- Climate, Environment & Health
ENERGY TRANSITION AT HOME - STORING SOLAR POWER SAFELY
Photovoltaic systems for domestic use are in demand as never before. Owners and planners of such systems are increasingly opting for the complete package consisting of a solar panel for energy generation, a solar inverter for energy conversion and a domestic electricity storage system. This means that the electricity generated does not have to be fed directly into the grid, but can be temporarily stored for self-consumption. This allows the electricity generated from photovoltaic systems to be used efficiently and economically. Since 2018, the number of solar power storage systems installed in Germany has doubled to 200,000 small systems, according to the German Solar Industry Association, and forecasts show a further upward trend.
RCT Power GmbH from Constance was ahead of this trend and started back in 2015 with the development of a stationary storage solution for private residential buildings and smaller industrial plants, perfectly matching the in-house solar inverters. Managing Director Thomas Hauser reports: "Our goal was to open up a new business field and offer a complete system consisting of solar inverter and battery system on the market. Such system solutions, which are compatible with any solar panel, operate particularly safely and reliably." The Institute for Data Processing and Electronics (IPE) at KIT has contributed significantly to the development of these home storage systems. Dr. Thomas Blank, head of the Electronic Packaging Laboratory, explains, "A research focus at IPE is on battery-driven, power electronic systems as well as technologies for their manufacture and assembly. Together with RCT Power, we have built a customized battery management system within three years that can be economically used and operated in stationary home storage systems for high voltage levels."
Home electricity storage systems provide intermediate storage of generated solar energy until the time of consumption. The battery management system (BMS) takes over the monitoring and control of the entire energy system and communicates with the solar inverter to store or deliver the electrical energy to the home or grid. The battery management detects and and prevents the critical conditions at an early stage. As a command center, the BMS guarantees that each individual battery cell is continuously monitored and kept within a defined operating range (voltage, current, temperature). If a cell leaves the permissible operating window, the BMS must return the energy storage system to a safe state by means of appropriate control mechanisms. This makes it a key component in preventing damage to the entire energy system, such as overcharging, deep discharging, overcurrent or temperature extremes.
While RCT Power specializes in solar inverters manufacture ing, the IPE research team contributed its expertise on power electronics and battery systems into the product development. A battery management system previously designed at the institute and intended for the e-mobility sector provided a good starting point for adaptation to RCT Power's individual needs. In addition to the monitoring functions of the BMS electronics, the safety of a battery storage system also depends heavily on the cell chemistry used. Lithium iron phosphate cells with a low fire risk turned out to be particularly suitable during the initial characterization. A cell-oriented battery monitoring system was developed at KIT for monitoring the individual cells. The IPE built optimally tailored electronic modules for the new home storage systems and handed them over to RCT Power for transfer to a product-optimized assembly concept. Since the product launch, sales of the independently tested RCT Power home storage systems have been steadily increasing. "We have focused on photovoltaic power storage for self-consumption and offer our customers modular home storage for new installations but also as a retrofit option," says entrepreneur Hauser.
Dr. Blank appreciates the learning effect of such industrial collaborations: "From a scientific point of view, it is important for the institute to bring system developments closer to the area of commercial, industrial use. Lastly, development methods are derived in a very general way from a better understanding of the cooperation partners' requirements, resulting in more targeted research at the institute."
"Developing the basic framework right through to series production in RCT Power's home storage systems was a good experience of how science and industry can exploit synergies.
"Our idea of a modular, efficient, and safe home storage system for photovoltaics became reality with the help of KIT's customized battery management."
Pictures: Markus Breig / KIT