If you’re considering going solar, the battery system you choose is just as vital as your solar panels. In your research, you may have come across the term “deep-cycle battery” and wondered if it’s a good fit for your solar setup.
So, can you use deep-cycle batteries for solar power? Deep-cycle batteries are ideal for solar power applications. They are designed to repeatedly discharge a large part of their charge over a long time before needing to be recharged. They are also durable, standing up to most weather and temperature extremes and allowing for a cycling lifespan of 10-20 years if properly maintained.
A battery bank is essential for off-grid houses to carry through the night when there’s no sunlight to produce electricity, so finding the right one is a decision with a daily impact on your life.
Considering all the stresses placed on a home-powering battery system, only one type of battery is best suited for the task: the deep-cycle battery. Read on to learn more about what makes deep-cycle batteries well-suited for solar applications.
What is a Deep-Cycle Battery?
What does “deep-cycle” even mean?
Deep-cycle as a battery descriptor is in contrast to shallow-cycle. These terms describe how much of the battery’s charge can be discharged before it needs recharging, and this charge-use-recharge pattern is called the “cycle”.
A shallow-cycle battery uses very little of its initial capacity before recharging – as little as 10%-15%. Meaning the battery is designed to function at an 85%-100% state of charge nearly all the time. If you discharge more than this regularly, you can cause damage and drastically reduce the battery’s usable lifespan. They also do not discharge their energy for very long periods and do not have a high cycle count before reaching their life’s end.
Car batteries are an example of a shallow cycle. Shallow cycle batteries specialize in short, high current bursts of energy (only about 10 seconds in length) to provide power to the starter. After the short burst, their job is complete, and the alternator slowly recharges them.
On the other hand, deep-cycle batteries discharge much more of their charge, up to 80%-100%, before recharging (though habitually using more than 80% capacity before recharging will cause damage). They can also provide this discharge for a more extended period, with 20 hours being the typical rating.
Deep cycle batteries are much more durable, allowing for a significantly longer cycle lifespan.
Deep-Cycle Use with Solar Power
Because of this extended, deep discharge and high durability, deep-cycle batteries are the choice for off-grid or hybrid home solar systems (and even perform well with solar vehicle systems).
Solar panels don’t produce much electricity outside their peak sun hours (which only last 4-7 hours a day), and none at night. That means a home’s battery system has to be capable of providing power for 17-20 hours a day.
The long discharge time and high use capacity of deep-cycle batteries are well-suited for this, and their functional lifespan of 5-20 years gives them the longevity needed for such an investment. Furthermore, their robust construction allows for good, year-round use in a wide range of temperature conditions.
3 Types of Deep-Cycle Battery for Solar Application
As with any technology, there isn’t simply one model of deep-cycle battery available. Though there are quite a few different varieties, three main deep cycle battery types are best for solarized contexts.
1. Flooded Lead-Acid Battery
The flooded lead-acid battery (FLA) is the oldest and cheapest deep-cycle variant. It’s the kind of battery that most people were introduced to in middle school science class.
FLA batteries operate by suspending two differently charged lead nodes (an anode and a cathode) in a vat of electrolyte liquid, usually a mix of concentrated sulfuric acid and water.
It is durable and reliable, tolerant of overcharging, and can deliver high currents. For these reasons (plus the cheap cost), it has proven popular amongst many solar enthusiasts. However, it does have some drawbacks.
It has a lower cycle life than the others, a typical usable capacity of only 30%-50%, and a charge efficiency of only 75%-80%. It also requires more regular maintenance to top off the electrolyte liquid and must be kept upright to avoid spillage of the loose liquid.
2. Valve-Regulated Lead-Acid Battery
The valve-regulated lead-acid battery (VRLA), is a more advanced version of the FLA.
The VRLA uses a thicker electrolyte liquid than the free-flowing one used in the FLA, and the liquid in the VRLA is sealed to avoid leaks. It requires less maintenance than the FLA, has, a much higher usable capacity of up to 60%-80%, a charge efficiency of 85%-95%, and a longer lifespan.
VRLAs are more expensive than FLAs and are more susceptible to damage from overcharging.
3. Lithium-Ion Batteries
Lithium-ion batteries are well-known for their applications in personal electronic devices and more recent uses in electric vehicles. But they’re also practical as deep-cycle batteries for solar home use.
Instead of suspending the anode and cathode in a liquid (free-flowing or gelled), lithium-ion batteries use a bath of lithium salts for their electrolyte-conducting material. This approach allows them to be much smaller and more compact than lead-acid batteries, amongst other advantages.
Lithium-ion batteries have a significantly longer lifespan (2000-5000 cycles compared to the around 500 of a lead-acid battery), a usable capacity of 80%-100%, and a charge efficiency of 99%. Also, they can charge up to five times faster than their lead-acid counterparts and have very little energy loss to low temperatures.
On the other hand, they do have some pretty well-known downsides. Lithium ions are the most expensive option for a deep-cycle battery, and trying to charge them at cold temperatures is famously frustrating.
There’s also no shortage of news-worthy instances of lithium batteries spontaneously combusting when the temperature gets too high. Because of these limitations, lithium ions might not be the best battery for everyone.
Conclusion: Using Deep-Cycle Batteries for Solar Power
Deep-cycle batteries have many qualities that make them ideally suited to the task of integration within a solarized home system.
With several model and price point options to choose from, they’re also versatile enough technology to be available to a wide variety of needs for solar consumers.