Northwest homeowners primarily install a Tesla Powerwall battery backup system to power their homes in the event of an outage.
While power outages have increased in recent years due to more severe weather-related events and outdated utility infrastructure, homeowners and businesses can turn to solar plus a Tesla home battery to keep the lights stay on when the grid goes down.
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Can solar panels power a house during a power outage?
It’s important to remember that your solar panels alone will not power your home in the event of a power outage unless you have a home battery backup system installed, like the Tesla home battery. This is by design to prevent energy from being sent to the grid where line workers are trying to restore power. Line workers cannot safely restore power to the grid if a home’s solar panel is actively supplying energy to the grid via net metering.
How does a Tesla battery backup work in a power outage?
A storm rolls through a neighborhood knocking out power. Homes go dark. The sound of the whistling wind is replaced by the incessant rumble of a few gas-powered generators. In some windows, the faint flickering of candles can be seen. However, for a homeowner with Tesla Powerwall, life goes on exactly as before.
As soon as a power outage occurs, your Tesla Backup Gateway instantly disconnects from the utility grid and Powerwalls delivers power to your home in a fraction of a second. In fact, the switch is so instantaneous that you might not even know you lost power. A quick glance at your monitoring system indicates the Powerwall is supplying your home with energy. Appliances, lights, internet, and TV can continue uninterrupted.
Before your Tesla battery backup system is installed, you’ll have to make some important decisions.
Budget, for one. The more Powerwalls you stack (you can have up to 10), the more of your home you’ll be able to back up.
You will often be able to decide what loads you’ll want to be backed up. Your fridge. Lights. Internet. The more that you choose to back up, the more Powerwalls you’ll need and the more energy you’ll consume.
Your Tesla Powerwall certified installer will separate these loads so that only these will draw on your Powerwalls during an outage. The rest of your home will remain without power.
How long does Tesla battery backup last in a power outage depends on your energy usage, the size of your solar energy system, and what time of year it is. As you might have guessed, an outage during a long, sunny Northwest summer day means that the solar panels will be producing much more energy than during a winter storm.
How many Powerwalls do I need?
The number of Tesla Powerwall 3s you need to power your home during a power outage depends on three main factors: your home’s daily energy usage, the devices you want to keep running, and the outage duration.
Step 1: Understand Your Energy Usage
Most homes in the U.S. use about 30 kWh (kilowatt-hours) of electricity daily. However, during an outage, you’ll likely focus on powering essential devices—like refrigerators, lights, and internet—which typically require around 10-15 kWh daily.
Step 2: Powerwall 3 Capacity
The Tesla Powerwall 3 has a usable capacity of 13.5 kWh. This means one Powerwall can power a home’s essentials for about one day under normal circumstances. If your energy needs are higher or you want to run more appliances (like heating systems or electric stoves), you may require multiple Powerwalls.
Step 3: Examples
Small Home or Critical Circuits Only: If you’re only running essential devices like lights, a refrigerator, and a Wi-Fi router (10-12 kWh/day), one Powerwall 3 will suffice for about a day without recharging.
Average Home Usage: For a home consuming 30 kWh daily, two to three Powerwalls are recommended to cover a full day, depending on whether solar panels can recharge the batteries.
Extended Outages: If you want backup for multiple days or whole-home coverage, consider adding three or more Powerwalls, especially if there’s no solar power to recharge them.
Step 4: Solar Integration
If you have solar panels, they can recharge the Powerwalls during the day, reducing the number of batteries needed. For example, a 9kW solar system can produce around 20-30 kWh per day in good sunlight, which could fully recharge two Powerwalls, extending your backup power indefinitely.
How long will the Powerwall 3 last in a power outage?
To determine how long your Powerwall battery storage system will last in a power outage, it’s important to understand your home’s energy consumption.
The average daily energy consumption of a home in Washington and Oregon can vary based on home size, energy efficiency, and household habits. However, here are some averages:
Washington Home Energy Consumption | Oregon Home Energy Consumption |
~12,000 kWh per year | ~10,500 kWh per year |
~33 kWh per day | ~29 kWh per day |
Key Assumptions
Tesla Powerwall 3 Capacity: The Tesla Powerwall 3 has a usable capacity of approximately 13.5 kWh.
⇨ Daily Solar Output: In Washington during winter, solar panels typically produce 2-3 hours of peak sunlight per day. For a 9kW system: Daily winter output = 9 kW × 2.5 hours = 22.5 kWh /day (average)
⇨ Home’s Daily Energy Usage: Let’s assume the average winter consumption for the home is 30 kWh/day (above-average due to heating needs).
⇨ Critical Circuits: During an outage, homeowners typically power only essential systems (e.g., refrigerator, lights, Wi-Fi, and heating). Assume the critical energy demand is 15 kWh/day.
Scenarios
1. No Sunlight During the Outage (Battery Only):
If the storm completely blocks sunlight (e.g., heavy snow on panels or overcast skies), the Powerwall 3’s 13.5 kWh capacity will cover:
⇨ Backup duration = Battery capacity / Critical load = 13.5 kWh /15 kWh/day≈0.9 days
⇨ Result: The Powerwall will power essential systems for approximately 21-22 hours without solar input.
2. Limited Solar Production During the Outage:
If the storm allows some sunlight (e.g., 2.5 hours of peak sunlight per day):
⇨ Daily solar production = 22.5 kWh.
⇨ Assuming the homeowner uses 15 kWh/day for critical loads, there is an excess of 7.5 kWh/day.
⇨ This excess can recharge the Powerwall partially or fully, depending on the storm’s duration and intensity.
Duration:
⇨ Each day, the Powerwall can contribute 13.5 kWh, while the solar system offsets the daily energy consumption with 22.5 kWh.
⇨ The system can theoretically maintain the home indefinitely, provided the panels receive enough sunlight daily to cover loads and recharge the battery.
3. Worst-Case: Intermittent Solar Production:
If solar panels produce only 10 kWh/day due to heavy snow or overcast skies:
⇨ Total energy available = 13.5 kWh (Powerwall) + 10 kWh (solar) = 23.5 kWh/day.
⇨ Critical circuits = 15 kWh/day energy consumption.
⇨ Excess energy = 23.5kWh − 15kWh = 8.5 kWh, used to recharge the battery.
⇨ The system can still last multiple days, as solar and battery energy work together to offset critical circuits.
Key Takeaways
⇨ No sunlight: ~21-22 hours of backup power from the Tesla Powerwall 3 alone.
⇨ Moderate sunlight (2.5 peak hours/day): Given the solar offset and battery recharge capabilities, the system could sustain essential loads indefinitely.
⇨ Severe overcast/snow limiting production: The system can last 2-3 days or more, depending on conditions and energy conservation.
Tesla home battery low energy operations
While in standby mode, and paired with a solar energy system, Powerwall will automatically attempt to recharge from your solar system every hour between 8 AM and 4 PM local time. However, if your solar system can provide sufficient energy to charge your Powerwall and your home, then recharging from your solar system will continue. If for some reason your Powerwall’s remaining energy decreases by more than 2.5%, then it will become inactive and wait for the next hour to attempt charging again.