cost is the lost income from the missing energy yield (indirect maintenance costs). In this study, we show an in-depth analysis of the used components, maintenance cycles, maintenance work for the on- and offshore station, and the risks assigned in prolonging the maintenance cycle of the modular multilevel converter (MMC). In addition, we investigate the potential to shift the start date of the maintenance work, based on a forecast of the energy generation. Our findings indicate that an optimized maintenance design with respect to the maintenance behavior of an HVDC energy export system can decrease the maintenance-related energy losses (indirect maintenance costs) for an offshore wind farm to almost one half. It was also shown that direct maintenance costs for the MMC (staff costs) have small effect on the total maintenance costs. This can be explained by the fact that the additional costs for maintenance staff are two orders of magnitude lower than the revenue losses during maintenance.
  
  
   
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2019

• Abdel-Khalek H, Schäfer M, Vásquez Torres RA, Unnewehr J, Weidlich A
  Forecasting Cross-Border Power Transmission Capacities in Central Western Europe Using Artificial Neural Networks
  2019 Energy Informatics, Band: 2, Ergänzungsband: 1, Seiten: 1 - 13
  
   
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2018

• Unnewehr J, Waldl H-P, Pahlke P, Herráez I
  Reducing operational costs of offshore HVDC energy export systems through optimized maintenance
  2018 17th Wind Integration Workshop