Case Study: How Does Battery Backup Really Work? How One Family Stayed Comfortable Thanks to Their Solar Battery System

Location: Southeast Queensland
System: Fronius Three-Phase Inverter + BYD Battery (44.16kWh storage)
Duration of Grid Outage: 7 days
How does battery backup really work : Zero disruption, total energy independence (because it was designed correctly)

How Does Battery Backup Really Work?

Introduction: When the Storm Hit

Imagine the lights flickering, then total darkness. A sudden storm swept through the area one evening, cutting off grid power at 8:45 PM. Most homes in the neighborhood went dark—but not this one.

Thanks to a well-designed solar and battery system, the family inside this home never missed a beat.

In this case study, we’ll show you what really happens when your battery system is prepared for a blackout—and how it kept this household powered for 7 straight days, through stormy skies, cloudy days, and full energy needs.

Day 1: The Unexpected Cut. How does battery backup really work after the power cuts

Power Cut: 8:45 PM
Battery Status: Just above minimum charge (5%)

When the grid failed, the battery was close to its programmed reserve limit. But even with the unexpected timing, the backup functionality kicked in immediately.

“The lights didn’t even flicker. Everything just kept working.”

how does battery backup really work? Charts display real time data — Grid power cut out at 8:45pm, which also was only a few minutes before the battery was about to reach the minimum state of charge – 5% in this case.

Shows backup mode activation just before hitting 5% minimum charge.

Day 2: Blackstart and Total Recovery

Thanks to the blackstart feature, the system powered up independently at 6:58 AM. The morning sun recharged the battery and covered household needs throughout the day.

Battery Recharged: Fully by 1:30 PM
Solar Generated: 56.38 kWh
Outcome: Full coverage for all household needs, including battery top-up.

chart withour grid power — As this system is able to blackstart, the system began generating power at 6:58am once the battery started to charge. This provided the home with 56.38kWh for the day to run all necessary loads and fill the battery, shown with the green line with the battery reaching 100% state of charge around 1:30pm. You can see how the battery can cover essential loads through the night.

Green line shows solar charging and battery reaching 100%. Chart displays how battery backup really works in real life.

Day 3: Full Power, Zero Sacrifice

Despite being off-grid, the family didn’t need to limit their lifestyle. They used high-draw appliances as needed—including a 9kW spike around 9:30 AM.

Overnight Battery Drop: Only to 77%
Mid-morning Peak Demand: ~9kW
Outcome: The system didn’t just survive—it thrived.

charts who how Does Battery Backup Really Works — With careful consumption overnight the battery only discharged to 77%, the customer continued to consume power as they wished through the day as you can see their highest power draw around 9:30am exceeded 9kW.

Peak energy usage and battery stability shown clearly.

Day 4: Still No Grid, Still Fully Powered

It was business as usual at home. Power consumption remained high in parts of the day, but solar again delivered a full recharge.

Battery Status: Reached 100% again
Lifestyle Impact: None

Steady solar input and consumption visible.

Day 5: Smooth Sailing

Consumption patterns were nearly identical to the day before, and the battery handled it effortlessly. A steady morning curve shows the perfect blend of solar generation and energy usage. By now you can start seeing how battery backup really works with a well designed solar and battery system.

Morning load smoothing and battery charging curve.

Day 6: Cloudy Skies, No Worries

This day brought the lowest solar generation due to poor weather—but because the household used slightly less energy, the system still met demand comfortably.

Weather: Overcast
Battery Status: Still sufficient
Outcome: Even without full sun, there was no power interruption.

Low solar generation but minimal consumption balance.

Day 7: Grid Power Returns… But Wasn’t Missed. This is how battery backup really works… when done right.

At 4:50 PM, grid power came back online. The system exited backup mode without drama—but after a full week of energy independence, the grid felt like a backup.

“We didn’t just survive the blackout. We lived normally—TV, Wi-Fi, cooking, even A/C on sunny days.”

Grid reconnection timestamped and smooth transition shown.

Key Takeaways: What This Case Proves

Blackstart Capability Matters

The system didn’t need the grid to reboot. It powered itself up from nothing.

Proper Sizing = Resilience

With 44.16kWh of storage and a quality solar setup, the system met every need—even high usage.

Real-World Reliability

This isn’t theory. This is a real household that went completely off-grid for a week without compromise.

Smart Energy Management

With slight behavior tweaks on cloudy days, the family stayed powered and comfortable. BYD offer a great solution for this scenario.

How Other Battery Brands Really Work In A Blackout

So, how does battery backup really work with other brands? Not all solar batteries behave the same when the grid goes down. Some offer full-home backup with advanced features like blackstart and app notifications. Others offer partial support or require very specific configurations to keep your home powered.

Here’s how the most common battery systems on the market stack up in a blackout scenario:

Sigenergy: Smart, Seamless, and Fully Three-Phase Capable

With a Sigen Gateway, Sigenergy offers instant full-home backup, even for three-phase properties. You’ll receive a notification through the My Sigen app when backup mode activates, so you can monitor energy use if the outage drags on.

✅ Full backup for single and three-phase homes
⚡ Instant blackstart
App notification lets you stay in control
Day-after-day support with solar recharging

SigenStor_5-in-1

Tesla Powerwall: Well-Known, with a Key Limitation for Three-Phase

The Tesla Powerwall supports instant full-home backup for single-phase homes. For three-phase setups, it only backs up one phase, and cannot blackstart after a full discharge—solar won’t restart until the grid returns.

✅ Strong for single-phase homes
⚠️ Limited to one phase on three-phase setups
❌ No blackstart for three-phase
One full discharge cycle per outage

how does battery backup really work with tesla?

Sungrow: Flexible, but Needs the Right Setup

Sungrow systems can be tailored to back up either essential loads or your whole home—depending on your inverter and battery choice. It’s a powerful solution with the right design, but not all systems offer full backup or blackstart by default.

✅ Essential or whole-home backup (customizable)
⚙️ Requires proper system design
⚡ Some models support blackstart
️ Best discussed with an expert to get it right

Alpha ESS: Reliable for Essentials, with Custom Design Needed

Alpha ESS systems typically offer backup to essential loads rather than full-home coverage. Blackstart is supported in some models, but like Sungrow, the system must be designed specifically for this functionality.

✅ Backup for essentials
⚠️ Full-home backup depends on system specs
⚡ Blackstart possible with the right model
Needs proper system configuration

LG Chem: Paired Backup Through Inverter Partner (Not always compatible with older installs)

LG Chem batteries don’t manage blackout backup themselves—they rely on the inverter brand they’re paired with (like Sungrow) to enable backup functionality. Depending on that pairing, the system may support essential circuits or full-home backup, but blackstart is often not supported.

✅ Backup possible (varies by inverter)
⚠️ No native blackstart capability
Backup performance depends on system design
️ Great battery, but not a standalone solution for outages

how does battery backup really work with LG?

Fox ESS: Good Backup Potential, But Must Be Properly Designed., Unknown reliability

Fox ESS systems can deliver backup power either to essential loads or the whole home, but the outcome heavily depends on the right combination of inverter, battery, and switchboard setup. Some models support blackstart, but not all.

✅ Backup to essentials or full-home
⚠️ Blackstart only in some configurations
System design is key to performance
Best to consult with a knowledgeable installer

Growatt: Backup Capable, But Basic

How does battery backup really work with Growatt? Growatt batteries can support essential circuits during an outage, but blackstart is typically not available. It’s a cost-effective solution, but not ideal if you’re looking for multi-day, self-recovering backup functionality.

✅ Basic backup for essentials
❌ No blackstart on most models
⚙️ Budget-friendly but limited in prolonged outages
⚠️ Not suited for full-home resilience

Enphase: Modular, Smart, and Growing in Backup Capabilities

Enphase IQ Batteries provide modular backup, often to essential loads only. They shine in smaller applications and are highly efficient, but for now, their ability to support whole-home or long-term backup is limited unless heavily scaled. Blackstart is supported in newer setups.