The inverter is the heart of any backup power system: it turns the direct current from batteries or solar panels into the ordinary 230 V your appliances use. Choosing the wrong inverter is the most expensive mistake you can make — you can't simply "add more" the way you can with batteries, and the wrong type won't keep the lights on during an outage at all. Here is what to check before buying, from the basics to the technical details.
Three types of inverter, and why grid-tie won't help in a blackout
| Type | Works without the grid | Battery | Solar panels | Who it's for |
|---|---|---|---|---|
| Grid-tie (on-grid) | No | No | Yes | Lower bills, selling energy to the grid |
| Off-grid | Yes | Yes | Often | Backup, cottages, homes with an unreliable grid |
| Hybrid | Yes | Yes | Yes | Homes that want both backup and solar |
Important: a grid-tie inverter shuts down together with the grid. This is a safety requirement — it must not feed voltage into a line where electricians may be working. So a solar array on a grid-tie inverter without a battery does not power your home during an outage, even in broad daylight.
For backup power you need an off-grid or a hybrid inverter. Off-grid "all-in-one" units (inverter, grid charger and solar controller in one box) are cheaper and simpler. Hybrids are more flexible: they can send surplus to the house or the grid, schedule loads, and usually switch over faster.
Pure sine wave is a requirement, not an option
Inverters with a modified (stepped) sine wave still exist at the very bottom of the market. Lamps and chargers don't care, but compressor and pump motors run hot and hum on that waveform, and gas boiler electronics may refuse to start or throw errors. For a home, buy only a pure sine wave inverter — every decent hybrid and off-grid model has it by default.
How to size the power
The inverter's rating is set by what has to run at the same time, not by everything you own.
- List the appliances that must work during an outage.
- Mark those that can switch on together and add up their power.
- Add a 25–30 % margin: an inverter shouldn't live at its limit.
- Check motor starting currents separately — they often matter more than the total.
| Appliance | Running power | Start-up (approx.) |
|---|---|---|
| Fridge | 80–150 W | 3–5 times higher |
| Gas boiler (electronics, pump, fan) | 60–150 W | almost no surge |
| Well pump | 0.5–1.5 kW | 3–7 times higher |
| Microwave | 0.8–1.2 kW | small |
| Electric kettle | 1.8–2.2 kW | no surge |
Example for a house: a 150 W fridge, 120 W boiler, 100 W of lighting, a 15 W router, a 100 W TV and a 1.1 kW well pump. Together that's about 1.6 kW, 2 kW with margin. But the pump can draw 4–5 kW for a fraction of a second when it starts. So this house needs a 5 kW inverter with a peak rating at least twice its nominal power — otherwise it will trip every time the pump kicks in.
Manufacturers state peak power together with a duration — for example, "16 kW for 10 seconds" on the 8 kW Deye SG05LP1. Compare that figure with the starting current of your heaviest motor.
Single-phase or three-phase
If your home has a single-phase supply, the choice is obvious. If it has three phases, look at the loads:
- A single-phase inverter backs up one phase. That's enough if everything you need during an outage can be moved onto one line.
- A three-phase inverter is needed for three-phase loads (a 400 V pump, a boiler, workshop machines) or when the load is large enough to be worth spreading across phases.
Warning: a three-phase inverter can't always deliver different power to different phases. If your load is heavily unbalanced (everything on one phase), check the maximum per-phase load in the specs — sometimes it's only a third of the nominal rating.
Battery voltage: 12, 24, 48 V or high-voltage
The higher the power, the higher the battery voltage should be — otherwise currents grow so large that you need cables as thick as a finger. A rule of thumb:
| Inverter power | Battery voltage | Why |
|---|---|---|
| up to 1 kW | 12 V | simple, affordable batteries; currents still moderate |
| 1–3 kW | 24 or 48 V | 48 V already halves the current |
| 3–12 kW | 48 V | the home standard with the widest battery choice |
| above 12–15 kW | high-voltage or several 48 V units in parallel | lower currents and thinner cables |
More on the difference in 48 V or high-voltage battery system.
Transfer time
When the grid fails, the inverter switches the house to the battery. Hybrids do it in a few milliseconds (Sol-Ark, for example, quotes 5 ms); budget off-grid all-in-one units usually take 10–20 ms. Lights and fridges don't notice, but a computer without its own UPS may reboot if the switch takes longer than 10 ms. If you run computers or a server at home, look for "transfer time" in the specs and pick the lower value.
Self-consumption
An inverter draws power even with no load — typically tens of watts for 5–12 kW models. Over a 10-hour outage that's 0.3–0.6 kWh, a noticeable share of a small battery. For small systems (an apartment with 1–2 kWh of storage), self-consumption often matters more than efficiency, so paying for "spare power" actually hurts.
Where to install it
- A dry, ventilated room: the inverter gets warm and its fans need air.
- Close to the battery: the shorter the DC cables, the lower the losses and the cheaper the installation.
- Not in a bedroom if the model has fans — they are audible under load.
- Within the temperature range the manufacturer specifies; for lithium batteries, above 0 °C while charging.
Pre-purchase checklist
- Type: hybrid or off-grid, not grid-tie.
- Pure sine wave.
- Nominal power 25–30 % above the simultaneous load.
- Peak power and its duration above the starting current of the heaviest motor.
- Number of phases matches your supply and loads.
- Battery voltage matches the power (see the table above).
- Compatible with your battery's BMS communication (CAN or RS485).
- Transfer time, if you have computers.
- Service and warranty support in Ukraine.
Summary
Load first, then the inverter, and only after that the battery. Work out what has to run at the same time, check the starting currents, and choose a hybrid or off-grid inverter with a pure sine wave. Next, move on to calculating battery capacity and the wiring diagram, and compare specific manufacturers in the brand overview.
