FAQ
TL;DR: Polish DSOs cap single-phase inverter output at 3.68 kW [Elektroda, Slawek K., #19566384] and, as one installer says, "Above 3.68 kWp go 3-phase" [Elektroda, Cytro12, post #18923192] Combine a 4 kW 3-phase plus 1 kW 1-phase inverter only if each phase stays under the cap [Elektroda, Tech132, post #18924050]
Why it matters: Oversized or badly balanced systems trigger grid-side shutdowns and void approvals.
Quick Facts
• Single-phase limit: 3.68 kW per phase (all Polish DSOs) [Elektroda, Slawek K., #19566384]
• Grid over-voltage trip: 253 V according to EN 50549-1 “PV inverters”
• Smallest 3-phase inverters: typically 3–3.3 kW AC [Elektroda, kosmos99, post #19570039]
• Remote curtailment planned for systems >10 kW [Elektroda, DEFENCE, post #20015017]
• PV modules lose ≈0.6 % output per year [NREL, 2022]
Can I run one 3-phase and one single-phase inverter on the same connection?
Yes. DSOs allow multiple inverters as long as each phase sees ≤3.68 kW AC and the total contracted power is respected [Elektroda, ksysju, post #18923184] Balance the single-phase unit on the most loaded or lowest-voltage phase to avoid asymmetry [Elektroda, Tech132, post #18924050]
What is the legal single-phase power limit in Poland?
The nationwide DSO limit is 3.68 kW AC per single-phase inverter [Elektroda, Slawek K., #19566384]. Exceed the figure and the utility forces a 3-phase connection [Elektroda, Cytro12, post #18923192]
Will a 4 kW 3-phase inverter plus a 1 kW single-phase unit pass the Energy Report?
It will, because each phase carries ≤3.68 kW and the total sits under 5 kW [Elektroda, Tech132, post #18924050] File an “installation update” rather than a new application to keep paperwork light [Elektroda, DEFENCE, post #19566064]
How do I pick the phase for a single-phase inverter?
Measure phase voltages at peak generation. Choose the phase showing the lowest daytime voltage or highest household load; this reduces the risk of 253 V trips [Elektroda, anaba255, post #18924184]
What voltage problems can a single-phase inverter create?
Feeding 3 kW into one phase can raise that phase by ≈5 V for a 0.2 Ω loop impedance, pushing it beyond 253 V and forcing shutdowns [Elektroda, 3301, post #19571636] Streets with heavy PV already touch 250 V by noon—a classic edge-case failure [Elektroda, DEFENCE, post #19571936]
How does a 3-phase inverter help with over-voltage?
A 3-phase unit spreads power evenly, so each phase voltage rises about one-third as much as a single-phase feed [Elektroda, kosmos99, post #19568595] It cuts nuisance trips but cannot fully equalise voltage if the feeder itself drifts high [Elektroda, Slawek K., #19569563].
Do multiple inverters need to communicate with each other?
No. They all synchronise to the grid, not to each other. You can simply parallel AC outputs at the main board; no hub or modbus link required [Elektroda, Slawek K., #20319063].
How can I calculate safe extra PV power before hitting 253 V?
Use the three-step rule:
- Measure open-circuit phase voltage U on a clear day.
- Obtain loop impedance Z from an electrician.
- Compute P = (253 − U) × 253 / Z [Elektroda, 3301, post #19571636]
If P is 2 kW, adding 3 kW will likely trigger trips.
What happens if my total inverter power tops 10 kW?
DSOs plan remote curtailment for systems above 10 kW and may move you to the new net-billing regime [Elektroda, DEFENCE, post #20015017] Staying below 9.99 kW avoids that switch and extra charges.
Are sub-3 kW 3-phase inverters available?
Rarely. Most brands start at 3 kW or 3.3 kW [Elektroda, kosmos99, post #19570039] Below that, designers choose two small single-phase units on different phases [Elektroda, anaba255, post #18924184]
Will mixing 255 W and 450 W panels on one inverter waste power?
Only if you place mixed panels on the same MPPT string. Separate strings keep each array at its own optimal point, so 450 W modules deliver full output [Elektroda, kosmos99, post #20014751]
My roof faces three directions. How do I handle multiple orientations?
Pick an inverter with two MPPTs and add a small extra single-phase unit for the odd-angle array, or install microinverters. Four orientations need four MPPT channels for peak efficiency [Elektroda, anaba255, post #18924184]