Partial or Whole-Home Backup? You're Probably Asking the Wrong Question.

Somewhere in your solar quote there's a line item that decides what your life looks like the next time the power goes out. Most homeowners skim right past it.

It says either partial backup or whole-home backup. And almost everyone reads that the way you'd expect: partial means some of my house stays on, whole-home means all of it does.

That's not what those words mean. And the gap between what they sound like and what they actually do is the single biggest source of buyer's remorse in home battery storage.

Let's fix that. By the end of this you'll know exactly what each one is, what each one costs, and — more importantly — the question you should actually be asking instead.

What "Partial Backup" Actually Is

Partial backup is sometimes called essential load or critical load backup, and the name is a clue: it's about circuits, not appliances.

Here's how it physically works. An electrician installs a second, smaller breaker box next to your main panel — a critical-load subpanel. Then they move the circuits you've decided are essential into it: the fridge, some lights, outlets for your Wi-Fi router, maybe the furnace blower or a sump pump.

When the grid goes down, your battery system severs the connection between the main panel and that subpanel, creating a closed loop. The circuits inside the subpanel stay alive. Everything outside it goes dark. Automatically, in milliseconds, whether you like your choices or not.

That subpanel isn't free, and it's a cost most quotes bury. Materials run about $200–$500, electrician labor adds $300–$800, and each additional circuit you want moved tacks on another $100–$200 — so budget roughly $500 to $1,500 for that box alone.

The upside is real, though: because you're only powering a fraction of the house, you need a smaller battery. Partial systems often start around $8,000 to $12,000 installed. Your battery drains slower and lasts longer, because it's not being asked to do much.

What "Whole-Home Backup" Actually Is

Here's where nearly everyone gets it wrong.

Whole-home backup is a wiring configuration, not a performance guarantee. Instead of building a subpanel and choosing circuits, the electrician ties your battery system in ahead of your main panel — so during an outage, every circuit in the house has access to power.

Notice that phrasing. Has access to. Not will receive.

Ironically, this is sometimes the simpler installation. Whole-home backup can be easier to wire in some cases, precisely because there's no separate subpanel to install and no circuits to relocate. No agonizing over which loads matter.

The cost is higher — typically $15,000 to $25,000 or more — but not primarily because of the wiring. It's because to make "whole-home" mean anything, you need enough battery capacity and enough inverter output to actually serve the demand.

And that's exactly where the fantasy collapses.

The Number That Ruins the Fantasy

We ran this math in detail recently, and it's worth repeating because it's the crux of everything.

A Tesla Powerwall 3 holds 13.5 kWh. Run essentials — fridge, lights, Wi-Fi, around 0.5 kW — and you get roughly 27 hours.

Now run your house the way "whole-home backup" sounds like it should let you. Central AC in August. Electric oven. Dryer. Maybe the EV charging. That's 7 kW or more.

13.5 ÷ 7 = under two hours.

Same battery. Same "whole-home" wiring. Dead before dinner.

So here's the uncomfortable truth: a whole-home connection with a single battery will not run your whole home. It will simply let you drain your battery in two hours instead of stopping you. If a home pulls the full output from one battery during an outage, it drains in about 2 hours — while running just critical loads, that same battery lasts 10–12 hours or more.

Whole-home backup only delivers what its name promises when you pair it with enough storage and output to sustain those loads — which usually means multiple batteries, a larger inverter, and a budget to match.

If you're staring at a quote right now trying to work out which line item you actually need, this is precisely the conversation worth having before you sign anything. A free consultation with IntegrateSun will map your actual appliances and outage habits to a real answer — not a label on a proposal.

The Real Problem With Partial Backup (Nobody Says This Out Loud)

Partial backup has a flaw, and it isn't the price or the subpanel.

It's that you have to guess, in advance, what you'll miss.

Homeowners don't think in circuits. They experience an outage as comfort lost. The air conditioning shuts off in August. The oven doesn't work. The EV won't charge. Suddenly a system that looked great on paper feels incomplete.

You sit with an electrician months before any outage, in a calm room, and pick circuits. Then a heat wave hits, the grid fails, and you discover that the thing you actually needed was the AC — which homeowners frequently assume is essential, but which is usually far too power-hungry for a critical-load system to support anyway.

Misidentifying what's truly critical is one of the most common failure modes of partial backup — you end up with either inadequate coverage, or non-essential loads eating your runtime.

And unlike a whole-home configuration, you can't change your mind during the outage. The circuits are the circuits.

So What Should You Actually Be Asking?

Not "partial or whole-home?" That question is about wiring, and wiring is the installer's problem.

Your question is: "During a real outage, what do I want to still be able to do — and how long do I need to do it?"

Answer that honestly and the rest falls out of it.

If the answer is keep the food cold, keep the lights on, keep the internet up, ride out a storm — partial backup is not a compromise. It's the right tool, it's cheaper, and your battery will run for a day or more instead of two hours.

If the answer is my life continues essentially uninterrupted, including cooling, cooking, and comfort, for multiple days — you need whole-home wiring and the storage and inverter output to back it up. That's a bigger system and a bigger number, and anyone quoting you whole-home backup on a single battery is selling you a label.

And if the answer is somewhere in between — which it is for most people — the honest path is often to start with a well-designed partial system and build toward more. Partial backup is best understood as a step, not a destination.

One thing that changes the entire calculation: pair any of this with solar. Panels refill the battery during daylight, which turns a fixed countdown into something closer to a self-sustaining loop. It's the difference between "my battery lasted 27 hours" and "we went four days and barely noticed."

Get an Answer Built Around Your House

You shouldn't have to reverse-engineer what a line item on a proposal means. And you definitely shouldn't find out what "whole-home backup" really meant during your first real outage.

A free IntegrateSun consultation starts from the right end of the problem: what you actually run, what you'd genuinely miss, how long your outages tend to last, and whether solar is in the picture. Then we tell you which configuration serves that — honestly, including when the cheaper option is the better one.

No pressure. No labels dressed up as promises.

Book your free consultation here.

Because the goal was never to buy "whole-home backup." It was to keep your house livable when the street goes dark.