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Generator Sizing Guide
Running vs Starting Watts
Every motor-driven appliance (A/C, fridge, pump) draws significantly more power when starting than when running. This "starting surge" or "inrush current" typically lasts 1–3 seconds but can be 2–3x the running wattage. Your generator must handle the highest single starting surge on top of all running loads simultaneously.
Generator Types
Type
Best For
Runtime
Portable (3–10 kW)
Home backup, events
8–12 hrs/tank
Standby (10–50 kW)
Whole-house, auto-start
Continuous (piped fuel)
Industrial (50–200+ kW)
Commercial, critical
Continuous w/ tank
Fuel Comparison
Fuel
Efficiency
Notes
Diesel
Most efficient
Long shelf life, readily available in Caribbean
Gasoline
Moderate
Easy to find, shorter shelf life (3–6 months)
Propane
Less efficient
Indefinite shelf life, clean burning
Natural Gas
Less efficient
Continuous supply if piped, no storage needed
Altitude & Temperature Derating
Altitude: Generators lose ~3.5% of rated power per 1,000 ft above 1,500 ft elevation due to thinner air reducing combustion efficiency.
Temperature: Above 40°C (104°F), generators lose ~2% per degree C due to reduced cooling efficiency and lower air density. Caribbean ambient temps of 30–35°C are within normal operating range.
Caribbean Hurricane Preparedness
• Stock minimum 3 days of fuel (more for extended outages)
• Store fuel in approved containers away from the generator
• Never run a generator indoors or in enclosed spaces — CO poisoning kills
• Test your generator monthly; run under load for 30 minutes
• Use a transfer switch — never backfeed into the grid
• Keep spare oil, filters, and spark plugs on hand
• Priority loads: refrigeration, water pump, lighting, communication
Load Priority Strategy
Essential: Loads you must run (fridge, water pump, lights, medical equipment). Size your minimum generator for these.
Important: Loads that significantly improve comfort (washing machine, microwave, computer). Include if generator capacity allows.
Optional: Loads that are nice to have (TV, pool pump, water heater). Only run if generator is well within capacity.
Disclaimer: This calculator provides estimates for preliminary generator sizing. Actual performance depends on specific generator models, load characteristics, fuel quality, maintenance, and environmental conditions. Always consult a qualified electrician for transfer switch installation and load management.
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