How long can my solar battery bank power my home?

A battery bank is a great addition to a solar energy system. Having a backup source of energy to avoid drawing from the grid, or during an emergency is both helpful and economical. Battery banks come in many shapes and sizes, along with different features. What’s more important is its ability to keep your home powered and the amount of power it can provide. While there isn’t a clear and easy answer, there is a way for you to work out how long your battery bank can power your home.

Understanding household power usage

The way your household is wired and consumes power will help you figure out the answer you are looking for. Households in the US have either a 120 volt or 240-volt electrical panel. Your electrical panels will consist of circuits to which your appliances are all connected. These circuits cover different parts of your home from your main electrical panel. 

What’s important is to know how much power your appliances consume, and which circuits they are connected to. While this is a hassle, it is an important step when figuring out a battery bank’s capability. As it is highly unlikely that a solar battery bank can fully power a home for days on end unless it is specifically built to do so. When installing a solar + storage system, we would carefully examine a household’s electricity usage, appliances, and home circuitry to appropriately configure a system.

While taking the time to count the electricity usage of every single device is tedious, there are resources to help you figure out the energy usage of your household appliances. The Home Energy Saver and ENERGY STAR both have lists including their estimated wattage usage and annual energy use in kWh/year. If you’re not able to find the information for your appliances online, all you would need to do is find the wattage of your product, and a rough estimate of the hours it runs per day. You might need to do some additional calculations, as some appliances will show their amp and voltage usage rather than their wattage. In that case, you can multiply the current draw in amps, by the voltage it uses (whether it’s 120 or 240 volts). Once you have mapped out the rough energy usage of your home, you will have an idea of the amount of power your home uses and how much of it your battery bank can cover.

How a battery bank powers a home

Battery banks can seem basic and straightforward at a glance. Although they are made to be able to support homes and their appliances draw power. Not all appliances draw power at a constant rate, some require a surge of power before settling down. These differences in power draw are important as they are also metrics used to measure the performance of a battery. 

Instantaneous power is the amount of energy the battery bank can provide over a short period (roughly 3 – 30 seconds). This normally happens with appliances like water pumps, blenders, and vacuum cleaners. Sometimes it’s referred to as the maximum power of the unit. It is worth noting that your maximum can also be limited by your solar energy system’s inverter. Continuous power is the amount of power that your solar energy system can provide during normal conditions in kilowatts. This would be with devices that draw a constant amount of energy, like a lightbulb or a charger.

When you’re looking at these metrics for a battery bank, you will then be able to look at your home’s appliance usage and work out exactly how much your battery bank can feasibly support. You will also be able to map out which circuits or appliances you will want your battery bank to prioritize over others.

What affects a battery bank’s ability to power my home?

Different factors determine how long a battery bank can power your home.

Your solar energy system

Your solar energy system will be a big factor in making the most out of your battery bank. Your solar energy will also charge your batteries as long as there is sunlight. This will give you added resilience during grid outages, especially during the day when your panels can provide power to your home. This will make it easier for you to determine what appliances and/or circuits are supported by your battery bank.

Your battery bank’s capacity

Knowing how much usable storage capacity your battery bank has will allow you to figure out how much energy you have available and for how long. Storage capacity is listed in kilowatt-hours (kWh) as it’s a measure of electrical power over time. You can then figure out how much wattage you can use over an amount of time. Like with any battery, the more power is used, the shorter the duration. To give an example, a battery bank with 12 kWh of usable storage can provide 4 kW of power over 3 hours, or 2 kW of power for 6 hours.

The appliances in your home

The appliances you use in your home will also factor into how long your battery will last. If you take the time to examine and note down the appliances around your home and how long they run, you will also be able to break down how long you can run certain appliances. With that, you can begin to make a list of which appliances you want the battery to support and which ones are a priority.

It is also worth noting that load management devices can also help you make the most out of your stored energy. Critical load panels are one way, as they act as a secondary electrical panel with fewer circuits that are made for battery power. Although load management devices are a step up in that they come with software to manage and safely run the batteries. This would avoid any risk of electrical damage and avoid the need for critical load panels and excess wiring work.

Calculating how long your battery can power your home

For example, if you have a battery bank with about 7 kW of continuous power. You want to power your refrigerator, washing machine, phone chargers, your internet router, the lights, the TV, and your microwave. You’d most likely have more than enough power to keep these appliances going for hours. Although the real challenge will be with climate control like a thermostat or AC unit. Climate controlling appliances draw much more power, between 3 – 5 kW depending on their type and use. Will also need to plan for how many of these devices you use each day.

If your electrical panel, inverter, or battery bank comes with an app, it would be best to check your power usage through there and determine if any changes need to be made to the devices running. Batter apps will even give you an estimate of the amount of time remaining based on the power usage. Even with battery power, it would be ideal to save power wherever possible. Reducing electricity usage can also save on your battery power and make the most out of your battery bank.

A quality solar panel system for you

If you are looking to start your transition to solar energy, we are here to help. Our website also has a free online estimate tool that generates a personalized report for you from a simplified questionnaire. That report will contain the potential savings you can net, and the cost of a solar energy system installed on your property. You can also contact us directly via phone at +1 (602) 363-8919 or via email at Scott@elitesolarenergy.org for more information regarding solar energy for your property.