# Backup Generator

### Operation of the generator

The generator is used in the off-grid system to charge the batteries or to cover loads.

• For charging the batteries there is an insert control based on the state of charge of the batteries, in which the generator is usually started as soon as the batteries reach a low state of charge of about 30%.
• Lead-acid batteries in particular require regular maintenance charges. This is also provided by the auxiliary generator if there is not enough PV energy available.
• The additional generator can also be used for power-dependent load coverage. The coverage of peak loads or the securing of a base load is conceivable.

#### SOC-based operation control

The auxiliary generator is started when the state of charge of the batteries (SOC, state of charge) is below the start threshold and continues to operate until the SOC is above the stop threshold again.

$$SOC \leq SOC_\text{Startschwelle} \Longrightarrow P_\text{Generator} = I_\text{Generator} \cdot U_\text{AC-Netz}$$

$$SOC > SOC_\text{Stopschwelle} \Longrightarrow P_\text{Generator} = 0$$

The power is calculated from the generator current. This is either the default generator current or the maximum permissible current of the MultiCluster box, if this is smaller.

If the auxiliary generator is not operated due to the SOC thresholds, the system continues to check for load-related use.:

$$(P_\text{Verbrauch} - P_\text{PV,AC}) > P_\text{Startschwelle, Last} \Longrightarrow P_\text{Generator} = I_\text{Generator} \cdot U_\text{AC-Netz}$$

$$(P_\text{Verbrauch} - P_\text{PV,AC}) < P_\text{Stopschwelle, Last} \Longrightarrow P_\text{Generator} = 0$$

#### Maintenance charges

Finally, it is checked whether equalisation or full charging is taking place and the generator must therefore run because the PV power is not sufficient for charging.

### Fuel consumption

The actual fuel consumption of the auxiliary generator depends on its utilization and specific consumption. The specific consumption $C_\text{spline, Verbrauch, Auslastung}$ is defined in the database entry.

Based on the load (current generator power $P_\text{Generator}$ to rated power $P_\text{Generator,Nenn}$) the actual fuel consumption $\dot{V}_{\text{Fuel}}$ is calculated:

$$\dot{V}_{\text{Brennstoff}} = C_\text{spline, Verbrauch, Auslastung} \cdot \frac{P_\text{Generator}}{P_\text{Generator,Nenn}}$$