# Grid-Tied vs Off-Grid vs Grid-Forming (GFL/GFM): What Actually Differs The real difference is one question: who provides the voltage and frequency reference? A clear explainer of GFL, off-grid and grid-forming for microgrids. The difference comes down to one question The three most confused terms differ in who establishes the voltage and frequency reference. Grid-tied / Grid-Following (GFL) When the grid exists, the PCS **follows** grid voltage and frequency and charges/discharges per EMS — used for peak-shaving and self-consumption. It cannot supply loads alone. Off-grid When the grid drops, the PCS powers local loads and must stabilise voltage/frequency itself — used for backup and weak-grid sites. Note: "off-grid" is a system state, while "grid-forming" is a control capability. Grid-Forming (GFM) The PCS actively **builds** the grid reference, supports multi-unit paralleling and works with diesel and PV — ideal for no-grid, island and mining sites. Stable off-grid operation usually requires grid-forming capability. VGRID grid-forming products [SP125HCPS](/en/product/sp125hcps) is a grid-forming microgrid PCS paralleling up to 15 units off-grid; [Leona-H135K](/en/product/sp135hapss) is grid-forming with 20+ units off-grid; [SP250HAG2T all-in-one](/en/product/sp250hag2t-2) supports diesel-hybrid and grid-forming. See [grid-forming / weak-grid microgrid](/en/page/grid-forming-weak-grid). ## Are off-grid and grid-forming the same? No. Off-grid is a state (no grid); grid-forming is a capability (actively building the reference). Off-grid operation usually requires grid-forming capability. ## Why does a weak grid need grid-forming PCS? Weak-grid voltage/frequency is unstable; a grid-following device struggles, while a grid-forming PCS actively supports the reference and improves continuity. ## Is there a paralleling limit? Limits vary by model and architecture. SP125HCPS parallels up to 15 units off-grid; beyond that, a system-level PCC-controller + contactor scheme is used (e.g. the 2.5MW mine project). ## Must an island project be grid-forming? Islands without a stable utility grid typically rely on grid-forming PCS to build the reference with redundant paralleling and diesel support — e.g. the Maldives island project.