Coupled Thermal-electric Simulation for Analyzing the Impact of Home Energy Systems on Low Voltage Grids

  Copyright: RWTH Aachen Electrical Profiles in a Grid-interactive building

Main goal of the project is the holistic thermal evaluation of buildings and their interaction with the electrical grid via numerical simulations. The focus is on electrical profiles of combined heat and power (CHP) plants and heat pumps (HP) as Home Energy Systems (HES). These components are connected to the electrical grid while meeting the heat demand of the building. To address this interdependence, the simulations of the electrical grid, the building itself and the thermal energy system must be combined.

The electrical grid is simulated in terms of load flow with NEPLAN. The main quantities of interest for this analysis are the voltage profiles and the degree of utilization of the cables. The investigation starts with an analysis of the electrical quantities in a purely heat driven system. The profiles of the buildings are integrated with the base load profiles of the single households and the generation profiles of domestic photovoltaic plants on the roofs.

The electrical load profiles for the base load are generated by superimposing the operation of individual appliances according to reasonable patterns. In order to get realistic electrical profiles for each HES, we consider a stochastical approach which includes uncertain influences on the thermal behavior. The statistical behavior of persons regarding air ventilation, domestic hot water demand and desired room temperature is considered. All these parameters influence the heat demand and additionally the electric behavior of the HES.

The electrical model includes the possibility for the HES to inject reactive power in the grid, in a controlled manner, to provide voltage stabilization services. The load profile thus synthesized is used as input in NEPLAN. After the simulation the electrical figures are analyzed numerically afterwards. The results obtained up to now show that the utilization capacity of the underground cables is the first problematic figure as the power of the HES in multi-family houses is high and this leads to a stressful utilization especially on lines which are directly connected to the substation transformer. The voltage profiles stay in a safety operation range during the observed times.

In the upcoming parts of the projects the analysis will deliver information for different types of grids (cities, suburban areas, villages etc.) and different types of houses (single family, multifamily and office buildings). Recommendations for the design of home energy systems (HP and CHP) in the context of dimensioning and control strategies for grid-interactive homes are outcomes of the project.

This research work is performed in cooperation with Fraunhofer Institute for Solar Energy (ISE) and Fraunhofer Institute for Building Physics (IBP). Grateful acknowledgement is made to BMWi (German Federal Ministry of Economics and Technology) for providing financial support, promotional reference 03ET1111B .