Solar panels and STEG outages: how to plan backup power
Panels alone, battery and backup output: understand what stays powered during an outage and plan your home or shop's needs.
Grid-connected panels alone cannot keep the power on during an outage. To provide backup, the project must include compatible equipment, an energy reserve and the circuits to be supplied. Battery capacity does not replace an assessment of this configuration.
Three key points:
- Reducing your bill and keeping appliances running are two objectives that require sizing.
- The equipment must support backup operation and be correctly integrated into the installation.
- Backup duration depends on the selected appliances, their power demand and the energy available when the outage begins.
Revised: 31 October 2026. Examples are fictional and are not ready-to-install configurations.
Why does a grid-connected installation disconnect?
Disconnection protection prevents the installation from feeding the public grid when it is down. It protects workers and infrastructure in particular. STEG’s July 2026 reference requires this protection for installations operating in parallel with the grid. Source: STEG low-voltage technical reference, page 40.
Even in bright sunshine, a suitable backup architecture is therefore needed to keep using some energy on site. Grid protection is not bypassed: the system must isolate the backed-up circuits before powering them.
What do a hybrid inverter and battery add?
Depending on its configuration, a hybrid inverter or battery converter can manage stored energy and create a local backup supply. A switching device then separates this supply from the public grid. Some systems power only appliances connected to a dedicated output or distribution board. Operating example described by manufacturer SMA.
Ask for the quotation to identify the circuits covered. The word “hybrid” or a battery on a sales sheet does not, on its own, describe how your building will behave during an outage.
For cafés and shops, choose priority uses
Start with what must remain available: essential lighting, till, connectivity, refrigeration or other equipment vital to your business. Record power ratings and startup currents. Heating appliances, motors and air conditioning may require different sizing.
A solution covering a few circuits may meet your goal with a different budget from backing up the entire premises. The assessment also specifies single- or three-phase operation, allowable simultaneous power and desired duration.
Fictional example: how long with 10 kWh?
Assume a battery with 10 kWh of nominal capacity, of which 80 % is usable, and overall discharge efficiency of 90 %. These parameters are chosen for the example and do not represent all gel or lithium batteries.
| Illustrative calculation | Result |
|---|---|
| Deliverable energy: 10 × 80 % × 90 % | 7,2 kWh |
| Priority appliances drawing 2 kW on average | About 3,6 hours |
| The same appliances drawing 1 kW on average | About 7,2 hours |
This calculation assumes a sufficiently charged battery, with no solar recharging during the outage. Age, temperature, settings and power peaks change the result. The power the inverter and battery can supply must be checked separately.
Specify your priority appliances and desired duration. With your bill, name, phone number and email, the team prepares a free, no-obligation assessment.
Does a backup battery replace a UPS?
Not necessarily. Some sensitive equipment cannot tolerate the transfer delay. SMA documentation specifies that the described system’s backup function is not an uninterruptible power supply under IEC 62040. This is a feature of that system, not a universal delay applicable to every inverter. Manufacturer source: switching time.
Specify whether you need power restored quickly or an appliance kept running without any noticeable interruption. This requirement must be reflected in the assessment and equipment selection.
Lower bills and a backup reserve: finding the right balance
Using a battery every evening and keeping a reserve for outages use energy differently. The assessment compares avoided expenses, losses, investment, maintenance and replacement, as well as the terms for valuing exported energy.
Base your decision on incidents observed at your site and their impact on operations, without assuming the same outage frequency everywhere in Tunisia. Also read our overview of STEG battery rules and solar advice.