Battery Backup
How Long Does a Home Battery Last During a Power Outage?
If you are considering solar for your Virginia home, you may also be wondering what happens when the power goes out. Here is what battery backup can actually do, and how to determine what your home would need.
Earth Right | Battery Backup | 7 min read
13.5 kWh
Usable capacity of a Tesla Powerwall 3
~9 hrs
Average major-event outage duration in 2024, per EIA
24+ hrs
Possible runtime on essential loads with a single battery
The Problem
Virginia Homeowners Need Power When the Grid Goes Down
A whole-home battery can keep your home’s electrical system running during a power outage. The amount of time it can do that depends on how much electricity your home is using and how much battery storage you have.
The basic: refrigerator, lights, internet, a few outlets, do not use much power. Running them off a battery for 12 to 24 hours is realistic for most Virginia homes. Keeping the HVAC and major appliances going requires more capacity, so sizing the system around how your home actually uses electricity, is more important than any number on a spec sheet.
How It Works
What Happens When the Power Goes Out
When the utility grid goes down, a properly installed battery backup system can automatically take over. You do not have to move extension cords around the house or decide which appliance gets plugged in. The battery connects to the home’s electrical system and supplies power to the circuits it was designed to back up.
From inside the house, the transition can be seamless.
How long the battery lasts from there depends on what is running. If the home is using very little electricity, the stored energy can last much longer. If the air conditioner, electric water heater, oven, and other high-demand equipment are running at the same time, the battery will use its stored energy much faster. That gives homeowners some control over how long their backup power lasts.
Runtime
How Long a Home Battery Can Actually Last
A typical home battery stores around 10 to 15 kilowatt-hours of energy. The Tesla Powerwall 3, for example, has a usable capacity of 13.5 kWh. That does not mean every Powerwall lasts the same number of hours in every home.
Think about it the same way you would think about fuel in a car. A vehicle traveling on the highway uses fuel differently than one sitting in traffic. A battery works the same way. The amount of electricity your home is drawing determines how quickly the stored energy is used.
A home running the refrigerator, internet, lights, and a few outlets may stay powered for many hours or more than a day. A home running central air conditioning and several electric appliances will use that same stored energy much faster.
13.5 kWh
For most homeowners, the useful question is not whether a battery lasts a certain number of hours. It is whether the system is sized to keep the parts of the home they care about running for the length of outage they are planning for.
System Design
Can a Battery Run the Entire House
It can, but with the right system. There is an important distinction between having enough energy stored and having enough power available at one time.
Your refrigerator, lights, outlets, and Wi-Fi equipment do not require much power compared with an air conditioner or electric water heater. Large equipment can place a much greater demand on the battery. That is why a whole-home system may use multiple batteries.
Adding battery capacity gives the home more stored energy to draw from. Adding battery units can also provide greater power output, which matters when several large electrical loads need to operate at once.
A smaller, efficient home may be well served by one battery. A larger Virginia home with central air, a well pump, electric appliances, and other significant loads may need two or more. An assessment can determine that before you make the investment.
Solar and Storage
How Solar Can Keep the Battery Going
This is one of the biggest advantages of combining solar and battery storage. A standard grid-connected solar system normally shuts down when the utility power goes out. That protects utility workers who may be working on the lines.
When solar is paired with a properly configured battery system, your home can disconnect from the utility grid while continuing to use your solar panels. During the day, solar can power the home and recharge the battery. The stored energy can then be used after the sun goes down.
Storm Watch Features: Many modern battery systems can monitor weather alerts and automatically charge to full capacity before severe weather arrives. That means more stored energy is available before an outage even begins.
A battery gives you stored energy when the grid is unavailable. Solar gives the system a way to produce more energy while the sun is available. For Virginia homeowners preparing for outages that could last beyond a single evening, that combination can provide significantly more backup capability than a battery operating on stored energy alone.
Energy Management
What Uses the Most Battery Power
The equipment that heats, cools, or moves a lot of air or water generally uses the most electricity. Central air conditioning is a good example. During a Virginia summer outage, keeping the house comfortable can use substantially more energy than keeping the refrigerator and lights running.
Electric water heaters, ovens, clothes dryers, space heaters, and well pumps can also draw considerable power. That does not mean you have to shut everything down during an outage. A properly sized system can be designed around these loads, and smart energy management can help prioritize what runs and when.
3,000+
Where to Start
A Practical Sequence for Virginia Homeowners
Review Your Home's Electricity Use
Pull your electric bills from the past 12 months and look at your highest-use months. Identifying which appliances and systems drive the most consumption gives you a real baseline for sizing rather than a generic estimate.
Decide What Needs to Stay On
Make a short list of non-negotiables during an outage: refrigeration, medical equipment, well pump, internet, lighting, HVAC. Separating essential from non-essential loads is the most important step in sizing a backup system correctly.
Think About How Long You Need Coverage
In Central Virginia, most weather-related outages resolve within a day. If you are in a rural area where restoration takes longer, that changes the capacity calculation. Your backup goal should match your actual risk, not a worst-case assumption.
Consider Whether Solar Is Part of the Plan
If you already have solar, or are considering it, a paired system extends your effective backup window significantly. A battery alone relies entirely on stored energy. A battery with solar can recharge each day as long as sunlight is available.
Get an Assessment Before Selecting a System
Battery systems are not one-size-fits-all. A system well-suited to one home may be undersized or oversized for another. A review of your actual usage and backup goals will point to the right capacity and configuration for your specific home.
Common Questions
Frequently Asked Questions
How long does a Tesla Powerwall last during an outage?
A Tesla Powerwall 3 stores 13.5 kWh of usable energy. How long that lasts depends on what the home is using. A home running essential loads can get significantly more time from the battery than a home running several high-demand appliances at once.
Can a Home Battery Run the Entire House?
Yes. Whole-home backup systems can be designed to support major electrical loads including HVAC and appliances. Larger homes or homes with higher electrical demand may require multiple batteries to handle the combined load.
Can Solar Recharge My Battery During an Outage?
Yes, when the solar and battery systems are designed for backup operation together. The battery isolates the home from the utility grid, allowing the solar system to continue producing electricity and recharge the battery during daylight hours.
What Drains a Battery the Fastest?
High-demand equipment including central air conditioning, electric water heaters, ovens, dryers, space heaters, and well pumps use stored energy quickly. How much they affect runtime depends on how often they run during the outage.
How Many Batteries Does My Home Need?
Is Battery Storage Worth Adding to Solar?
Find Out What Your Home Actually Needs
Earth Right provides home energy assessments, solar, battery backup, attic solutions, and roofing services across Virginia. A conversation with our team starts with your home, not a sales pitch.
Call us at 434.661.5656 or email info@erepower.com