IFs increments basic energy stock levels (BENST) every year by production (ENP) and imports (ENM) and decrements them by demand or consumption (ENDEM) and exports (ENX).
This is the basic stock level only because the actual stock value (ENST) cannot go negative. If the basic stock level is negative, stocks are set at zero and a shortage (ENSHO) exists. If the basic stock level is positive there is no shortage and stocks equal the basic level.
The energy shortage enters the economic model in the calculation of gross sectoral production.