Photovoltaic systems are becoming more and more widespread and are thus actively contributing to the energy transition. Whether on single-family homes, industrial buildings or open land, these systems enable savings in energy costs and can increase the security of supply with the right application of the system. In the first part, this master's thesis examines various concepts in which photovoltaic systems and home storage can be operated in combination. An adapted uninterruptible power supply (UPS) should be used as highly cost-efficient home storage. Furthermore, an existing PV system with associated household is used to work out which cost savings are possible through the energy storage system and to what extent the overall system pays for itself over its useful life. In the following section, the various energy storage systems that are currently mainly used are discussed and how they differ from each other in terms of their performance. In order to use a UPS as a home storage system, its originally on lead-acid batteries based storage capacity must be increased. Reused lithium-ion batteries are used for this purpose. To ensure safe operation, a safety system is being developed that works in combination with the UPS and continuously monitors the battery pack. This monitoring system is set up in the laboratory and integrated into the UPS after successful tests. The entire system is then tested and the behaviour of the UPS in relation to the lithium-ion battery is checked. Thus, it is shown that older uninterruptible power supplies, which use different battery chemistries in their original design, can be converted to new technologies and work in combination with reused energy storage devices.