*4.3.3 Cumulative heat transfer (Qc)*

The cumulative heat transfer represents the total amount of heat stored at any instant from the start of the charging process as Eq. (8) given below shows. It adds on to the total heat from the starting of the experiment and this cumulative heat indicates the total amount of heat either stored while charging or retrieved while discharging of the storage tank

$$\mathbf{Q}\_{\mathcal{L}} = \sum\_{0}^{t} \dot{m} \mathbf{C}\_{p} (T\_{H-in} - T\_{H-out})\_{t} \Delta t, \mathbf{W} \tag{8}$$

*t* = Instantaneous time
