Emergency power systems range from a $200 portable generator for basic circuit load to a $15,000+ whole-home solar array with battery backup. Most households need something in between. This guide covers the sizing formulas, equipment selection, and fuel storage calculations for three realistic emergency power tiers: portable generator, portable solar + battery bank, and permanent transfer switch installation.
Power Demand Assessment: What Do You Actually Need to Run?
Before selecting equipment, calculate your critical load — the wattage required to run only the loads that matter during an outage. Running everything is expensive and fuel-intensive; running only critical loads is manageable.
| Appliance | Running watts | Startup surge watts | Priority |
|---|---|---|---|
| Refrigerator (full-size, Energy Star) | 100–400 | 600–1,200 | High |
| Chest freezer (7 cu ft) | 30–100 | 200–400 | High |
| Well pump (1/2 HP) | 750 | 1,500–2,000 | High (if applicable) |
| Window AC unit (5,000 BTU) | 400–600 | 1,200–2,000 | Medium |
| LED lighting (10 bulbs @ 10W) | 100 | None | High |
| Phone/device charging | 30–100 | None | High |
| CPAP machine | 30–60 | None | High (medical) |
| Gas furnace blower | 400–800 | 1,200–2,000 | High (cold climate) |
| Electric water heater | 3,000–5,500 | Same | Low (use propane) |
Minimum critical load (most households): Refrigerator + lights + device charging = approximately 600–800 running watts, with a 1,500–2,000 watt startup surge when the refrigerator compressor starts.
Tier 1: Portable Generator
Conventional vs Inverter Generator
- Conventional generator: Produces AC power directly from the engine at a fixed RPM. Lower cost per watt — a 3,500W conventional generator runs $350–500. Disadvantages: runs at full RPM regardless of load (louder, more fuel consumption), produces voltage fluctuations unsuitable for electronics and sensitive equipment.
- Inverter generator: Converts engine power to DC, then inverts to clean AC. Runs at variable RPM based on load — quieter and more fuel-efficient at partial load. Produces “clean” sine wave power suitable for electronics, medical devices, and modern appliances. A 2,200W inverter generator (Honda EU2200i, Yamaha EF2200iS) costs $900–1,200; a 3,500W model costs $1,300–1,800.
Recommendation: For critical load with electronics and medical devices, use an inverter generator. For non-electronics loads (water pump, sump pump, basic lighting) a conventional generator is adequate.
Generator Sizing Formula
Size for: running watts + highest single startup surge. Do not add all startup surges — only the largest appliance starts at any given moment.
Example household: Refrigerator (400 running, 1,200 surge) + lights (100W) + devices (100W) + well pump (750 running, 2,000 surge). Running total: 1,350W. Largest surge: well pump at 2,000W. Required generator size: 1,350 + 2,000 = 3,350W minimum → select a 3,500W or 4,000W generator.
Fuel Consumption and Runtime
Generator fuel consumption at typical loads:
| Generator size | Fuel at 50% load | Fuel at 100% load | Runtime per gallon (50% load) |
|---|---|---|---|
| 2,200W inverter (Honda EU2200i) | 0.10 gal/hr | 0.2 gal/hr | 8–9 hours |
| 3,500W inverter | 0.22 gal/hr | 0.42 gal/hr | 4.5 hours |
| 5,500W conventional | 0.48 gal/hr | 0.85 gal/hr | 2.1 hours |
Fuel storage: For a 72-hour outage running a 2,200W inverter generator at 50% load for 8 hours per day: 8 hrs × 0.10 gal/hr × 3 days = 2.4 gallons. For 2 weeks at the same rate: 11.2 gallons. Store fuel in approved containers with fuel stabilizer (Sta-Bil or PRI-G) — untreated gasoline degrades in 30–60 days; stabilized fuel lasts 12–24 months.
Tier 2: Solar Panel + Battery Bank
Solar systems eliminate fuel dependency and operate silently — the major advantages over generators. The tradeoff: higher upfront cost and reduced output on cloudy days.
System Components
- Solar panels: Monocrystalline panels (400W per panel at ~$250–350) are the standard for efficiency and durability. Two 400W panels (800W array) = 3–5 kWh per day in most US locations (assuming 4–6 peak sun hours/day).
- Charge controller (MPPT): Converts panel voltage to battery charging voltage. Size for 25% above the panel array wattage. For an 800W array: 40A MPPT controller (~$80–120). MPPT controllers are 20–30% more efficient than PWM controllers — use MPPT for any system over 200W.
- Battery bank: Deep-cycle batteries rated in amp-hours (Ah). Target: store 2 days of critical load without recharging. At 600W critical load running 8 hours/day = 4.8 kWh/day × 2 days = 9.6 kWh needed. Lithium iron phosphate (LiFePO4) batteries are the preferred chemistry — 80–100% usable capacity versus 50% for lead-acid. A 100Ah LiFePO4 at 12V = 1.2 kWh usable. For 9.6 kWh: 8 × 100Ah batteries in series/parallel, or 1 × Epoch 200Ah 24V LiFePO4 ($700–900).
- Inverter: Converts battery DC to household AC. Size for 150% of peak load to handle surge. For 1,500W critical load with 2,000W surge: a 2,000W pure sine wave inverter (~$150–300). Pure sine wave only — modified sine wave damages motors, compressors, and sensitive electronics.
Portable all-in-one option: The Jackery Explorer 2000 Plus (~$2,000), EcoFlow Delta Pro (~$2,700), or Goal Zero Yeti 3000X (~$3,000) integrate battery, inverter, and solar input in a single portable unit. These are significantly more expensive per watt-hour than a DIY system but require no electrical knowledge to install.
Tier 3: Whole-House Transfer Switch
A transfer switch safely disconnects your household from the grid before connecting a generator, preventing backfeed that can electrocute utility workers and damage your generator. Two types:
- Manual transfer switch (critical circuit panel): A sub-panel installed next to the main breaker with 6–10 critical circuits transferred to generator power. Cost: $200–500 for the panel + $300–600 electrician installation. You manually flip to generator when power is out. The Reliance Controls TF151W (~$100) and similar products handle 6–15 circuits.
- Automatic transfer switch (ATS): Detects grid power loss and automatically starts a standby generator, transferring power within 10–30 seconds. Requires a stationary generator (Generac, Kohler, Briggs & Stratton) hard-connected to natural gas or LP. Full system cost: $8,000–15,000+ installed. Best for households with medical dependencies or frequent outages.
Code requirement: All transfer switch installations require an electrician and building permit in most jurisdictions. Do not use a “suicide cord” (generator cord plugged into a dryer outlet) — it is illegal, creates backfeed hazard, and voids homeowner’s insurance.
Generator Safety: Carbon Monoxide
Carbon monoxide (CO) from generator exhaust kills multiple people per year in the United States, primarily during power outages when generators are run in garages, basements, or too close to the house. CO is colorless and odorless — the only warning is a CO detector.
- Run generators 20+ feet from any building opening (doors, windows, vents)
- Install battery-powered CO detectors on every level of the home before an outage occurs
- Never run a generator in a garage even with the door open — CO accumulates faster than garage ventilation removes it
Where to Go Next
Emergency cooking without grid power — rocket stove, propane, and solar cooker methods — is in emergency cooking: 7 methods when the grid goes down. For radio communication during extended outages, the HAM and GMRS options are in HAM radio for preppers: license study, setup, and emergency use.
