Battery Types for Energy Storage Applications

There are four types of battery mainly used for solar energy storage applications. They are:

- Lithium-ion (LMO, NMC, NCA, LFP)
- Lead acid (Flooded, VRLA)
- Nickel based (NiCd)
- Flow (RFB, HFB)

Below is the summary of each of these technologies with their advantages and disadvantages.

Lithium-ion

Li-Ion batteries come in a range of different chemistries. There are four main types often used for large-scale solar battery storage applications. The Pros and Cons of each chemistry is mentioned below.

• Lithium Manganese Oxide (LMO)

Advantage: Fast charging
Disadvantage : Only recently entered the C&I market

• Lithium Nickel Manganese Cobalt Oxide (NMC)

Advantage: High specific energy 
Disadvantage : Only recently entering the C&I market

• Lithium Nickel Cobalt Aluminum Oxide (NCA)

Advantage: High specific energy and more stability
Disadvantage: Relatively new

• Lithium Iron Phosphate (LFP)

Advantage: Long cycle life, don’t require ventilation or cooling 
Disadvantage: Risk of thermal runaway

Summarizing Li ion Battery

• These batteries have high energy density and a low self-discharge.
• They do not need prolonged priming when new. One charge is sufficient.
• They are low maintenance and a periodic discharge is not necessary.
• Most of them are still comparatively expensive to manufacture and are subject to aging.
• They require protection circuit to maintain voltage and current within limits.

Lead acid

Lead acid batteries are:

 -Inexpensive with prices range between 382$ and 399$.
 -Have the lowest self-discharge rate among the rechargeable batteries here. 
 -Have high specific power, low specific energy and are capable of high discharge currents. 
 -Not environmentally friendly. 
 -Are heavy 
 -Are relatively inefficient as for their charge and discharge compared to other batteries. 
 They are of two types Flooded lead acid and VRLA batteries.

• Flooded 

 Advantage: Reliable
Disadvantage: Requires watering, transportation restrictions, need ventilation

• Valve Regulated Lead-Acid (VRLA)

Advantage: Valves to regulate off gassing, little to no maintenance, can be installed in hard-to-reach applications. 
Disadvantage: Sensitive to temperature

Nickel based

Nickel based batteries have been used in large-scale energy storage projects as they perform well in all types of temperatures. Nickel-Cadmium (NiCd) is the most common Nickel based battery technology used. They are often preferred for off-grid installation as they provide a reliable backup system and don’t require regular maintenance.

• Nickel-Cadmium (NiCd)

Advantage: long cycle life, don’t require ventilation or cooling
Disadvantage: Low specific energy, Risk of thermal runaway, Toxicity of Cadmium.

Flow Batteries

Flow batteries are comparatively new to the battery storage market. In recent times they are becoming a strong competitor to Li ion batteries in energy storage domain. They are rechargeable batteries in which electrolyte flows through one or more electrochemical cells from one or more tanks. In these batteries one can easily increase the energy storage capacity by increasing the quantity of electrolyte stored in the tanks. The choice of redox pairs is often used as a description of the type of flow battery. Some well-known redox pairs are:

• Vanadium / vanadium
• Iron / chromium
• Zinc / bromine

Advantages of Flow Batteries are given below.

-Modular and scalable
 -Low flammability, low cost and low environmental impact
 -No need for complex heating and cooling
 -Overcharging or discharging doesn’t damage electrodes and electrolyte
 Disadvantages
 -Relatively low efficiency (e.g. compared to the Li-ion battery) 
 -High cost for repair and maintenance

Li ion and Flow batteries as Storage Options

Though Li ion battery’s lion’s share in energy storage market is a well-known fact, flow battery is a newer technology that is expected to emerge as strong storage option in coming years. In this context, vanadium flow battery (VRB) is grabbing headlines in the form of redox flow batteries where they form the redox pairs. Currently, both Lithium ion as well as VRBs is being touted as good batteries for RE storage economy though they have their own pros and cons. Technological advances in flow batteries are also bringing down costs and improving their safety and ecological footprint profile. The big question now is: Which technology will win? The answer might not be that straightforward and here are some facts to consider.

How does Vanadium redox flow battery (VRB) stack up against Li ion batteries?

Points of comparison around important metrics are discussed below.



Cell design
Lithium batteries store their energy in cells and can be best analogized to small, self-contained devices that get hot. Vanadium flow batteries store their energy in tanks. Advantage of VRBs here is that it is easier to adapt them to industrial-scale applications by making the tank size bigger without adding a lot of cost.

Cost
As per Bloomberg New Energy Finance, “The average cost of a lithium-ion based storage system is $1,750 a kilowatt hour”. The cost includes the cells, electronics, installation and balance of systems expenses. By 2020, it is expected to go down to $400 a kilowatt-hour. Contrast this with VRBs that already provide complete energy storage systems for $500 per kilowatt-hour and by 2020, those energy storage systems will be produced for $150 a kWh.

Scalability and large-scale deployment

VRB can be stacked up to increase storage capacities but Li ion is boxed in by design. Unit cost for large-scale VRB goes down, whereas it goes up for lithium-ion batteries. This means on a large-scale deployment, VRB can be cost completive with lithium-ion batteries today.

Longevity 

The main criterion for grid batteries is that they should last for years. Lithium ion batteries have a finite life and their performance degrades over time and is also impacted by heat and other operating conditions leading to a drop to a 50 percent level after 1,200 to 1,500 discharges. VRBs in contrast can operate forever. That’s why suited for grid batteries that have the requirement to last for years .The active ingredient in VRB is a rechargeable electrolyte, which never wears out due to the type of chemical reaction involved.

Applicable Markets and Issues

Lithium is a small, expensive battery with a finite lifetime. To build a storage system for running demand response programs or a backup system that can provide four to six hours of power, thousands of cells are needed. Thermal runaway is a potential issue too. VRBs are made for industrial-size applications
from a few kilowatts to several megawatts. And there is no danger of thermal reactions.

Round Trip Efficiency

VRBs are ideal for “grid-constrained” solar and wind-farms that struggle to sell their electricity at times of peak production and find other forms of storage uneconomical. VRBs boast a longer continuous discharge run time (6-10 hours versus 2-5 hours) than lithium-ion batteries. The downside however is their relatively lower round-trip efficiency of 70 per cent compared to 85 per cent with lithium batteries.