Energy management for buildings
Management system for the solar-based energy supply of residential buildings

In the “iHEM” research project, an integrated energy supply using solar energy is being developed for residential construction. A specially developed energy management system coordinates the systems for generating solar power and solar heat with electricity and thermal storage systems as well as a micro-CHP unit. The underlying management concept is based on dynamically generated forecasts of the generation and demand profiles.

When supplying individual buildings with solar energy, there are always gaps in supply due to changing weather conditions and day/night cycles, provided no further measures such as energy storage or energy management are taken. With the integration of individual buildings into power and heat grids, which are expected to include a higher share of renewable resources in the future, a management system like this and a production- and demand-dependent operation of the plants only benefits the networks.

Direct consumption or storage of solar power at the place of production is becoming increasingly attractive given declining feed-in tariffs resulting from the temporarily enforced downregulation of small, grid-connected PV systems and rising electricity prices. This calls for effective and cost-efficient energy storage technologies as well as intelligent generation and load management.

Research focus

The aim of the joint project is the research, development and evaluation of a modular energy management system that can be used in new buildings as well as in existing buildings. To this end, the complex system is first simulated component-by-component and then in its entirety. A complete system is to be set up in the laboratory for testing purposes. Afterwards, a "real" building will be equipped with the new energy management system for demonstration purposes.

A special feature of the concept is the combination of electrical and thermal energy supply. Synergy effects are to be optimally utilised in order to permit a largely decentralised energy supply. For this purpose, the system is to be continuously optimised by incorporating dynamic weather data, performance forecasts and consumer behaviour.

Special emphasis is placed on simulating the entire system, hardware development for the control unit including all communication interfaces, creating algorithms for dynamic forecasts of production and consumption behaviour, linking individual buildings to virtual districts, the optimised operation of lithium-ion batteries as electrical energy storage and the hot water storage tank for the various thermal systems and circuits. Furthermore, appropriate business and operator models that could ensure an economically feasible operation of the systems will be analysed.

In this research project, a total of nine partners from industry and research are working to harness solar energy and solar heat for sustainable energy generation for individual buildings in a more sustainable and targeted manner. A combination of electrical and thermal energy storage is to support an energy-efficient and grid-friendly energy supply. A fuel cell operated with natural gas is to provide power and heat during periods with particularly low light intensity.

Successes

The overall system has been designed. Therefore, existing energy potentials  as well as the system and plant technology have been examined. The overall system simulation is based on separate modelling of the single components. The models were adapted and provided for various types of buildings such as old and new buildings as well as single and multi-family homes, for fuel cells, battery storage systems, solar thermal and photovoltaic systems, and thermal storage systems. Hardware development for the control unit was completed, including the necessary communication technology and a draft for component control.

In addition, the corresponding software and user interface were defined. The coupling of different data sources with intelligent, statistical methods in order to improve solar radiation forecasts has been implemented successfully. All components, except for the fuel cell, were set up as prototypes in the test laboratory. The integration of power electronics, the battery storage system and the management component is currently underway. During the testing phase, fuel cell and solar thermal as well as PV modules are simulated. It has already been determined that the demonstrator system will be set up at Sailer GmbH in Ehingen following the laboratory phase.

Currently a demonstartor system is created, tested and evaluated at the company Sailer, which is located in Ehingen.

Application

Individual components of iHEM are already available on the market:

BlueGEN is a fuel cell heater for supplying residential buildings and small commercial units with electricity and heat. The solid oxide fuel cell (SOFC) from the manufacturer SOLIDpower GmbH has a rated electrical output of 1.5 kW with a very high electrical efficiency of up to 60%. The unit is power-controlled for this reason. Its thermal output is 0.6 kW. Currently, the fuel cell is operated with natural gas. With the introduction of power-to-gas technologies (P2G), the fuel cell could be operated with renewable energy sources in the future.

Lithium-ion battery storage system: the modular battery used in the iHEM project is a lithium-ion battery storage system with a rated voltage of 358 V, a rated capacity of 24 Ah and a rated energy of 8.4 kWh. Modularity allows for adaptation to different system sizes.  Further special properties of the employed lithium-iron phosphate-graphite cell chemistry from Sony are the discharge depth of just under 100% and a lifetime of up to 10,000 charging cycles. These attributes support efficient economising with self-generated electricity.