COMPARING LEAD-ACID BATTERIES AND LITHIUM-IRON BATTERIES
While lead-acid batteries have long dominated the market for their low cost and established manufacturing base, the soaring popularity of lithium-iron batteries over the last couple of decades has made it a strong contender. In fact, now lead-acid and lithium-iron are the two main kinds of batteries used for commercial and residential purposes.
Both lead-acid and lithium batteries are
effective and wildly popular energy storage solutions. However, the two vary
distinctly in terms of chemistry, cost and performance.
Here’s how these two technologies stack up in different departments.
DEPTH OF DISCHARGE (DOD)
A battery’s depth of discharge is the measure of the percentage of energy that can be safely drained without causing any damage to it. To put it simply, it refers to the total battery capacity that can be safely consumed before it needs to be charged.
When it comes to lead-acid batteries, they can be safely discharged up to 50 percent. Continuing to use the battery beyond that point will negatively affect its lifespan and effectiveness. Lithium-iron batteries typically have higher depth of discharge values. 80 to 85 percent of the energy capacity can be drained before they need to be charged.
For solar power applications, the optimum lithium battery chemistry is lithium iron phosphate (LiFePO4). They don’t require the routine maintenance that FLA batteries need or a well-ventilated environment.
A battery’s efficiency is one of the most important metrics to consider when making a purchase. The more efficient a battery is, the more energy it discharges with respect to how much it consumes.
For example, in the case of solar energy panels, lead-acid batteries have an efficiency rating of 80 to 85 percent. What this means is that for every 1000 watts of solar power absorbed by the batteries, only 800 to 850 watts are available for use. Compare this with lithium-iron batteries which have efficiency ratings of over 95 percent. For every 1000 watts, you’d have more than 950 watts of power available for use.
More efficient batteries also charge faster. With respect to the solar panel system you have set up, it may also mean you can use fewer solar panels, a relatively smaller backup generator, and lower battery capacity.
RATE OF CHARGE
What’s more is that higher efficiency ratings mean batteries can be charged at a faster rate than ones with lower efficiency. This is due to the fact that they are designed to handle more amperage from the charger. More amperage means more current. Considering lithium-iron batteries have higher efficiency ratings, they also have a faster rate of charge.
The rate of charge is expressed as a fraction that indicates the value in amp hours. For example, a battery with a 500 Ah rating receives 100 charging amps in five hours.
Because lead-acid batteries have a relatively limited amount of current that they can handle, it is common for them to overheat when they are charged with a higher amperage charger.
ENERGY DENSITY or CAPACITY
A battery’s capacity or energy density is the measure of the amount of energy it can store (and, of course, discharge) within a given physical space. Capacity values for batteries tend to vary between manufacturers and models.
Generally speaking, lithium-iron battery systems tend to have higher energy density values than lead-acid batteries. This means that they can store a higher amount of energy for the same size. Standard lithium-iron batteries tend to be larger than lead-acid ones, however. And they are typically more difficult to install.
However, considering you may need several more lead-acid batteries to do the job that fewer lithium-iron setups can do, the trade off isn’t much. For example, to provide power to a 5.13 kW system you’ll need eight lead-acid batteries, but only two lithium-iron batteries to do the same job. Lithium-iron battery systems can also fit into smaller and tighter spaces if your energy requirements are high.
When it comes to upfront and installation costs, lead-acid batteries are the more affordable option. Compared to a standard lithium-iron setup of the same size, a lead-acid battery system will typically cost you several hundreds—sometimes thousands—of dollars less. Costs depend on the size of the battery system and their installation needs.