Solar Battery Types, Meaning, Pros and Cons Explained
Solar battery types are lead-acid, nickel cadmium, lithium ion, flow battery, sodium nickel chloride, and nickel iron batteries. The best type of solar battery is the lithium ion (Li-ion) battery. This is due to its composition, reliability, efficiency and resilience.
In this article, solar batteries will be discussed. as shown in the following outline;
-Types of Solar Battery based on Electrode Structure
-Types of Solar Battery based on Internal Composition
-Advantages and Disadvantages of the Different Types of Solar Battery
-Comparison of the Types of Solar Battery
-Best Type of Battery for Solar System
What is a Solar Battery?
A solar battery is simply a device which is used to store solar energy.
This device is usually rechargeable, meaning that it can both reserve and discharge energy according to the existing need.
A solar battery derives its importance and popularity from the fact that it is needed by many solar systems, in buildings and other facilities, at both small and large scales.
Basically, the solar battery reserves power which has been generated through the conversion of solar energy by a solar panel.
It serves as a backup component, and is most needed for off-grid configurations, where the solar system is the sole source of power (without any support from the grid).
Also, the power (converted solar energy) which is stored by a solar battery, is usually excess power which is not immediately consumed.
This excess power becomes useful when solar energy. in the form of sunlight. is not being supplied to the solar system. Such times may be either sundown or non-sunny weather periods.
The use of solar batteries is particularly prevalent in commercial and residential buildings, where consistency of power supply is highly relevant.
It is important to acknowledge that the solar battery is not a critical component of a conventional solar system. This implies that solar systems can function efficiently in the absence of a solar battery. However, the incorporation of this component presents several potential benefits.
For a solar battery to be used in an optimal manner, there are various requirements which generally need to be met. These requirements are concerned with the ventilation, moisture and temperature conditions of installation. The amount of power that can be stored by the solar battery is dependent on its storage capacity.
Types of Solar Battery: What are the Types of Solar Batteries?
The four main types of solar battery are lithium-ion, lead-acid, nickel-cadmium and flow battery.
There are various criteria which may be used to classify solar batteries into different groups. Two important examples of such criteria are the Electrode Structure and the Internal Composition of the battery.
-Types of Solar Battery based on Electrode Structure
1). Flat Plate Solar Battery
This type of solar battery has a relatively simple structure,
It usually has an internal composition of lead acid, and is recommendable for applications with less power demand. This is due to the relatively low resilience of flay plat batteries in general.
The flat plate solar battery is ideal for situations with short periods of need for backup power.
Structurally, the flat plat solar battery has a flat and broad geometry, with a large center of gravity.
2). Tubular Plate Solar Battery
The tubular plate solar battery may also be internally composed of lead acid material.
However, lithium-ion solar batteries can come a tubular structural design.
Tubular plate solar battery is also referred to as inverter battery, in some contexts. It has a number of advantages over the flat plate solar battery.
One of these advantages is with regards to storage capacity. The tubular plate solar battery has a generally larger positive plate than flat plate battery, and this enables more electrolyte mobility.
The large surface area gives tubular solar batteries an average of 20 percent more storage capacity than flat plate batteries of similar weight and size.
It is more recommendable to use the tubular plate solar battery in scenarios where backup power is needed for longer periods of time; as this battery is capable of delivering relatively small amounts of current for prolonged periods, when charged.
The tubular solar battery owes some of its advantages to the fact that it is a more widely-accepted structural design which has undergone more intensive development than its counterpart; the flat plate solar battery.
The following table compares the two types of solar battery based on electrode structure;
| Comparison Criteria | Flat Plate Solar Battery | Tubular Plate Solar Battery |
| Composition | Lead acid | Mostly lead acid |
| Electrode Geometry | Flat (both positive and negative) | Flat (negative);
Broad, lattice structure with large surface area (positive) |
| Storage/Retention Capacity | Relatively low | Relatively high |
| Discharge Pattern | Short duration | Long duration |
| Voltage/Current Discharge Ratio | High | Low |
-Types of Solar Battery based on Internal Composition
3). Lead Acid Solar Battery
The lead acid solar battery has been in use for over a century, since its invention in 1859, by French physician Gaston Planté [4].
Dilute sulfuric acid commonly serves as the electrolyte in lead acid batteries, and their application is widespread, particularly in the automobile sector. Lead acid solar battery can be alternatively referred to as ‘deep cycle solar battery’ (this term is also often used for other solar battery types).
Based on the nature of electrolyte, two main categories of lead acid solar battery exist. These are the flooded lead acid battery and the valve-regulated (sealed) lead acid battery.
The flooded lead acid battery is also called wet cell battery [1]. It usually requires distilled water to top up the electrolyte, which occurs in molten or liquid form.
Valve-regulated lead acid battery is also referred to as dry-cell battery, and its electrolyte occurs in semi-solid form, not requiring any supplementation like the flooded lead acid battery.
The valve-regulated (sealed/dry-cell) battery also occurs in two categories, which are the Gel (suitable for cold temperature conditions) battery and the Absorbed Glass Mat (AGM) (suitable for warm temperature conditions) battery, the former having a longer lifespan than the latter.
While lead acid batteries are relatively inexpensive, they have a number of shortcomings, especially due to the toxicity of their internal composition (which may have negative effects on the environment at their disposal) and their relatively short lifespan as well as low retention capacity.
It is also important to recall that both the flat plate and tubular plate types solar battery (as classified based on electrolyte structure) fall under lead acid category, when classified in terms of their internal composition.
4). Lithium-Ion Solar Battery
Lithium-ion represents the most common type of solar battery on the market.
The popularity and wide acceptance of lithium-ion solar battery is as a result of the use lithium-ion battery technology for other applications; including smart phones and electric vehicles [3].
As the name implies, this type of solar battery stored energy through chemical reactions that involve lithium ions.
Generally, in these chemic reactions, lithium releases free electrons that flow from the anode to the cathode of the battery.
For this to occur, lithium-ion batteries are equipped with lithium-salt electrolyte (usually Lithium hexafluorophosphate; LiPF6), through which electron flow occurs [7]. This electrolyte provides the ions needed for the necessary chemical reactions to occur.
When discharging, the electron-flow direction in a lithium-ion battery reverses, so that electrons begin to flow from the cathode to the anode, by which power is supplied to the plugged-in terminal.
For the lithium-ion solar battery; solar energy serves as the mechanism that drives the initial flow (and accumulation) of electrons to the cathode, which is the means by which power storage occurs.
Among the advantages which lithium-ion batteries have is their lifespan, which is estimated to be much longer than that of the lead acid battery.
These batteries are also more structurally resilient, and have a higher Depth of Discharge (DoD) than lead acid batteries in general. However, the average cost of lithium-ion solar battery is also high compared to other battery types.
Lithium-ion batteries are less prone to discharges (power losses) when on standby; and are suitable for connections where excess power is sold to the utility grid.
5). Nickel-Cadmium Battery
There are some reasons why the nickel cadmium solar battery is less popular than its counterparts (lead acid and lithium ion).
One of these is the toxicity of the electrolyte in this type of solar battery, and another is the cost of accessing the component materials. In terms of performance, nickel cadmium battery also has some shortcomings.
The use of nickel cadmium (Ni-Cd) batteries dates back to the late nineteenth century, a period during which battery technology in general was still being developed.
Nickel cadmium batteries found application in aircrafts and similar machinery, with numerous efforts made to improve their efficiency and performance.
An alkaline electrolyte composed of nickel oxide and cadmium, makes up the internal constitution of this type of solar battery.
Compared to other types, nickel cadmium batteries have a generally low efficiency. They also have a relatively-low energy density and high discharge rate. They are therefore not suitable for permanent off-grid applications.
6). Sodium Nickel Chloride (Na-NiCl2) Solar Battery
Sodium constitutes the anode of this type of solar battery, while nickel and sodium chloride constitute the cathode [5].
The sodium nickel chloride solar battery is a high-temperature battery, meaning that it functions optimally at high temperature of between 270°C and 350°C.
It works based on chemical reactions whereby free electrons from sodium flow from the anode, toward the cathode.
Like the lithium-ion battery, sodium nickel chloride batteries where originally designed for electric vehicles at the time of their introduction in the late twentieth century. However, the suitability of their characteristics has caused them to be equally used in renewable technology systems such as solar power.
A sodium nickel solar battery is typically characterized by attributes such as high energy density, environmental compatibility, and resilience. However, because of their high-temperature characteristics, these batteries are not suitable for all conditions of application.
7). Nickel Iron (Ni-Fe) Solar Battery
The composition of this type of solar battery similar to that of the nickel-cadmium battery.
It comprises of an alkaline electrolyte, which is often potassium hydroxide [6].
The anode is usually composed of iron-rich steel wool substrate and the cathode is usually composed of nickel-plated steel wool substrate.
Nickel iron solar batteries have a relatively long lifespan, although this occurs alongside typically low efficiency, and high passive-discharge rate.
There is also a significant degree of instability with regards to the voltage output of these batteries, meaning that they are not very reliable backup devices for solar systems in general.
8). Flow Battery
Also known as Solar Flow Battery (SFB), this represents a new development in battery technology as a whole.
A solar flow battery can be likened to a fuel cell. It differs from all other types of batteries on the basis of electrolyte mobility.
Whereas in conventional batteries, the electrolyte is stationary and is contained within the cell, in close contact with electrodes; the electrolyte in a flow solar battery is mobile.
Usually contained in separate tanks from the main battery cell, this electrolyte is pumped such that it flows through a micro-porous, conductive membrane in the battery unit, causing the flow of electrons [2].
The conductive membrane occurs in combination with a power stack, into which the electrolyte flows. The capacity of the battery usually varies with the size of the tanks and the amount of flowing electrolyte.
Solar flow batteries work by redox (reduction and oxidation) reactions.
When energy is supplied to the battery from the source (which is solar, in this case), it causes electrons to be mobilized in one of the external electrolyte tanks (the positive tank, called the anolyte). This process is driven by oxidation reaction.
The electrons flow into the negative electrolyte tank (the catholyte), where they are stored through the process of reduction. These electrons are what flow into plugged-in devices and supply power when the battery is switched on.
Solar flow batteries are expected to become more prominent, due to their flexibility of scaling (increase or decrease of capacity) and their relatively simple structure.
Advantages and Disadvantages of the Different Types of Solar Battery (based on compositional characteristics)
1). Lead Acid Solar Battery
Advantages
-This is the cheapest and most cost-effective type of solar battery
-Highly reliable
-Relatively easy to recycle and dispose
-One of the most reliable types of solar battery
-They are suitable for off-grid, backup applications
Disadvantages
-They have a relatively short lifespan
-The lead acid solar battery requires high level of maintenance to function optimally
-Low depth of discharge (DoD)
-They require ventilation and well-controlled environmental conditions to operate optimally
2). Lithium-Ion Solar Battery
Advantages
-High Energy Density
-High Efficiency
-Minimal maintenance is required
-High Depth of Discharge
-High output voltage
Disadvantages
-They may be structurally fragile and require a protective circuit framework to be used safely
-Temperature sensitivity makes this type of solar battery difficult to maintain
-Relatively expensive to manufacture (typically cost up to 40% more than Nickel Cadmium; Ni-Cd)
3). Nickel-Cadmium Solar Battery
Advantages
-Durability
-Able to operate under a wide range of temperature conditions
-Requires minimal maintenance
-High current output
-Relatively inexpensive
-Suitable for large-scale utilities (due to their durability)
Disadvantages
-High level of toxicity, due to the presence of cadmium
-Rapid self-discharge rate
-Difficulty of disposal and recycling
-Relatively low energy density
4). Sodium Nickel Chloride (Na-NiCl2) Solar Battery
Advantages
-High energy density
-Durability
-Does not usually require air conditioning like other high-temperature batteries
Disadvantages
-Sensitivity to temperature (functions optimally at high temperature
-Relatively low efficiency
-Ceramic electrolyte is fragile
5). Nickel Iron (Ni-Fe) Battery
Advantages
-Relatively long lifespan
-High Depth of Discharge (DoD)
Disadvantages
-Instability of voltage output due to internal resistance
-Relatively low efficiency
-High rate of water consumption
6). Solar Flow Battery (SFB)
Advantages
-High Depth of Discharge
-Easy Scalability
-Low rate of passive discharge
-Long cycle-life and lifespan (up to 30 years on average)
-Minimal required maintenance
-Thermal resistance
Disadvantages
-Relatively expensive to develop
-Not flexible, due to the need for liquid electrolyte
-Must be large in order to store substantial amount of power
-Generally slow rate of charge and discharge
Comparison of the Types of Solar Battery
The following table provides a comparison of the three most common types of solar battery; which are lead acid, lithium ion and Nickel Cadmium respectively.
| Comparison Criteria | Lead Acid | Lithium Ion | Nickel Cadmium |
| Efficiency (%) | 70-90 | 80-99 | 70-90 |
| Electrolyte | Sulfuric acid (H2SO4) | Lithium hexafluorophosphate (LiPF6) | Potassium Hydroxide (KOH); Nickel Oxide Hydroxide; Metallic Cadmium |
| Average Cost ($/KWh) | 100 | 135 | 1,000 |
| Average Depth of Discharge (DoD) (%) | 50 | 95 | 15 |
| Storage Capacity (Ah) | 100-1,800 | 20-5,000 | 100-1,800 |
| Reliability | Reliable | Highly reliable | Highly reliable |
| Thermal Tolerance range | Broad | Broad | Narrow |
| Lifespan (years) | 3-5 | 5-15 | >20 |
| Environmental Impact | Severe | Minimal | Severe |
| Grid Suitability | Low | Fair | Low |
| Off-Grid Suitability | Fair | High | High |
Best Type of Battery for Solar System
The best type of battery for solar system is the lithium-ion battery.
This assessment is based on different important criteria which have been highlighted in this article.
The criteria include temperature tolerance, cost, environmental impact, efficiency, depth of discharge, lifespan and grid/off-grid suitability.
On average, the lithium-ion solar battery scores best across the different criteria of assessment. This implies that they may be the best choice for use in a solar system.
Conclusion
A solar battery is a device which stores power that has been generated from solar energy.
Along with solar panels and inverters, the solar battery is a component of a solar system.
However, it is not an essential component, as the solar system may yet function optimally in the absence of a solar battery. The key role of the battery is to provide backup power when solar energy is not readily available to be used to generate power.
Various types of solar battery exist. The classification of these batteries may be based on the electrode structure/geometry, or on the internal composition of the battery.
Based on electrode structure, two types of solar battery can be identified. These are the Flat Plate solar battery, and the Tubular Plate solar battery.
Perhaps the most important classification of solar batteries is based on internal composition. This classification takes account of the electrolyte and electrode materials of the battery.
Types under this category include lead acid, lithium ion, nickel cadmium, nickel iron, and sodium nickel chloride solar batteries.
In order to determine which type of battery is best for a solar system, it is important to assess the types of batteries based on some important criteria; such as the energy efficiency, depth of discharge, storage capacity, lifespan, mechanical resilience, reliability, environmental impact, thermal tolerance, grid-suitability and cost.
References
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