With the wide-spread usage of Electricity nowadays – Electrical Energy Storage (EES) is one of the key developing technology. Unlike many other forms of energy – Electricity is difficult to store.
Two characteristics of Electricity lead to issues in its use and at the same time creates need for EES.
Firstly, Electricity has to be consumed at the same time as it is generated. Which means that always the generation has to exactly go up and or down according to demand and this is practically impossible.
Secondly, the places of generation of Electricity and consumption are generally far apart and the spread or density may vary – for example the density of consumption may be high in a city compared to the village. Any fault in power lines means disruption in Electricity.
EES can step in and offer solution in both of the above scenario.
EES helps to make power available during peak demand times by storing part of the electricity generated during off-peak times. This helps in reducing costs on a major scale.
EES aids to improve the reliability of the electrical system by providing power during power outages or during a natural disaster etc. EES also helps to maintain the quality of power to a great extent.
Solar Power generation is highly dependent on EES. An IMS Research report expects the market for storing power from solar panels – which was less than USD200 million in 2012 – will catapult to USD19 billion by 2017.
Electric Vehicles is the most promising technology to help reduce our dependence on fossil fuel and here too EES plays a vital role.
According to market research firm IHS, the energy storage market is set to “explode” to an annual installation size of 6 giga-watts (GW) in 2017 and over 40 GW by 2022 — from an initial base of only 0.34 GW installed in 2012 and 2013.
An early development and still a good solution to store electricity is the BATTERY. However, only DC power could be stored in Batteries – which adopt electro-chemical processes to do this. Recently there have been substantial developments in Battery technology – that aid in utility scale load levelling. CAPACITORS also are being used for Electricity storage. The main limiting factor in a capacitor is the amount of electricity that could be stored in a capacitor. The advantage of capacitor is that the electricity transmission is very fast and also that the degradation of capacitor unlike batteries - is very slow. Electrochemical double layer capacitors (EDLC) – a new technology is showing great promise – which will hopefully make Capacitors a leading device for electricity storage.
FUEL CELL is a device that generates electricity from chemical energy – wherein mainly Hydrogen is the fuel (sometimes Hydro-carbons like Methanol is used). Fuel Cells are also a kind of Battery and they require constant source of fuel to sustain the chemical reaction. NASA Space programs gave an impetus to Fuel Cells research and there are a lot of strides in this technology.
Many newer methods and technologies are evolving for the storage of electricity and a few are as listed :
COMPRESSED AIR: Excess electricity generated during off peak or reduced loading periods are used to compress air – which is stored in unused and old underground mines. This compressed air is then drawn and used to run turbines – generating electricity during peak requirements of electricity.
LIQUEFACTION OF AIR: When surplus electricity is available – air is compressed & cooled and liquefied - and this air is then expanded – to run a turbine generating electricity.
FLYWHEEL: Electricity when available in excess – is made to store mechanical energy by winding a spring loaded flywheel. This flywheel then rotates using the energy stored and runs a generator – that generates electricity.
PUMPED STORAGE HYDRO-ELECTRICITY: Surplus electricity is used to pump large volumes of water to a higher altitude – which is then stored there and this stored water is released at a later time when electricity is needed ( during peak time ) – and by running the turbines with this pumped and released water – electricity is generated.
SUPER-CONDUCTING MAGNETIC ENERGY: These systems store energy in the magnetic field created by the flow of direct current in a super-conducting coil – which has been cooled to a very low temperature. Once the super-conducting coil is charged – the current will not decay and stay forever. Since DC current is stored – an inverter is needed to transform the power into AC (alternating current). Though this looks simple on paper – there are some challenges to be solved before it become cost effective.
BATTERY: Though there are many newer technologies available – Battery continues to be the work horse for electricity storage. Only DC power can be stored in a battery. An Inverter is used to convert the DC power stored to AC power when needed. If you look at any battery, you'll notice that it has two terminals. One terminal is marked (+), or positive, while the other is marked (-), or negative. Metal Plates are connected to these terminals which are assigned positive and negative polarity. These plates are immersed in an acidic solution. These plates interact chemically with the solute and either gives off or gain electrons. These electrons may be channeled through the terminals – creating electric current. This chemical reaction is reversible and that is how we can recharge the battery.
BATTERY TYPES: There are many classifications of battery based on (a) capacity (b) material used etc. Lead Acid, Metal Hydride and Lithium ion batteries are the most common Batteries in use today.
The battery type used in Electric cars or UPS is called Lead Acid battery.
The Metal Hydride and Lithium Ion Batteries, which are very high in efficiency – are generally used for smaller applications – like Mobile Phones etc.
Lead Acid Battery are classified into 2 types based mainly on the need for Water Top up – (a) Low Maintenance Flooded type and (b) Sealed Maintenance free type (SMF). In flooded type the acid is in liquid form mixed with water and needs to be topped up with distilled water once every 4-6 months. In the SMF type the acid is in a gel form and is fully sealed, needing no water topping at all.
RECHARGEABLE BATTERY: Recharging of battery is one of the greatest innovation in this field. Rechargeable batteries are a type of battery in which the power stored can be depleted and then again replenished. This is done by an electrically reversible electro-chemical process and in layman’s terms they are called as charging and discharging. Batteries that can be charged again after depletion are called rechargeable batteries and those that cannot be recharged are called disposable batteries. Compared to disposable batteries, rechargeable ones have lower costs. Though rechargeable batteries have higher initial cost and need a charger too, while considering in high usage scenarios, the rechargeable ones work a lot cheaper than disposable battery. Rechargeable batteries have also lower environmental impact. Rechargeable batteries come in many sizes and shapes and for many applications including automotive, electric tools, toys, camera etc.
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