Three modes — three different results on the bill
One of the most frequent questions in support sounds like this: "I set up the hybrid, but I see no savings — which mode should I switch on?". The answer almost always comes down to the choice of power-source priority. A hybrid inverter has three of them — SUB, SBU and USB. The names are simply the order in which the inverter takes energy: Solar, Battery, Utility (grid). By shuffling these three letters, the manufacturer defines three different strategies, and each gives its own result on the electricity bill.
Let us go through each mode in plain terms, and at the end — advice on what to switch on in winter and what in summer.
SUB — "reliable winter"
SUB stands for Solar → Utility → Battery. The logic is this: the home runs on solar; if solar is not enough, the inverter tops up energy from the grid; and the battery, meanwhile, is kept charged at 100% the whole time, waiting for its moment.
The point of the mode is reliability. In SUB the battery acts as a reserve in case of a blackout, not as a daily "workhorse". As long as the grid is there, you essentially use solar plus the socket, while the stored capacity stays untouched. The moment the power goes out, you have a full battery ready.
This is a mode of calm: you cycle the battery's charge-discharge less and always have a reserve for an emergency. The price of that reliability is that you get almost no daily savings from the battery — the grid is used more actively.
Who is it best for? For those whose main pain is not the electricity bill but the outages themselves. If your region has frequent and unpredictable blackouts, SUB gives you the main thing: confidence that at the moment of an outage the battery is charged to the brim and the home keeps running without a pause. Solar still lowers the daytime draw from the grid — you do not pay for what you can take from the roof. The stored capacity is simply, deliberately, kept as a reserve rather than spent every day.
SBU — "maximum savings"
SBU is Solar → Battery → Utility. Here the priorities are different: first we take everything we can from solar, then we discharge the battery, and only as a last resort do we turn to the grid.
The point of the mode is to squeeze the maximum out of your own generation and stored energy. The grid switches on only when neither solar nor the battery covers consumption any more. This is precisely the mode recommended for maximum savings: you pay the grid the minimum, because you "eat" your own energy first.
The flip side is that in SBU the battery is constantly working: charging during the day, discharging in the evening and at night. This is a normal working scenario, but the battery is less often at 100%, so the reserve for a sudden blackout is smaller than in SUB.
In plain terms, SBU is the "own energy first, bought energy second" mode. During the day, solar both powers the home and charges the battery; when the sun sets, the energy stored over the day takes over; and only when the battery is at its lower limit does the inverter turn to the grid. For a home whose main goal is to minimise the bill, this is the most logical choice in the season when generation is sufficient. That is why SBU is called the maximum-savings mode.
USB — grid priority
USB is Utility → Solar → Battery, that is, grid priority. The home runs primarily on the grid, with solar and the battery as auxiliaries. This is a rare mode: it makes sense only where the solar part of the system is secondary and the main source is a stable grid. For the classic task of "save on electricity and have a reserve for a blackout", USB is usually not chosen.
In practice USB can be found where the solar station was installed not for savings but for a narrow task — for example, to back up a separate load while the main supply comes steadily from the grid. For a typical private house with a full panel array and an ample battery, this mode leaves the system's main trump card — its own generation — unused. So if you are hesitating between the three options, USB can almost always be discarded first.
Mode comparison
| Mode | Source order | Role of the battery | When to use |
|---|---|---|---|
| SUB | Solar → Utility → Battery | Reserve, always charged at 100% for a blackout | "Reliable winter": when a reserve for emergencies matters |
| SBU | Solar → Battery → Utility | Working: daily charge-discharge, grid last | "Maximum savings": recommended for summer |
| USB | Utility → Solar → Battery | Auxiliary | Rarely: when solar is only an auxiliary resource |
What to switch on in winter and what in summer
The practical advice from support experience is short:
- In winter it is more sensible to keep SUB. There is little sun, blackouts are more likely, and it matters more to you that the battery is always full as a reserve. In this mode you do not risk meeting an outage with a half-empty battery.
- In summer it makes sense to switch to SBU. There is plenty of sun, generation covers consumption with a margin, and you can calmly discharge the battery every evening, minimising the grid bill. The reserve, meanwhile, is restored daily by the sun.
In other words, this is not "one correct mode forever" but a seasonal strategy: SUB for the cold period with a solar deficit, SBU for the sunny months. USB remains a niche option for systems where solar is merely a supplement to the grid.
Do not be afraid to switch the mode depending on circumstances. It is a routine operation, not "interfering with the system": you are simply telling the inverter in what order to take energy this season. Many people set the mode once during installation and never return to it — and then wonder why in winter the battery turned out half-empty exactly during an outage, or why in summer the electricity bill barely fell. A few seconds in the menu twice a year, and the system works the way you expect it to.
What else affects real savings
The mode itself is the source priority, but savings also depend on how correctly the system is assembled and configured. Two points from practice worth keeping in mind:
- The BMS link. Until the inverter "sees" the battery over the digital channel, it manages it by voltage only and does not use the capacity to the full. How to set the link up correctly (battery type LIB, Protocol ID) is described in the article on the Veichi SV to Felicity link.
- Sufficient battery capacity. In SBU the point of savings appears when the battery is enough to cover the evening-and-night consumption. If the capacity is too small, the inverter quickly "hits" the grid and the savings effect melts away. See the battery models in the batteries for solar panels section.
You can choose the inverter itself for your system in the hybrid inverters section.
And one more observation from practice: the mode is a tool, not a "magic savings button". If the home's consumption is chaotic, with heavy loads coming on when the sun is already gone and the battery capacity is short, then even a perfectly chosen SBU will work no miracles. So before choosing a mode it helps to have at least a rough idea of your daily consumption profile: when the load peaks in the home, how much energy the array actually gives in the current season, and whether the battery covers the evening "tail". When these three things line up, the mode sits naturally on top of them — and the savings become visible from the very first month.
Frequently asked questions
Which mode is the most economical — SUB or SBU?
For maximum savings — SBU: the inverter takes solar first, then the battery, and the grid only as a last resort. SUB is more reliable for a blackout but uses the grid more actively.
Which mode should I switch on in winter?
In winter people usually keep SUB so the battery is always charged at 100% as a reserve in case of outages.
Which mode should I switch on in summer?
In summer SBU is recommended — there is enough sun, so you can discharge the battery daily and minimise the draw from the grid.
What does USB mean and why is it rarely used?
USB is grid priority (Utility → Solar → Battery). It is used only where solar is an auxiliary source, so for the task of saving and backup it is usually not suitable.
Why do I see no savings even in SBU?
The most common reasons are that the inverter is not set up for the BMS link (it manages the battery by voltage only) or the battery capacity is not enough to cover the evening consumption, and the system quickly switches to the grid.
Can I switch modes through the year?
Yes, and it is a normal routine operation. Many owners keep SUB in the cold period with frequent outages and switch to SBU for the sunny months. A few seconds in the menu twice a year noticeably affect both savings and readiness for a blackout. The main thing is not to "set it once and forget", but to consciously choose the priority for the current season and your consumption profile.
