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The gross development of any country is directly measured by its per capita energy consumption. Now with almost each nation trying to fall under the gamut of developing and further developed nation, the energy demand of the world is poised to increase. Estimates from the major research organization suggest that the world energy demand shall increase by more than 100% in the next 15~20 years (refer Figure 1). This means that the energy generation need to be ramped up in a similar fashion. However with the world focussing on renewables as a potential generation source and with the every altering energy requirements, both generation and consumption patterns around the world are changing at an imprecise rate. This directly means that the local and/or federal grid(s) may not always be able to accommodate such changes and the utilities need to source/dump additional energy to bridge the generation and demand gap. Additionally with various government(s) around the world focussing on secure and reliable supply of electricity 24x7x365, the stage is set for energy storage (batteries to be more appropriate).
A battery in the simple terms could be defined as a device which stores and delivers electrical energy when required. It basically comprises a positive and a negative electrode separated by an electrolyte (a liquid/semi-solid medium). The electrodes are usually two dissimilar metal (or metal polymer) where chemical reaction takes place when the battery is in use. During discharging, the electrode with the high electron affinity will release electron (which is known as anode) and the electrode with the low electron affinity will gain electron (which is known as cathode). This electron would travel through the load and thus allowing the battery to supply energy (refer Figure 2). Since the discovery and initial development of battery in the 18th century, various chemicals have been utilized to create batteries, which indirectly led to various compositions. Out of all those variants, use of lead acid and lithium ion battery have been prominent. While lead acid have been dominant, the energy storage market is now observing a significant shift to lithium ion battery. For a novice, it is hence necessary to understand the basics of both the battery technology and their implied advantages. Further it is also necessary to have a complete understanding about the indicators which led such shift.
Invented in early 1859 and put to commercial use in the early 19th century, Lead acid battery utilizes lead as a base material with the anode and cathode made up of lead & lead oxide respectively and mixture of sulphuric acid & water as an electrolyte. The battery utilizes chemical reaction between electrolyte and the cathode & anode to generate electricity. The amount of charge stored in/delivered by the battery depends on the concentration of the electrolyte and the area of the plate. While this was the basic chemistry, there were lot of variants of lead acid battery as mentioned below:
- Flooded battery: These are the traditional batteries which allowed the end user to access each and every battery cell. Such access allowed the end users to refill distilled water if the battery dried out. These batteries were used mostly in automobiles (due to its ability to provide surge currents) and for emergency power backups.
- Sealed battery: The sealed battery is similar to flooded battery with only difference that the entire battery is sealed and the user does not have access to battery. This battery was popular amongst engine starting and limited deep cycle applications (i.e. applications requiring enhanced use of battery thus discharging at a deeper level).
- Absorbed Glass Mat (AGM): In this type, the separator in the lead acid battery was replaced by a glass fibre mat. This mat while allowed for electrical inter-connection also enabled the battery to easily transport gases during over-charging, instead of losing it to atmosphere.
- Gel type battery: Here, the liquid electrolyte was completely replaced by a semi solid gel type electrolyte. This allowed the battery to be applicable in extreme conditions as the gel had lower freezing and higher boiling point. The gel type battery however were not capable of providing surge currents and were used most commonly in energy storage applications like off-grid systems.
- Valve Regulated Lead Acid battery (VRLA): Any of the above mentioned battery when they utilized valve for letting the excess gas out during charging were known as VRLA batteries. VRLA were utilized in power applications like off grid supplies, portable electrical devices and applications that require affordable large-scale power storage (like in conventional and nuclear submarines).
While the applications of the lead acid battery were ubiquitous, the ever increasing need of energy in the late 19th century required the amount of storage to increase exponentially. The batteries while cheap had various shortfalls which led the world to explore alternative technologies:
- Heavy in weight: Probably one of the first limitations of the lead acid battery is its weight, which could be directly related to its specific energy density (refer to Figure 2). The lower specific energy density directly means that the battery would require more material if it needs to deliver same amount of energy.
- Inefficient charging/ discharging: Charging/ Discharging a lead acid battery needs more amount of energy and this is simply because it’s charging/ discharging efficiency is only around 85%. The (commercially used) newer battery technologies have charging efficiencies around 95%.
- Longer charging time: Another issue with charging a lead acid battery is its charging time. Typically charging a lead acid battery may follow a 20-80 rule, meaning charging the last 20% of the battery capacity may take 80% of the time.
- Limited life time: Cycle life or more commonly the life of the Lead acid battery technology is relatively shorter. A typical battery discharged to 50% of its capacity (from fully charged state) lasts for around 400 cycles. However, if these batteries were not fully charged (a case as mentioned above) and the cycle life reduces to below 350. Further increasing the DOD of lead acid battery would lower its life exponentially. This means that the applications like off – grid, UPS may need a battery replacement between every 2/3 years, thus increasing the OPEX of the project.
- Limited communication capability: Applications like off-grid, grid energy storage and power plant storage in addition to deep discharging would also need the battery to communicate its typical characteristics like individual cell voltage, temperature, current, etc. during charging and/or discharging. The lead acid battery is not capable of providing such communication firstly and any efforts to develop the same would overshoot the cost of such instrument over the cost of the battery.
- Toxic in nature: Lead is highly toxic metal and once the battery becomes inoperative, it is necessary to ensure its proper collection and eco-friendly recycling. If disposed without suitable measures, both lead and acid could produce a range of adverse health effects affecting the entire ecosystem around such disposal area.
While this article dealt with Lead acid batteries, its types, applications and their advantages, the next article would focus on lithium ion battery explaining its variants & advantages over lead acid battery which has enabled a steep shift towards the technology. Further it would also give readers an overview of the market scenario for lithium ion battery and its applicability in Indian scenario. Keep looking at this space for our next article.
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