By: Jennifer Hwang, Wenyuan Bao
During an era where scientists are investigating greener sources of energy storage, ultracapacitors have emerged, with enormous storage capacity compared to batteries. Ultracapacitors function similarly to capacitors, gaining potential energy from the buildup of opposite charges on the two capacitor plates. Because capacitance (capacity of energy storage) rises in proportion to increased surface area of plates, scientists are seeking to maximize the surface areas of capacitor plates. To do so, scientists coat the metal plates with spongy, porous material, known as activated carbon, which increases the surface area by 10,000 to 100,000 times. Then, the plates are immersed in an electrolyte of positive and negative ions dissolved in a solvent known as dielectric, a polarizable insulator which increases the surface charge in a capacitor and hence, capacitance (ScienceDaily).
A potential, greener replacement of activated carbon is biochar, a byproduct resulting from the burning of organic matter; thus, as fuel consumption increases, biochar production also increases. Because biochar is nontoxic, easily disposed of, and less costly than activated carbon, it is a more sustainable material that can increase surface area of the plates. By using biochar instead of activated carbon, producers can drive down the cost of ultracapacitors, leading to integration of ultracapacitors into more devices, such as electronics (Supercapacitors).
There are several disadvantages associated with ultracapacitors. Most ultracapacitors offer lower voltage than standard batteries, so a series of ultracapacitors is needed to have voltage equal to a battery. Also, voltage across an ultracapacitor drops significantly as the ultracapacitor discharges, so voltage is unsteady. Furthermore, ultracapacitors have very low internal resistance compared to standard batteries; if the circuit is shorted, ultracapacitors will discharge very quickly and create sparks, creating a fire hazard (ScienceDaily).
However, ultracapacitors, if further developed, could store as much energy as batteries and avoid the environmental threat of poisonous metals (nickel, cadmium, mercury) used in batteries. Furthermore, the coupling of ultracapacitors with fuel cells would popularize environmentally-friendly, fuel-efficient automobiles (GigaOm).
In the future, ultracapacitors, which effectively provide sudden surges of energy, could be coupled with batteries in many electronic devices. For example, in electric cars, ultracapacitors could provide power for acceleration, and the battery could provide range. Ultracapacitors could also provide surges of power during stops and starts of cars. In addition, on electric grids, ultracapacitors could be set up to absorb power surges, allowing transmission lines to operate closer to 100 percent capacity, which would be more cost-friendly than adding new transmission lines. Therefore, with further development, ultracapacitors could eventually replace batteries in certain devices, providing a more efficient, durable storage device (WorldandI).
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How Ultracapacitors Work (and why they fall short). GigaOm. http://gigaom.com/cleantech/how-ultracapacitors-work-and-why-they-fall-short/. (accessed: June 10, 2012).
Supercapacitors: Cheaper, Greener, Alternative Energy Storage. ScienceDaily.
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Ultracapacitors Challenge the Battery. WorldandI. http://www.worldandi.com/subscribers/feature_detail.asp?num=23938. (accessed: June 10, 2012).