Should You Choose Lithium or Lead-Acid Batteries for Solar Storage?
If you’re like most homeowners, you put a lot of time into researching the best products for your home, particularly when those products have vast differences. As an increasing number of homes begin incorporating solar power to be more sustainable and energy-efficient, one question that a number of homeowners have is whether to opt for lithium ion or lead-acid batteries for their solar power systems. To understand which of these batteries is the best choice for your home, let’s examine the differences.
How They Work
Before getting into comparisons of performance and other features, it is helpful to have a basic understanding of how the two types of batteries function. First, consider the lead-acid battery. These batteries feature a positive and negative plate, each made out of different types of lead compounds. These plates are then placed into diluted sulfuric acid inside the battery. The two plates are connected with a wire. A chemical reaction between the plates and sulfuric solution create a flow of electrons. This generates an electric current in the circuit.
Meanwhile, lithium batteries are made up of many smaller batteries known as cells. Cells receive electrical current through conductive substances, usually aluminum foil on one side and copper foil on the other. Within each cell, at opposite ends, are a positive electrode made of mixed metals and containing lithium and a negative electron made of graphite. Each cell is filled with an electrolyte substance that facilitates the movement of lithium ions from the positive to the negative electrode, providing a charge.
The first thing many consumers will want to know when investigating a purchase is the price. This is an area where lead-acid batteries outperform lithium batteries, at least in terms of the initial cost. The purchase and installation cost of a lead-acid battery typically runs about $3,000 to $5,000 as compared to the cost and installation of lithium batteries which range on average from $11,000 to $13,000.
Note that these are average costs. Costs can vary greatly depending upon the manufacturer and storage size of the batteries. However, for the same storage size, lead-acid batteries are typically a fraction of the price of lithium batteries. However, it is important to note that this cost estimate is for the purchase of one battery and does not consider the frequency that the different types must be replaced.
Life of a Battery
When we consider battery life, it is important to note that it is not best measured in years as different people use batteries in different ways, meaning that the same battery could last two people considerably different amounts of time. Instead, batteries are measured in terms of charge cycles. When a battery is discharged and charged back up with solar panels once, this is one charge cycle.
A lead-acid battery will typically last for approximately 1,200 charge cycles. By comparison, a lithium battery has a potentially unlimited amount of charge cycles. This means that a lithium battery will last much longer than a lead-acid one. Homeowners opting to purchase lead-acid batteries will replace them much more frequently.
A better way of assessing the life of the two batteries is to examine their warranties. Lead-acid batteries typically have warranties of 3 – 5 years. Meanwhile, lithium batteries tend to have warranties of 10 – 15 years. For example, a typical lithium warranty may be for 10 years or 10,000 cycles, whichever comes first.
Discharge Depth is another important term to understand when evaluating batteries. This refers to the percentage of battery capacity that can be used before the battery has to be recharged. For example, if a battery can only discharge half of its charge before it needs to be recharged, that would be considered 50% discharge depth.
This is another area where lithium batteries outperform lead-acid batteries. Lithium batteries have a discharge depth of 85% or greater while lead-acid batteries have a discharge depth that maxes out at 50% with many at rates between 20% and 40%. In fact, discharging more than 50% of a lead-acid battery can negatively affect its life.
Energy density is a measure of the amount of power a battery can hold in proportion to its physical size. Lithium batteries have a much greater energy density than do lead-acid batteries. This means lithium batteries can be much smaller than lead-acid batteries while storing the same amount of solar energy.
This translates to a number of benefits for lithium batteries. First, they are a great fit for a home where space is an important consideration. Secondly, they are more lightweight in nature, often approximately one-third the weight of a lead-acid battery.
Efficiency & Charge Speed
Similar to solar panels, it is important to consider the efficiency of batteries. Battery efficiency is a measure of the amount of energy stored that is actually able to be used. For example, a 1,000-watt battery with 90% efficiency would have 900 watts of usable energy.
Lead-acid batteries tend to be 80-85% efficient while lithium batteries tend to be 95-98% efficient. This varies a bit with age and condition. Improved efficiency has a relationship to the speed at which a battery can be charged. Lead-acid batteries take longer to charge than their lithium counterparts, with lithium charging two to four times faster than lead-acid batteries, depending on the type. Another factor that plays into this difference is that lead-acid batteries can overheat if they charge too fast.
A big area that leads homeowners to opts for lithium batteries over lead-acid batteries is maintenance. Lithium batteries require not regular maintenance while lead-acid batteries require more regular service to keep them operational.
Lead-acid batteries need to be refilled with distilled water every two to four weeks. Additionally, most types of lead-acid batteries require an equalization charge every 90 days. The terminal connections and cables should also be regularly cleaned in order to prevent corrosion. Ultimately, many homeowners appreciate not having to remember to perform such regular maintenance.
Ultimately, lead-acid batteries have one major benefit: lower price. However, lithium batteries have greater energy efficiency, charge faster, last longer, have a higher discharge depth, and require no maintenance. Additionally, while lead-acid batteries are cheaper upfront, a lithium battery that lasts more than ten years will quickly become more affordable in the long-run. These are some of the reasons why lithium batteries are becoming increasingly popular.
Most homeowners would benefit from selecting a lithium battery in terms of convenience, performance, and long-term cost. However, there may be some situations where a homeowner would benefit from a lead-acid battery. If the home is a vacation home that is rarely used, a lead-acid battery may be a suitable choice. Additionally, if the battery is only as a backup system for emergency power outages, a lead-acid battery would be the best option again.
Ultimately, the difference between selecting a lead-acid or a lithium battery likely depends upon how frequently it will be used. For everyday use, lithium is by far the best choice. In more special cases with periodic use, lead-acid batteries are still quite popular.