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Which batteries are best for solar? Lead Acid or Lithium?

If you’ve done any research on batteries for solar energy storage you understand that topic can get as heated as politics and religion. Just the other day I shared a post on my facebook page regarding solar generators and turns out, the very first comment started a huge solar battery debate.

Whether you’re going off-grid or looking for solar backup, finding the right type of battery for your solar energy storage is just as critical as sizing it correctly. 

In this article we’ll compare the two main battery types used in off grid and solar backup systems: Lead Acid and Lithium Ion. We’ll compare their pros and cons, and share which battery is best in which type of situation. 

Here's the summary:

LEAD-ACID is a tried-and-true technology that has been used in off grid energy systems for decades.  While they have a relatively shorter life span than lithiums, they are also 1/3 of the price tag.  They are heavy and bulky, and depending on the type, may require regular maintenance.  Overall, they’re a great battery for off-grid and backup systems.

LITHIUM is a lighter, more compact battery with a longer lifespan. They do have temperature limitations and are more expensive than their lead-acid counterparts. 

Let’s go over the pros and cons of each option in more detail, and explain why you might choose one over the other for your system.

Lead Acid

There are many variations of lead acid batteries, each designed for it’s own particular application. Generally speaking, lead acid batteries are broken down into two main categories: Flooded (FLA) and Sealed (SLA). 

- Flooded Lead Acid (FLA)

FLA batteries are the most common lead acid battery type and are widely used in the automotive industry. Until recent years, they have been the battery of choice for many off grid systems. The biggest upside to FLA batteries is the cost. They have the least cost per amp-hour vs. any other battery.
The downside however, is their need for regular maintenance. Although they are very reliable if maintained properly, maintenance could be quite time consuming if you have a large enough system. Failing to provide regular upkeep can shorten the life of the battery and void the warranty. Also, since FLA batteries aren’t sealed, they need to be installed in a ventilated enclosure to allow battery gases to escape.

Flooded Lead Acid battery

Pros

  • Lowest upfront cost
  • Reliable

Cons

  • Requires regular maintenance
  • Releases fumes
  • Temperature sensitive
  • Is not spill-proof

- Sealed Lead Acid (SLA)

Sealed Lead Acid batteries come in two types: AGM (Absorbent Glass Mat) and Gel. Both have similar characteristics, however, for this article we’ll focus on AGM batteries since they are more commonly used in solar applications.

Absorbent Glass Matt (AGM) battery is a type of lead acid battery in which the electrolyte is absorbed into a fiberglass mat and thus lowering it’s internal resistance. As a result, AGM batteries can handle higher temperatures and self-discharge more slowly than other types of batteries. This also makes them higher in efficiency (comparable to lithium batteries, which is around 95%, as compared to 80% or less for FLA batteries).

solar battery
AGM deep cycle battery

AGM batteries are self-contained so they don’t need to be refilled with water, like FLA’s. For that reason, they are a great choice for properties that aren’t occupied full-time, like an off-grid vacation cabin. 

Other advantages of AGM batteries are that they can withstand a wide temperature range, are very cost effective, have a long life span (up to 10 years), and can be used safely without spilling or releasing toxic fumes.

In recent years, solar marketing has put so much focus on lithium batteries that to use anything else in your off grid system is to say that you know nothing about solar. This is certainly not true of AGM batteries. Overall, due to their wide range of advantages, they are a great option for off grid power systems.

Pros

  • Requires minimal maintenance
  • Sealed, making them spill proof and safe
  • High efficiency
  • Larger temperature range
  • Long life span (up to 10 years)
  • Easy to replace or add more batteries

Cons

  • Heavy and bulky compared to lithium
  • Short life span if deep cycled daily
  • Needs to be kept full (float charged) when not in use, or charged often when not in use

lithium ion

Like FLA batteries, Lithium batteries come in a variety of technologies. The best technology for solar applications is Lithium Iron Phosphate (LiFePO4). This technology is safe, stable, and maintenance free for years. Lithium’s can also be put through deeper cycles than FLA or AGM batteries.

Lithium batteries are lightweight and compact, making them a great option for portable energy storage. Other advantages include: A long life cycle (3000-10,000 cycles) and higher charge and discharge efficiencies. It also looses less capacity when idle, which is useful for solar backup systems where energy is only used occasionally. 

The biggest disadvantage to Lithiums is cost. A lithium solar battery can cost up to 4 times as much as a FLA battery and 3 times as much as an AGM battery system.

Lithium Iron Phosphate (LiFePO4) battery

Pros

  • Requires no maintenance
  • Sealed, making them spill proof and safe
  • High efficiency
  • Longest life span (up to 15 yrs)
  • Lightweight and compact
  • Stays charged longer
  • Can be charged faster in less time

Cons

  • Highest cost
  • Smaller temperature range
  • More difficult to replace or add more batteries