"Solar generator" is a marketing term, not an engineering one. Nothing is being generated. The product is a lithium battery, an inverter and a charge controller in one enclosure, and the solar panel is an optional accessory. Once you see it that way the whole category becomes easy to evaluate, because you only need to understand two numbers.
Watts and watt-hours
Watts is the rate. It tells you what the unit can run at any instant, and it is set by the inverter. A 2,000 watt unit can run a 1,500 watt kettle; a 600 watt unit cannot, no matter how big its battery is.
Watt-hours is the quantity. It tells you how long. A 2,000 Wh battery running a 100 watt load lasts roughly 20 hours; running a 1,000 watt load, roughly two.
Confusing them is the source of nearly every disappointed review in this category. Someone buys a large-capacity unit and finds it will not start a well pump, or buys a high-output unit and finds it empty in 90 minutes. Check both numbers against your list, always.
Turning your appliance list into watt-hours
Multiply each device's average draw by the hours you need it, and be honest about duty cycle. A refrigerator's compressor is rated at perhaps 700 watts, but it runs maybe a third of the time, so its real consumption is closer to 230 watts averaged over an hour.
| Load | Average draw | Hours | Watt-hours |
|---|---|---|---|
| Refrigerator (35% duty) | 245 W | 24 | 5,880 |
| Wifi router and modem | 15 W | 24 | 360 |
| CPAP, no humidifier | 35 W | 8 | 280 |
| LED lighting | 40 W | 6 | 240 |
| Phone and laptop charging | 80 W | 3 | 240 |
That is about 7,000 watt-hours for a full day, and it explains why a 1 kWh unit is an overnight device rather than a whole-day one. Note also that inverters are not perfectly efficient: budget 10 to 15 percent losses, so plan on needing roughly 8 kWh of stored capacity for that day.
Why the chemistry matters
Most current power stations use lithium iron phosphate cells, usually written LiFePO4 or LFP. Compared with the older lithium cobalt chemistries, LFP tolerates far more charge cycles before meaningful capacity loss, is markedly more thermally stable, and holds up better to sitting at a full state of charge, which is exactly what a backup device does for most of its life.
It is slightly heavier per watt-hour. For a device that mostly sits in a closet, that is a trade worth making, and it is why the category converged on LFP.
What batteries do that engines cannot
- Run indoors. No combustion, no exhaust, no carbon monoxide. This is the single biggest practical difference, and it is what makes apartments, condos and medical equipment feasible.
- Silence. A fan may run under heavy load. That is all.
- Instant, automatic response. Many models pass utility power through and switch to battery in milliseconds, so a desktop computer or a CPAP never notices the outage.
- No maintenance and no fuel to go stale. Top it up every few months and it is ready for years.
- They can be recharged by the sun, which resets the clock every day rather than counting down.
What batteries cannot do
- Run heat. Resistive heating is brutal: a 1,500 watt space heater empties a 2 kWh battery in about 80 minutes. Electric ranges, dryers and water heaters are in the same category. This is the honest limit.
- Cover a whole house for days, not without a stack of expandable modules that costs real money.
- Refill quickly from a wall outlet in a blackout, for obvious reasons. Recharge sources are the grid before the storm, solar during it, or a running generator.
How long does solar actually take?
Solar panel ratings are measured under standard test conditions that your roof will rarely reproduce. Real output depends on latitude, season, tilt, orientation, temperature and cloud, and the useful planning figure is not panel watts but daily sun-hours for your location.
As a rough model: 400 watts of panel in a location averaging four peak sun-hours yields around 1,600 Wh per day before losses, so call it 1,200 to 1,400 Wh realised. Refilling a 2 kWh battery therefore takes the better part of two good days, or one excellent one. Peak sun hours are the honest planning input, and they vary by season as much as by latitude; the concept is solar irradiance expressed in a form you can multiply. The EIA's explainer on photovoltaics and electricity covers how panels actually convert light, and the Department of Energy's Solar Energy Technologies Office publishes the system-level research behind it.
Expandable systems and the whole-home question
The line between "power station" and "home battery" has blurred. Larger units accept external battery modules that stack capacity into the tens of kilowatt-hours, and some support 240 volt output, which finally puts well pumps and dryers within reach. Installed with a transfer switch, that is functionally a home battery system.
Compared with a standby generator at similar capacity, you trade unlimited runtime for silence, zero emissions, no permits for the plug-in configuration, and the ability to recharge from your own roof. Which matters more depends entirely on whether your outages last six hours or six days.
Sizing rule of thumb
- Total the watt-hours you need for the longest outage you realistically plan for.
- Add 15 percent for inverter losses.
- Check that the continuous watt rating exceeds your largest simultaneous load, and that the surge rating covers your biggest motor.
- If you want to run past one day without grid power, add solar sized to replace at least half your daily draw.
Do those four steps and you will buy the right unit the first time, which is the whole point of a category where the correct answer is a number and not a brand.