I have seen so many off grid energy systems with defunct lead-acid batteries. They work as designed for a few years if you are careful, and then they lose their depth of charge. I’ve been working with Lithium-Ion batteries over the past year, and while significantly more complex, they have some amazing advantages. Based on my experience, I predict that in a few years, we’ll move away from lead-acid batteries.
I believe right now we are at a clear crossroads when it comes to choosing a battery type for energy storage for off grid energy systems. We are at the transition between lead-acid batteries, the tried-and-true technology used for decades, and lithium-ion’s promise of higher density, improved resiliency, and longer cycle life.
Recently we’ve seen companies successfully gain traction with cost effective lithium-ion technologies. Li-Ion batteries are selling for as low as $400/kWh. Tesla, LG Chemical, Sonnen, Simpliphi Power, and Lithionics all have reliable products at reasonable prices. And recently the German car manufacturer Mercedes-Benz announced that they are also getting into the stationary storage market with Mercedes-Benz Energy.
But what about lead-acid batteries? They’ve been around for so long that they are practically a commodity. Their quality ranges significantly depending on the manufacturer, but the technological differences are minimal. Manufacturers like Trojan, Rolls/Surrette, and MK/Deka have been in the game for decades. Why disrupt this two-century old technology? And what makes lithium-ion a game changer?
Advantage № 1 — Superior in Size & Weight
While superior energy density is not critical for stationary applications, it is essential for electric vehicles and portable electronics. Increased energy density greatly improves the deployment and installation process for stationary energy storage.
The graph above illustrates how lithium-ion batteries are about a third of the weight and half of the volume when compared to lead-acid (flooded, AGM, and gel). Lithium-ion batteries are in a league of their own when compared to all other battery types since they are significantly more energy dense.
Advantage № 2 — Superior Resilience
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All batteries are vulnerable to damage from excessive discharging and extreme temperatures. Lead-acid batteries are generally less resilient to this kind of abuse and are harmed if discharged too quickly or deeply. Lead-acid batteries lose potential cycles if they are discharged below 50% of their State of Charge (SOC) or if discharged faster than C/8. On the other hand, lithium-ion batteries can be discharged to about 80% SOC and at a rate of C/2 without any long term damage. The table above shows common characteristics of the three types of batteries; flooded lead-acid, valve-regulated lead-acid, and lithium-ion.
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A helpful way to think of charging and discharging a battery is to imagine it like a balloon. If you repeatedly inflate a balloon to its maximum capacity and then completely deflate it, the balloon material might fatigue from the excessive stress. Now imagine with another balloon you repeatedly inflate and deflate it from 50% to 90% full, the material will experience less stress and will last longer than the first balloon. The plates inside the battery undergo a comparable stress as the balloon material. In this example, lithium-ion batteries are simply made from a better, stronger balloon material when compared to lead-acid.
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