Decoding the dominant load

Aug 12, 2023

As load-shedding continues to plague South Africa, the choice of a reliable backup battery becomes crucial. MyBroadband conducted a comprehensive comparison of various battery technologies to determine the best option. Among the contenders, lithium-ion batteries, specifically LiFePO4 and Li-NMC, emerged as the top choices due to their exceptional performance and extended lifespan. While lead-acid batteries can be a budget-friendly alternative, their shorter lifespan and limited usage during load-shedding periods make them less favourable. With their superior performance, longer lifespan, and overall value, lithium-ion batteries prove to be the clear winner for load-shedding backup solutions. This article was republished courtesy of MyBroadband.

A critical component of any backup energy system is energy storage in the form of batteries. However, it is essential to consider the pros and cons of different battery technologies before buying a battery.

MyBroadband compared lead-acid, gel, absorbent glass mat (AGM), lithium iron phosphate (LFP/LiFePO4), and lithium-nickel-manganese-cobalt-oxide (Li-NMC) batteries in terms of lifespan, performance, safety, and value.

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With the frequency of Eskom load-shedding, lithium-ion batteries — which include LiFePO4 and Li-NMC — come highly recommended. However, lead-acid units can still be viable for those on a budget who do not let the battery discharge beyond 50% and don’t use the batteries during every bout of load-shedding.

Keep in mind that, even with careful monitoring, lead-acid batteries will need to be replaced more frequently than lithium-ion alternatives.

Lithium-ion battery types compared

There are effectively two primary types of lithium-ion backup batteries available in South Africa — lithium iron phosphate (LFP or LiFePO4) and lithium-nickel-manganese-cobalt-oxide (Li-NMC) batteries.

Both technologies offer similar performance, with only slight differences between the two.

LiFePO4 batteries generally perform better than Li-NMC units when the state of charge is low, while Li-NMC batteries are more stable and perform better at lower temperatures. Regarding lifespan, LiFePO4 units typically last longer than Li-NMC batteries.

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According to Eco Tree Lithium, Li-NMC batteries commonly offer a lifespan of 2,000 to 2,500 cycles, while LiFePO4 units can last up to 5,000 cycles. However, it should be noted that Tesla’s Powerwall packs Li-NMC batteries, and it provides a warranty of up to ten years, or until it reaches 38.2MWh of throughput, depending on how it is used. While dependent on usage, this works out to around three to four years before degradation starts for Li-NMC units and seven to ten years for LiFePO4 units.

The rate of degradation is also slower for LiFePO4 units. LFP batteries offer better overall value and a lower upfront cost than their Li-NMC alternatives. This is because Li-NMC batteries require considerable amounts of Nickel, Manganese, and Cobalt for the cathode material.

On the other hand, LiFePO4 units use iron and phosphate as cathode materials, which are abundant and less expensive. LFP batteries are also considered safer than Li-NMC batteries at high temperatures.

The chemistry of LFP units is more stable, and they release no oxygen. This makes flammability at high temperatures less of a concern. While Li-NMC technology is also considered stable, its chemistry releases oxygen, which could cause big problems if the unit is used or installed incorrectly.

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Lead-Acid vs Lithium-ion

Lithium-ion batteries offer significant benefits over their lead-acid counterparts and, despite being more expensive, are more affordable in the long run. Lead-acid batteries are typically good for 150–200 cycles when discharged to no more than 50% of their capacity, which, according to GeeWiz, will only provide a lifespan of a few months with consistent load-shedding between stage 4 and stage 6.

However, being more affordable, they are a suitable option for those on a budget that are willing to monitor battery levels closely.

For reference, a price per kWh comparison between lead-acid and lithium-ion batteries is provided in the table below. The second table re-evaluates the batteries taking the recommended maximum depth of discharge into account.

Even on a price per kWh basis, lithium-ion batteries are significantly more expensive than lead-acid units. However, with lithium-ion batteries offering more cycles, they require replacement less frequently.

Another aspect to consider is the depth of discharge (DoD), which effectively determines the useable capacity of batteries.

Lead-acid packs could shed cycles faster if their battery levels are allowed to fall below 50%. This has a significant impact on capacity. Upgrading to a gel battery — effectively a sealed and valve-regulated lead-acid battery with a gel electrolyte — can increase the DoD and provide additional cycles.

The same can be said for AGM batteries, which feature similar chemistry to standard lead-acid units but incorporate fibreglass mats sandwiched between lead plates to stop the free flow of the electrolyte solution. This makes AGM batteries spill-proof and require less maintenance than traditional lead-acid units, but they are significantly more expensive.

Lithium-ion batteries are far superior to lead-acid batteries and their variants, especially considering South Africa’s consistent load-shedding. They can discharge to 100% without any long-term side effects. However, they should be set to a DoD of 80% to maintain battery life.

According to Qnovo, battery capacity loss tends to accelerate fast when lithium-ion batteries are discharged below 80%. At a DoD of 80%, lithium-ion batteries can offer up to 5,000 cycles — 25 to 33 times longer than standard lead-acid.

Some of the most prominent lithium-ion battery brands — and the technologies they use — are listed below.

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