Grid impedance is the electrical impedance of the utility network as seen from the connection point of a PV or storage system, usually derived from the short-circuit power available at the point of common coupling. When a PV system injects power, the impedance of the feeder causes the voltage at the connection point to rise in proportion to the power injected. A low grid impedance means a stiff grid that can absorb a lot of PV power before voltage limits are reached, while a high value points to a resistive feeder or one already loaded with much PV. Impedance between inverters and the grid, including conductors and transformers, can push terminal voltage up enough to cause over-voltage trips and also affects the stability of inverter controls. Some inverters report an event and disconnect from the grid when the grid voltage or grid impedance at their connection point is too high. Weak, high-impedance grids can produce low-frequency resonance between paralleled string inverters and the network, so designers check grid impedance at the PCC and keep short-circuit power well above plant size. For most commercial systems the grid capacity at the PCC dwarfs the PV system, so grid impedance is negligible and the utility supplies the value when it is needed. Related concepts include voltage rise, short-circuit ratio, transformer impedance and symmetrical components.
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explainsc1 drafted · lead Voltage rise
Impedance between the PV system and the grid raises the voltage seen at the inverter terminals; injected power raises voltage at the connection point roughly in proportion.
sec=3 h=c1f980e19b60sec=3 h=40033c0d0f22sec=h56 h=30ae0962fc12c2 drafted · lead Inverter-grid resonance at low short-circuit ratio
High-impedance (weak) grids can cause low-frequency resonance instabilities between the grid and paralleled inverters; inverter control stability depends on impedance to the PCC.
sec=h112 h=1832b34f9198sec=3 h=c1f980e19b60sec=3 h=40033c0d0f22related_toc3 drafted · lead Short-circuit ratio
Schneider recommends calculating grid impedance at the PCC and keeping short-circuit power at least 8 times plant installed power.
sec=h112 h=1832b34f9198c4 drafted · lead High grid impedance
SMA inverters disconnect from the grid when grid voltage or impedance at the connection point is too high.
sec=h424 h=9d464275e542sec=h429 h=9d464275e542sec=h434 h=9d464275e542c5 drafted · lead Point of interconnection
Grid impedance is evaluated at the point of common coupling from the available short-circuit power.
sec=3 h=c1f980e19b60sec=3 h=40033c0d0f22sec=h112 h=1832b34f9198c6 drafted · lead Voltage drop
AC conductors should limit voltage drop between inverters and PCC to a maximum of 1% of nominal voltage.
sec=3 h=c1f980e19b60sec=3 h=40033c0d0f22c7 drafted · lead Medium voltage transformer
Transformer short-circuit impedance adds to total system impedance seen by the inverter.
sec=3 h=c1f980e19b60sec=h112 h=1832b34f9198sec=h7 h=b98f50085d22c8 verified · fact Symmetrical components
Source impedance is expressed as positive-, negative- and zero-sequence components in fault analysis.
sec=h5 h=1174e69c8460sec=h22 h=9afda1f25756verified by: review-workflowverified on: 2026-10-24review note: support check: partial - u28 lists positive-, negative- and zero-sequence source impedances in fault analysis, but it doesn't call this 'grid impedance' explicitly, though it is the utility source impedance.
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