Grid

Grid integration

The construction and grid integration of large European offshore wind farms is arguably the biggest challenge facing electricity grids in Europe. Grid integration of the planned wind farms with an expected generation capacity of up to 41 GW in the entire North Sea region can only be realized with considerable effort using today’s technology. The sometimes very extensive planned outputs of over 1,000 MW and coastal distances of up to 200 km to possible grid connection points make it necessary to use unconventional transmission systems. Integrating the planned generating capacity into the existing transmission grids and transporting the generated energy away to the centers of consumption also poses a special technical challenge.

Grid connection

The framework conditions for grid connection have changed fundamentally as a result of an amendment to the Energy Industry Act. The transmission system operators in Germany have hereby been obligated to connect offshore wind farms to their grid. As a result, it is now possible to make the grid connection more efficient by connecting several wind farms together to the grid using unconventional high-power transmission systems, e.g. gas-insulated pipelines. In particular, the feasibility of a future North Sea interconnected grid of the planned wind farms is being investigated here.

System integration

In addition to the connection to the mainland, the effects of a central wind energy feed-in in the area of the North Sea on the transmission grid and the European electricity trade will also be investigated. The objectives are the development of a market model and, based on this, the identification of grid bottlenecks as well as the determination of the influence of high wind energy feed-in on the use of thermal power plants. Based on the resulting findings, various grid expansion scenarios and congestion mitigation measures, e.g. redispatch of thermal power plants, will then be investigated in the further course of the research. In addition to the expansion of the existing network, the introduction of an additional pan-European overlay network is also being analyzed.

Optimized network management

The increasing expansion of wind energy use leads to increased demands on grid operation management due to its strong fluctuations and poor predictability.

Local distribution networks

Therefore, the development of a secure and plannable power supply for electricity grids with a high proportion of wind energy is imperative. The goal is both to develop cost-efficient and effective methods, and to increase the capacity effect and generation share of wind energy in local electrical distribution networks. In order to achieve this goal, time-variable power generation by wind energy must be supported by technical measures such as the integration of energy storage systems and by industry-specific load management. The Bremen Institute for Measurement, Automation and Quality Science is therefore developing a simulation for local power grids and investigating the behavior at high wind energy levels in various case studies. Furthermore, the institute is working on the determination of grid-friendly expansion paths of renewable feeders and on the integration of the hydrogen economy into the local distribution grid.

Control strategies

In addition, the energy potential of wind energy is fundamentally investigated in terms of technical feasibility and achievable economic benefits. On the basis of software for the technical and economic simulation of electrical grids, which is to be further developed, proactive management strategies are developed and evaluated on the basis of scenarios. Furthermore, it is investigated how and with which effort the consumer-internal storage effects can be extended by additional latent cold storage.

The findings from the scenarios and the control strategies developed in the process, together with the tariff models to be investigated, can be incorporated in the future into the planning for the design of wind energy farms and local power grids and, in the long term, lead to the implementation of proactive load and storage management in power supply grids.

Electricity production costs offshore wind energy

Offshore wind energy is a key technology for the generation of renewable energy. However, due to their relatively high costs, including more complex installation and maintenance processes, offshore wind turbines (WTGs) have so far only been competitive to a limited extent and are significantly dependent on subsidies. The research of the ForWind member Institute for Planning and Control of Production Engineering and Logistics Systems at the University of Bremen starts at this point and tries to reduce the LCOE along the entire value chain of WTGs from currently 117/MWh to 35/MWh by various measures. In order to realize a reduction in LCoE of this magnitude, the Bremen Institute for Production and Logistics is developing and implementing, among other things, a concept for the digitization of WTGs along their complete life cycle. On the one hand, the main focus is on an Industry 4.0 integration of the OWEA through a digital twin and the Internet of Things (IoT). In addition to an improved exchange of information, intelligent strategies and tools for predictive maintenance are to be introduced by means of the data infrastructure thus created. In addition, optimized installation and logistics processes during the erection phase of the WTGs will be designed, aiming at cost reduction during the erection phase. The concepts developed will be validated by means of a 12+MW turbine prototype and by starting a first pre-series of 4-6 WTGs.

International integration of offshore wind energy

In recent years, the Institute of Electrical Energy Systems at the University of Hannover has been working with several partners to develop new technically and economically efficient ways of connecting offshore systems in the German Bight to international energy systems in the short and medium term. The scientific issues concerning the control, operational management and planning of such systems are becoming increasingly relevant in view of the imminent expansion of wind energy capacities in the North Sea.

Projects on the research topic “Network

Research focus

Island network control

In many developing countries, there is no nationwide interconnected power supply network. This is only possible via so-called decentralized island grids. The Institute for Electrical Drives, Power Electronics and Devices (IALB), University of Bremen, is working on the control of such island grids, which are fed by several feed-in units from mainly renewable sources.

Transmission systems

The expansion of renewable energies in Europe also requires an expansion of the European transmission grid. The strong resistance of the population to the construction of new overhead lines will in many cases necessitate the construction of underground transmission systems for the 400 kV level. Since there is as yet insufficient operational experience for longer distances and especially for so-called intermediate cabling, there is a considerable need for research in this area.

The research objective is to investigate the behavior of underground transmission systems in interaction with today’s heavily overhead dominated grid. Advantages and disadvantages of the different techniques are compiled and the requirements for safe network operation are analyzed. Overhead line, cable and gas-insulated pipe (GIL) conductors are considered to find the economically and technically optimal line for a given application. Particular attention is paid to the use of GIL, as it has particularly favorable electrical parameters and promises very good thermal load capacity. An EU research project, in which IEH is involved together with ForWind, the company Siemens and the company ILF, is to investigate the use of a GIL system for connecting offshore wind energy. Among other things, the electrical and thermal load capacity as well as the thermal influences on the environment are tested.

Areas of focus:

• Comparison of conventional and other transmission technologies, e.g. high voltage direct current (HVDC) and GIL.
• Thermal modeling of piping systems
• Transmission behavior
• Transient analysis, interactions

Efficiency increase of wind energy systems and grid connection

If wind turbines are considered over their entire impact chain, there is great potential for increasing efficiency, from energy generation in the turbine to grid connection. From energy conversion and support structures to connection to the power grid, costs can be reduced and operating times extended.

Wind Power Forecast

Accurate forecasts of wind performance are now an indispensable component in ensuring the growing contributions of wind energy to the energy supply. ForWind develops wind power forecasting techniques based on the best available weather forecast models. Vertically high-resolution wind profiles from weather forecasts are used as input data, which are processed in further physical-statistical models according to the specific use.

Wind power forecasts are produced for larger regions as well as for individual sites. Essential is the additional possibility to quantify the prediction uncertainty by specifying confidence intervals.

ForWind uses the developed forecast models intensively as a research tool. Different scenarios are simulated to further develop the models. In this context, measurement data on wind speed and the power fed simultaneously from wind turbines help to evaluate and improve the models for different regions and wind farms. By coupling the models with statistical methods of post-processing, individual predictions are optimized. Detailed studies show the evolution of prediction performance for spatially distributed onshore and offshore systems.

Zinc/air micro fuel cell

Basic research in the field of fuel cells is a key prerequisite for developing compact and environmentally friendly storage technologies for wind turbines. The fuel cell systems developed to date often consist of environmentally harmful or rare materials and/or are cost-intensive to manufacture. In addition, very elaborate and complex system technology is required for operation, since a suitable energy carrier (e.g. hydrogen) must be supplied from outside.

The Bremen Institute for Metrology, Automation and Quality Science (BIMAQ) at the University of Bremen is developing technologies for miniaturized fuel cells as key components for self-sufficient microsystems and is working on their optimization from the point of view of system integration. The intention is to develop long-life power supplies that can be manufactured cost-effectively and, because of their integration capability, no longer dominate the size of the microsystems on offer. This enables the construction of large and efficient energy storage systems for the wind turbines.

The starting material zinc ensures a very high energy density as a reaction partner with atmospheric oxygen, and an aqueous potassium hydroxide solution (caustic potash solution) is used as the electrolyte. A simple and housing-less design additionally favors automated production as well as recycling of the environmentally friendly materials. The layers of the fuel cell can also be manufactured over a large area, so the cell can be punched out in any size and geometry and fitted with electrical connections. Due to its low-cost production and low-cost materials, the zinc/air fuel cell has the potential to drive the commercialization of fuel cells and open up new sales opportunities for the companies involved.