Lithium-ion Vs. AGM Batteries

Batteries play a crucial role in solar power systems. They provide the DC that is to be converted to AC by the inverter for use in appliances. In hybrid solar power systems however, that is, systems that incorporates both solar panels and a battery bank, they mostly serve energy storage purposes. In other words, they store energy produced from solar panels for use by the appliances in the absence of production from the solar panels.

All batteries have essentially the same components: electrolytes, positive and negative terminals and separators integrated into 'cells'. These components are often differentiated based on the nature and/or type of the chemical material from which they are made.

In a Lithium-ion battery, graphite is mostly used in the negative electrode. The positive electrode is generally one of three layered materials of lithium salts. (Recently, graphene containing electrodes [based on 2D and 3D structures of graphene] have also been used as components of electrodes for lithium batteries.) And the electrolyte is typically a mixture of organic carbonates containing mixtures of lithium salts. (A modified variant of Li-ion batteries, the lithium polymer battery, or more correctly lithium-ion polymer battery (abbreviated as LiPo, LIP, Li-poly, lithium-poly and others), uses a polymer electrolyte instead of a liquid electrolyte.)

In an AGM battery, the acid electrolyte of a typical lead-acid battery is held in glass mats, as opposed to freely flooding the plates. This is done to eliminate the need for constant checks and to eliminate the emission of fumes or gases on a continuous basis and the attending dangers.

Comparison Based On Key Metrics

Depth of Discharge (Winner: Lithium-ion)

The depth of discharge of a battery is the percentage of a battery that can be discharged without damaging the battery. Lithium-ion can withstand discharge of about 86-98% while lead-acid can only handle 30-50% discharge. This means that they do not require scheduled cycling like their AGM counterparts. It also gives a lithium-ion battery an operating range of almost 30%-40% than an AGM. This makes LIBs less prone to damages that are caused by exceeding the depth of discharge.

Performance (Winner: Lithium-ion)

Battery efficiency, also known as round trip efficiency, is the how well a battery charges or discharges when being used. Lithium-ion batteries are more efficient (up to 98%) than AGM (85%) meaning that they allow faster charging and discharging and In this case, the transfer is from electrical to chemical energy during battery charging and chemical back to electrical during discharge.. This could mean fewer panels and lesser battery capacity.

Energy Density (Winner: Lithium-ion)

Li-ion batteries have the highest energy densities of any battery technology today (100-265 Wh/kg or 250-670 Wh/L). This means that they can store more energy per mass than their AGM counterparts and thus require lesser installation space. This means they weigh lesser and lighter while providing the same amount of output than AGM counterparts. However, being sensitive, Li-ion batteries require additional safety systems as part of their battery management systems to limit voltage and internal pressures. This can inadvertently increase their weight and, in some cases, limit their performance.

The Felicity LiFePo4 Battery
Lifespan (Winner: Lithium-ion)

Generally, all batteries degrade over time. Li-ion batteries are no exception. They are subject to aging, during which they their rated lose capacity and fail before their expected lifespan. Depending on usage habits, lithium-ion batteries can degrade at less than a percentage point year-over-year and thus generally outlast AGM batteries. Regardless, in a properly designed system with shallow cycle and controlled temperature, AGM batteries can last up to a decade and even longer.

Warranty (Winner: Lithium-ion)

Typically, manufacturers can back their lithium-ion batteries with up to 10 years, whereas other battery types generally are backed by a maximum of only 2 years.

Cost (Winner: AGM)

Lithium-ion batteries cost way higher than AGM batteries. Prices of a LIB can reach up to 10X that of the AGM battery. The lower cost of AGM batteries is what keeps them in competition with Lithium-ion batteries. Since this is the most practical consideration for majority of buyers, an AGM system may be regarded as the better choice of the two. Regardless, when the cost of purchase is adjusted over the lifecycle, Lithium-ion batteries come out cheaper.

Overall (Winner: AGM)

There are other factors besides the battery technology that are to be taken into consideration by the user and the system designer when deciding which battery type to use in designing a system. Among those, the users budget, power needs and power environment play decisive roles in the type of battery type users will ultimately choose to invest in. The nature of appliances that will run on the system and the expected lifespan of the system are also significant factors.

AGM batteries have been in use for a long time and therefore have a greater history of field use and testing than lithium-ion batteries. This means that installers and users have more experience with AGM batteries than the new Lithium-ion batteries. This makes them more practical and prudent options. This explains why we are more confident recommending them to our clients, most of whom are homeowners and businesses, than Lithium-ion batteries regardless of their more advanced attractions. With the most research effort being invested in optimizing Lithium-ion battery technology than any other battery technology (the 2019 Nobel Prize in Physics was awarded for research in Lithium-ion battery technology), and even as costs is being driven down to meet the boom in demand, we consider lithium-ion batteries the batteries of the future.

An already large and still increasing range of available options can lead to information anxiety that can result in a poor decision being made. In situations like this, Solarkobo has university-trained engineers who have acquired years of field experience to help users make the best choice of batteries that fit their budgets and meets their power needs.


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