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How Long Can Solar Battery Last in A Blackout?

Unlocking the power of solar energy and saving money on energy bills becomes a reality with a solar home battery. But when the lights go out, can your solar battery still keep your home running? This blog post is here to shed light on how long a solar battery can serve as a reliable backup during an outage. We’ll also introduce you to some of the finest solar batteries on the market today. Whether you’re on the verge of adopting a solar battery system or simply intrigued by their functionality, we invite you to join us on this illuminating journey. Let’s delve into the world of solar batteries together and uncover the brilliance they offer!

How long can a solar battery power a house?

In the absence of air conditioning or electric heating, a 10 kWh solar battery can independently supply essential household functions for a minimum of 24 hours, and even longer with prudent energy management. When combined with solar panels, the battery storage gains the capability to energize additional electrical systems and offer extended backup power.

A recent investigation carried out by the Lawrence Berkeley National Laboratory focused on Photovoltaics and Energy Storage Systems (PVESS) reveals that, excluding heating and cooling needs, a compact PVESS with a mere 10 kWh storage capacity (representative of smaller market sizes) can serve as a complete backup solution during a 3-day outage in nearly all U.S. counties, regardless of the time of year.

However, the specific duration for which solar battery storage can sustain a home varies depending on three primary factors:

  • The capacity of the battery storage.
  • The output efficiency of the solar panel system.
  • The electricity requirements during a power outage.

Below, we will guide you on how to effectively manage your electricity consumption to align with your solar and battery capacities. Let’s begin by determining your battery storage capacity.

Home Battery Capacity

Battery capacity, a critical factor in determining the duration of a house’s power during an outage, refers to the amount of energy a battery can store. Measured in kilowatt-hours (kWh), battery storage capacity can range from as little as 1 kWh to over 10 kWh, with the latter being the typical size for most homes. To enhance energy reserves further, multiple batteries can be combined, offering even greater capacity.

When facing a power outage, a fully charged home battery provides access to the stored energy, typically the full 10 kWh. However, it is essential to reserve a minimum charge of 5-10% to ensure the health of the battery and facilitate the initiation of solar inverters for recharging with solar power each morning.

For instance, a 10 kWh battery should maintain at least 0.5 kWh of capacity in reserve, leaving 9.5 kWh available to power essential electrical systems during an outage. On its own, 9.5 kWh of battery storage can support crucial functions for a day or two. Nevertheless, it is essential to be mindful of higher energy-consuming appliances, such as central air conditioning, which can utilize around 3 kWh per hour and significantly impact battery duration.

To expand the power options during a power outage, pairing the battery with solar panels becomes an ingenious solution. The solar panels can recharge the battery during daylight hours, providing an ongoing renewable energy source to supplement the stored power. This pairing not only extends the duration of power availability but also contributes to a more sustainable and eco-friendly energy ecosystem.

Solar System Output

The synergistic combination of battery storage with solar panels offers a remarkable advantage, akin to creating your very own self-sustaining utility within the confines of your home. This becomes especially valuable during extended power outages, as without battery storage, the local utility typically disconnects solar systems to avoid the risk of backflow electricity harming repair workers and the grid.

However, with the inclusion of battery storage, your solar system gains the ability to operate autonomously during grid failures, a phenomenon known as “islanding.”

When you have a solar system alone, it needs the electric grid to work. But if you add a battery to the solar system, it becomes more independent. Even if there’s a power outage and the grid is down, the solar system with a battery can still keep working and provide power to your home. This ability of the solar system to work on its own during grid failures is called “islanding.”

Now, let’s delve into the electricity production of a solar system. Solar panel systems are rated in kilowatts (kW), representing the energy output they can generate in an hour of peak sunlight. For instance, a 5kW solar system can produce up to 5kWh of electricity per hour under optimal conditions. However, since conditions may not always be ideal, a performance ratio of around 75% is commonly assumed.

A house with solar panels on the roof.
A house with solar panels on the roof.

The United States experiences an average of 3.5 to 5.5 peak sunlight hours per day, depending on the region. To determine the daily output of a solar system, you can multiply its capacity by the sunlight hours and the performance ratio. For example, a 5kW solar system with 4.5 peak sunlight hours per day yields:

5kW solar system x 4.5 sunlight hours per day x 0.75 performance rating = 16.875kWh per day

In many instances, this output is more than sufficient to power essential electrical systems while also replenishing a 10kWh battery for overnight usage. However, electricity needs can vary significantly from one home to another, so it’s crucial to consider individual appliances and their energy consumption levels.

Your Electricity Needs During a Power Outage

The duration for which solar battery storage can power your home is contingent on your electricity consumption, which, in turn, depends on the appliances and systems you use. During a power outage, it is advisable to prioritize essential electricity needs and then plan for the remaining capacity. Common priorities for many homeowners during an outage include the refrigerator, kitchen and cooking appliances, water heating, lights, TV, and device charging, and finally, heating and cooling.

Heating and cooling ranks last on the list not due to its insignificance, but because these operations consume substantial electricity, making it necessary to limit their usage regardless of your battery capacity. The prudent approach is to first budget electricity for essential needs and then assess the available battery capacity for heating and cooling.

Notably, if you have a gas furnace, it won’t require much electricity to maintain heat during an outage, providing a more efficient solution for keeping warm.

To better understand the solar and battery capacity required for essential systems during a 24-hour power outage, let’s explore an example scenario. You can use the tables provided below as a customizable menu to plan your battery storage budget according to your specific needs and priorities. This way, you can ensure optimal usage of your solar energy and battery storage, empowering your home with reliable and sustainable power during unforeseen power interruptions.

Refrigerator: 1.5 kWh per day

MODELDAILY ENERGY USE (KWH)
Older 15-cubic foot unit (1996)5 kWh/day
Newer Energy Star 17-cubic foot unit1.16 kWh /day

A refrigerator is a crucial appliance to power during a power outage to prevent food and drinks from spoiling. The amount of electricity a refrigerator uses can vary based on its age and energy efficiency.

If you have a modern refrigerator with energy star certification, it typically consumes around 1-2 kWh of electricity per day. However, older models, like those from the year 1996, may consume closer to 5 kWh per day.

To minimize refrigerator electricity usage, try to open the door less frequently and consider raising the temperature slightly. If you anticipate a planned power outage, such as a Public Safety Power Shutoff (PSPS), you can set the refrigerator temperature very low before the event. Once the grid power is out, you can adjust the temperature to a higher setting. This ensures that the fridge starts off cold, reducing the battery capacity required to power it during the outage.

Let’s consider an example where you have a relatively modern energy star certified fridge that uses 1.5 kWh per day.

Cumulative energy usage: 1.5 kWh

Kitchen and cooking: 1 kWh per day

APPLIANCEENERGY USE (KWH)
Electric Oven2.3 kWh per hour
Oven (Surface)1 – 1.5 kWh per hour
Microwave Oven0.12 kWh per 5 minutes
Coffee Maker0.12 kWh per brew / 0.4 kWh per hour on warmer
Dishwasher (Energy Saver Cycle)0.5 kWh per load
Toaster0.04 kWh per use

Even when faced with a power outage, people still need to prepare meals. In extensive outages, dining out or ordering delivery might not be feasible.

For instance, let’s consider a typical day where you make a pot of coffee and toast in the morning (0.2 kWh), heat up leftovers in the microwave for lunch (0.12 kWh), and bake a frozen pizza for dinner (0.75 kWh) to clear out the freezer. Altogether, this amounts to just over 1 kWh of electricity consumption throughout the day.

Cumulative energy usage: 2.5 kWh

Electric water heating: 2.5 kWh a day

ApplianceEnergy Use (kWh per day)
Electric Water Heater4-5 kWh (operating for 2-3 hours)
Heat Pump Water Heater (50-75 gallon)Approximately 2.5 kWh per day

Heating water makes up about 18% of the energy used at home, using around 162 kWh every month. On a regular day, the water heater runs for 2 to 3 hours, using about 4-5 kWh of electricity daily. More efficient heat pump water heaters need only about 2.5 kWh per day.

But during power outages, things are different. To save electricity, you might want to take shorter showers, use cold water for washing hands and dishes, and delay doing laundry for a day or two.

If you have a gas-powered water heater, it won’t affect your battery use.

But for now, let’s say you try to use only 2.5 kWh of electricity for water heating.

Cumulative energy usage: 5 kWh

Lights: 1 kWh per day

Bulb TypeEnergy Use (kWh per hour)
CFL/LED (8 W) equivalent to 25 W incandescent0.008 kWh
CFL/LED (15 W) equivalent to 60 W incandescent0.015 kWh
CFL/LED (27 W) equivalent to 100 W incandescent0.027 kWh
CFL/LED (38 W) equivalent to 150 W incandescent0.038 kWh

When compared to larger household appliances, lights consume minimal electricity, especially if you opt for energy-efficient options like compact fluorescent (CFL) or LED bulbs. Even the most power-hungry bulbs, such as a 38W LED or a 150W incandescent, use only 0.038 kWh of electricity per hour.

Considering this, if you allocate 1 kWh of battery storage daily for lighting purposes, you could power up to 26 bulbs for an hour each. This generous capacity would more than suffice to provide ample light for activities like using the bathroom, accessing the closet, and preparing for bedtime.

Remaining battery budget: 6 kWh

With 6 kWh of battery capacity remaining after accounting for lighting needs, you have the opportunity to allocate power for other essential appliances and systems during power outages. It is essential to strike a balance in distributing your available battery storage efficiently to meet the varying electricity requirements of different household functions. By doing so, you ensure a reliable and well-prepared energy supply in case of unexpected electricity disruptions.

TV and device charging: 2 kWh

DeviceEnergy Use (kWh per day/hour)
WiFi Router0.024 kWh per day
Modern TV: LED/OLED 4k or 1080P HDTV0.014 to 0.18 kWh per hour
TV: Plasma0.4 to 0.48 kWh per hour
Desktop Computer0.06 kWh per hour
Laptop Computer0.02 to 0.05 kWh per hour
Tablet0.032 kWh per day

During a power outage, it’s tough to go without internet and TV. You may try reading a book for a while, but the allure of your screens is hard to resist.

To keep your WiFi operational, you’ll need approximately 0.024 kWh. If you’re working from home, using your laptop for 8 hours will require an additional 0.4 kWh. Plus, if you plan to unwind with a movie or indulge in a 3-hour Netflix binge, that will need another 0.54 kWh.

Altogether, this adds up to 1.18 kWh, but let’s round it up to 2 kWh to account for phone charging and the possibility of multiple devices running simultaneously.

With a Remaining battery budget of 8 kWh, you have enough power to sustain these devices and also allocate energy for other essential needs during the outage. It’s essential to manage your electricity usage wisely to ensure you have a reliable source of power and stay comfortable and connected throughout the duration of the power interruption.

Air Heating and Cooling: Variable

ApplianceEnergy Use (kWh per hour)
Heating 
Electric Furnace (with fan)10.5 kWh
Portable Heater1.5 kWh
Baseboard Heater (6-foot unit)1.5 kWh
Cooling 
Window/Wall AC (8k to 18k BTU)0.73 to 1.8 kWh
Central AC (3 ton – 12 SEER)3.0 kWh
Fans 
Pedestal Fan0.03 kWh
Ceiling Fan0.025 to 0.075 kWh

As evident from the table, heating and cooling appliances consume a significant amount of electricity. Without solar panels and only a 10 kWh battery, you’d have approximately 2 kWh available to allocate for running fans or space heaters during a power outage.

However, if you have a battery charged by solar panels, you would have a considerable surplus of electricity to use for fans and space heaters. With this setup, you might even have enough power to run central AC for a few hours, depending on the capacity of your equipment. Having a solar-charged battery significantly enhances your ability to maintain comfort and convenience during power outages, as it allows you to make the most of your stored electricity for essential appliances and systems.

Medical Equipment

DeviceEnergy Use (kWh per hour)
Nebulizer1 kWh
Oxygen Concentrator0.46 kWh
Sleep Apnea Machine (CPAP)0.2 kWh


Another important thing to think about is how to power medical equipment during a power outage. Some devices, like nebulizers, use a lot of electricity and can quickly use up a 10 kWh battery. Making sure that important medical equipment has a steady and dependable power source becomes even more important during emergencies because these devices directly affect the health and well-being of the people who need them. It’s essential to understand how much energy medical equipment requires and plan ahead to ensure it keeps working properly, especially when using battery storage during power outages.

Is Getting a Solar Battery Worth It?

The frequency of weather-related power outages in the US has significantly increased by approximately 78% between 2011 and 2021, making them a growing concern for homeowners. If you value a clean, quiet, and automated backup energy solution that can keep your home powered for several days during outages, then investing in solar panels and battery storage is undoubtedly a worthwhile choice. Not only can the battery keep your home running smoothly, but it can also contribute to the stability of the local grid, as was evident during the events in California in September 2022.

Beyond providing backup power during emergencies, solar and battery systems offer the added benefit of reducing your energy costs. By efficiently managing your power consumption and utilizing electricity during off-peak hours when rates are lower (sometimes up to 20 cents per kWh!), you can significantly save on your monthly energy bills.

Furthermore, adopting solar and battery technology has significant local and global implications, as it aids in reducing the reliance on fossil fuels, which are major contributors to air pollution and climate change.

If you’re interested in understanding how much you can save with solar and battery systems, click here to explore the potential cost savings and benefits. Embracing these sustainable energy solutions not only helps you achieve energy independence but also contributes to a greener and more environmentally conscious future.