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How Long Will A Whole-Home Battery Last During A Grid Outage?

How long will my battery last in the event of an outage?

This commonly asked question depends on a variety of factors. Typically, whole-home battery backup systems are designed to provide power that lasts a single household throughout the night, or when solar panels aren’t producing enough energy during the day. According to U.S. Energy Information Administration (EIA), US households consume a daily average of 28.9 kilowatt-hours (kWh) of electricity. Therefore, a single whole-home backup battery system, with a full charge of 13.5 kWh of energy storage, will usually last between 8 to 12 hours for a typical US household during a grid outage. However, the battery system’s backup purpose and energy storage capacity will essentially be determining factors for how long a battery will last. It’s recommended to have a complete energy survey with an analysis of the home’s electrical usage to accurately assess the power backup needs. 

How to Expect Battery Backup Duration

Battery systems designed with larger storage capacities will offer extended time for backup power. Whole-home battery systems need to be designed large enough to cover higher consumption from electrical loads such as AC units or pool pumps. These power-hungry appliances will use stored backup energy quickly. This is a major factor to consider for circuits connected to the backed-up electric breaker panel. Home backup power durations will vary greatly by the energy consumed. For example, electrical circuits with lower power requirements will draw less energy from the battery, thereby lessening the usage of stored energy. This directly correlates to how quickly the battery’s stored energy depletes over time. 

Mitigating & Extending Backup Power Durations 

Solar panels can recharge batteries while also offsetting energy usage from both the grid and batteries. Produced solar energy prolongs off-grid power time by recharging batteries during the day with excess energy not used by the house or sent to the grid. Replenishing batteries from solar panels will also vary depending on factors that affect energy production, such as shading and the surrounding environment. Overall, these combinations of variables determine how long the battery will last. 

Know Exactly How Long The Battery Will Last

Today, modern battery systems can conveniently display information through internet-connected smartphone apps. These smartphone apps provide users with real-time detailed information about battery status, solar energy production, and home electricity consumption. Apps from manufacturers such as the SPAN, Tesla, and FranklinWH help users comprehend energy usage during a grid outage. The SPAN smart electric panel allows users to manage their energy usage in greater detail than previously possible. Users of the SPAN smart panel can prioritize energy for certain home circuits to prolong backup power duration during an outage. Thereby offering an ultimate tool for optimizing battery backup duration efficiency and performance.  Energy storage systems like the Tesla Powerwall 2 and FranklinWH aPower, allow users to configure battery settings in their respective apps. The apps show users how power flow reacts when changes are made to the batteries’ settings. This enables them to fine-tune how stored energy is distributed for particular scenarios or applications. 

Another helpful feature of these apps is “Storm Watch” mode. This feature is great for automatically preparing batteries for a potential grid outage caused by severe weather. Systems are connected to a weather service via the internet, and when activated, prioritize fully charging the batteries from the grid. Having a fully charged battery before a grid outage is an ideal practice, as it ensures maximum power longevity. Without this feature enabled, the battery’s state of charge will be whatever it is when the grid goes out. So if the grid goes out and the battery is at a 30% charge level, then it is to be expected that the battery will not last as long as if it were at 90% before the grid outage. These apps from the manufacturers also show an estimated time for how long the battery will last. Estimates are based on its state of charge and active electrical loads being powered during an outage. 

State of Charge vs Fuel Capacity 

Consider the power use applications, when deciding to go with either a whole-home battery backup or a gas/diesel generator. Whole-home fossil fuel generators are typically designed to power large electrical loads when there is a grid outage. These generators require a substantial-sized fuel tank to power large electrical load appliances simultaneously. Generators are a preferable option for users that want to power large appliances/circuits but aren’t concerned with their energy usage. Keep in mind though, that generator options have higher costs associated with operating daily and maintenance of mechanical parts and are EXTREMELY LOUD when in operation. The fuel tank will only provide fuel for so long until its capacity runs dry. Converting combustion fuel to electricity isn’t efficient as an option not requiring combustion to generate energy, and can be subject to performance reliability. With battery backup options paired with solar panels, users are able to “refuel” their batteries’ “fuel tank” daily whenever the sun is shining. This is a huge advantage over traditional combustion generators. As a result, solar paired with batteries is more reliable as it provides energy independence more efficiently than other options are capable of. Energy storage systems paired with solar panels help ensure that the home is self-sustaining during an outage and that its inhabitants have peace of mind knowing their power is secure.