The Eversol‑MFH project was carried out from 2020 to 2023 in the city of Cottbus and focused on the development and field testing of highly efficient, solar‑powered multi‑family housing. The core technical work involved the installation of a large thermal storage unit, a photovoltaic (PV) inverter, and a lithium‑ion battery system in two prototype solar houses. The thermal storage was coupled to a solar‑thermal collector array and a district heating network, allowing surplus solar heat to be injected into the local heating grid. A back‑flow valve was later added to the solar‑thermal circuit to prevent self‑circulation, and its effect was quantified through detailed measurements. The project also evaluated the integration of a fresh‑water station and the detection of abnormal flow conditions, thereby improving overall system reliability.
Continuous monitoring of the houses was performed over three full years (2020‑2022). Temperature sensors were placed at the storage core, wall interior and exterior, and at the storage layers to calculate heat losses through the wall. The data set enabled a comprehensive assessment of the thermal performance of the storage, the PV‑inverter, and the battery. The analysis revealed that the solar‑thermal surplus could be effectively routed into the district heating network, increasing the self‑consumption of solar energy by a significant margin. Recommendations were derived for further optimisation, such as adjusting battery charge‑discharge schedules and tightening control parameters to maximise the utilisation of solar gains. The project also investigated the potential of coupling the houses to the district heating network during periods of high solar output, demonstrating that the surplus heat could be shared with neighbouring buildings, thereby enhancing overall energy efficiency.
In addition to the technical investigations, the project organised several workshops in Cottbus and online. These meetings served to present different tariff models, including flat‑rate rental schemes and tenant‑electricity contracts, and to discuss the integration of renewable energy supply into lease agreements. Feedback from tenants was collected through surveys, and the results were incorporated into the final recommendations. The workshop outcomes were compiled into a publication series (Freiberger Forschungshefte) and made available to stakeholders.
Collaboration was carried out by a consortium of partners. The housing developer egWohnen 1902 supplied the building sites and coordinated the construction of the prototype houses. The technology provider E3DC supplied the lithium‑ion battery system and the PV inverter. The district heating operator supplied the connection to the local heating network and provided data on heat demand. The project was funded by the German Federal Ministry of Economic Affairs and Climate Action, with additional support from the Federal Ministry of Housing, Urban Development and Building. The project timeline included an initial design phase (2020‑2021), installation and commissioning (2021‑2022), and a final evaluation and reporting phase (2022‑2023). The final report, which summarises the technical findings, performance data, and policy recommendations, is intended to inform future developments of solar‑powered multi‑family housing and the integration of renewable energy into urban districts.