State of charge estimation of thermal storages for distributed generation systems

The aim of this work is the development of three different models to calculate the enthalpy content of a stratified water thermal storage tank from discrete temperature measurements. The difficulty related to enthalpy value evaluation comes from the discrete temperature measurement along the storage (often only 2 to 4 temperatures along the volume height are known): the actual temperature distribution between two subsequent probes is unknown. Three different models based on three different approaches were developed and compared, basing on experimental data. A first model calculates the enthalpy value considering the measured temperatures and the thermal power difference between generation and consumption. The second model uses a mathematical pre-defined temperature shape fitted considering real-time experimental data. The latter model is based on a 1-D physical approach using a multi-nodal method. All the models were validated against the experimental data obtained from the distributed generation laboratory installed in Savona, Italy.