Battery Types

If you need a crash course on solar and storage batteries, you’re in the right place. With more options available on the market for consumers, it is helpful to have a baseline knowledge of batteries so that you can make the best choice for your home.

Early versions of battery storage used lead acid batteries (varieties included Flooded, Sealed, AGM, Gel). Early mobile electronics batteries were mainly Nickel-based (NiCd, NiMH). 

Nowadays, solar and battery backup batteries are lithium ion batteries. As battery technology continues to improve and expand, so do our options for using batteries as home energy storage. 

Let’s break down the main battery chemistries used for home backup so that you can make an informed decision for your own storage setup, and learn why Mountain Microgrids exclusively uses LFP batteries.

The three lithium ion battery types seen in solar and backup batteries are LFP, NMC, and NCA.

Comparing Lithium Ion Battery Chemistries

LFP (aka LiFePO4)  - Lithium Iron Phosphate

We’re starting with the battery chemistry that has made some major improvements in recent years, making it a frontrunner as a solar and storage battery option: LFP. 

We at Mountain Microgrids use LFP batteries in our products for many reasons.

For starters, it is lower cost, partly due to the materials being more abundant. As far as performance, LFP has a very low self-discharge rate (3% per month), a round trip efficiency of 92%, and can run 5000 cycles at 80% depth of discharge. To put it simply, it holds its charge better, is efficient, and has a long lifespan, able to store and release more electricity over time compared to the other lithium ion chemistries.

In addition to its impressive performance, LFP is more safe and stable compared to the others meaning it is less prone to thermal runaway, catching fire, or exploding (which is a pretty important feature). It can operate within the temperature range of -20 - 75°C. 

And lastly, the materials used in this battery are ethically sourced and not harsh on the environment.

NMC - Lithium - Nickel Manganese Cobalt

You may have heard of NMC being used in electric vehicles or your personal electronics. It is also a battery chemistry used in many solar and backup batteries. 

The main benefit to the NMC chemistry is its higher energy density, meaning you can pack more energy in a more compact space. While higher energy density is very useful, there is a down side. The higher the energy density, the lower its thermal stability. NMC batteries are more likely to experience thermal runaway if damaged, misused, or in extreme temperatures.

The NMC battery is less efficient and has a shorter lifespan than its LFP counterpart. The self discharge rate is higher at 4% per month, and can reach up to 2000-2500 charge cycles in its lifetime. 

Lastly, and perhaps most importantly, are the environmental impacts of manufacturing the NMC battery. This particular chemistry requires cobalt. Mining for cobalt causes environmental degradation and pollution. There is also insufficient supply for cobalt, making it expensive and not sustainable for the needs of our increasingly electrifying population. 

On top of environmental damage, mining cobalt is dangerous and toxic. Unfortunately, the demand for cobalt to power lithium-ion batteries promotes exploitative practices such as child labor and other human rights violations. 

NCA - Lithium - Cobalt Aluminum Oxide

NCA is a chemistry primarily used in portable electronics and EV. While it has a longer lifespan compared to NMC, it is overall less safe due to its high energy density and more expensive.

The graph below compares the three battery chemistries and how many cycles can be completed (how many times the battery can be charged and discharged) based on various starting capacities (what percentage of the battery is charged). 

In blue are the LFP data. Overall, LFP outperforms NMC and NCA as far as number of cycles.

Sources: 

• New Tests Prove: LFP Lithium Batteries Live Longer than NMC - OneCharge 

• Degradation of Commercial Lithium-Ion Cells as a Function of Chemistry and Cycling Conditions - IOPscience (PDF)

Commonalities

Compared to lead acid batteries, which were the type previously used for off-grid systems, lithium-ion batteries are very low/no maintenance across the board. 

There are also ways to recycle your old batteries, such as through Redwood Materials.