====== Round trip efficiency for seasonal storage systems ======
The round trip efficiency is defined as follows:

$\eta = \frac{E^-}{E^+}$
^$\eta$ |Efficiency [%] |
^$E^-$ |Electricity re-injected to the grid after storage [kWh] |
^$E^+$ |Electricity taken from the grid for storage [kWh] |