Guides · Faisalabad, Lahore, Punjab
SBU, SUB and Utility-First Modes on Hybrid Inverters Explained
Short answer
SBU mode (Solar, Battery, Utility) runs your home on solar first, then the battery, and uses the grid only when the battery reaches a low point; SUB mode (Solar, Utility, Battery) runs on solar first, then the grid, and keeps the battery full for load-shedding. Utility-first mode runs the house from the grid and uses solar and battery mainly as backup. Under net billing, SBU usually makes the most of your own solar; in areas with long, frequent outages, SUB protects your backup.
These setting names come from the "output source priority" menu found on many hybrid inverters. Names, letters and menu numbers vary by brand and model, so always check your own inverter's manual.
Two settings, two questions
Most hybrid inverters have two separate priority settings. People often mix them up.
| Setting | The question it answers | Common options |
|---|---|---|
| Output source priority | Where does the power for my appliances come from first? | Utility first, Solar first / SUB, SBU |
| Charger source priority | What is allowed to charge my battery? | Solar first, Solar and utility, Solar only |
This guide covers the first one in detail. Charging the battery from the grid is a separate decision, covered in our guide should you charge your solar battery from the grid at night?
Hybrid inverter modes
SBU
Solar → Battery → Utility
SUB
Solar → Utility → Battery
Utility first
Grid runs the loads; solar and battery support
The output modes explained
SBU: Solar, Battery, Utility
- Daytime: solar runs the loads. Any surplus charges the battery.
- When solar is not enough (evening, cloud, a big load starting): the battery tops up or takes over.
- When the battery falls to its set low point: the inverter switches the loads to the grid until the battery is recharged to a set high point, usually by the next day's sun.
- Grid off: solar and battery carry the backup loads as normal.
SBU uses the battery every day. It reduces the units you buy from the grid, especially in the evening.
SUB: Solar, Utility, Battery
- Daytime: solar runs the loads first.
- When solar is not enough: the grid makes up the shortfall. The battery stays charged and idle.
- Grid off: the battery takes over the backup loads.
SUB keeps the battery in reserve for load-shedding and reduces battery cycling. It uses less of your own stored solar, so you buy more evening units from the grid. On some brands this mode is called "Solar first".
Utility first
- Grid on: the grid runs the loads. Solar may still charge the battery, and on some models it also helps carry loads.
- Grid off: solar and battery take over.
This works like a UPS with solar charging. It rarely suits a home that installed solar to cut its bill.
Brand names you may see
Some inverters label modes differently, for example "self-consumption", "backup", "time of use" or "economic" modes on many on-grid-style hybrid platforms. The idea is the same: who supplies the load first, and when the battery is used. Your inverter's monitoring app usually shows the active mode. See our monitoring app guide.
Side-by-side
| Point | SBU | SUB / Solar first | Utility first |
|---|---|---|---|
| Uses your solar for loads | Yes, first | Yes, first | Only when grid fails (model-dependent) |
| Uses battery every evening | Yes | No, kept for outages | No |
| Units bought from grid | Lowest | Medium | Highest |
| Battery ready for load-shedding | Down to the low point you set | Full | Full |
| Battery wear | Daily cycling | Low | Low |
| Suits | Net billing, evening loads, moderate outages | Long or frequent outages, small battery | Rarely suits a solar home |
Which mode should you use?
Under net billing
Since February 2026, new solar connections are on net billing. Units you export earn much less than units you buy. Every unit of your own solar that you store and use in the evening is worth your full tariff. That generally makes SBU the better everyday mode for homes with a battery. Our net metering and net billing guide explains the rates.
Under heavy load-shedding
If your feeder has long or unpredictable outages, a battery that is half-empty at 9 PM may not last through a two-hour outage. Two options:
- Use SUB, so the battery stays full until the grid fails.
- Use SBU but raise the low point, so the inverter returns to the grid while a healthy reserve remains for outages.
Option 2 is often the best balance. You still use part of the battery every evening and keep a reserve for load-shedding.
If your battery is small
A small battery cycled hard every night in SBU may leave little for outages. SUB, or SBU with a high reserve, is safer. Our battery size guide shows how to size a battery that can do both.
Without a battery
SBU and SUB make little sense without a battery. The inverter runs on solar with grid support. See can a solar inverter work without a battery?
The settings that go with SBU
SBU depends on two switching points. Depending on the model, they are set as a battery voltage or as a state of charge (SOC) percentage.
| Setting | What it does | How to think about it |
|---|---|---|
| Back to grid (low point) | Battery level at which loads move to the grid | Higher = more reserve for outages, less daily use |
| Back to battery (high point) | Battery level at which loads return to the battery | Usually near full, so the battery recharges properly first |
On lithium batteries that talk to the inverter, SOC-based settings are clearer than voltage. Leaving a reserve also helps battery life, because the battery is not taken near empty every night. See our guide to lithium battery lifespan and care.
Avoid setting the two points too close together, or the inverter may switch back and forth between grid and battery repeatedly.
Peak hours and timed settings
Many homes with a sanctioned load of 5 kW or more have a time-of-use meter, where evening peak units cost more. Some hybrid inverters let you schedule modes by time, for example using the battery only during peak hours. This can be worth setting up if your bill shows a large share of peak units. Our guide to reading your electricity bill shows where to find them.
Export and the mode setting
Output priority does not decide whether the inverter exports surplus to the grid. That is usually a separate "grid feed-in" or export-limit setting. If you have no net billing approval, export should be limited. Our zero export device guide explains why.
Common mistakes
- Leaving a utility-first default, then wondering why the bill barely changed.
- SBU with a very low switch-back point, so the battery is empty when night-time load-shedding starts.
- Changing battery parameters. Change only the mode and switching points; leave battery type and charging values to your installer.
How we set up your hybrid inverter
At commissioning, our engineers set the output mode, switching points and charging settings to match your load pattern, outage pattern and net billing status. We explain them during handover so you know what each setting does, and we can adjust them as your needs change. Hybrid inverter options are on our solar inverter price page, and our guide to hybrid vs on-grid vs off-grid helps if you are still choosing a system type.
Get today's price or a free site survey
- WhatsApp or call: 0336 666 4321
- Email: info@solarworks.pk
- Head office: Main Boulevard, Sargodha Rd, Block F FDA City, Faisalabad
- Lahore branch: 2nd Floor, Jeff Heights, Gulberg, Lahore
- Hours: 9:00 AM to 6:00 PM, daily
We serve customers throughout Punjab. See our Faisalabad and Lahore pages, or contact us. Site surveys are normally free.
Frequently asked questions
What is SBU mode on a solar inverter?
SBU stands for Solar, Battery, Utility. The inverter runs your loads from solar first, then from the battery, and switches to the grid only when the battery reaches the low point you set.
What is the difference between SBU and SUB?
In SBU the battery supplies the house before the grid, so it is used every evening. In SUB the grid supplies the shortfall before the battery, so the battery stays full for load-shedding.
Which mode is best under net billing?
For most homes with a battery, SBU, because each stored unit you use yourself avoids buying a full-tariff unit. Set a sensible reserve if your area has evening outages.
Why is my battery empty when load-shedding starts?
Your inverter is probably in SBU with a low switch-back point, so the battery was used up in the evening. Raise the low point or switch to SUB.
Does SBU mode reduce battery life?
It cycles the battery every day, which uses up its cycle life faster than SUB. Lithium batteries are built for daily cycling, and keeping a reserve rather than emptying it fully each night helps.
Should I change these settings myself?
You can usually change the output mode safely from the menu or app. Leave battery type, voltage and charging current settings to your installer, because wrong values can damage the battery.
Sources
- PowMr, "Solar Inverter Operating Modes Explained: SBU, SUB, and Priority Settings": https://powmr.com/blogs/news/solar-inverter-operating-modes-explained-sbu-sub-and-priority-settings
- WKS hybrid inverter configuration manual (PDF, French)
- Power Forum, "Axpert Max 72: problem in SNU charging" (charger priority labels): https://powerforum.co.za/topic/13632-axpert-max-72-problem-in-snu-charging/
- Daily Pakistan, "Peak electricity hours cut to 11pm" (21 Aug 2025)