PV + Battery + Genset vs Load during grid outage
This simulator evaluates whether a combination of solar PV, battery storage, and diesel genset can sustain a critical load during a grid outage over a 24-hour period, determining island survival time and minimum battery SOC. Engineers use it for microgrid feasibility studies, resilience planning, and sizing backup generation for critical facilities.
The simulation steps through each hour of a grid outage starting at the specified outage hour. For each hour, solar generation (from a midday bell-curve profile) is compared against the critical load profile. Solar surplus charges the battery (limited by battery power rating and available SOC headroom); deficits are met first by battery discharge, then by the diesel genset if available fuel remains.
The island fails (collapses) in any hour where total available generation — solar + battery discharge + genset — falls short of the critical load. Survival time is reported as the number of hours before the first unmet-load event. Battery SOC is tracked each hour to show how deep the battery discharges during the outage.
The dispatch strategy is simple but realistic: solar is always used first, battery fills deficits up to its power and energy limits, and the genset runs only when both solar and battery are insufficient. This represents a common load-following microgrid control strategy per IEEE 1547.4 Guide for Island Operation of Distributed Resource Systems.
IEEE 1547-2018 (Standard for Interconnection and Interoperability of Distributed Energy Resources) governs the interconnection requirements for DER systems including intentional islanding. Section 8 specifically addresses island operation requirements, including frequency and voltage operating ranges, ride-through requirements, and reconnection procedures.
IEEE 1547.4-2011 (Guide for Design, Operation, and Integration of Distributed Resource Island Systems) provides design guidance for intentional island microgrid systems and covers protection coordination, black-start capability, and seamless transfer between grid-connected and island modes.
NEC Article 706 governs the BESS installation, while NEC Article 702 covers optional standby systems (genset). For critical facility applications, NFPA 110 specifies emergency and standby power system requirements including minimum runtime (typically 2 hours for Level 1, or as required by the authority having jurisdiction). NFPA 855 covers BESS safety in buildings.
Outage start time dramatically affects island viability. An outage beginning at 18:00 (6 PM) starts with declining solar generation and an evening load peak — the most challenging scenario. An outage beginning at noon arrives with peak solar, charging the battery before evening demand. Always simulate the worst-case outage start hour for sizing.
The genset provides crucial backup when battery and solar are exhausted, but fuel supply is finite. Runtime depends on genset size, load, and tank capacity. A typical 60 kW diesel genset consumes 4–6 gallons/hour at 75% load — an 8-hour fuel supply requires 32–48 gallons on-site. Fuel replenishment logistics must be planned for extended outages.
Seamless transfer (sub-cycle switching to island mode) requires static transfer switches and pre-programmed island controller settings. Anti-islanding protection under IEEE 1547 must be defeated for intentional island operation, typically through a dedicated island mode switch that bypasses the passive anti-islanding algorithms and activates the island controller.
Enter the critical load (kW peak) — this is the load that must be served during the outage, not the full facility load. Enter the solar array size, battery energy (kWh) and power (kW), and genset rating with available fuel hours.
Set the outage start hour to simulate different scenarios: 18:00 is typically worst-case for solar + battery systems due to the evening peak. Click and drag sliders to find the minimum battery and genset sizing that achieves island hold for 24 hours.
The pass/fail banner and SOC chart show survival time and how deeply the battery discharges. The Energy Balance Summary reports solar energy contributed, battery energy used, and genset fuel consumed. Increase battery energy first (higher impact), then genset rating and fuel hours, until the simulator shows a full 24-hour island hold.
Intentional islanding is the deliberate operation of a portion of the electric grid in island mode, disconnected from the utility grid, to supply local loads during a grid outage. IEEE 1547-2018 Section 8 permits intentional islanding when agreed to by the area electric power system operator. It requires an island controller, dedicated protection systems, and pre-authorization — it is not the same as default anti-islanding protection in standard grid-tied inverters.
Solar generation is zero at night and peaks at midday. An outage starting at 18:00 arrives as solar is ramping down and evening load is ramping up — the battery must supply 12–14 hours of overnight load with minimal solar recharging. The same battery that holds 24 hours for a noon-start outage may collapse after 6–8 hours for an 18:00-start outage. Always simulate the worst-case start time for critical facility sizing.
Black start is the ability to restore power to a de-energized microgrid without external grid support. Not all inverters can black-start — grid-following inverters require a grid voltage reference to synchronize. Grid-forming inverters (or a diesel genset) can establish the island voltage and frequency, allowing other sources to synchronize and supply load. IEEE 2030.9 covers microgrid planning including black-start requirements.
Required energy = average critical load (kW) × 8 hours. For a 50 kW average load over 8 hours: 400 kWh required. Add margin for battery losses (÷ discharge efficiency ≈ 0.95), SOC limits (÷ 0.80 usable fraction), and partial solar recharging. Minimum battery nameplate: 400 ÷ 0.95 ÷ 0.80 ≈ 526 kWh. Battery power rating must exceed the peak critical load: if the load peaks at 80 kW, the battery must be rated at ≥ 80 kW discharge.
Standard grid-tied inverters comply with IEEE 1547-2018 anti-islanding requirements and disconnect from both the grid and loads within 2 seconds of detecting grid loss — they cannot power loads during a grid outage. Islanding-capable systems require an energy storage inverter with island mode (grid-forming capability), an automatic transfer switch to disconnect from the grid, and a dedicated critical load panel. Examples include Tesla Powerwall, SunPower SunVault, and commercial-scale multimode inverters from SMA, SolarEdge, and Schneider Electric.
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