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Most Commonly Asked Solar Battery questions (FAQs)

1. How long will the solar backup batteries last?

The life of a solar battery depends on the battery technology. Typically, the solar battery’s useful lifespan ranges between 5 to 15 years. If you install a solar battery today, there is a good chance you will need to replace it at least once if you want to match the 25-year lifespan of your solar panel system. However, just as the lifespan of solar panels has increased significantly in the past decade, solar battery technology is starting to see dramatic technological advancements that are improving its life, performance, and value. 

2. What is the most significant factor that impacts battery life?

Temperature. That is why the primary factor that will impact how long your batteries will last is proper storage in a reasonably cool location. The battery’s temperature profoundly affects the lifespan of a solar battery backup, so it is crucial to ensure that the enclosure is maintained correctly, there is proper cooling to reduce heat, and protection from freezing temperatures.

If a solar battery’s temperature drops below 30 degrees Fahrenheit, it will require more voltage to reach maximum charge; when that same battery rises above the 90 degrees Farenheight threshold, it will overheat and require a reduction in charge. To help with this problem, many leading battery manufacturers, like Tesla, LG, and Q Cells provide temperature moderation as a feature. Choosing a quality battery manufacturer and maintenance efforts to ensure proper temperature controls will significantly extend the life of your batteries. 

3. How long can a solar battery power my home? 

It depends on a variety of variables, including how much energy your household consumes in a given day, the capacity and power rating of your solar battery, what loads your battery will help support, and whether or not you are connected to the electrical grid. A battery should be sized to run your home for multiple days, even if your solar panels are not producing energy. Some batteries have the ability to be recharged by your solar panels even if there is a power outage. 

Forme Pro Tip: Ideally, your solar panels should be able to recharge your battery backup even in an outage. But not all solar batteries have this capability.

According to the US Energy Information Administration (EIA), the average US household uses roughly 30 kilowatt-hours (kWh) of energy per day, and a typical solar battery is typically 10 kWh of capacity. Therefore, if you wanted to run your whole home off of your solar battery, you will need at least three (3) batteries to help offset your daily consumption.

But real-life application is a bit more complicated since you will also be generating power for about 6-7 hours during the day during peak sunlight hours to help offset the need to utilize your battery. On the other hand, most batteries systems cannot run at maximum capacity and generally peak at a 90% DoD. For those who own an Electric Vehicle (EV) like a Tesla Model 3 you’ve experienced how your car battery charges up to 90% by default. You shouldn’t charge your solar battery to 100% unless you absolutely must. Long-term, this reduces your battery’s longevity.

As a result, your 10 kWh battery likely has a useful capacity of 9 kWh.

Ultimately, if you are pairing your battery with a solar PV array, one or two batteries can provide sufficient power during the evening when your panels are not producing. However, without a renewable energy solution like solar panels, you may need three batteries or more to power your entire home for 24 hours. Additionally, if you are installing home energy storage in order to disconnect from the electric grid and become off-grid, you should install at least an extra day or two of backup power to account for days where you might have cloudy weather. 

Top Solar Battery Questions You Should Ask

Can I run my house on solar battery backup power only?

Yes. But it would be expensive and depend on your usage, PV generation, and battery.

How much would it cost to run on solar battery only? 

Expensive, and would depend on multiple factors like your consumption, consumption patterns, battery manufacturer, battery type, battery size, solar energy system size, and amount of sunlight.

How do I size my battery system?

30% of daily usage is average 4 to 9 consumption 

What is the max I can run on battery? 

Typically 5KW to 8KW demand loads.

When the grid goes down, will the batteries recharge from solar?

Yes, it can if your battery has an “islanding” capability. 

Can the batteries charge at night? 

No. The solar panels capture sunlight and charge batteries with PV. 

Is a residential ESS (Energy Storage System) safe? 

Yes, technology has made leaps and bounds. But should be appropriately installed, permitted, and meet the NFPA (National Fire Protection Association) code. The biggest concern is thermal runaway. 

Pro Tip: Check out our solar glossary for more help on commonly used solar acronyms.

Can my solar battery be outside?

This is system-specific. For solar batteries that you want to store outside, they should have a NEMA 3R rated enclosure.

What is a priority load panel?

Reduced storage size by running only critical loads