Apartment backup
For residents keeping internet, lighting and a small workstation running without rebuilding the whole electrical installation.
Sources and methodology
Updated: 2026-10-17
Source-based desk research and explicit calculations; no hands-on testing claimed. Missing values remain unknown. Installation compatibility needs a separate assessment.
Typical loads
Measure router, optical-network terminal, laptop and LED lights individually. A refrigerator cycles and adds compressor starting demand. Keep electric heating, cooking and water heating outside a compact backup budget.
System architecture
A portable battery with AC outputs can feed individual appliances. A fixed essential-circuit board needs installer-designed isolation and transfer. For equipment that cannot tolerate interruption, check a documented UPS transfer time and test recovery.
Illustrative sizing
Illustrative envelope: 100–500 W of essentials for 2–6 hours. At 250 W for 4 hours, AC energy is 1 kWh; with 80% usable depth and 92% conversion, storage is about 1.36 kWh before ageing reserve. Inverter surge must still be checked separately.
Solar and generator
Balcony solar depends on permission, secure mounting, orientation and shade. It is not assumed to recharge the system daily. A combustion generator is not an indoor or balcony backup solution.
Worked example: internet and home working
The values below are assumptions for a reproducible example, not measurements. Replace power and time with your appliance data. Actual running time can differ from the period an appliance remains connected.
On small screens, scroll the table sideways to see all values.
| Load | AC/DC | W | Hours | Wh |
|---|---|---|---|---|
| Router + optical terminal | AC | 18 | 4 | 72 |
| Laptop | AC | 45 | 4 | 180 |
| LED lighting | AC | 12 | 3 | 36 |
| Total delivered to loads | 288 | |||
Calculation assumptions: 80% usable battery fraction; 92% inverter efficiency for AC loads only. Nominal storage is (DC Wh + AC Wh / 0.92) / 0.80. 391.3 Wh.
This threshold excludes inverter idle consumption, DC distribution losses, ageing and weather reserve. For example, an additional 10 W for 4 hours adds 40 Wh to the DC budget and 50 Wh to nominal storage at an 80% usable fraction. Enough energy does not establish startup capability, BMS limits or UPS operation.
What changes the result?
A 90 W laptop replacing the 45 W example for four hours adds 180 Wh of AC demand: about 245 Wh more nominal storage. A 1500 W kettle running for ten minutes needs 250 Wh but also 1500 W instantly; the power check can rule out a system even when its energy would be sufficient.
Recommended equipment categories
Backup power
Keep essential loads operating with a defined autonomy and transfer requirement.
Batteries
Compare usable storage, DC voltage and discharge limits before choosing capacity.
Inverters
Match continuous AC demand, starting surge and battery voltage.
Guides for this solution
Frequently asked questions
Is this a final installation recommendation?
No. Verify model manuals, actual loads, protection and site conditions with a qualified professional. Calculations and equipment classes are preliminary planning aids.
Where do I buy and who sets the price?
Purchase is with the external supplier, who controls price, delivery, inventory and returns. Confirm delivery to Romania before ordering. Commercial disclosure →