The premise
Robbert is running a Victron three-phase 5 kVA home-battery setup. A battery without solar is half a system, so he keeps adding panels. When net metering ends, panels that used to pay back via export only really pay if you can store the energy. That makes the panel layout question more important, not less.
Plenty of comments on previous videos came back to the same thing. How do you actually wire panels? How do you pick an inverter that matches? This video is his attempt to walk through the math with a real example.
Reading the panel sticker
Robbert grabs a random panel listed on Marktplaats. The sticker carries the numbers that matter:
- Open circuit voltage (Voc): 36.9 V
- Current at Pmax (Imp): 8.16 A
- Rated power: 250 W
Two rules carry over from battery wiring. Panels in series add voltage and keep current the same. Panels in parallel keep voltage the same and add current. The total wattage is the same either way. Configuration just trades amps for volts, which changes cable thickness and which inverters fit.
Three configurations on the same panels
| Wiring | Panels | Voltage | Current |
|---|---|---|---|
| 4 panels in parallel | 4 | 36.9 V | 32.64 A |
| 6 panels in series | 6 | 221.4 V | 8.16 A |
| 12 panels in series | 12 | 442.8 V | 8.16 A |
| 6 panels in 3p × 2s | 6 | 73.8 V | 24.48 A |
The 32.6 A all-parallel layout needs heavy cable. The all-series layouts keep the current low and let you run thinner wire. Solar cable is double-insulated and rated for high DC voltages, so the 442 V case is not a cable problem.
For 12 panels at 250 W each, total array power is 3000 W regardless of how you wire them.
Matching the panels to an inverter
Robbert walks through two Goodwe inverters against the same 12-panel string.
GoodWe GW2000
- Max string voltage: 500 V (the string fits)
- MPPT range: 40 to 450 V (fits)
- Max input current: 12.5 A (8.16 A fits)
- Max output: 2000 W (the array is 3000 W, so the inverter is undersized)
GoodWe GW3000
- Max string voltage: 500 V (fits)
- MPPT range: 80 to 450 V (fits)
- Max input current: 18 A (fits)
- Rated output: 3000 W (matches)
Same panels, same string, different inverter. The 3000 W unit lets the whole array work. The 2000 W unit caps it. The calculation is not optional.
When to use a series-parallel mix
The 6-panel series-parallel layout, 24.48 A at 73.8 V, looks inefficient if you're feeding a grid-tied AC inverter. It's the right layout if you're feeding a Victron SmartSolar MPPT charge controller instead.
Take the Victron MPPT 100/30 as an example.
- The 100 is the max input voltage, so the string must stay below 100 V.
- The 30 is the max output current to the battery.
The 73.8 V / 24.48 A layout fits both limits cleanly. A 12-panels-in-series string at 442 V would not. MPPT controllers generally want lower voltages than grid-tied AC inverters, so the panel layout has to change with the inverter type.
What Robbert is running
- 12 panels in series on the back roof, AC-coupled
- 12 panels on the back veranda, AC-coupled
- 15 panels on the front of the house, AC-coupled
- 6 panels on the shed, going through a Victron MPPT directly into the battery pack
AC-coupled inverters are second-hand and cheap (he mentions paying about €40). They handle long cable runs well, send AC straight into the meter cupboard, and don't need expensive DC cabling. The downside is two conversion steps (DC to AC, then AC back to DC for storage), which costs efficiency. On a small string headed for the battery, the MPPT path is the better trade.
What you cannot do
Wiring the inverter output into a wall socket is a fire hazard. Picture 2000 W coming out of the panels while the kitchen pulls 5000 W. The grid sees only the 3000 W shortfall, well under the 16 A fuse's trip point. The wall cable, rated for 16 A and 3600 W, is now carrying 5000 W. Nothing trips. Something starts smoking.
A solar inverter must land on its own dedicated 16 A circuit in the meter cupboard, with a clear AC disconnect between the inverter and the circuit breaker. Some inverters have a DC disconnect on the bottom; if yours doesn't, add one between the panels and the inverter so you can isolate during maintenance.
MPPT vs grid-tied inverter
The two devices solve different problems.
- A grid-tied AC inverter converts panel DC to grid AC and pushes it back through the meter. With a home battery on the AC bus, the Multiplus can pull some of that AC back into the battery.
- An MPPT charge controller converts panel DC into the right DC voltage to charge a battery directly. It is not grid-connected and cannot export. It is only there to charge.
If you want to export from the battery, you need a grid-tied inverter capable of bidirectional flow. The Victron Multiplus in Robbert's setup does both: it charges from the grid and discharges back to it.
Takeaways
- Read the sticker. Voc and Imp drive every later calculation.
- Series adds volts, parallel adds amps. Total wattage doesn't change.
- Match the string voltage and current to the inverter's specs before buying.
- AC inverters want high-voltage long strings. MPPTs want lower voltages, often through series-parallel mixes.
- Solar must land on its own circuit in the meter cupboard, never a wall socket.
