## 5 Discussion
Simulation results for one building have shown for PV self-consumption that through optimized heat pump operation and overcharging of the thermal buffer storages, up to 50% of cost savings could be achieved during the course of one day under ideal conditions. It has been found that the hurdles for the optimization of self-consumption are that in summer only DHW is prepared and thus less demand exists, and also that DHW storages tend to be too small. In addition, that in winter and the transition time the PV system's power output dos not match the heat pump's demand results in additional electricity taken from the grid. It was recommended to install larger thermal buffer storages and to match the installed PV winter power output to the heat pump's demand. In addition, general conditions such as low or no PV feed in the tariff and high electricity tariff costs together with no installed battery storage are ideal cases for this optimization approach. In addition, the utilization of flexible electricity tariffs was examined on the building level. Thereby, it is important that the tariffs show enough monetary variability whereas e.g., forwarding the fluctuations of the spot market to the end user would show too little incentive. Even with adequate flexible tariffs, enough thermal flexibility and thus larger thermal buffer storages and/or a higher comfort tolerance of the buildings occupants are required. The size of the thermal buffer storages is thereby not only relevant because of their maximum thermal capacity, but also because of the temperature levels at which the heat pump is operating. Simulation results have shown that even with enough storage capacity available, the higher temperatures reduced the heat pump's COP to such a degree that the monetary benefit of the optimization was reduced. Based on the here described work, simulation-based studies were also published previously [51; 52] addressing the potential of a participation in aFRR (secondary reserve) markets. Thereby, for a single building of the Plus-Energy settlement with battery storage, up to 48% of the heat pump's electricity demand could be provided by aFRR within a yearly balance, only reducing PV self-consumption from 36% to 34%. Thereby, the main problems were the very short activation durations from the aFRR market that lead to problems in heat pump cycling, which could be addressed by cluster management and by a change in the legal framework. Within the ongoing research project Sim4 Blocks, in the future, building optimization for six buildings shall be implemented. Further, it is planned to operate those buildings aggregated as a single virtual power plant also including activation calls by an aggregator. The limitations of this work are that only a very specific system combination--an agrothermal collector with a low-temperature DHC network on the district level, and on the building level mainly single family houses with high energy efficiency standard, decentralized heat pumps and PV systems--is investigated, which can limit the transferability of the results. In addition, agrothermal collectors are limited to areas with sufficient space; even in Wustenrot, as a rural municipality, it has proven to be difficult to find adequate areas. In addition, part of the presented results are simulation-based, and they still have to be proven in real operation. Conceptualization, M.B. and D.P. ; methodology, M.B., R.Z., R.O., R.P., and V.S. ; software, M.B. and R.O. ; validation, M.B. and R.O. ; formal analysis, M.B., R.Z., R.P., and R.O. ; data curation, M.B., R.Z., R.O., and R.P. ; writing--original draft preparation, M.B., R.Z., R.O., and R.P. ; writing--review and editing, M.B. and R.Z. ; supervision, D.P. and V.S. ; project administration, V.S. ; funding acquisition, D.P. and V.S.