SMA Backup 1P BU-SBSE-1P-50 — Automatic Single-phase Backup
SMA Backup 1P BU-SBSE-1P-50: external box for automatic single-phase backup of systems with a Sunny Boy Smart Energy inverter. In a blackout it powers the whole single-phase supply up to 63 A and 7,300 W, without a backup loads panel.
Switchover configurable from 0 to 600 s, IP65 for indoor and outdoor use, standby under 1 W, 506 x 260 x 236 mm. It is the component that takes backup from the 3,680 W manual output of the built-in SPS to 7,300 W automatic. A connected battery is required.
The SMA Backup 1P BU-SBSE-1P-50 is the external box that adds automatic single-phase backup to systems with a Sunny Boy Smart Energy hybrid inverter. When the grid fails it switches the system to island mode, powering all single-phase loads up to 63 A and 7,300 W, with no need for a separate backup loads panel.
This is the component that makes backup automatic
Sunny Boy Smart Energy inverters already have the SPS (Secure Power Supply) function on board, but it is worth being clear about what it does: it provides 3,680 W on a dedicated socket and the switchover is manual. In a blackout someone has to physically go to the inverter and activate it, and the loads must be plugged into that socket.
With the BU-SBSE-1P-50 the picture changes: the switchover happens on its own, the available power rises to 7,300 W and it is the entire single-phase supply that is powered, not one line. It is the difference between "I have a socket that works if I notice" and "the house keeps running".
It is not an uninterruptible power supply
The switching time is configurable from 0 to 600 seconds. Even set to the minimum, the transfer happens through contactors: it is not the sub-10-millisecond switchover of a UPS or an electronic EPS output. In practice computers, NAS and electronic equipment will restart; refrigerators, pumps, lighting, heating and the hob resume without anyone noticing.
The configurable delay is not a flaw but a function: on grids with frequent micro-interruptions it prevents the system from entering and leaving island mode at every disturbance, which would needlessly stress the contactors and the battery.
BU-SBSE-1P-50 Technical Specifications
| Function | Automatic grid / island switchover, single-phase |
| Maximum load current | 63 A |
| Backup power | 7,300 W |
| Switching time | Configurable from 0 to 600 s |
| Distribution system | TN-C-S |
| Protection rating | IP65, indoor or outdoor installation |
| Standby consumption | Under 1 W |
| Compatible inverters | Sunny Boy Smart Energy SBSE 3.6 / 4.0 / 5.0 / 6.0-50 |
| Battery required | Yes, island energy comes from the storage |
| Mounting | Wall-mounted, upstream of the main panel |
| Dimensions | 506 x 260 x 236 mm |
| Weight | 6.16 kg |
The point to clarify with the designer: earthing in island mode
The device is declared for TN-C-S distribution systems. Many low-voltage installations use a TT system instead, with the user's earth electrode independent of the distributor's. When the system switches to island mode the grid is no longer present, and the neutral's earth reference must be re-established locally: this is a matter to be resolved at the design stage with the professional who draws up the wiring diagram, not improvised on site. Coordination with the downstream residual-current device (RCD), which works under different conditions in island mode, must also be verified.
What you can actually do with it day to day
With 7,300 W available and an SMA Home Storage battery of 9-13 kWh, during a grid outage the home keeps running almost normally: fridge and freezer do not defrost, the boiler or heat pump stays powered, lights and sockets work, and you can use the induction hob or the oven — not both together. Autonomy depends on the storage: with moderate consumption, a 10 kWh battery comfortably covers an evening and a night.
Frequently Asked Questions
Does it work at night or under a cloudy sky?
Yes. In island mode the energy comes from the battery, not from the modules: operation is independent of the photovoltaic production at the moment. During the day, if there is sun, the PV contributes and extends the autonomy.
Do I need a backup loads panel?
No, and it is the main advantage over solutions with a dedicated EPS output. The box is installed upstream of the main panel and powers the entire single-phase supply up to 63 A: there is no need to separate at the design stage which circuits to keep on backup and which not.
Can I install it on a system already in operation?
Yes, provided the inverter is a Sunny Boy Smart Energy of the compatible series and there is a connected battery. Wall mounting and wiring upstream of the panel make it suitable for retrofits too, without replacing the inverter.
Do I need to notify the grid operator?
Adding island-mode operation changes the system configuration compared with the one declared in the connection application: the documentation must be updated, with the installer's declaration of conformity and notification to the distributor. Where the system is under an incentive scheme, that side must be checked too.
How many watts do I really need for my home?
The calculation is based on simultaneous loads, not on the contract. Fridge, freezer, lighting, router and boiler together stay under 1,000 W; a heat pump running adds 1,500-3,000; an oven or an induction hob alone can exceed 3,000 W. The 7,300 W cover everything with margin except the simultaneous use of the large kitchen appliances.
