Whole-Home Backup Without the Grid: Stacked Power Stations vs a Standby Generator

Somewhere around the third spreadsheet tab, the math starts to look obvious. An Anker SOLIX F3800 holds 3.84kWh and runs $3,500–$5,500 depending on the week's promotion. Your house pulls something like 29kWh on an average US day. Twenty-nine divided by 3.84 is 7.6 — call it eight units, place a bulk order, done. Whole-home backup, no electrician crawling through the attic, no permit, no propane tank rusting in the side yard.

Except a single F3800 system doesn't go to eight units. It tops out at seven — one base unit plus six expansion packs — for a hard ceiling of 26.9kWh, which is less than one full day of unrestricted whole-home draw. You've hit the wall before you finished the spreadsheet. This is the exact moment a lot of serious off-grid researchers quietly stop comparing power stations to each other and start asking a different question: at what point does a wall of batteries stop being cheaper than a generator?

The stacking trap: "whole-home capable" is a claim about the plug, not the math

Every stackable power station on the market advertises itself as home-backup-capable, and technically most of them are — if by "capable" you mean it can be wired into a transfer switch or smart panel and physically deliver power to circuits in your house. That's a true claim, and mostly an irrelevant one. The question that actually decides whether it backs up your home isn't whether it can plug in; it's whether it holds enough energy, at high enough voltage, for long enough, to matter during the outage you're actually worried about.

Two things quietly cap what "stackable" can do for you, and neither shows up on the hero photo of six matte-black boxes wired together in a garage.

The first is a hardware ceiling. Every stacking ecosystem has a maximum, and it's lower than the marketing implies. Anker's SOLIX F3800 caps at one base unit plus six BP3800 expansion batteries — 26.9kWh, full stop; a seventh pack simply isn't supported. EcoFlow's DELTA Pro Ultra goes further, up to 15 units and 90kWh through its Smart Home Panel 2, with output scaling from 7.2kW to 21.6kW as you add inverter hubs — genuinely large, but at that point you're mounting the better part of a small server rack of lithium, not "adding a box."

The second, and the one nobody puts in the ad copy, is that stacking doesn't get cheaper per kWh the way a generator gets cheaper per hour of runtime. A generator's big costs — the unit, the transfer switch, the trenching, the permit — are paid once. After that, an extra day of runtime costs a tank refill: a few gallons of propane, call it $10–$20. A power station's big cost never goes away: every extra day of autonomy is another $3,000–$9,000 box, because the battery is the product, not an accessory to it. One cost curve goes nearly flat after install. The other is a straight line that keeps climbing at the same slope, box after box. Somewhere on that chart the two lines cross — and which side of the crossing your house sits on is the whole decision.

Do the math yourself: kWh you need vs. kWh you can stack

The comparison only means something once you've run your own numbers, and it takes about five minutes with a utility bill or a whole-house power meter.

1. Find your real daily draw. Pull your last bill's kWh-per-month figure and divide by 30. An average US home lands near 29kWh/day; an average European home, which more often heats with gas and runs far less air conditioning, tends to sit closer to 8–11kWh/day. Our load-audit worksheet walks the circuit-by-circuit version of this if you want more precision than a bill average.
2. Decide curated or brute-force. A curated critical-load list — fridge, well or sump pump, wifi, lighting, one medical device — usually runs 4–10kWh/day. Backing up everything, air conditioning included, means using the full daily figure from step one.
3. Multiply by the days of autonomy you actually want. Size for your region's worst realistic outage — a multi-day ice storm or hurricane, not the five-minute blink that's over before the fridge compressor even notices.
4. Derate before you divide. Usable capacity runs 90–95% of rated, and inverter losses take another 5–10% off what actually reaches your circuits. Divide your kWh target by roughly 0.85–0.9 before dividing it by a unit's rated capacity.
5. Divide by what one system actually holds, then price the whole stack. That's your real budget — not the "starting at $X" figure on the product page, which is always the single smallest configuration money can buy.

System	Base capacity	Max stacked	Output	Typical price*	Runtime ceiling
Anker SOLIX F3800	3.84kWh	26.9kWh (1 base + 6 packs)	6,000W, split-phase 120/240V	~$3,500–$5,500 base unit; ~$5,300+ for a 7.68kWh backup kit	Hard ceiling — under one full day of unrestricted whole-home draw
EcoFlow DELTA Pro Ultra	~6.1kWh	90kWh (up to 15 units)	7.2kW, expandable to 21.6kW	~$5,600–$9,400 for a 12.2kWh two-unit start; roughly $500–$800/kWh at scale	Large but still finite — a full 90kWh stack often prices past $45,000–$70,000+
Standby generator (22kW, US)	—	—	22kW continuous	$10,000–$18,000 installed; $20,000+ on hard sites	Effectively unlimited on natural gas; 8–12 days on a 500-gal propane tank

*Power-station pricing swings 30–40% with flash sales — treat these as planning ballpark, not a quote, and check the current price before you buy anything.

Worked example: the curated list, where stacking wins

A household with a 6kWh/day critical-load list — fridge, well pump, wifi, lights, one medical device — wants three days of autonomy with no sun: 18kWh, call it 21kWh after derating. One F3800 base unit plus two expansion batteries gets to 11.5kWh — just over half that no-sun target, not the full three days from storage alone. What closes the gap isn't a bigger stack, it's daily solar input: paired with even a modest 800–1,000W of portable solar, the battery is topping back up every clear afternoon, which turns "three days of stored charge" into "indefinite, as long as the sun shows up every day or two." All-in hardware cost: roughly $7,000–$9,000. No permit, no trench, no annual service call, and it rides in the back of a truck if you ever move.

Worked example: true whole-home, where the generator wins

Run the same math against an unrestricted 29kWh/day US household, sized for three days with zero recharge: 87kWh, call it 100kWh after derating — past even the DELTA Pro Ultra's 90kWh ceiling on its own, and at roughly $500–$800/kWh a 90kWh stack alone prices out somewhere between $45,000 and $70,000-plus, before adding the Smart Home Panel 2 hardware and the multiple inverter hubs needed to actually deliver 21.6kW to a real panel. A 22kW standby generator covers the identical load for $10,000–$18,000 installed — and where the battery stack is done at 90kWh, the generator just keeps running, because refilling its tank costs a delivery-truck visit, not another $5,000 box.

US vs Europe: same math, different starting numbers

The physics is identical on both sides of the Atlantic; the inputs aren't. In the US, a permanently installed natural-gas or propane standby generator sized in 14–26kW steps is a mature, common trade — Generac and its competitors have a dealer in most counties, and the split-phase 120/240V panel is identical on every house, which is exactly why F3800- and DELTA Pro Ultra-class stations bother supporting it at all.

In Europe, permanently installed gas standby generators are far rarer. Most homes run on 230V single-phase (or 400V three-phase on larger rural properties) and don't have the buried natural-gas or propane infrastructure that makes a US standby unit a same-day quote. The nearer equivalent is a wired-in inverter generator with an automatic transfer switch, sized more modestly, because whole-home electric heating and central air conditioning are both far less universal — a European household's daily draw is commonly closer to 8–11kWh than the US's 29kWh, which shrinks every number in the table above in your favor. Stackable power stations sell under the same brand names in European 230V/50Hz SKUs, and the equivalent gotcha isn't split-phase legs — it's confirming the unit's continuous output amperage actually covers a heat pump, electric hob or shower running at the same time as everything else, rather than assuming "whole-home" on the box means what it says.

So which is your actual move?

Run your own numbers from the table above, then check which list you land on.

Stack power stations if:

• Your real target is a curated critical-load list, not the whole panel unrestricted.
• You already have, or are adding, solar — the battery earns its keep daily, not only in an outage.
• You want zero permit, zero trench, zero annual service call, and the option to take it with you.
• Your math above lands under roughly 15–20kWh of needed autonomy.

See current pricing and configurations on the stackable systems this math is built on:

Install a standby generator if:

• You want the whole panel, air conditioning included, with nothing curated or rationed.
• Your region's worst realistic outage runs multiple days, not hours.
• Your math above lands north of 20kWh of needed autonomy — the point where stacking gets expensive fast.
• You'd rather pay for fuel by the gallon than for capacity by the battery pack.

Get a real installed number for a standby unit sized to your panel and your region:

Plenty of households eventually end up with both, on a timeline — a stack for the daily solar value and the short, frequent blinks, a generator or fuel-fired hybrid inverter for the multi-day tail event a stack alone can't outlast without sun. You don't have to build both on day one. If you're weighing a single battery against a generator rather than a full stack, we've run that narrower comparison separately: standby generator vs home battery. Build the one your own math actually points to here, and layer the second in later if your risk picture changes.

Common questions