Fraunhofer Institute for Solar Energy Systems ISE| Duration: | July 2011 - June 2014 |
| Contracting Authority/ Sponsors: | Fraunhofer Gesellschaft in the course of the Tomorrow Projects |
| Project Partners: | Fraunhofer Institute for Environmental, Safety, and Energy Technology UMSICHT, Oberhausen; Fraunhofer Institute for Silicon Technology ISIT, Itzehohe; Fraunhofer Branch Advanced System Technology IOSB-AST, Ilmenau |
| Website: | http://hybrider-stadtspeicher.de/ |
Urban Hybrid Energy Storage – Domestic Batteries for Intermediate Storage of PV Electricity
Fig. 1: Design of a modular lithium-ion battery system for intermediate storage of PV electricity.
Thermographic image of the lithium-ion battery module during the discharging phase with a C-rate of 1 (discharge in one hour) without activated cooling.
Fig. 3: Efficiency values of the lithium-ion battery module for different C-rates (charging and discharging in one hour, two hours and five hours respectively).
Decentralised battery systems for intermediate storage of PV electricity are essential to further expanding the use of renewable energy. Integrated into buildings, these storage solutions must be highly efficient, safe, reliable and durable. In addition, they must be easy to combine with existing and future PV system installations. In order to meet these requirements, we are developing innovative battery systems based on lithium-ion technology within the Fraunhofer project on ”Urban Hybrid Energy Storage”. The systems are distinguished particularly by their modularity, a sophisticated cooling system and intelligent battery management with accurate algorithms for state determination.
Lithium-ion batteries are ideally suited for intermediate storage of PV electricity due to their specific characteristics. However, a series of complex development steps is needed to progress from single cells to a functional battery system. The cells are connected to form so-called battery modules (Fig. 1). They must be actively cooled in dependence on the operating point, be easily integrated into a battery system and be monitored by a battery management system.
In the construction of the battery modules, our main priority is to ensure that the temperature distribution is as homogeneous as possible and that the system does not need to run the integrated cooling system over a wide operating range (Fig. 2), but without causing premature aging of the cells or inducing states critical to safety. With this approach, the peripheral losses – e.g. due to the ventilator – can be reduced and thus the system efficiency raised and the lifetime lengthened.
The battery management is designed such that several modules are monitored and controlled by one unit. A separate circuit board for each module is planned only for so-called cell balancing, which is intelligently integrated into the flow channel of the ventilation unit. This reduces the amount of hardware needed compared to systems with integrated module management. As a result, costs can be reduced at the system level.