What Size Power Station Do You Need? The Honest Math

Ask a search engine what size solar generator you need, and the top answers come from the brands that sell them, each one sizing you into its own catalog. This page has nothing to sell you. It works the sizing question from appliance spec sheets and one formula, and the honest answer for most people is smaller and cheaper than the vendor calculators say. One example of what the math rules out before you spend anything: a 1,500-watt space heater flattens even a $650, 2,048 Wh station in about 70 minutes. Here is the whole guide in one table, with the math behind each row further down.

A quick decoder before the math. Capacity is measured in watt-hours, abbreviated Wh: a 576 Wh battery can push out 576 watts for one hour, or 57.6 watts for ten hours. A kilowatt-hour (kWh) is 1,000 Wh, the same unit on your utility bill. “Portable power station” and “solar generator” are the same box; vendors say “solar generator” when they want to bundle solar panels with it. And this page sizes the battery only. For which brand to buy at the size you land on, and why the battery chemistry called LFP (lithium iron phosphate) matters more than the logo, see the power station brands guide.

The Only Formula You Need

Hours of runtime = battery watt-hours × 0.85 ÷ device watts.

The 0.85 is not pessimism, it is the vendors’ own number for what survives the inverter, the electronics that turn stored battery power into wall-style AC power. Jackery’s product pages state it plainly: “Working time = 240Wh* 0.85 / operating wattage of your device.” Treat 85 percent as the friendly case: when TheSolarLab ran a 2,048 Wh Pecron flat-out near its maximum load, the delivered energy worked out to 75 percent. Big loads waste more; small steady loads do better.

The worked example running through this page is a 576 Wh EcoFlow RIVER Max, a discontinued unit that was still turning up brand new on clearance shelves this summer (it is the brands guide’s storm-kit example), rated at 600 W output with a 1,200 W surge. By the formula, it holds 576 × 0.85, about 490 usable watt-hours. Keep that number in mind as the scenarios go by: it is what a “500 Wh class” station really gives you.

The second number that matters is the output limit in watts. A battery can hold plenty of energy and still refuse to start your appliance, because every motor briefly demands far more than its running draw. Honda’s generator sizing chart, which has no power station to sell you, puts a refrigerator at 200 running watts but 1,600 starting watts. That is why surge ratings exist, and why a station’s continuous watts and surge watts both matter for anything with a compressor or a pump in it.

What Your Stuff Actually Draws

Every number here is from the maker’s own spec sheet or a federal EnergyGuide label, not from a sizing calculator.

Two things jump out of that table. Almost everything you care about during an outage draws less than a light bulb used to, and the two exceptions, anything that makes heat and anything with a motor, are in a different universe. That split is the entire sizing problem.

What Size Power Station for Camping?

The 250 to 600 Wh class covers a weekend, with room to spare, unless you bring the internet with you. A Starlink Mini is the biggest single load most campers now carry: at the spec sheet’s 25 to 40 W average, eight hours of dish time costs 200 to 320 Wh at the dish, before inverter losses. Starlink’s own support page says the Mini “will typically consume 20-40 watts on average (15 when Idle.)” On the RIVER Max’s ~490 usable Wh, the formula gives 490 ÷ 30, roughly 16 hours of continuous dish; a documented field test in the site’s Starlink Mini guide had a 497 Wh unit reading 12.7 hours to empty while running a Mini through its AC brick, and the measured number, not the division, is the one to plan on.

Everything else is small. A MacBook Air stores 53.8 Wh per full charge, so topping it up nightly for two nights is about 108 Wh before losses. Phone charges, lights, and a camera battery are smaller still. A weekend of phones, lights, laptop, and evening Starlink fits inside 500 Wh; skip the dish and a 250 Wh unit does it. Buy the next size up only if you plan to run the dish all day, or you want the same box to double as storm backup at home, which is the argument the next three sections make for you.

What Size Power Station for a CPAP?

Budget about 550 Wh of rated battery per night, and treat the 1 kWh class as the safe buy. A CPAP (continuous positive airway pressure) machine is the one medical device on this page, so size it against the worst case, not the average. ResMed’s AirSense 11 user guide lists “Typical power consumption 56.1W” and “Peak power consumption 73.2W”. At the typical figure, an eight-hour night is 56.1 × 8, about 449 Wh delivered, or roughly 530 Wh of rated battery; at the peak figure the same night needs about 690 Wh. A 576 Wh unit covers a night only if the machine actually behaves like the typical number, while a 1 kWh unit covers it at either figure. Three typical nights fit in a 2 kWh unit, and most of a week fits in 4 kWh.

Two practical notes. First, humidification is where the energy goes, though ResMed’s spec sheet does not say which settings produce its typical figure. The clearest evidence is ResMed’s own battery guide, whose sizing tables cover the previous-generation AirSense 10 through the company’s DC converter and build in a 50 percent safety margin: 12 amp-hours of battery for an 8-hour night at a mid-range pressure with no humidifier, 44 amp-hours with the humidifier at its top setting on standard tubing, and more still with a heated tube. That is over three times the energy for the same night, from humidification alone. Turning it off or down is the biggest runtime lever you have. Second, the machine’s 65 W power supply is a trivial load for any station’s inverter. Capacity, not output watts, is the only CPAP question.

How Long Will a Power Station Run a Fridge?

About 18 hours per 1,000 Wh of battery, using a real fridge’s real numbers. A GE 19.2-cubic-foot top-freezer carries a federal EnergyGuide label of 422 kWh per year. That is 422,000 ÷ 365, about 1,160 Wh per day, an average draw of just 48 watts, because the compressor only runs part of the time. So: a 1,024 Wh station holds ~870 usable Wh, which is 870 ÷ 1,160 of a day, roughly 18 hours. A 2 kWh unit runs the same fridge about a day and a half. Riding out a 3-day storm outage on battery alone means 3 × 1,160 ÷ 0.85, call it 4 kWh of rated capacity, before you charge a single phone.

The start-up caveat from the formula section applies here in full: Honda’s sizing chart shows a fridge needing 1,600 starting watts against 200 running watts. A 600 W-continuous station with a 1,200 W surge, the RIVER Max’s exact rating, sits right at the edge for some compressors; the 1,500 to 2,000 W-class inverters on the current 1 to 2 kWh units clear it comfortably. If a fridge through a storm is your main mission, the honest shopping list is a 2 kWh LFP unit plus solar panels to refill it each day, or a 4 kWh unit if you want to ignore the weather. Pricing in the 1 kWh class is theatrical: Pecron’s E1000LFP sells for $399 against a struck-through $799 list, while Bluetti’s Elite 100 V2 lists at $899 with a page coupon cutting it to $499, all read on August 31, 2026, which is exactly why the brands guide exists.

What Size for a Work-From-Home Outage Day?

A 500 Wh-class unit just barely covers a full remote workday; 1 kWh covers it without rationing. The two loads that matter are the internet and the laptop. A Starlink Mini at its 25 to 40 W average across a nine-hour workday is 225 to 360 Wh delivered. A MacBook Air burning through two full charges is another ~108 Wh. Add phone top-ups and a router or monitor and the day lands somewhere near 450 Wh delivered, which is ~530 Wh of rated battery. The 576 Wh RIVER Max class finishes that day on fumes; a 1 kWh unit finishes with margin for the evening. If your home internet is cable or fiber, your modem and router in place of the dish draw less, and the day gets cheaper still.

The trap in this scenario is heat and coffee. The workday math above survives a laptop’s 40-to-60-watt charger; it does not survive a 900 W space heater under the desk or a 1,000 W drip brewer. Boil water on the gas stove or a camp stove, wear a sweater, and the office runs all day on a box the size of a toaster.

Can a Power Station Run a Space Heater?

Yes, and it is the fastest possible way to waste your money. Heat is the one thing batteries are terrible at. A common Lasko ceramic heater draws 1,500 W on high and 900 W on low. On a 2,048 Wh station, the formula gives 2,048 × 0.85 ÷ 1,500: one hour and ten minutes, from a machine that costs $649 and up in that capacity class (Pecron’s E2400LFP is the reference price as of August 31, 2026). On low, not quite two hours. The 600 W-rated RIVER Max cannot run either setting at face value; its X-Boost mode raises the ceiling (“power high-wattage appliances up to a whopping 1800W”), and EcoFlow’s own examples for the mode are hairdryers, vacuums, and lawnmowers. However the electronics manage that load, X-Boost adds zero watt-hours: the unit’s ~490 usable watt-hours buy about half an hour of 900 W-class heating, whichever box meters it out.

The same physics applies across the resistive-heat family: hair dryers, toasters, kettles, electric blankets on high. During a winter outage, the battery’s job is the furnace’s fan, the fridge, the phones, and the internet. The heat itself needs to come from combustion, insulation, or blankets, because at 1,500 W even a 6 kWh flagship battery buys you an afternoon.

What About the Sump Pump?

This is the scenario where output watts, not watt-hours, disqualify the small units. Zoeller’s spec sheet for the Model 53, a workhorse residential sump pump, lists the motor at 4.8 to 9.7 amps across the pump’s 115 V and 230 V versions; the common 115 V household version sits at the top of that amps range, which works out to about 1,100 running watts, before the start-up surge that every motor adds. Honda’s chart is again the honest reference for what motor surges look like: its refrigerator row jumps eight-fold from running to starting. A pump needs a station in the 2,000 W-continuous class with a proportionally larger surge rating, which in practice means the 2 kWh-and-up units.

The energy side is friendlier than it looks, because a sump pump with a working float switch runs in bursts, not continuously. A pump that cycles for a total of one hour across a stormy day consumes roughly 1 kWh delivered at its ~1,100 W draw. The sizing answer is therefore the same 4 kWh class as the 3-day fridge scenario, but the two loads add up: the same big station cannot run both a hard-cycling pump and the fridge for days without solar input. If your basement floods every time the power fails, price a battery-backup sump system alongside a power station before you decide; it is the same money aimed at a narrower, surer job.

What Solar Generator Can Power a Whole House?

Now the tier the ads sell hardest, and the one where the math turns brutal. The average U.S. residential electric customer bought 10,791 kWh in 2022, the most recent year on the U.S. Energy Information Administration’s FAQ page, which is about 30 kWh a day. Cover 30 kWh a day at 85 percent efficiency and you need roughly 35 kWh of battery per day of outage. No portable box holds that. The machines built for this are expandable systems: EcoFlow’s DELTA Pro Ultra starts at one 6,144 Wh battery and advertises “6kWh-90kWh capacity” with “7.2-21.6kW output, powerful enough to run your whole home even with a central AC,” at $4,199 for the starter unit (against a $5,799 list price) plus $1,499 for the Smart Home Panel that wires it into your circuits, as of August 31, 2026. Anker’s SOLIX F3800 plays the same game from a 3,840 Wh battery with “6,000W, 120V&240V Dual Voltage” output.

Three hard requirements separate this tier from everything above it. First, 240 volts: your central air conditioner, well pump, and electric dryer do not run on a regular outlet; a central AC alone typically uses 3,000 to 4,000 W at about 240 volts on a hard-wired circuit, per Trane. Run that compressor from the flagship’s single 6.1 kWh battery and it is empty in well under two hours of compressor time. Second, an installed connection: the Electrical Safety Foundation International’s rule is blunt, “Transfer switches are the only way to safely power your home’s electrical system,” because a generator or battery fed into house wiring without one can backfeed the utility lines “and injure workers trying to restore power.” That is an electrician visit on top of the hardware. Third, money: the $4,199 starter unit plus the $1,499 panel comes to $5,698 in hardware before the electrician arrives, its single battery covers well under a day of average whole-house use, and stacking batteries toward genuine multi-day coverage multiplies the bill.

The honest alternative is circuit triage: back up the circuits that matter and let the rest wait for the grid. Add up the fridge (1.2 kWh a day), internet and laptops (under 0.5), phones, a few LED lights, and the furnace fan burst-cycling, and essential life runs on 2 to 3 kWh a day, a tenth of the house’s average appetite. That budget fits a 4 to 6 kWh system recharged by solar panels, with no 240 V circuits and no panel install, for a fraction of the whole-home price. Size for the life you need during an outage, not for the house’s habits when the grid is doing the work.

Sizing the Solar Panels That Refill It

Two numbers decide this, and neither is the wattage on the panel’s box. The first is the station’s solar input limit: a RIVER Max, for instance, accepts at most “200W 10-25V DC 12A Max” from panels, so hanging 400 W of glass on it wastes half. Check your unit’s input spec before buying any panel. The second is what panels really deliver. In OutdoorGearLab’s controlled clear-sky tests at 6,300 feet, the best portable panels delivered 171 to 193 watts from 200 and 220 W ratings, 86 to 91 percent, and those were ideal conditions with cool air and a perfect angle. Haze, heat, bad angles, and partial shade all cut from there.

Treat those lab numbers as the ceiling and plan lower: a conservative planning yield, this page’s own judgment rather than a measured figure, is roughly two-thirds to three-quarters of the rating in good sun. Do the refill math with that number. A 220 W panel delivering ~160 W refills a drained 576 Wh unit in three and a half to four hours of strong sun, and puts back a fridge-day of energy (1.2 kWh) in seven to eight. That is the whole logic of the “2 kWh plus solar” storm kit: the battery bridges the night, the panel pays the fridge bill each afternoon.

Frequently Asked Questions

How many watt-hours do I need per day in an outage?

Essentials are cheaper than intuition says: a full-size fridge averages about 1.2 kWh a day per its EnergyGuide label, a Starlink Mini costs 200 to 320 Wh across eight hours, a CPAP night is roughly 450 Wh (eight hours at ResMed’s 56.1 W typical figure), and laptops and phones are rounding errors. A 2 to 3 kWh daily budget covers an essentials-only household.

Will a power station run a refrigerator overnight?

Yes. Using the EnergyGuide math above, 1,000 Wh of rated battery runs a modern full-size fridge for about 18 hours, provided the station’s inverter and surge rating can start the compressor; Honda’s sizing chart puts refrigerator starting draw at 1,600 W.

Can a solar generator really power a whole house?

Only the installed, expandable systems, and only with 240 V output, a transfer switch or smart panel wired in by an electrician, and a battery bank of roughly 35 kWh for each day of outage (the EIA-average 30 kWh of daily use divided by the 0.85 efficiency factor), so multi-day coverage means the top of the expansion range (up to 90 kWh), solar recharge, or a trimmed-down load. A portable unit plus circuit triage covers essentials for a fraction of the cost.

What size solar panel pairs with a power station?

Match the panel to the station’s rated solar input, not the other way around. Lab tests of the best panels measured 86 to 91 percent of rated output under ideal clear-sky conditions; since field conditions are worse, a sensible planning number (this page’s judgment, not a lab figure) is roughly two-thirds to three-quarters of the rating in good sun.

The one-sentence version of this entire page: add up your real loads from their spec sheets, multiply battery capacity by 0.85, and buy the smallest LFP unit that clears your worst realistic day, then pick the maker with the brands guide and, if internet-through-an-outage is the point, the Starlink Mini guide.

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