# How Storage Coordinates with Diesel Generators: PV-Diesel-Storage Strategy Grid OK → self-use/arbitrage; grid loss → STS off-grid; low SOC → diesel; recovered → exit. PV-diesel-storage logic with VGRID. Core goal of PV-diesel-storage Daily self-consumption plus automatic load carry during outages, with diesel auto-relay at low SOC — the most common reliable combo for off-grid and weak-grid sites. Operating strategy **Grid OK**: self-consumption / peak arbitrage, surplus to grid. **Grid loss**: STS transfers off-grid; critical loads uninterruptible. **Low SOC**: EMS auto-starts diesel for top-up. **Recovered**: exit diesel; battery leads again. VGRID solution and case [SP250HAG2T](/en/product/sp250hag2t-2) and [SP375/500HAG2](/en/product/sp375-500hag2) all-in-ones integrate PCS+MPPT+EMS+STS with diesel-hybrid and grid-forming; paralleling fits mines and sites. The Zambia 200kW/430kWh [PV-diesel-storage project](/en/cases) uses two standard all-in-ones in parallel, EMS auto-starts diesel and PCS balances multi-cluster SOC. ## What role does diesel play? Diesel is emergency/long-duration top-up, auto started by EMS at low SOC — no manual attendance. ## What does diesel-hybrid require of the PCS? The PCS must support diesel-hybrid mode and transfer, smoothing power while paralleling — e.g. VGRID grid-forming all-in-ones. ## How to fix uneven cluster SOC? Use PCS self SOC balancing + cluster management (Cambodia, Zambia cases) to avoid over-discharge. ## Where does PV-diesel-storage fit? Mines, sites, oilfields, islands, African off-grid sites with unstable/no grid needing long backup.