How do I calculate the watt-hours I need?

List every device, multiply its running wattage by the hours you'll use it, and add the totals. A CPAP at 30W for 8 hours is 240Wh; a laptop at 50W for 3 hours is 150Wh. Sum those to get your raw energy need, then multiply by about 1.15 to cover inverter and conversion losses. Because you can only count on roughly 85% of a station's labeled capacity, divide that figure by 0.85 to find the rated watt-hours to shop for. A 490Wh raw load becomes about 660Wh of rated capacity — which is why a 1kWh unit gives comfortable headroom over a 519Wh one.

What size solar generator do I need to run a refrigerator?

A full-size refrigerator averages 100-150W but surges to 600-1200W when the compressor starts, so you need both enough continuous watts and enough surge headroom, not just capacity. A 500W station can't reliably start it; a 1500-2000W unit like the Jackery Explorer 1000 v2 (1500W, 3000W surge) or OUPES 2000W (2000W, 4500W surge) can. For runtime, a fridge uses roughly 1-2kWh per day, so a 1024-1070Wh station runs one for most of a day, and pairing it with solar or stepping up to the 3584Wh Jackery HomePower 3600 Plus extends that across a multi-day outage.

Is a bigger solar generator always better?

No. A bigger battery means more weight, more cost, and slower recharge, so oversizing wastes money and portability you paid for. A 3584Wh Jackery HomePower 3600 Plus is the right call for whole-house backup but absurd for charging phones on a hike, where a 5.7-pound MARBERO 296Wh does the job. Size to your real loads plus a modest reserve — aim for a station whose rated capacity is about 20-40% above your calculated daily need — rather than buying the largest unit you can afford. The exception is if you plan to add appliances later or want the same unit to cover both camping and home backup.

What size solar panel do I need to recharge it?

Match the panel to how much you drain per day, not to the battery size. Panels deliver only about 60-80% of their rating in real conditions, over maybe 4-5 useful sun hours. A 100W panel realistically nets 300-400Wh a day — fine to top up a 300Wh kit but too slow to keep a 1kWh station full if you're using it hard. If you drain 500-1000Wh daily, you want 200W or more: the EcoFlow Delta 3 Classic accepts a 220W panel and refills in about 5.8 hours of good sun, and the Anker SOLIX C1000 Gen2 takes up to 600W of solar for a sub-2-hour recharge.

What size solar generator do I need for camping versus home backup?

Camping rewards small and light: for a weekend of devices, lights, and a CPAP, a 288-519Wh kit is plenty, and even a fridge trip is covered by a single 1kWh unit topped up with solar. Home backup is about surge and sustained watts: to keep a fridge, a few lights, routers, and phones alive through an outage you want 1000-2000Wh and 1500W-plus output, and to run a well pump, sump pump, or electric appliances you need a 3000Wh-plus, 3600W-class system. See our camping and home-backup guides for use-case picks.

What Size Solar Generator Do I Need? A Sizing Guide

Q: What size solar generator do I need?

It depends on two things: how much energy you'll use (watt-hours) and how much power your biggest device draws at once (watts). Add up each device's wattage times the hours you run it, add about 15% for losses, and plan to use roughly 85% of a station's rated capacity. For phones, a laptop, lights, and a CPAP overnight, a 288-519Wh kit like the Anker SOLIX C300 or GRECELL 500W is enough. Add a fridge or power tools and you want a 1kWh, 1500W-plus unit like the Jackery Explorer 1000 v2 or EcoFlow Delta 3 Classic. For whole-house backup with a well pump, step up to a 3600W unit like the Jackery HomePower 3600 Plus.

The Two Numbers That Matter: Watt-Hours for Runtime, Watts for What Runs at Once

Nearly every sizing mistake comes from confusing two specs that sound alike but answer completely different questions. Get them straight and the rest of this guide is arithmetic.

Watt-hours (Wh) measure capacity — the total pool of energy in the battery, and therefore how long the generator runs before it’s empty. A 296Wh unit like the MARBERO 296Wh holds roughly a third of the energy of a 1070Wh Jackery Explorer 1000 v2. Watt-hours decide runtime.

Watts (W) measure power — how much a device pulls at any instant, and how much the generator’s inverter can push out at once. A station’s continuous watts is the ceiling on what you can run simultaneously; its surge watts is a brief allowance for the spike when motors start. The MARBERO’s 300W output and the Jackery’s 1500W output are worlds apart even before you look at their batteries.

Watt-hours tell you how long. Watts tell you what. A big battery with a small inverter still can’t start a microwave, and a big inverter with a small battery dies in minutes. You have to size both.

Every device has both a running wattage (what it draws while working) and, for anything with a motor or compressor, a surge wattage (a short, higher spike at startup). You size capacity against the running numbers and hours; you size output against the single biggest running number, with surge in reserve.

How to Size Capacity: The Watt-Hour Math

Sizing capacity is a three-step calculation. Do it once for a realistic day of use and you’ll know exactly which tier you belong in.

Step 1 — List devices, multiply watts by hours. Write down each device, its running wattage, and how many hours you’ll actually use it. Multiply and add. Here’s a common off-grid or outage day:

CPAP (no humidifier): 30W × 8 h = 240Wh
Laptop: 50W × 3 h = 150Wh
Phones × 2: 20W × 3 h = 60Wh
LED lantern: 8W × 5 h = 40Wh
Raw total: 490Wh

Step 2 — Add about 15% for losses and reserve. The inverter and DC conversion aren’t perfectly efficient, and you never want to run a battery to a hard zero. Multiply your raw total by 1.15:

490Wh × 1.15 = ~564Wh that you’ll actually pull from the battery.

Step 3 — Size up for usable capacity (~85%). You can only count on roughly 85% of a station’s labeled watt-hours in the real world, once you account for the inverter, low-battery cutoffs, and capacity that fades in cold weather. Divide by 0.85:

564Wh ÷ 0.85 = ~663Wh of rated capacity to shop for.

That 490Wh of devices needs a station rated near 660Wh — not 490Wh. This is exactly why a 519Wh kit feels tight for a full day while a 1kWh unit runs the same loads with room to spare and still has charge in the morning.

Our example points squarely at the 700-1500Wh tier. A 519Wh unit would cover it in a pinch but leave nothing in reserve; the 1024Wh EcoFlow Delta 3 Classic or 1070Wh Jackery Explorer 1000 v2 handles it comfortably and absorbs the extra device or the cold night you didn’t plan for.

Don’t want to do the math by hand? Our solar generator size calculator does all three steps for you — enter your devices and hours and it returns the rated watt-hours and output you need, then matches you to real kits.

How to Size Output: Continuous Watts and Motor Surge

Capacity tells you nothing about whether a device will even turn on. That’s the inverter’s job, and it has two limits.

Your biggest single device must fit under continuous watts. Add up everything you’d run at the same time, and make sure the total stays below the station’s continuous rating — but the real gatekeeper is usually one hungry appliance. A 1000W microwave runs fine on the Jackery Explorer 1000 v2 (1500W) but will instantly overload a 500W GRECELL 500W, no matter how full its battery is. A 1500W space heater or hair dryer needs a 1800-2000W unit like the Delta 3 Classic or OUPES 2000W.

Motors and compressors need surge headroom. Anything with a motor — a refrigerator, a well pump, a power tool, an air conditioner — draws a spike two to three times its running wattage for a fraction of a second at startup. A fridge that runs at 150W can surge past 600W. That’s why surge ratings exist: the 300W stations (600W surge) in the entry tier can just barely blink a small fridge on, while the Jackery 1000 v2 (3000W surge) or OUPES 2000W (4500W surge) start one without flinching. When in doubt, check both the running watts and the startup surge of your heaviest motor load and confirm both fit.

Capacity-Tier Guide: Which Size Fits Your Needs

Once you’ve run the math, this table maps your number to a tier, a job, and a real kit from our reviews. Output and surge ratings are listed because, as above, capacity alone never tells the whole story.

Capacity tier	Best for	Typical output	Example kits
Under 300Wh	Phones, tablets, a laptop, camp lights, a CPAP for a night; ultraportable tent and day-trip use	300W (600W surge)	MARBERO 296Wh, Anker SOLIX C300 (288Wh), Jackery Explorer 300 (292Wh)
300-700Wh	A weekend of devices plus a small 12V cooler or CPAP with headroom; light home essentials	500W (1000W surge)	EBL 500W (519Wh), GRECELL 500W (519Wh)
700-1500Wh	A fridge for most of a day, short outages, RV and van life, running a microwave or power tools	1500-2000W (3000-4500W surge)	Jackery Explorer 1000 v2 (1070Wh), EcoFlow Delta 3 Classic (1024Wh), Anker SOLIX C1000 Gen2 (1024Wh), OUPES 2000W (1024Wh)
1500-3000Wh	Multi-day outages, a fridge plus lights and electronics for a day-plus, larger appliances	1800-2000W-plus	Expandable units bridge this tier: the OUPES 2000W grows from 1024Wh to 5120Wh with extra batteries, and the Anker C1000 and Jackery 1000 v2 accept add-on packs
3000Wh+	Whole-house backup, well and sump pumps, dryers, 240V loads, powering a household for days	3600W (7200W surge)	Jackery HomePower 3600 Plus (3584Wh)

Notice how output scales with capacity but isn’t locked to it: the OUPES 2000W and Anker C1000 Gen2 share a 1024Wh battery yet push 2000W, while the same-capacity Delta 3 Classic pushes 1800W. If your limiting factor is a single high-wattage appliance rather than total energy, shop the output column first.

Matching Solar Input to Your Recharge Needs

A generator that never recharges fast enough is just a battery on a countdown. If you’re off-grid for more than a day, the solar input has to keep pace with what you drain.

Two things shrink a panel’s rating in the real world. First, panels deliver only about 60-80% of their nameplate under a clear sky, less through cloud, haze, or a bad angle. Second, you get roughly 4-5 useful sun hours a day, not a full 12. So a 100W panel realistically returns 300-400Wh per day, and a 200W panel 600-800Wh.

Line that up against your drain. If you use 500Wh a day, the bundled 100W panels on the entry kits will fall behind — they’re top-up chargers that keep a small battery alive, not units that refill a 1kWh station. Step up to a 200W-class panel: the Jackery Explorer 1000 v2 reaches 80% in about 6 hours on its 200W panel, and the EcoFlow Delta 3 Classic refills its 1024Wh in roughly 5.8 hours on a 220W panel. If you need speed or run heavy loads, look at stations with high solar ceilings — the Anker SOLIX C1000 Gen2 accepts up to 600W of solar for a sub-2-hour recharge, and the OUPES 2000W takes up to 800W.

Common Sizing Mistakes to Avoid

Buying on watt-hours alone. A huge battery with a small inverter still can’t start a microwave or a fridge. Always check continuous watts against your biggest device.
Ignoring surge. Motor loads spike two to three times their running wattage at startup. A unit that handles a fridge’s 150W running draw can still trip on its 600W surge if the surge rating is too low.
Trusting the nameplate capacity at 100%. Plan on about 85% usable, and less in the cold, or you’ll come up short exactly when you’re relying on it.
Undersizing solar. A 100W panel can’t keep a hard-used 1kWh station full. Size the panel to your daily drain, not to the battery.
Oversizing “just to be safe.” Extra capacity is extra weight, cost, and recharge time. Aim for roughly 20-40% above your calculated need, not the largest unit you can afford.
Forgetting the future. If you’ll add appliances or want one unit for both camping and home backup, choose an expandable model like the OUPES 2000W rather than replacing the whole kit later.

Run the three-step capacity math, confirm your biggest device fits under continuous watts with surge to spare, and match the panel to your daily drain — that’s the whole method. For a shortcut, plug your devices into the size calculator, then browse the full lineup on our best solar generators hub. Ready to shop by use case? See our picks for the best solar generator for camping and the best solar generator for home backup.