Modern district heating plants increasingly combine heat pumps, electric boilers, combined heat and power (CHP), biomass, waste heat, solar thermal and peak-load boilers. This diversification creates options - but only if the plant can choose when to use each source. Figure 1. Heating plant with tank thermal energy storage. That is where tank thermal energy storage becomes valuable. It does not produce heat, but it decouples production from demand: heat can be produced when t