Watt-Hours (Wh) — The Most Important Number
When you're shopping for a solar generator, watt-hours is the single most important spec on the label. Here's exactly what it means and why it matters.
Think of watt-hours (Wh) as the "fuel tank" of your generator. A 1000Wh generator holds 1000 watt-hours of energy. A 2000Wh generator holds twice that. The bigger the tank, the longer you can run your devices — plain and simple.
To figure out how long your generator will power something, divide the generator's Wh capacity by the device's wattage. A 60W mini fridge running on a 1000Wh generator lasts roughly 16 hours (1000 ÷ 60 = 16.7 hours). In practice, subtract about 10–15% for inverter efficiency losses.
Runtime (hours) = Generator Capacity (Wh) ÷ Device Power Draw (W)
Always multiply by 0.85 to account for real-world efficiency losses.
| Device | Power Draw | Hours on 1,000Wh | Hours on 2,000Wh |
|---|---|---|---|
| Mini Fridge | 60W | 16 hrs | 33 hrs |
| Laptop | 45W | 22 hrs | 44 hrs |
| LED Lights (4x) | 40W | 25 hrs | 50 hrs |
| Phone Charging | 10W | 100 hrs | 200 hrs |
| Window A/C | 1,200W | 0.8 hrs | 1.6 hrs |
| CPAP Machine | 30W | 33 hrs | 67 hrs |
| 55" TV | 80W | 12 hrs | 25 hrs |
| Coffee Maker | 900W | 1.1 hrs | 2.2 hrs |
Some brands advertise total capacity but you can only safely use 80–90% before the battery management system cuts off power. Always look for "usable capacity" in the specs, or plan to use 85% of the rated Wh as your real-world number.
Watts (W) vs Watt-Hours (Wh) — The Confusion Explained
This trips up almost every first-time buyer. Here's the clearest way to understand the difference.
Watts is how fast you spend money. Watt-hours is how much money you have in your wallet. A coffee maker "spends" 900W per hour. If your wallet holds 1000Wh, the coffee maker empties it in about 1 hour. A laptop "spends" only 45W — so that same 1000Wh wallet lasts 22 hours.
Watts (W) measure the rate of power consumption at any given moment. Your device's wattage label tells you how much power it demands while running. You need to make sure your generator's AC output wattage is high enough to actually power the device — not just store enough energy for it.
Watt-hours (Wh) measure total stored energy. This determines how long you can run things. The two specs work together: you need enough Wh to last as long as you need, and enough W output to actually start and run your devices.
Pure Sine Wave vs Modified Sine Wave — Why It Matters
Every solar generator has an inverter that converts DC battery power to the AC power your devices use. There are two types of inverter output:
Pure Sine Wave
Recommended- Clean, smooth power wave — identical to grid power
- Safe for ALL devices including CPAP, medical equipment, laptops
- Required for inductive loads (motors, compressors)
- All premium generators use this
- No buzzing, humming, or device damage
Modified Sine Wave
Use With Caution- Choppy, stepped power wave — cheaper to produce
- Can damage sensitive electronics over time
- CPAP users: do NOT use modified sine wave
- Found only in older or very cheap units
- May cause buzzing in audio equipment
Every quality solar generator sold today uses pure sine wave inverters. If you see "modified sine wave" in the specs, skip it — the $50 savings isn't worth the risk to your devices.
AC Output Rating — Continuous vs Surge
The output wattage rating determines what devices you can actually run — not just power for a few minutes, but sustain continuously.
Every generator lists two output numbers: continuous watts (what it can sustain indefinitely) and surge/peak watts (a brief burst it can handle for startup). Motors — like those in refrigerators, air conditioners, and sump pumps — draw 2–3x their running watts at startup. If the generator can't handle the surge, it shuts down or trips a breaker.
A mini fridge runs at 60W but surges to 180–200W when the compressor kicks on. A generator rated for 300W continuous and 600W surge handles it fine. A 100W continuous generator would fail at startup.
| Output Level | What You Can Run | Common Use |
|---|---|---|
| Up to 1,000W | Phones, laptops, LED lights, CPAP, small fans, tablets, small TV | Camping, basic emergency |
| 1,000W – 2,000W | All above + mini fridge, electric blanket, slow cooker, small heater | Extended camping, home backup |
| 2,000W – 3,000W | All above + window A/C, microwave, hair dryer, power tools | Full home backup, off-grid |
| 3,000W+ | All above + central HVAC (mini-split), large appliances, shop tools | Off-grid living, whole-home backup |
Always plan to use no more than 80% of your continuous rating during normal operation. Running a generator at 100% output for extended periods puts stress on the inverter and can shorten its lifespan.
Battery Chemistry — LFP vs NMC
The battery chemistry determines how long your generator lasts over its lifetime — and it's one of the most overlooked specs in buying decisions.
LFP — Lithium Iron Phosphate
Recommended- 3,500+ charge/discharge cycles
- 10+ year lifespan with regular use
- Thermally stable — much safer, no fire risk
- Performs well in cold weather
- Heavier and slightly lower energy density
- Higher upfront cost — worth every penny
NMC — Nickel Manganese Cobalt
Budget Option- 500–800 charge/discharge cycles
- 3–5 year lifespan with regular use
- Higher energy density — lighter units
- Greater fire/thermal runaway risk
- Performance drops faster in cold
- Cheaper upfront, more expensive over time
Always choose LFP if it's within your budget — it's worth it long term. An NMC battery that lasts 3 years and needs replacement costs you more over a decade than an LFP unit that runs for 10+ years. Jackery, EcoFlow, and Anker all offer LFP options at competitive prices.
| Spec | LFP | NMC |
|---|---|---|
| Cycle Life | 3,500+ cycles | 500–800 cycles |
| Expected Lifespan | 10+ years | 3–5 years |
| Safety | Very High | Moderate |
| Cold Performance | Good | Poor below 32°F |
| Weight | Heavier | Lighter |
| Upfront Cost | Higher | Lower |
| 10-Year Total Cost | Lower | Higher |
Solar Input — MPPT vs PWM
The solar charge controller determines how efficiently your generator converts sunlight into stored power. It's the difference between charging in 4 hours vs 6+ hours.
MPPT Controller
Modern StandardMaximum Power Point Tracking continuously adjusts its operating point to extract the maximum power from your solar panels at any given moment. Works in partial shade. Charges up to 30% faster than PWM. All quality generators use MPPT.
PWM Controller
Older TechPulse Width Modulation simply switches power on and off rapidly. It wastes potential energy, especially in partial shade or overcast conditions. Significantly less efficient — found mainly in old or very cheap units.
On a cloudy day where your panels produce 60% of rated output, an MPPT controller might squeeze 58% of rated power — a PWM controller might only get 40–45%. Over a full day of charging, that's a significant difference in how much energy you recover.
How Many Solar Panels Do You Need?
Most generators have a maximum solar input rating (e.g., "400W solar input"). Pair panels up to that rating for fastest charging. Here's the calculation:
Charging Time (hours) = Generator Capacity (Wh) ÷ Panel Wattage
Example: 2000Wh generator ÷ 400W solar input = 5 hours to full charge (in ideal conditions). In practice, multiply by 1.4–1.6 for real-world sun variability — so roughly 7–8 hours of good sunlight.
| Generator Capacity | Recommended Solar Input | Charge Time (ideal) | Charge Time (real world) |
|---|---|---|---|
| 500–800Wh | 100–200W | 4–8 hrs | 6–12 hrs |
| 1,000–1,500Wh | 200–400W | 3–6 hrs | 5–9 hrs |
| 2,000–3,000Wh | 400–800W | 4–7 hrs | 6–11 hrs |
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Quick Reference — Which Specs Matter Most by Use Case
Not all specs are equally important for every use case. Here's where to focus your attention.
| Use Case | Capacity (Wh) | AC Output (W) | Weight | Battery Type |
|---|---|---|---|---|
| Camping | 500–1,500Wh Moderate priority |
500–1,500W Moderate priority |
Critical Under 25 lbs ideal |
Either OK LFP preferred |
| Emergency | Critical 2,000Wh+ recommended |
High 2,000W+ for fridge |
Less critical It's stationary |
LFP only Long-term storage |
| Off-Grid | Critical 3,000Wh+ or expandable |
Critical 3,000W+ for appliances |
Not important Fixed installation |
LFP required Daily cycling |
| Van Life | 500–1,500Wh Moderate — solar tops up daily |
500–1,500W Enough for van needs |
Critical Weight & size matter |
LFP preferred Daily cycling |
If you're buying for emergency or off-grid use, consider generators with expandable battery capacity (like Jackery's Explorer Plus series or EcoFlow's Delta Pro). Start with 2,000Wh, add batteries later as your budget allows. This is far cheaper than buying a 5,000Wh unit upfront.