In short
- Output priority says who feeds the house first: the grid, the sun, or the sun then the battery.
- Charger priority says who may charge the battery: only the sun, or the grid as well.
- SBU with solar-only charging gives the most self-consumption, at the price of buying power when the battery runs low.
Axpert-family inverters, sold under many badges, share the same menu logic. The program numbers move a little between models and firmware versions, so keep your manual close, but the choices are the same almost everywhere.
Output source priority
| Setting | Who feeds the house | Battery used |
|---|---|---|
| Utility first (USB) | The grid, as long as it is there. | Only during a grid cut. |
| Solar first (SUB) | The sun, topped up by the grid. | Only if the grid fails. |
| SBU priority | The sun, then the battery, then the grid. | Every evening, down to the level you set. |
On a site with no grid at all, the choice hardly matters. With a grid, SBU is the setting that actually uses the battery you paid for; utility first keeps it as a backup that ages on the shelf.
Charger source priority
The second setting decides what may charge the battery. Solar first (CSO) charges from the panels and lets the grid help only when the sun is gone. Solar and utility (SNU) uses both at once and fills the battery fastest. Only solar (OSO) never takes a watt from the grid for charging. If you pay one price day and night, OSO with SBU is the usual pair for self-consumption. With cheap night power, some owners prefer SNU and a battery that starts the day full.
The level where SBU hands back to the grid
SBU switches the house back to the grid below a battery voltage you set, and returns to the battery above another one. Set them too close and the inverter flips between the two all evening; set the first one too low and the battery runs deep every night. Lithium owners usually raise the first threshold well above what the lead-acid defaults suggest.
Seeing it on your curves
Axpert Monitor reads the inverter through its RS232 port and keeps the day: PV power, load, battery voltage and mode. With SBU you should see the mode change from solar to battery after sunset, and to grid only when the voltage reaches your threshold. If the mode says grid at eight in the evening on a sunny day, one of the thresholds is off.
Common questions
Does Axpert Monitor change these settings?
No. It only reads the inverter; you change the priorities on the inverter’s own menu.
Which setting saves the most?
Usually SBU with solar-only charging, if the battery is big enough for your evening. Your curves tell you after a week.
Why does my inverter keep switching between battery and grid?
The two voltage thresholds of SBU are probably too close. Leave a wider gap between them.
