Long Term European Field Tests for Microgrids

Integrating a large number of renewable and distributed energy resources requires an active interaction between generators and loads. In the recent years, several pilot installations have been realized which demonstrate different concepts for energy management in low voltage distribution grids. This paper describes selected pilot installations, where long term field tests on microgrids have been performed in low voltage grid segments: Kythnos island, Greece; "Am Steinweg" estate, Stutensee, Germany; Mannheim-Wallstadt, Germany. Goals of these pilot installations are to validate three representative approaches for energy management: Island with no connection to a feeder; Interconnected grid segment, centrally dispatched; Interconnected grid segment, focus on customer integration. Long term tests focus on the reliable contribution of DER to energy supply. As a result, all concepts have proven reliable and suitable for further long term application. The results will play a role in the development of grid connection requirements

Analysis of the minimum activation period of batteries in frequency containment reserve

The capacity of battery energy storage systems (BESS) to adjust power output swiftly and precisely makes them ideal for provision of frequency containment reserve (FCR), the fastest type of frequency control. Since BESS are only recent providers of FCR, there is uncertainty in the applicable requirements while regulation adapts to BESS. In this paper, the minimum activation period as an unresolved regulation issue is investigated. Therefore, two generic methods to calculate the resulting limits of the normal operation range are introduced (considering and not considering corrective power) and compared for a minimum activation period of 15 and 30 minutes. The operation of BESS providing FCR was simulated based on the two calculation methods for numerous system designs. Results of these simulations demonstrate the significance of the regulation on BESS operation and design. Shorter minimum activation period reduces required corrective energy and increase income potential from FCR significantly

SWOT analysis of an extended reactive power range of PV-inverters serving smart electricity grids

There is a high and increasing PV-penetration in Germany leading also to strong impacts on the distribution grids those systems are connected to. Therefore grid codes and standards were defined requiring the PV power electronics interfacing to the grid to alleviate negative impacts by reactive power provision (besides other measures). Current standards define a rather small fraction of reactive-power provision proportional to the active power feed-in. This paper discusses the pros and cons of extending the range of reactive power provision. On the one hand it unveils new opportunities for enhanced “grid-friendly” operation together with a sensitivity analysis; on the other hand it shows necessary developments on the power electronics side. Since in general inverters may also support grid operation during times of no PV feed-in, they can also alleviate impacts caused by other components such as charging stations for electric vehicles on grid voltage. This paper shows that under voltages due to high electric vehicle penetration can be solved by an extended reactive power range of PV-inverters

NEMO - a novel techno-economic tool suite for simulating and optimizing solutions for grid integration of electric vehicles and charging stations

With an increasing use of electric vehicles (EV) grid operators need to predict energy flows depending on electromobility use profiles to accordingly adjust grid infrastructure and operation control accordingly. Tools and methodologies are required to characterize grid problems resulting from the interconnection of EV with the grid. The simulation and optimization tool suite NEMO (Novel E-MObility grid model) was developed within a European research project and is currently being tested using realistic showcases. It is a combination of three professional tools. One of the tools aims at a combined techno-economic design and operation, primarily modeling plants on contracts or the spot market, at the same time participating in balancing markets. The second tool is designed for planning grid extension or reinforcement while the third tool is mainly used to quickly discover potential conflicts of grid operation approaches through load flow analysis. The tool suite is used to investigate real showcases in Denmark, Germany and the Netherlands. First studies show that significant alleviation of stress on distribution grid lines could be achieved by few but intelligent restrictions to EV charging procedures

Demand Side Management in dezentral geführten Verteilnetzen: Erfahrungen und Perspektiven

The paper summarizes actual experiences with demand response pilot projects and the implemented tariffs in Europe and the United States. The main focus lies on the distribution network and the connected residential and commercial customers. The achieved potential for demand response is shown on an empirical as well as on theoretical basis. Many demonstrations projects were started in Scandinavia and in the United States to increase the security of supply. The achieved load reductions reached in some cases more than 30% of peak demand. Next to time of use tariffs that were extended by critical peak prices also real time pricing tariffs were tested. The theoretical demand response potential was calculated for specific appliances. It was found to be 2.3 kWH per average houshold and day. The power for automated load control is estimated at 67 to 105 W per household