Plan an apartment backup system
A practical planning guide: define the job, work through the energy and compatibility constraints, then prepare a supplier brief.
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.
Define the requirement
Start with a list of individual appliances you can safely plug into a portable backup source. Router, laptop and LED lighting often give more useful continuity per kWh than heating appliances. Record the fridge's measured daily energy and starting behaviour if it is included. A system serving individual plugs has a different installation scope from one energising fixed household circuits.
Work through the system
For a 250 W average essential load over four hours, plan 1 kWh AC. At the illustrative 80% usable fraction and 92% conversion, nominal storage is about 1.36 kWh. Check sockets, output limits and transfer behaviour on the actual unit. If uninterrupted networking matters, check both the router and optical terminal; keeping only one powered may not maintain connectivity.
Before selecting equipment
Choose a dry, ventilated position that preserves escape routes and manufacturer clearances. Do not connect an inverter output to a wall socket to energise the apartment. Fixed-circuit backup needs professional isolation and transfer design. Combustion generators are unsuitable indoors, in garages or on enclosed balconies. Roof or balcony PV needs permission, structural mounting and a realistic shade assessment before it enters the energy budget.
Worked case and decision
For a four-hour interruption, a 15 W router, 40 W lighting load and 60 W laptop need 460 Wh if all run throughout. A refrigerator adds energy according to its measured duty cycle and adds a separate compressor-start requirement. By contrast, operating a 1500 W electric heater for the same four hours adds 6000 Wh. Excluding that heater can change the proposal from a large storage installation to a modest essential-load system. Agree on those exclusions before selecting equipment. A portable unit supplying selected appliances directly has different installation requirements from equipment connected to fixed apartment wiring. Confirm building rules, accessible ventilation, noise and the location of charging equipment. Never assume a balcony makes a combustion generator safe; exhaust can enter nearby dwellings. Review transfer behaviour for routers and computers if even a short interruption is unacceptable.
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.
Turn the explanation into a procurement brief
Record included and excluded loads, system voltage, simultaneous power, starting demand and required duration. Keep efficiency and seasonal assumptions beside the result. Compare only documented values for the exact model; a missing catalog field means it needs verification, not that a feature exists. Ask the supplier for the manual, Romania delivery terms and warranty procedure before ordering.
After selecting components, a qualified installer should verify cables, protection, source isolation, ventilation and site conditions. Do not use a worked energy example as wiring instructions. When changing a load or battery, revisit both the energy budget and power check. A supervised operating test should confirm assumptions without exceeding manufacturer limits.
Sources and technical reading
- Victron Energy · Technical information / Wiring Unlimited ↗
- U.S. Consumer Product Safety Commission · Carbon monoxide ↗
Independent editorial explanation. Numerical examples are illustrative calculations, not specifications attributed to a product.