Solar Generator Sizing Guide for Home Power Outages
Short answer: To size a solar generator for home backup, calculate your total daily Wh consumption, add a 25% safety margin, then match to a unit with that capacity. Most households need 1,500–3,500 Wh for essential appliances during a 24-hour outage. This guide gives you the exact formula and a step-by-step calculation for your specific situation.
Why Generic Recommendations Fail
Most solar generator guides tell you to “get a 2,000 Wh unit for home backup.” That number is meaningless without knowing what you’re running. A home with a chest freezer, well pump, and medical equipment has completely different needs than a home that only needs to keep the fridge cold and the router running.
Proper sizing requires three things: knowing your loads, understanding duty cycles, and accounting for surge requirements. This guide walks through all three.
Step 1 — Identify Your Critical Loads
Start by listing only the appliances you actually need during an outage. Not everything — just what matters.
| Appliance | Typical running watts | Notes |
|---|---|---|
| Refrigerator | 80–150W | Runs 30–50% of time (duty cycle) |
| Chest freezer | 30–100W | Very efficient, low duty cycle |
| Router / WiFi | 10–20W | Continuous draw |
| LED lights (per bulb) | 8–12W | Only hours you use them |
| Laptop | 45–85W | When actively charging |
| Phone charging | 5–20W each | 1–2 hours per charge |
| CPAP (without heat) | 30–60W | 8 hours/night |
| CPAP (with humidifier) | 100–150W | Significantly higher draw |
| Well pump (½ HP) | 375W running | Surge: 1,500–2,600W at startup |
| Sump pump | 300–800W | Intermittent, high surge |
| Window AC (5,000 BTU) | 500W | High draw — plan carefully |
Step 2 — Calculate Your Daily Wh
For each appliance: Wh = Watts × Hours × Duty Cycle
Duty cycle is the percentage of time an appliance actually draws power. A fridge rated at 120W doesn’t draw 120W for 24 hours — the compressor cycles on and off, typically running 35–50% of the time.
| Appliance | Watts | Hours | Duty cycle | Daily Wh |
|---|---|---|---|---|
| Refrigerator | 120W | 24h | 40% | 1,152 Wh |
| Router | 15W | 24h | 100% | 360 Wh |
| LED lights ×4 | 40W | 6h | 100% | 240 Wh |
| Laptop | 65W | 4h | 100% | 260 Wh |
| Phone ×2 | 20W | 2h | 100% | 40 Wh |
| Total | 2,052 Wh |
Step 3 — Add Safety Margin
Multiply your total daily Wh by 1.25 (25% safety margin). This accounts for inverter inefficiency (typically 5–10%), battery degradation over time, and underestimated loads.
Example: 2,052 Wh × 1.25 = 2,565 Wh minimum capacity needed
Step 4 — Check Surge Requirements
Capacity (Wh) tells you runtime. Surge output (W) tells you whether the unit can start your appliances at all. Motors — fridges, pumps, AC units — need 2–7× their running wattage for 1–2 seconds at startup.
If your fridge has a 120W compressor, it may need 300–360W to start. If you also have a well pump (375W running, ~2,200W surge), your power station must handle that peak simultaneously with other running loads.
Rule: Your power station’s surge rating must exceed your highest single startup surge, plus your other simultaneous running loads.
Sizing by Scenario
| Scenario | Essential loads | Daily Wh | Recommended capacity | Example unit |
|---|---|---|---|---|
| Minimal backup | Fridge + router + phone | ~800 Wh | 1,000 Wh+ | EcoFlow Delta 2 |
| Standard home | Fridge + router + lights + laptop | ~1,500–2,000 Wh | 2,000–2,500 Wh+ | EcoFlow Delta 2 Max |
| Home + medical device | Above + CPAP | ~1,900–2,400 Wh | 2,500 Wh+ | Bluetti AC200P |
| Home + well pump | Standard + ½ HP pump | ~2,500–3,500 Wh | 3,500 Wh+ (high surge) | EcoFlow Delta Pro |
| Extended outage (48h+) | All of above | ~4,500–7,000 Wh | 5,000 Wh+ | Bluetti AC300+2×B300 |
Honest Recommendation
For most households running a standard fridge, router, lights, and phones during a 24-hour outage, a 2,000–2,500 Wh unit is the right starting point. The EcoFlow Delta 2 Max (2,048 Wh) covers this scenario cleanly at $899.
If you have a well pump, sump pump, or medical equipment with surge requirements, step up to the EcoFlow Delta Pro (3,600 Wh, 7,200W surge) — the surge capacity matters as much as the total Wh.
What sizing calculators won’t tell you: Battery capacity degrades over time. A unit rated at 2,048 Wh will deliver 80% of that after 3,000 cycles. Factor in long-term degradation if you’re sizing for a decade of use.
Who This Guide Is Not For
If you need to run central air conditioning, electric water heaters, or electric ranges during an outage, a solar generator is not the right tool — those loads require 5,000–10,000W that no portable unit can sustain. A whole-home standby generator is the correct solution for whole-home backup.
Related Guides
- How many Wh do I need to run a fridge for 24 hours?
- EcoFlow Delta Pro vs Bluetti AC300: honest comparison
- Can the EcoFlow Delta Pro run a well pump?
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Frequently Asked Questions
- How do I calculate what size solar generator I need?
Multiply each appliance’s wattage by daily hours of use and duty cycle to get daily Wh. Add all loads together and multiply by 1.25 for a safety margin. The result is your minimum required capacity. - What size solar generator do I need for a whole house?
A solar generator cannot power a whole house. Central AC (3,000-5,000W), electric water heaters (4,000W+), and electric ranges exceed portable generator limits. Solar generators cover essential loads: fridge, lights, router, phones, and small appliances. - Is 2000 Wh enough for home backup?
A 2,000 Wh solar generator covers a standard fridge, router, LED lights, and phone charging for approximately 20-24 hours. It is sufficient for most overnight power outages but not multi-day scenarios.