Step 9 / 14

How does a hybrid (off-grid) inverter work?

Tommatech, Growatt, Must or Axpert: the brands differ but the insides are largely the same. Switch the operating state at the top (solar, night, grid) and watch how the energy path changes. Then use 'Find the fault' to track down the commonest faults by measuring.

🧭 On-grid, off-grid, hybrid: what do they mean?

Three kinds of solar inverter. The difference is simple: is there a battery, and is it connected to the grid? Pick one and follow the energy.

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Panels

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📦

Inverter

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🏠

Home

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🔋

Battery

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Grid

battery both ways; the grid is a backup and a charging source

The best of both: it uses the sun first, then the battery, then the grid. When the grid goes down a relay flips and the home keeps running from the battery. 'Hybrid' simply means 'mixed': it manages several sources together.

✓ Power during cuts and solar savings too; when the battery runs out the grid takes over.

✗ The most expensive and most complex; with the most parts inside, it also has the widest range of faults.

📍 Where it's used: Homes and shops with power cuts, anyone who needs the boiler and fridge to keep running.

	On-grid	Off-grid	Hybrid
Battery?	✗	✓	✓
Connected to the grid?	✓	✗	✓
Works during a power cut?	✗	✓	✓
Feeds power to the grid?	✓	✗	±

So what is a "hybrid off-grid" inverter? It's the name on Tommatech, Growatt SPF, Must and Axpert-type units, the subject of this page. Off-grid: it never sells power to the grid. Hybrid: it still uses the grid as a backup and to charge the battery. So: solar first, then battery, then grid, and power keeps flowing during a cut. (Units that can also sell to the grid are called "hybrid on-grid".)

Solar panels

DC voltage from the panels in series. It varies with the sun and is zero at night. The string voltage must sit in the inverter's MPPT range and never exceed its maximum.

Oscilloscope

Multimeter≈320 V DC (string)

Tap a block to see what it does and what you'd measure there.

🔧 Inside the inverter: what's where?

This drawing isn't a photo; it follows the typical layout of 3–5 kW hybrid inverters. Positions vary by brand, but the parts look the same and come in the same order. Tap a region.

Energy path:

Tap a region to see what it does and how to spot it on the board.

🔒 This content is in the repair pack

The repair pack unlocks all interactive content in one go: diagrams and current flows, the Repair Workshop, simulations, concepts, IC guides, the Component Library and comparison guides. One sample in every section is free.

Repair pack: 5,000 ₺, members get 10% off → 4,500 ₺. Or 1-week access for 1,000 ₺.

⚠ Safety: The DC bus capacitors sit at ≈400 V and stay charged for minutes after switch-off; the battery side is low voltage but can deliver hundreds of amps. Before opening the cover, disconnect the grid, panels and battery and discharge the DC bus; never short the battery cables.

Next step: Step 10Motor drivers: from small to big→

Go further

Battery → DC bus: the push-pull topology Inside solar charging: the MPPT topology and simulator Repair Workshop: find the inverter fault by measuring Inverter fault codes: meaning and measurement How the sine is made: H-bridge and SPWM Concept: dead time Concept: bootstrap The basis of MPPT charging: the buck topology