Partial backup keeps a short list of essential circuits running, usually with one battery. Whole-home backup connects the battery to your entire electrical panel, usually with two or three batteries. The catch most quotes skip: “whole-home” describes the wiring, not what can run at once. Every backup plan hits two limits, power (kW) and stored energy (kWh), so the real question is which of your loads matter in an outage and for how long.
Partial vs Whole-Home Backup at a Glance
| Partial (essential loads) | Whole-home | |
|---|---|---|
| How it is wired | Chosen circuits move to a separate backed-up subpanel | Battery connects at the main panel; every circuit stays wired in |
| Typical battery storage | One battery, about 10 to 13.5 kWh | About 30 kWh or more, often two or three batteries |
| Installed cost before incentives (EnergySage, H1 2026) | About $5,000 to $18,000 | About $24,000 to $40,000 |
| What usually runs | Fridge, lights, internet, outlets, gas furnace fan, garage door | Anything on the panel, as long as the total stays under the battery’s kW limit |
| Runtime with no solar recharge | About 2 to 3 days on a light essentials load | Hours, not days, if you use power normally |
| Main watch-out | You lose anything you did not pick, including outlets you forgot about | Large loads can drain the battery fast or trip it if they start together |
Cost ranges are EnergySage Marketplace averages from the first half of 2026 and exclude solar panels. Runtime rows use the worked example below.
The Two Limits Every Backup Plan Hits
Quotes lead with kWh. In an outage, kW decides first.
Power (kW): what can run at the same time
Every battery has a continuous power rating. A Qcells Q.HOME CORE G3 cabinet delivers 7.6 kW continuously; a Tesla Powerwall 3 is rated 11.5 kW. Add up everything running at one moment, and if the total goes over the rating, the battery shuts down to protect itself.
Big 240-volt appliances are where this bites. Rough running loads, from simple amps times volts math (check your own nameplates):
- Level 2 EV charger on a 40-amp circuit: 32 amps at 240 volts, about 7.7 kW. That alone uses an entire G3 cabinet.
- Electric dryer on a 30-amp circuit: commonly about 5 kW while heating.
- Central air conditioning: often 3 to 5 kW running for a typical home, plus a short starting surge several times higher. The battery’s surge rating has to cover that start.
A fridge, LED lights, and a Wi-Fi router together draw about 210 watts, according to EnergySage’s sizing example. The gap between those two lists is the whole decision.
Energy (kWh): how long it lasts
Stored energy decides how many hours you get. The average US home uses about 28.5 kWh a day. A 13.5 kWh battery running the whole house at that pace lasts roughly 11 hours, EnergySage calculates, while the same battery can carry a light essentials load for one to three days.
What solar changes (and when it doesn’t)
Solar is the variable that turns hours into days. As a rough rule, each kW of panels makes about 4 to 5 kWh on a clear Southern California day (check your own address in NREL’s PVWatts calculator). A 6 kW system can refill a 12.5 kWh battery by mid-afternoon if the house is only running essentials. If the house is running normally, the same panels barely keep up.
Two catches. A standard grid-tied solar system shuts off in an outage to protect line crews; it keeps producing only if the battery system can isolate your home and keep the inverters running. And shutoffs often come with smoke, storms, or short winter days, so plan as if the first day is cloudy.
Worked Example: One Battery vs Two
Here is our own arithmetic for the same home with one and two Qcells G3 cabinets (12.46 kWh usable each), with no solar recharge. It assumes the 210-watt essentials load from EnergySage (about 5 kWh a day) and the 28.5 kWh US daily average for normal use.
| Setup | Power limit | Essentials only (5 kWh/day) | Normal use (28.5 kWh/day) | Can AC, dryer, and EV charger run together? |
|---|---|---|---|---|
| One G3, partial backup | 7.6 kW | About 2.5 days | Not wired in | No |
| One G3, whole-home wiring | 7.6 kW | About 2.5 days, if you keep to essentials | About 10.5 hours | No (about 16.7 kW needed) |
| Two G3s, whole-home wiring | 15.2 kW | About 5 days | About 21 hours | Not all at once; any two, yes |
Our calculation is from the sources listed, before inverter losses, assuming the air conditioner runs at 4 kW. Real runtimes are usually somewhat lower, and longer when solar recharges the battery.
The middle row is where many homeowners end up: whole-home wiring on one battery. It is not a bad setup. It behaves like partial backup with more choices, and you make those choices during the outage instead of before it.
Which One Fits Your Home
Start with the outage you are actually planning for, not the battery. The EIA counted an average of 11 hours without power per US customer in 2024, but about 9 of those came from major storms; without them, the average was about 2 hours. That is why EnergySage concludes partial backup makes more sense for most homes. Your own outage history matters more than the national average.
| The outage you plan for | What usually covers it |
|---|---|
| A few hours, a few times a year | One battery on essential circuits |
| Overnight, and you need AC or electric heat | Two batteries on the main panel, or one with load control and a short list of big loads |
| One to three days (planned shutoffs, storms) | Essentials plus solar that keeps recharging matters more than a third battery |
| Medical equipment that cannot stop | A battery plus a separate plan from your medical provider (see below) |
Partial backup is probably enough if
- You cook and heat with gas, or can live without the electric range and dryer for a day.
- Your goals are a cold fridge, lights, internet, a home office, and phone charging.
- You would rather spend the difference (often $10,000 or more) on solar, a roof, or savings.
Whole-home backup is worth pricing if
- You work from home and cannot lose a day, or you live in a planned-shutoff area.
- Air conditioning, a well pump, or electric heat is a safety need, not a comfort.
- Your home is all-electric, so “essential” already includes 240-volt loads.
The middle path: whole-home wiring with load control
You do not have to pick between “short list” and “buy three batteries.” Many installers wire one or two batteries at the main panel and add load control that sheds the EV charger, dryer, or pool pump when the battery gets close to its limit. You keep access to every circuit without paying for enough kW to run them all at once.
The hardware choice changes the price. A separate essential-loads subpanel is usually the cheapest wiring; a full smart panel that lets you switch circuits from an app usually costs a few thousand dollars more; individual load controllers sit in between. Ask for whichever one you are getting as its own line on the quote, and which loads it sheds first.
If someone depends on medical equipment
A battery helps, but it should not be the only plan for equipment that cannot stop. Ask your medical provider what backup the device needs. In California, utilities’ Medical Baseline programs add extra warnings before planned shutoffs; PG&E aims to notify customers starting 48 hours ahead, though enrolled homes are still shut off. That lead time is when you set the battery’s backup reserve to 100% so it is full when the power goes.
Renting, or not ready for panel work? A plug-in portable power station can carry a fridge, router, and phones through a short outage. It is a stopgap, not backup for the house.
What This Means for a Qcells Q.HOME CORE G3
If your quote is for a Qcells G3, check one thing before anything else: the G3 does not back up your home on its own. In its standard Grid Support setup, it shifts solar and off-peak energy for bill savings, and when the grid goes down, so does your power. Backup requires the Q.HOME HUB G3, which disconnects your home from the grid and can also bring in a generator.
Qcells’ own materials describe both outcomes: its product page says “whole home backup,” while its homeowner flyer lists critical loads such as the refrigerator, lights, and internet. Which one you get depends on how the installer wires the HUB, so the circuit list in writing matters more than the marketing. For specs, pricing, and warranty, see our Qcells Q.HOME CORE G3 review.
Six Questions to Get Answered in Writing
- Is this quote for backup, or for bill savings only? If it is a Qcells G3, does it include the Q.HOME HUB G3?
- Partial or whole-home, and which circuits exactly? Ask for a written list, not “essentials.”
- What is the continuous kW and surge rating of the whole system? Can it start my air conditioner (compare with the compressor’s locked rotor amps on its nameplate)?
- What load control is included, and which loads shut off first when the battery is near its limit?
- Does my solar keep producing and recharging the battery during an outage?
- Is a main panel upgrade, meter collar, or other electrical work included, and is it priced separately?
If you are comparing several bids, our guides on how to compare solar quotes and red flags in a solar installation quote cover the rest of the paperwork. If you are still deciding whether a battery is worth it at all, read: Is solar battery storage worth it in 2026, or compare a battery with a generator in solar generators vs home solar systems.
Incentives, briefly: the federal 30% Residential Clean Energy Credit does not apply to batteries placed in service after December 31, 2025, according to the IRS. In California, check the state’s SGIP battery program for what is open to you, and see our 2026 solar incentives guide. This is general information, not tax or financial advice.
Frequently Asked Questions
How many batteries do I need for whole-home backup?
EnergySage puts it at about 30 kWh or more, usually two or three batteries. To run central AC, an electric dryer, and an EV charger together, you also need enough combined kW, or load control that keeps them from overlapping.
Will my solar panels work during an outage?
Only if the battery system can isolate your home from the grid and keep the solar inverters running. A grid-tied system without that shuts off for line-worker safety.
Does the Qcells Q.HOME CORE G3 provide whole-home backup?
Not on its own. Backup requires the Q.HOME HUB G3, and whether that covers selected circuits or the whole panel depends on the installer’s wiring.
Get a Backup Plan, Not Just a Battery Price
Send us a photo of your main electrical panel, your last 12 months of electric bills, and a list of what you need running in an outage. A person on our team (not an instant calculator) will tell you whether partial or whole-home backup fits, how many batteries that takes, which circuits will run, and the full price with model numbers. No hard close. Request your backup estimate or call (818) 650-8010. Curious how that differs from an online quote? Read instant solar quote vs. a human-reviewed estimate.
Sources
- EnergySage: Solar battery backup, what it costs and how to size it (updated August 25, 2026; installed cost ranges, 28.5 kWh daily average, essentials example)
- EnergySage: Best batteries for whole-home backup (updated May 11, 2026; 30 kWh whole-home threshold, Powerwall 3 continuous power)
- U.S. Energy Information Administration: 2024 electricity interruptions (December 1, 2025)
- Qcells: Q.HOME CORE G3 product page and Solar Builder: Qcells goes AC-coupled with the Q.HOME CORE G3 (HUB role in backup)
- Tesla: What does Powerwall back up?
- NREL: PVWatts calculator (solar production by address)
- PG&E: Medical devices and power shutoffs (Medical Baseline notifications)
- IRS: Residential Clean Energy Credit and CPUC: Self-Generation Incentive Program