How to compare solar battery options

Image via MIT Energy Initiative

The most important specifications are the battery's capacity and power capabilities, depth of discharge (DoD), round-trip efficiency, warranty, and manufacture.

Let's discuss the significance of each of these specifications below.

Capacity and Power

Although capacity indicates how big your battery is, this metric doesn't give you any information about how much electrical power your battery can exert at any given time. For solar batteries, the power rating is a metric indication that exemplifies the amount of electricity a battery can deliver at one given moment, measured in standard kilowatts (kW).

If you choose a battery with a high capacity and a low power rating, you would viably receive a low amount of electricity (sufficient to only power a few electrical products) for a long time. Conversely, if you select a battery with a low capacity and a high power rating, you would receive enormous electrical power, but only for a few hours.

Depth of Discharge (DoD)

Generally, most solar batteries need to retain some of their charge at all times due to their chemical composition. If you simply utilize 100% of your battery's power, it's longevity will be severely shortened.

Essentially, the depth of discharge (DoD) of a battery refers to the amount of the battery's capacity that has been utilized. Many solar battery manufacturers will specify a defined maximum DoD for efficient performance and optimal results.

For instance, a 10 kWh battery possessed a DoD of 80%, you shouldn't utilize more than 8 kWh before recharging the battery. To put it simply, a higher DoD means that you will be able to effectively use more of your battery's capacity. Hence, your battery's DoD is a critical component that determines its overall value.

Round-trip efficiency

A solar battery's round-trip efficiency refers to the amount of energy that can be feasibly used as a standard percentage of the amount of energy that it took to collect it. For instance, if you give five kWh of electricity into your battery and only receive three kWh of useful electricity in return, your battery possesses a 60% round-trip efficiency (3 kWh / 5 kWh = 60%). Generally speaking, a higher round-trip efficiency indicated the economic value and return you will receive from your battery's constant operation.

Battery life and warranty

Understandably, your solar energy battery will charge and drain throughout the day. While this consistent fluctuation is normal, your battery's ability to store more of its charge will gradually decrease the more you use it. In this sense, your solar energy battery is much like the battery in your smartphone. When you first purchase your phone, you can easily charge it to replenish its capacity. However, as the smartphone grows older, you'll start to notice that its battery isn't storing the charge it used to when the phone was new.

Accordingly, your solar battery will come with a warranty that guarantees the battery's longevity in a particular number of years. Because battery performance eventually disintegrates over time, many manufacturers will similarly guarantee that batter will retain a specific amount of its capacity over the course of the warranty. Therefore, the most basic answer to the prevailing question "how long will my battery last?" depends entirely on the brand of battery you purchase and how much of its capacity will it gradually lose over time.

For instance, your battery may be warrantied for 10 years or 5000 cycles at 60% of its initial capacity. This means that at the conclusion of your warranty, the battery will have lost no more than 40% of its energy storing capabilities.


There are various types of organizations designing, developing, and manufacturing solar battery products, from tech startups to automotive companies. Although a primary automotive company entering the preliminary energy storing market might likely have a broader history of manufacturing products, they may not possess the best technology. On the contrary, a tech startup might possess this technology, but may lack manufacturing experience.

Whether you select a produced by a traditional manufacturer or a burgeoning startup depends wholly on your priorities. By evaluating the warranties associated with available solar battery products, you can receive more guidance that's required to make your decision.

How long do solar batteries typically last?

In most cases, a fully charged solar battery can power your business overnight when your solar panels are ineffective. To create a more definite calculation, you'll need to understand a few key variables, including what the capacity and power rating is for your battery, how much energy your commercial establishment consumes in a given day, and whether or not you're connected to an electric grid.

For the sake of brevity, we'll analyze the size of a battery that's required to provide an adequate solar storage system with national data from the United States Information Administration (USIA). The average business uses approximately 45 kWh of energy each day and a typical solar battery can deliver about 10 kWh of standard capacity. Thus, using this information, you could reasonably conclude that about 4 solar energy batteries could power your entire business.

In actuality, the answer is much more complex. Using your battery, you will also be generating strong power throughout the day. As it was aforementioned, most batteries cannot operate at maximum capacity throughout the day, even at peak sunlight hours.

Solar energy system battery duration

The typical lifespan of a solar battery is between 5 and 15 years. Therefore, if you purchase and install a new solar battery today, you'll certainly have to replace it at least once to accommodate the 25 to 30-year lifespan of your solar energy system. Though, just as the lifespan for solar panels has increased in the past decade, there is potential for solar batteries to follow suit.

These batteries are always affected by temperature, so protecting your battery from extreme temperatures and climates can expand its shelf life. When a battery drops below 30° F, more voltage would be necessary to produce a maximum charge. When the battery reaches temperatures above 90° F, it will generally overheat and require a decline in charge. Many battery manufacturers, like Tesla, provide temperature moderation features with their products. Though, if the battery you purchase doesn't possess this feature, you should consider other alternatives such as earth-sheltered enclosures.


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