Czy wolisz polską wersję strony elektroda?
Nie, dziękuję Przekieruj mnie tamHi. In my part of the world, we have a broad mix of residential houses connected by either of single-phase or 3-phase connections.
For single-phase connections, solar inverters are limited to 5kVA. This limit is set by the grid operator to help prevent voltage rise imbalance between the phases. For 3-phase connections, 3-phase inverters are capped at 15kVA to limit the amount of potential power flowing from homes back to the grid.
I’m trying to understand if voltage rise would still be an issue when all solar energy is consumed within the household. For example, consider a 15kVA single-phase inverter that’s designed to prevent grid export by adjusting output to match household consumption.
My intuition suggests that voltage rise on the grid side of the meter should be negligible.
Can anyone confirm this? I'm trying to lobby my grid operator to relax rules surrounding single-phase inverters with the capability of zero-export.
• In true steady-state zero-export operation, a 15 kVA single-phase inverter injects essentially no current into the utility conductor, so the external voltage rise that worries a grid operator is, in theory, negligible.
• The grid still sees only the customer’s net load (import), so normal limits for phase-to-phase imbalance and over-voltage are not violated under this condition.
• However, grid codes are written for the non-ideal realities of transients, control-loop delays, measurement errors and fault modes. Those conditions can momentarily export several kilowatts on one phase and create exactly the voltage-rise/imbalance the operator wants to avoid.
• Therefore, most utilities keep the 5 kVA-per-phase cap unless the zero-export function is certified, monitored and failsafe.
Why voltage rises
• At the point of common coupling (PCC) the phase voltage is
ΔV = I·Z_line (1)
where I is the net current flowing into the utility conductor.
• For conventional PV export, I is positive (from house to grid), so ΔV is a rise.
• If the inverter constantly throttles so that I ≈ 0, (1) collapses to a few millivolts set by metering error → no external rise.
Current paths in a zero-export house
• Inverter → local loads: currents circulate inside the premises.
• Grid → PCC → loads: the grid only supplies any shortfall.
• Grid never sees reverse current, hence no incremental voltage rise.
Transient and abnormal conditions
a) Load step:
Air-conditioner (8 kW) turns off while inverter still delivering; for 200 ms the PCC current can be ≈ 35 A export (8 kW / 230 V).
On a rural 0.4 Ω service drop this is 14 V rise — enough to push the phase to 254 V and trip neighbours’ appliances.
b) Sensor failure:
If the CT falls off the cable the inverter may default to full production. That is 65 A export on a single phase from a 15 kVA inverter.
c) Firmware lock-up, communication loss, etc.
Internal voltage rise
Even with zero export, current still flows through the house conductors between inverter and loads. That raises the inverter terminal voltage relative to the PCC.
• Not a utility problem, but it can cause the inverter itself to trip if the wiring is long or undersized.
Phase imbalance
The transformer neutral sees only the unbalanced component of net currents of all customers. A single-phase generator that occasionally exports 15 kW can swing the neutral voltage and force the other two phases low. Zero-export suppresses the steady component but not necessarily the dynamic swings.
• New grid codes (IEEE 1547-2018, UL 1741-SA, EN 50549, AS/NZS 4777.2:2020) include a formal “export-limit” or “dynamic-export” mode with test procedures (< 0.1 s response, < 1 % overshoot).
• Utilities in California, New Zealand, Ireland and parts of Germany now allow >5 kVA per phase if the inverter has certified zero-export plus remote monitoring.
• Hybrid PV + battery systems are increasingly used as a buffer: the battery soaks excess power during transients, further cutting export spikes.
• Response-time budget
– CT / Rogowski-coil sampling: 1–2 ms
– DSP calculation: 1–3 ms
– PWM modulation step: 10–20 ms (half-cycle)
All three must stay < 50 ms to keep an 8 kW step below 0.4 kWh export per event.
• Typical compliance margin
Many installers program a permanent 50–200 W import bias so the PCC current is always slightly into the house; this guarantees no unintended export but reduces self-consumption a few kWh per month.
• Fail-safe hierarchy
1. Loss of CT signal → immediate curtail to 0 kW
2. Internal watchdog → restart in curtailed mode
3. Grid-code mandated anti-islanding still applies.
• Safety: Over-voltage can damage neighbours’ equipment and stress pole transformers.
• Regulatory: Operating beyond approved limits may breach the electricity distributor’s connection agreement and void liability insurance.
• Privacy: Real-time export monitoring often uploads consumption profiles; data handling must meet local privacy laws (e.g., GDPR, Australian Privacy Act).
Potential challenges & mitigation
• Fast load shedding → add battery or supercapacitor buffer
• Firmware updates → subject them to re-commissioning test
• Cumulative impact of many systems → propose feeder-level monitoring
• Even perfect zero-export does not solve flicker caused by rapid PV ramp (cloud edge, load steps); some utilities cap single-phase power on that basis alone.
• Capacitive or inductive reactive-power commands can still shift local voltage a few volts without active-power export.
• Rules sometimes distinguish between inverter name-plate and export limit; exceeding the former may still be disallowed regardless of export setting.
• Demonstrate a 15 kVA single-phase with battery buffer under IEC 62933-2-2 micro-grid transient tests and publish the PCC voltage trace.
• Study cumulative neutral displacement on a feeder with high penetration of zero-export, single-phase PV.
• Investigate AI-based predictive curtailment that anticipates load steps from historical patterns.
Key resources
• IEEE P2004 “Recommended Practice for Inrush and Fast Transient Limits of DER” (draft)
• EPRI report 3002023483 “Field Validation of Export-Limiting Inverters”
• Australian ENA “Dynamic Export Limits Implementation Guide”, 2023
A correctly engineered zero-export system does remove the steady-state voltage-rise driver, so from a pure physics standpoint a 15 kVA single-phase inverter will not push the grid voltage up when it is truly not exporting. Utilities, however, regulate for real-world imperfections— millisecond-scale transients, sensor failures, phase imbalance and cumulative risk.
To convince them, present certified hardware, fast-acting control proof, fail-safe design and field data. Pairing with a small battery buffer and offering remote monitoring often tips the balance toward approval.
