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Understanding Solar Battery Chemistry: A Comparison

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Solar batteries help store the excess energy your solar power system produces that isn’t immediately used to power your home. They can also interact with the electricity grid to charge when needed or add power back into the grid when it’s financially beneficial to do so.

But how do solar batteries actually work? Does battery chemistry matter when it comes to the features and benefits of the main types of solar batteries?

This article will provide a battery chemistry comparison of each of the leading solar battery storage options, and look at the pros and cons in terms of capacity, lifespan, and cost.

What is Battery Chemistry?

Battery chemistry is the mixture of chemicals that allows for a reaction within the cells of a battery, enabling electrical energy to become chemical energy, and chemical energy to become electrical energy. Different battery types are based on the different compositions of chemicals inside the cells, which determines their power level and backup power storage capacity when they store electricity.

What Types of Batteries are Used for Solar Energy Storage?

Rechargeable batteries can be discharged and recharged for their expected lifespan before the chemical reaction becomes inert due to use. The batteries used in a solar battery bank are an industry-specific subset of these batteries that are designed for extra-long life and regular use.

Solar batteries for energy systems are large enough to accept the voltage from solar panels and store enough energy in order to discharge the appropriate amount of power that your home needs. Thus, a battery chemistry comparison typically comes down to analyzing the tradeoffs between capacity and longevity.

The biggest difference between a traditional single-use battery and a rechargeable battery is the latter’s ability to absorb incoming energy and store it inside cells, without causing the chemical composition of the cells to deteriorate. Rechargeable batteries are made up of chemicals that can reverse their charge in order to retain energy, rather than deteriorate over time.

Attempting to charge a battery that wasn’t designed to have a charge reintroduced into the cells, such as in-home disposables (AA, AAA, C, D, 9V, etc.) can result in overheating and damage, due to the reactions in the cells.

Five main types of solar batteries are used for power storage:

  • Lithium-Ion
  • Lead-Acid
  • Lithium-Iron-Phosphate (LFP)
  • Nickel-Cadmium
  • Flow Battery

Other less popular options for solar power storage include Nickel-Metal hybrid and Nickel-Zinc, but they have a smaller capacity and less durability when compared to the other options.

Lithium-Ion Battery Chemistry

Lithium-ion batteries are one of the most affordable versions of rechargeable battery technology. This battery’s versatility and size adaptability make it a leader in the light rechargeable battery category, which is why you’ll find it in electric cars, mobile phones, and laptops.

These solar battery cells contain an intercalate lithium compound and electrolytes. The lithium ions move through the electrolytes to the positive terminal, where they discharge and reverse direction to charge the battery. The charge “rocks” back and forth within the electrolyte solution to create a positive charge for discharging and a negative charge to draw in power for storage.

Pros of Using Lithium-Ion Technology for Solar Batteries

You should consider using lithium-ion batteries for home solar storage for several reasons:

  • High energy density (it holds more power than other rechargeables)
  • Fewer maintenance requirements
  • Higher efficiency
  • Longer lifespan
  • Higher energy-to-weight ratio
  • Minimal charge loss while not in use

Cons of Using Lithium-Ion Technology for Solar Batteries

Lithium-Ion batteries do have a few notable problems:

  • Increased risk of overheating and fire
  • Low resiliency
  • Increased health and environmental risk

If the lithium component leaks, it is toxic to the environment, humans, and animals, as it can cause burns, allergic reactions, and poisoning. Correct placement of the battery storage area is essential to reduce these risks.

Lead-Acid Battery Chemistry

Lead-Acid batteries consist of cells with porous lead in a solution of sulfuric acid and water. The energy is created and discharged by transforming the lead into lead sulfate crystals, and then back into lead and sulfuric acid when a device is attached to the terminals.

Pros of Using Lead-Acid Technology for Solar Batteries

Lead-Acid batteries have powered vehicles and equipment for decades. They are heavy, but they last for years with proper maintenance and charging, offering a low-cost, long-life alternative to more advanced storage options. Lead-Acid batteries have many advantages:

  • 85% efficacy (compared to an average of 70% in other rechargeable battery types)
  • Deep cycle capability (the capability to discharge most of its charge frequently, such as when starting a car)
  • Long life cycle (capable of lasting anywhere between 3-12 years, depending on maintenance and use)

Cons of Using Lead-Acid Technology for Solar Batteries

Because the lead-acid battery is one of the most common batteries used in automobiles, we know many of its disadvantages, which include:

  • Electrolyte and water loss due to the gassing process
  • Movement can damage the electrodes attached to the soft lead terminals
  • Sulfur spillage harms the environment, humans, and animals
  • Reduced charge ability in freezing temperatures

You can keep lead-acid batteries healthy by storing them in an appropriate location and paying attention to corrosion, temperature, and water levels.

Lithium-Iron-Phosphate (LFP) Battery Chemistry

The LFP battery is a type of lithium-ion battery that uses lithium, iron, and phosphate instead of lithium and cobalt oxide. The lithium, iron, and phosphate interact with the graphitic carbon electrodes to create the chemical reaction necessary to discharge electricity and accept voltage for storage. It is a low-cost and low toxicity alternative to the Lithium-Ion battery.

Pros of Using LFP Technology for Solar Batteries

The chemical change in the cells of the Lithium-Iron-Phosphate increases this battery’s appeal by providing:

  • Lower human and environmental impact
  • Lower cost
  • Better aging and lifespan
  • Higher peak power ratings
  • Better thermal stability

The thermal stability of the LFP battery chemistry has given it an advantage over its more common lithium-ion sibling. Its low impact on the environment makes it a great choice for the eco-conscious user, and a great addition to energy-conservation efforts.

Cons of Using LFP Technology for Solar Batteries

Even though the lithium-iron-phosphate battery chemistry is better in some respects than the lithium-ion battery, it still falls short in others. It might be preferable for situations where heat can cause problems, but it still isn’t as versatile and useful. Other disadvantages include:

  • Low electrical conductivity
  • Poor low-temperature performance
  • Deep discharge issues
  • Issues with safe transport
  • Required protection from elements and temperature

Like the lithium-ion battery, storing an LFP solar battery requires consistent temperature control with an adequate maintenance schedule to ensure peak performance.

Nickel-Cadmium Battery Chemistry

Nickel-cadmium batteries are high-powered and energy-efficient. They are mainly used for industrial, transportation, and aviation applications. These batteries are composed of nickel and cadmium in an alkali solution that charges and discharges the elements as positive or negative energy is introduced.

Pros of Using Nickel-Cadmium Technology for Solar Batteries

The nickel-cadmium battery has several advantages, including:

  • Lower self-discharge rate (the rate at which the chemicals within the cells reduce their ability to store energy)
  • High recyclability
  • Broad temperature storage range
  • Long cycle life
  • Low maintenance requirements

Nickel-cadmium batteries resemble alkaline batteries (like AA and AAA) in shape because of the way the positive and negative poles are rolled to physically separate the terminals. Vented nickel-cadmium batteries have a long life (up to 20 years or more, depending on the type) and can function in temperatures ranging from −4 °F to 113 °F (−20 °C to 45 °C).

Cons of Using Nickel-Cadmium Technology for Solar Batteries

The main drawback of the nickel-cadmium battery is the actual cadmium contained within the cells. Cadmium is a toxic, heavy metal that has to be handled by individuals trained in hazardous waste removal. Due to health concerns, the European Union has banned its use except in medical equipment. Other drawbacks include:

  • Nitrogen impurities can cause increased self-discharge occurrence
  • High electrolytic resistance (overcome with increasing technology)
  • High cost

Nickel-cadmium batteries have to be stored away from wet areas, and the terminals must be kept clean. However, sealing the terminals to keep them clean can result in higher self-discharge and memory loss within the cells.

Additionally, overcharging can result in the loss of water in the form of gas, which reduces the amount of charge the cells can hold. The use of cheap charging devices can rapidly damage the cells because of overcharging and cause a significant decrease in longevity.

Flow Battery Chemistry

A flow battery has a unique composition compared to other batteries. It consists of two tanks of chemicals, such as a liquid bromine solution and hydrogen, that are pumped past a membrane held between two electrodes. The ion exchange through the membranes creates the charge that powers the cells.

Such a battery requires enough room for the tanks holding the chemicals, the pipelines they use, and the electrical components that pump the liquids through the membranes and to the terminals.

Pros of Using Flow Technology for Solar Batteries

The unique battery type has several advantages, including:

  • Nearly limitless lifespan
  • Higher technology
  • More flexible layout
  • No flammable liquids
  • Well-suited for large-scale storage

Large facilities with plenty of space can benefit from these batteries because they can install a larger tank to store more electrolytes. The size of the tanks increases available storage, and the increased space between the various components reduces the electrolytes’ interaction, thus increasing lifespan.

Cons of Using Flow Technology for Solar Batteries

Even though flow batteries seem to be a great idea, the flexible setup has some major disadvantages for the home, including:

  • Low energy density (larger tanks are needed for useful charges)
  • Large membrane separators needed to increase charge and discharge rates
  • High costs
  • Large space required for the separate chemical tanks
  • Need to replenish electrolytes frequently inside tanks

Which Type of Solar Battery is Right for You?

After weighing the pros and cons of the five battery types discussed above, most would agree that the lithium-ion battery is the best choice for storing solar energy. It remains the industry standard for solar battery storage due to its high capacity, long life, and space-saving design.

If you are concerned about your budget, then lithium-ion might be out of your price range, so lead-acid batteries are a budget-friendly alternative. However, while it can last for many years and has a low cost, it’s an older technology, so it may not work as well with a high-tech setup.

Battery Chemistry Matters When It Comes To Solar Storage

Adding battery systems to your residential solar power setup is an additional step you can take to reduce your reliance on the electricity grid, and solar panels and batteries can work together to provide the solar power your home needs.

Choosing the correct solar battery can mean increased savings and reliability. Selecting the best battery storage solution for your needs often comes down to the battery's composition and chemistry. It’s important to understand the fundamentals of each of the five major types of solar batteries, including their advantages and disadvantages.

When it’s time to install your solar panel system and battery storage system, you should consult with the solar experts at Palmetto. We have the experience and know-how to install the correct battery efficiently, swiftly, and correctly, to meet your long-term energy needs. We even offer our Palmetto Protect service, so you can get the ongoing support and maintenance you deserve.

To learn how much you could lower your home’s energy bills by switching to solar energy, get started today with our free Solar Design & Savings Estimate tool.

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