Schematic illustration of a supercapacitor

A supercapacitor (SC), also called an ultracapacitor, is a high-capacity

capacitor A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals. The effect of a ...

, with a

capacitance Capacitance is the capability of a material object or device to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized a ...

value much higher than other capacitors but with lower

voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge t ...

limits. It bridges the gap between

electrolytic capacitor An electrolytic capacitor is a polarized capacitor whose anode or positive plate is made of a metal that forms an insulating oxide layer through anodization. This oxide layer acts as the dielectric of the capacitor. A solid, liquid, or gel ...

s and

rechargeable batteries A rechargeable battery, storage battery, or secondary cell (formally a type of energy accumulator), is a type of electrical battery which can be charged, discharged into a load, and recharged many times, as opposed to a disposable or pri ...

. It typically stores 10 to 100 times more energy per unit volume or mass than electrolytic capacitors, can accept and deliver charge much faster than batteries, and tolerates many more charge and discharge cycles than

. Supercapacitors are used in applications requiring many rapid charge/discharge cycles, rather than long-term compact energy storage — in automobiles, buses, trains, cranes and elevators, where they are used for

regenerative braking Regenerative braking is an energy recovery mechanism that slows down a moving vehicle or object by converting its kinetic energy into a form that can be either used immediately or stored until needed. In this mechanism, the electric traction m ...

, short-term energy storage, or burst-mode power delivery. Smaller units are used as power backup for

static random-access memory Static random-access memory (static RAM or SRAM) is a type of random-access memory (RAM) that uses latching circuitry (flip-flop) to store each bit. SRAM is volatile memory; data is lost when power is removed. The term ''static'' differe ...

(SRAM). Unlike ordinary capacitors, supercapacitors do not use the conventional solid

dielectric In electromagnetism, a dielectric (or dielectric medium) is an electrical insulator that can be polarised by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the m ...

, but rather, they use

electrostatic Electrostatics is a branch of physics that studies electric charges at rest (static electricity). Since classical times, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word for am ...

double-layer capacitance and

electrochemical Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference, as a measurable and quantitative phenomenon, and identifiable chemical change, with the potential difference as an outco ...

pseudocapacitance, both of which contribute to the total capacitance of the capacitor, with a few differences: * Electrostatic double-layer capacitors (EDLCs) use

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes ...

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials ...

s or derivatives with much higher electrostatic double-layer capacitance than electrochemical pseudocapacitance, achieving separation of charge in a

Helmholtz Hermann Ludwig Ferdinand von Helmholtz (31 August 1821 – 8 September 1894) was a German physicist and physician who made significant contributions in several scientific fields, particularly hydrodynamic stability. The Helmholtz Association, ...

double layer at the

interface Interface or interfacing may refer to: Academic journals * ''Interface'' (journal), by the Electrochemical Society * '' Interface, Journal of Applied Linguistics'', now merged with ''ITL International Journal of Applied Linguistics'' * '' Int ...

between the surface of a conductive electrode and an electrolyte. The separation of charge is of the order of a few

ångström The angstromEntry "angstrom" in the Oxford online dictionary. Retrieved on 2019-03-02 from https://en.oxforddictionaries.com/definition/angstrom.Entry "angstrom" in the Merriam-Webster online dictionary. Retrieved on 2019-03-02 from https://www.m ...

s (0.3–0.8 nm), much smaller than in a conventional capacitor. * Electrochemical pseudocapacitors use

metal oxide An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the E ...

conducting polymer Conductive polymers or, more precisely, intrinsically conducting polymers (ICPs) are organic polymers that conduct electricity. Such compounds may have metallic conductivity or can be semiconductors. The biggest advantage of conductive polymer ...

electrodes with a high amount of electrochemical pseudocapacitance additional to the double-layer capacitance. Pseudocapacitance is achieved by Faradaic

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary partic ...

charge-transfer with

redox reactions Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a de ...

intercalation Intercalation may refer to: * Intercalation (chemistry), insertion of a molecule (or ion) into layered solids such as graphite *Intercalation (timekeeping), insertion of a leap day, week or month into some calendar years to make the calendar foll ...

or electrosorption. * Hybrid capacitors, such as the

lithium-ion capacitor A lithium-ion capacitor (LIC) is a hybrid type of capacitor classified as a type of supercapacitor. It is called a hybrid because the anode is the same as those used in lithium-ion batteries and the cathode is the same as those used in supercapa ...

, use electrodes with differing characteristics: one exhibiting mostly electrostatic capacitance and the other mostly electrochemical capacitance. The electrolyte forms an ionic conductive connection between the two electrodes which distinguishes them from conventional electrolytic capacitors where a dielectric layer always exists, and the so-called electrolyte, ''e.g.'', MnO₂ or conducting polymer, is in fact part of the second electrode (the cathode, or more correctly the positive electrode). Supercapacitors are polarized by design with asymmetric electrodes, or, for symmetric electrodes, by a potential applied during manufacturing.

History

Development of the double layer and pseudocapacitance models (see

Double layer (interfacial) A double layer (DL, also called an electrical double layer, EDL) is a structure that appears on the surface of an object when it is exposed to a fluid. The object might be a solid particle, a gas bubble, a liquid droplet, or a porous body. The ...

Evolution of components

In the early 1950s,

General Electric General Electric Company (GE) is an American multinational conglomerate founded in 1892, and incorporated in New York state and headquartered in Boston. The company operated in sectors including healthcare, aviation, power, renewable energ ...

engineers began experimenting with porous carbon electrodes in the design of capacitors, from the design of

fuel cell A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen fuel, hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most bat ...

s and

Activated charcoal "Activated" is a song by English singer Cher Lloyd. It was released on 22 July 2016 through Vixen Records. The song was made available to stream exclusively on ''Rolling Stone'' a day before to release (on 21 July 2016). Background In an inter ...

is an

electrical conductor In physics and electrical engineering, a conductor is an object or type of material that allows the flow of charge (electric current) in one or more directions. Materials made of metal are common electrical conductors. Electric current is gen ...

that is an extremely porous "spongy" form of carbon with a high

specific surface area Specific surface area (SSA) is a property of solids defined as the total surface area of a material per unit of mass, (with units of m2/kg or m2/g) or solid or bulk volume (units of m2/m3 or m−1). It is a physical value that can be used to dete ...

. In 1957 H. Becker developed a "Low voltage electrolytic capacitor with porous carbon electrodes". He believed that the energy was stored as a charge in the carbon pores as in the pores of the etched foils of electrolytic capacitors. Because the double layer mechanism was not known by him at the time, he wrote in the patent: "It is not known exactly what is taking place in the component if it is used for energy storage, but it leads to an extremely high capacity." General Electric did not immediately pursue this work. In 1966 researchers at

Standard Oil of Ohio The Standard Oil Company (Ohio) was an American oil company, a successor of the original company established in 1870 by John D. Rockefeller. It was established as "Standard Oil Company of Ohio" as one of the separate entities created after t ...

(SOHIO) developed another version of the component as "electrical energy storage apparatus", while working on experimental

designs.J. G. Schindall, The Change of the Ultra-Capacitors, IEEE Spectrum, November 200

/ref> The nature of electrochemical energy storage was not described in this patent. Even in 1970, the electrochemical capacitor patented by Donald L. Boos was registered as an electrolytic capacitor with activated carbon electrodes. Early electrochemical capacitors used two aluminum foils covered with activated carbon — the electrodes — that were soaked in an electrolyte and separated by a thin porous insulator. This design gave a capacitor with a capacitance on the order of one

farad The farad (symbol: F) is the unit of electrical capacitance, the ability of a body to store an electrical charge, in the International System of Units (SI). It is named after the English physicist Michael Faraday (1791–1867). In SI base unit ...

, significantly higher than electrolytic capacitors of the same dimensions. This basic mechanical design remains the basis of most electrochemical capacitors. SOHIO did not commercialize their invention, licensing the technology to NEC, who finally marketed the results as "supercapacitors" in 1978, to provide backup power for computer memory. Between 1975 and 1980 Brian Evans Conway conducted extensive fundamental and development work on

ruthenium oxide Ruthenium oxide may refer to either of the following: * Ruthenium(IV) oxide, RuO2 * Ruthenium(VIII) oxide, RuO4 {{Short pages monitor Device properties can also be seen to be dependent on device temperature. As the temperature of the device changes either through operation of varying ambient temperature, the internal properties such as capacitance and resistance will vary as well. Device capacitance is seen to increase as the operating temperature increases.

Energy capacity

Supercapacitors occupy the gap between high power/low energy

s and low power/high energy rechargeable Rechargeable batteries, batteries. The energy W_max (expressed in Joule) that can be stored in a capacitor is given by the formula :

W_\text=\frac\cdot C_\text \cdot V_\text^2

This formula describes the amount of energy stored and is often used to describe new research successes. However, only part of the stored energy is available to applications, because the voltage drop and the time constant over the internal resistance mean that some of the stored charge is inaccessible. The effective realized amount of energy W_eff is reduced by the used voltage difference between V_max and V_min and can be represented as: :

W_\text=\frac\ C \cdot\ ( V_\text^2 - V_\text^2 )

This formula also represents the energy asymmetric voltage components such as lithium ion capacitors.

Specific energy and specific power

The amount of energy that can be stored in a capacitor ''per mass'' of that capacitor is called its

specific energy Specific energy or massic energy is energy per unit mass. It is also sometimes called gravimetric energy density, which is not to be confused with energy density, which is defined as energy per unit volume. It is used to quantify, for example, sto ...

. Specific energy is measured Gravimetry, gravimetrically (per unit of mass) in Watt-hour per kilogram, watt-hours per kilogram (Wh/kg). The amount of energy can be stored in a capacitor ''per volume'' of that capacitor is called its energy density (also called volumetric specific energy in some literature). Energy density is measured volumetrically (per unit of volume) in watt-hours per litre (Wh/L). Units of liters and dm³ can be used interchangeably. commercial energy density varies widely, but in general range from around 5 to . In comparison, petrol fuel has an energy density of 32.4 MJ/L or . Commercial specific energies range from around 0.5 to . For comparison, an aluminum electrolytic capacitor stores typically 0.01 to , while a conventional lead-acid battery stores typically 30 to and modern lithium-ion battery, lithium-ion batteries 100 to . Supercapacitors can therefore store 10 to 100 times more energy than electrolytic capacitors, but only one tenth as much as batteries. For reference, petrol fuel has a specific energy of 44.4 MJ/kg or . Although the specific energy of supercapacitors is defavorably compared with batteries, capacitors have the important advantage of the specific power. Specific power describes the speed at which energy can be delivered to the Electrical load, load (or, in charging the device, absorbed from the generator). The maximum power P_max specifies the power of a theoretical rectangular single maximum current peak of a given voltage. In real circuits the current peak is not rectangular and the voltage is smaller, caused by the voltage drop, so IEC 62391–2 established a more realistic effective power P_eff for supercapacitors for power applications, which is half the maximum and given by the following formulas : :

P_\text=\frac\cdot\frac

, :

P_\text=\frac\cdot\frac

with V = voltage applied and R_i, the internal DC resistance of the capacitor. Just like specific energy, specific power is measured either gravimetrically in kilowatts per kilogram (kW/kg, specific power) or volumetrically in kilowatts per litre (kW/L, power density). Supercapacitor specific power is typically 10 to 100 times greater than for batteries and can reach values up to 15 kW/kg. Ragone charts relate energy to power and are a valuable tool for characterizing and visualizing energy storage components. With such a diagram, the position of specific power and specific energy of different storage technologies is easily to compare, see diagram.

Lifetime

Since supercapacitors do not rely on chemical changes in the electrodes (except for those with polymer electrodes), lifetimes depend mostly on the rate of evaporation of the liquid electrolyte. This evaporation is generally a function of temperature, current load, current cycle frequency and voltage. Current load and cycle frequency generate internal heat, so that the evaporation-determining temperature is the sum of ambient and internal heat. This temperature is measurable as core temperature in the center of a capacitor body. The higher the core temperature the faster the evaporation and the shorter the lifetime. Evaporation generally results in decreasing capacitance and increasing internal resistance. According to IEC/EN 62391-2 capacitance reductions of over 30% or internal resistance exceeding four times its data sheet specifications are considered "wear-out failures", implying that the component has reached end-of-life. The capacitors are operable, but with reduced capabilities. Whether the aberration of the parameters have any influence on the proper functionality or not depends on the application of the capacitors. Such large changes of electrical parameters specified in IEC/EN 62391-2 are usually unacceptable for high current load applications. Components that support high current loads use much smaller limits, ''e.g.'', 20% loss of capacitance or double the internal resistance.Maxwell Application Not
''Application Note - Energy Storage Modules Life Duration Estimation.''
Maxwell Technologies, Inc. 2007 The narrower definition is important for such applications, since heat increases linearly with increasing internal resistance and the maximum temperature should not be exceeded. Temperatures higher than specified can destroy the capacitor. The real application lifetime of supercapacitors, also called "service life", "life expectancy" or "load life", can reach 10 to 15 years or more at room temperature. Such long periods cannot be tested by manufacturers. Hence, they specify the expected capacitor lifetime at the maximum temperature and voltage conditions. The results are specified in datasheets using the notation "tested time (hours)/max. temperature (°C)", such as "5000 h/65 °C". With this value and expressions derived from historical data, lifetimes can be estimated for lower temperature conditions. Datasheet lifetime specification is tested by the manufactures using an accelerated aging test called "endurance test" with maximum temperature and voltage over a specified time. For a "zero defect" product policy during this test no wear out or total failure may occur. The lifetime specification from datasheets can be used to estimate the expected lifetime for a given design. The "10-degrees-rule" used for electrolytic capacitors with non-solid electrolyte is used in those estimations and can be used for supercapacitors. This rule employs the Arrhenius equation, a simple formula for the temperature dependence of reaction rates. For every 10 °C reduction in operating temperature, the estimated life doubles. :

L_x =L_0\cdot 2^\frac

With *L_x = estimated lifetime *L₀ = specified lifetime *T₀ = upper specified capacitor temperature *T_x = actual operating temperature of the capacitor cell Calculated with this formula, capacitors specified with 5000 h at 65 °C, have an estimated lifetime of 20,000 h at 45 °C. Lifetimes are also dependent on the operating voltage, because the development of gas in the liquid electrolyte depends on the voltage. The lower the voltage the smaller the gas development and the longer the lifetime. No general formula relates voltage to lifetime. The voltage dependent curves shown from the picture are an empirical result from one manufacturer. Life expectancy for power applications may be also limited by current load or number of cycles. This limitation has to be specified by the relevant manufacturer and is strongly type dependent.

Self-discharge

Storing electrical energy in the double-layer separates the charge carriers within the pores by distances in the range of molecules. Over this short distance irregularities can occur, leading to a small exchange of charge carriers and gradual discharge. This self-discharge is called leakage current. Leakage depends on capacitance, voltage, temperature and the chemical stability of the electrode/electrolyte combination. At room temperature leakage is so low that it is specified as time to self-discharge. Supercapacitor self-discharge time is specified in hours, days or weeks. As an example, a 5.5 V/F Panasonic "Goldcapacitor" specifies a voltage drop at 20 °C from 5.5 V to 3 V in 600 hours (25 days or 3.6 weeks) for a double cell capacitor.

Post charge voltage relaxation

It has been noticed that after the EDLC experiences a charge or discharge, the voltage will drift over time, relaxing toward its previous voltage level. The observed relaxation can occur over several hours and is likely due to long diffusion time constants of the porous electrodes within the EDLC.

Polarity

Since the positive and negative electrodes (or simply positrode and negatrode, respectively) of symmetric supercapacitors consist of the same material, theoretically supercapacitors have no true Electrical polarity, polarity and catastrophic failure does not normally occur. However reverse-charging a supercapacitor lowers its capacity, so it is recommended practice to maintain the polarity resulting from the formation of the electrodes during production. Asymmetric supercapacitors are inherently polar. Pseudocapacitor and hybrid supercapacitors which have electrochemical charge properties may not be operated with reverse polarity, precluding their use in AC operation. However, this limitation does not apply to EDLC supercapacitors A bar in the insulating sleeve identifies the negative terminal in a polarized component. In some literature, the terms "anode" and "cathode" are used in place of negative electrode and positive electrode. Using anode and cathode to describe the electrodes in supercapacitors (and also rechargeable batteries including lithium ion batteries) can lead to confusion, because the polarity changes depending on whether a component is considered as a generator or as a consumer of current. In electrochemistry, cathode and anode are related to reduction and oxidation reactions, respectively. However, in supercapacitors based on electric double layer capacitance, there is no oxidation nor reduction reactions on any of the two electrodes. Therefore, the concepts of cathode and anode do not apply.

Comparison of selected commercial supercapacitors

The range of electrodes and electrolytes available yields a variety of components suitable for diverse applications. The development of low-ohmic electrolyte systems, in combination with electrodes with high pseudocapacitance, enable many more technical solutions. The following table shows differences among capacitors of various manufacturers in capacitance range, cell voltage, internal resistance (ESR, DC or AC value) and volumetric and gravimetric specific energy. In the table, ESR refers to the component with the largest capacitance value of the respective manufacturer. Roughly, they divide supercapacitors into two groups. The first group offers greater ESR values of about 20 milliohms and relatively small capacitance of 0.1 to 470 F. These are "double-layer capacitors" for memory back-up or similar applications. The second group offers 100 to 10,000 F with a significantly lower ESR value under 1 milliohm. These components are suitable for power applications. A correlation of some supercapacitor series of different manufacturers to the various construction features is provided in Pandolfo and Hollenkamp. In commercial double-layer capacitors, or, more specifically, EDLCs in which energy storage is predominantly achieved by double-layer capacitance, energy is stored by forming an electrical double layer of electrolyte ions on the surface of conductive electrodes. Since EDLCs are not limited by the electrochemical charge transfer kinetics of batteries, they can charge and discharge at a much higher rate, with lifetimes of more than 1 million cycles. The EDLC energy density is determined by operating voltage and the specific capacitance (farad/gram or farad/cm³) of the electrode/electrolyte system. The specific capacitance is related to the Specific Surface Area (SSA) accessible by the electrolyte, its interfacial double-layer capacitance, and the electrode material density. Commercial EDLCs are based on two symmetric electrodes impregnated with electrolytes comprising tetraethylammonium tetrafluoroborate salts in organic solvents. Current EDLCs containing organic electrolytes operate at 2.7 V and reach energy densities around 5-8 Wh/kg and 7 to 10 Wh/L. The specific capacitance is related to the specific surface area (SSA) accessible by the electrolyte, its interfacial double-layer capacitance, and the electrode material density. Graphene-based platelets with mesoporous spacer material is a promising structure for increasing the SSA of the electrolyte.

Standards

Supercapacitors vary sufficiently that they are rarely interchangeable, especially those with higher specific energy. Applications range from low to high peak currents, requiring standardized test protocols.P. Van den Bossche et al.:
The Cell versus the System: Standardization challenges for electricity storage devices
' EVS24 International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium, Stavanger/Norway 2009 Test specifications and parameter requirements are specified in the generic specification * International Electrotechnical Commission, IEC/European Committee for Standardization, EN 62391–1, ''Fixed electric double layer capacitors for use in electronic equipment''. The standard defines four application classes, according to discharge current levels: # Memory backup # Energy storage, mainly used for driving motors require a short time operation, # Power, higher power demand for a long time operation, # Instantaneous power, for applications that requires relatively high current units or peak currents ranging up to several hundreds of amperes even with a short operating time Three further standards describe special applications: * IEC 62391–2, ''Fixed electric double-layer capacitors for use in electronic equipment - Blank detail specification - Electric double-layer capacitors for power application'' * IEC 62576, ''Electric double-layer capacitors for use in hybrid electric vehicles. Test methods for electrical characteristics'' * BS/EN 61881-3, ''Railway applications. Rolling stock equipment. Capacitors for power electronics. Electric double-layer capacitors''

Applications

Supercapacitors do not support alternating current (AC) applications. Supercapacitors have advantages in applications where a large amount of power is needed for a relatively short time, where a very high number of charge/discharge cycles or a longer lifetime is required. Typical applications range from milliamp currents or milliwatts of power for up to a few minutes to several amps current or several hundred kilowatts power for much shorter periods. The time t a supercapacitor can deliver a constant current I can be calculated as: :

t=\frac

as the capacitor voltage decreases from U_charge down to U_min. If the application needs a constant power P for a certain time t this can be calculated as: :

t=\frac\cdot C\cdot(U_\text^2-U_\text^2).

wherein also the capacitor voltage decreases from U_charge down to U_min.

General

Consumer electronics

In applications with fluctuating loads, such as laptop computers, Personal digital assistant, PDAs, GPS navigation device, GPS, portable media players, Mobile device, hand-held devices, and photovoltaic systems, supercapacitors can stabilize the power supply. Supercapacitors deliver power for flash (photography), photographic flashes in digital cameras and for LED flashlights that can be charged in much shorter periods of time, ''e.g.'', 90 seconds. Some portable speakers are powered by supercapacitors.

Tools

A cordless electric screwdriver with supercapacitors for energy storage has about half the run time of a comparable battery model, but can be fully charged in 90 seconds. It retains 85% of its charge after three months left idle.

Grid power buffer

Numerous non-linear loads, such as Electric vehicle, EV chargers, Hybrid electric vehicle, HEVs, air conditioning systems, and advanced power conversion systems cause current fluctuations and harmonics. These current differences create unwanted voltage fluctuations and therefore power oscillations on the grid.M. Farhadi and O. Mohammed
Real-time operation and harmonic analysis of isolated and non-isolated hybrid DC microgrid
IEEE Trans. Ind. Appl., vol.50, no.4, pp.2900–2909, Jul./Aug. 2014. Power oscillations not only reduce the efficiency of the grid, but can cause voltage drops in the common coupling bus, and considerable frequency fluctuations throughout the entire system. To overcome this problem, supercapacitors can be implemented as an interface between the load and the grid to act as a buffer between the grid and the high pulse power drawn from the charging station.

Low-power equipment power buffer

Supercapacitors provide backup or emergency shutdown power to low-power equipment such as Random-access memory, RAM, SRAM, micro-controllers and PC Cards. They are the sole power source for low energy applications such as automated meter reading (AMR)R. Gallay, Garmanage
Technologies and applications of Supercapacitors
, University of Mondragon, 22 June 2012 equipment or for event notification in industrial electronics. Supercapacitors buffer power to and from

, mitigating the effects of short power interruptions and high current peaks. Batteries kick in only during extended interruptions, ''e.g.'', if the Mains electricity, mains power or a

fails, which lengthens battery life. Uninterruptible power supplies (UPS) may be powered by supercapacitors, which can replace much larger banks of electrolytic capacitors. This combination reduces the cost per cycle, saves on replacement and maintenance costs, enables the battery to be downsized and extends battery life. Windrad-Nahaufnahme

Supercapacitors provide backup power for actuators in wind turbine pitch systems, so that blade pitch can be adjusted even if the main supply fails.

Voltage stabilizer

Supercapacitors can stabilize voltage fluctuations for Overhead power line, powerlines by acting as dampers. Wind and photovoltaic systems exhibit fluctuating supply evoked by gusting or clouds that supercapacitors can buffer within milliseconds.

Micro grids

Micro grids are usually powered by clean and renewable energy. Most of this energy generation, however, is not constant throughout the day and does not usually match demand. Supercapacitors can be used for micro grid storage to instantaneously inject power when the demand is high and the production dips momentarily, and to store energy in the reverse conditions. They are useful in this scenario, because micro grids are increasingly producing power in DC, and capacitors can be utilized in both DC and AC applications. Supercapacitors work best in conjunction with chemical batteries. They provide an immediate voltage buffer to compensate for quick changing power loads due to their high charge and discharge rate through an active control system. Once the voltage is buffered, it is put through an inverter to supply AC power to the grid. It is important to note that supercapacitors cannot provide frequency correction in this form directly in the AC grid.

Energy harvesting

Supercapacitors are suitable temporary energy storage devices for energy harvesting systems. In energy harvesting systems, the energy is collected from the ambient or renewable sources, ''e.g.'', mechanical movement, light or electromagnetic fields, and converted to electrical energy in an energy storage device. For example, it was demonstrated that energy collected from RF (radio frequency) fields (using an RF antenna as an appropriate rectifier circuit) can be stored to a printed supercapacitor. The harvested energy was then used to power an application-specific integrated circuit (ASIC) for over 10 hours.

Incorporation into batteries

The UltraBattery is a hybrid rechargeable lead-acid battery and a supercapacitor. Its cell construction contains a standard lead-acid battery positive electrode, standard sulphuric acid electrolyte and a specially prepared negative carbon-based electrode that store electrical energy with double-layer capacitance. The presence of the supercapacitor electrode alters the chemistry of the battery and affords it significant protection from sulfation in high rate partial state of charge use, which is the typical failure mode of VRLA battery, valve regulated lead-acid cells used this way. The resulting cell performs with characteristics beyond either a lead-acid cell or a supercapacitor, with charge and discharge rates, cycle life, efficiency and performance all enhanced.

Medical

Supercapacitors are used in defibrillators where they can deliver 500 joules to shock the heart back into sinus rhythm.

Transport

Aviation

In 2005, aerospace systems and controls company Diehl Aerospace, Diehl Luftfahrt Elektronik GmbH chose supercapacitors to power emergency actuators for doors and evacuation slides used in airliners, including the Airbus 380.

Military

Supercapacitors' low internal resistance supports applications that require short-term high currents. Among the earliest uses were motor startup (cold engine starts, particularly with diesels) for large engines in tanks and submarines. Supercapacitors buffer the battery, handling short current peaks, reducing cycling and extending battery life. Further military applications that require high specific power are phased array radar antennae, laser power supplies, military radio communications, avionics displays and instrumentation, backup power for airbag deployment and GPS-guided missiles and projectiles.

Automotive

Toyota Yaris, Toyota's Yaris Hybrid-R concept car uses a supercapacitor to provide bursts of power. PSA Peugeot Citroën has started using supercapacitors as part of its stop-start fuel-saving system, which permits faster initial acceleration. Mazda's i-ELOOP system stores energy in a supercapacitor during deceleration and uses it to power on-board electrical systems while the engine is stopped by the stop-start system.

Bus/tram

Maxwell Technologies, an American supercapacitor-maker, claimed that more than 20,000 hybrid buses use the devices to increase acceleration, particularly in China. Guangzhou, In 2014 China began using trams powered with supercapacitors that are recharged in 30 seconds by a device positioned between the rails, storing power to run the tram for up to 4 km — more than enough to reach the next stop, where the cycle can be repeated. Construcciones y Auxiliar de Ferrocarriles, CAF also offers supercapacitors on their Urbos 3 trams in the form of their Acumulador de Carga Rápida, ACR system.

Energy recovery

A primary challenge of all transport is reducing energy consumption and reducing emissions. Recovery of braking energy (recuperation or

) helps with both. This requires components that can quickly store and release energy over long times with a high cycle rate. Supercapacitors fulfill these requirements and are therefore used in various applications in transportation.

Railway

Supercapacitors can be used to supplement batteries in starter systems in Diesel engine, diesel railroad locomotives with diesel-electric transmission. The capacitors capture the braking energy of a full stop and deliver the peak current for starting the diesel engine and acceleration of the train and ensures the stabilization of line voltage. Depending on the driving mode up to 30% energy saving is possible by recovery of braking energy. Low maintenance and environmentally friendly materials encouraged the choice of supercapacitors.

Cranes, forklifts and tractors

Kuantan Port Container Yard with Rubber Tyre Gantry

Mobile hybrid Diesel engine, Diesel-electric rubber tyred gantry cranes move and stack containers within a terminal. Lifting the boxes requires large amounts of energy. Some of the energy could be recaptured while lowering the load, resulting in improved efficiency. A triple hybrid forklift truck uses fuel cells and batteries as primary energy storage and supercapacitors to buffer power peaks by storing braking energy. They provide the fork lift with peak power over 30 kW. The triple-hybrid system offers over 50% energy savings compared with Diesel or fuel-cell systems. Supercapacitor-powered Shunt truck, terminal tractors transport containers to warehouses. They provide an economical, quiet and pollution-free alternative to Diesel terminal tractors.

Light-rails and trams

Supercapacitors make it possible not only to reduce energy, but to replace overhead lines in historical city areas, so preserving the city's architectural heritage. This approach may allow many new light rail city lines to replace overhead wires that are too expensive to fully route. In 2003 Mannheim adopted a prototype light-rail vehicle (LRV) using the British Rail Class 377#MITRAC, MITRAC Energy Saver system from Bombardier Transportation to store mechanical braking energy with a roof-mounted supercapacitor unit. It contains several units each made of 192 capacitors with 2700 F / 2.7 V interconnected in three parallel lines. This circuit results in a 518 V system with an energy content of 1.5 kWh. For acceleration when starting this "on-board-system" can provide the LRV with 600 kW and can drive the vehicle up to 1 km without overhead line supply, thus better integrating the LRV into the urban environment. Compared to conventional LRVs or Metro vehicles that return energy into the grid, onboard energy storage saves up to 30% and reduces peak grid demand by up to 50%. Paris-tramway

In 2009 supercapacitors enabled LRVs to operate in the historical city area of Heidelberg without overhead wires, thus preserving the city's architectural heritage. The SC equipment cost an additional €270,000 per vehicle, which was expected to be recovered over the first 15 years of operation. The supercapacitors are charged at stop-over stations when the vehicle is at a scheduled stop. In April 2011 German regional transport operator Rhein-Neckar, responsible for Heidelberg, ordered a further 11 units. In 2009, Alstom and RATP Group, RATP equipped a Alstom Citadis, Citadis tram with an experimental energy recovery system called "STEEM". The system is fitted with 48 roof-mounted supercapacitors to store braking energy, which provides tramways with a high level of energy autonomy by enabling them to run without overhead power lines on parts of its route, recharging while traveling on powered stop-over stations. During the tests, which took place between the Porte d’Italie and Porte de Choisy stops on Île-de-France tramway Line 3a and 3b, line T3 of the Tramways in Île-de-France, tramway network in Paris, the tramset used an average of approximately 16% less energy. VLT Rio 09 2016 3392

In 2012 tram operator Geneva Public Transport began tests of an LRV equipped with a prototype roof-mounted supercapacitor unit to recover braking energy. Siemens is delivering supercapacitor-enhanced light-rail transport systems that include mobile storage. Hong Kong's South Island metro line is to be equipped with two 2 MW energy storage units that are expected to reduce energy consumption by 10%. In August 2012 the Zhuzhou Electric Locomotive Works, CSR Zhuzhou Electric Locomotive corporation of China presented a prototype two-car light metro train equipped with a roof-mounted supercapacitor unit. The train can travel up 2 km without wires, recharging in 30 seconds at stations via a ground mounted pickup. The supplier claimed the trains could be used in 100 small and medium-sized Chinese cities. Seven trams (street cars) powered by supercapacitors were scheduled to go into operation in 2014 in Guangzhou, China. The supercapacitors are recharged in 30 seconds by a device positioned between the rails. That powers the tram for up to . As of 2017, Zhuzhou's supercapacitor vehicles are also used on the new Nanjing streetcar system, and are undergoing trials in Wuhan. In 2012, in Lyon (France), the :fr:Sytral, SYTRAL (Lyon public transportation administration) started experiments of a "way side regeneration" system built by Adetel Group which has developed its own energy saver named ″NeoGreen″ for LRV, LRT and metros. In 2015, Alstom announced SRS, an energy storage system that charges supercapacitors on board a tram by means of ground-level conductor rails located at tram stops. This allows trams to operate without overhead lines for short distances. The system has been touted as an alternative to the company's ground-level power supply (APS) system, or can be used in conjunction with it, as in the case of Rio de Janeiro Light Rail, the VLT network in Rio de Janeiro, Brazil, which opened in 2016.

Buses

The first hybrid bus with supercapacitors in Europe came in 2001 in Nuremberg, Germany. It was MAN's so-called "Ultracapbus", and was tested in real operation in 2001/2002. The test vehicle was equipped with a diesel-electric drive in combination with supercapacitors. The system was supplied with 8 Ultracap modules of 80 V, each containing 36 components. The system worked with 640 V and could be charged/discharged at 400 A. Its energy content was 0.4 kWh with a weight of 400 kg. The supercapacitors recaptured braking energy and delivered starting energy. Fuel consumption was reduced by 10 to 15% compared to conventional diesel vehicles. Other advantages included reduction of emissions, quiet and emissions-free engine starts, lower vibration and reduced maintenance costs. Expo 2010 Electric Bus

in Luzern, Switzerland an electric bus fleet called TOHYCO-Rider was tested. The supercapacitors could be recharged via an inductive contactless high-speed power charger after every transportation cycle, within 3 to 4 minutes. In early 2005 Shanghai tested a new form of electric bus called capabus that runs without powerlines (catenary free operation) using large onboard supercapacitors that partially recharge whenever the bus is at a stop (under so-called electric umbrellas), and fully charge in the bus terminus, terminus. In 2006, two commercial bus routes began to use the capabuses; one of them is route 11 in Shanghai. It was estimated that the supercapacitor bus was cheaper than a lithium-ion battery bus, and one of its buses had one-tenth the energy cost of a diesel bus with lifetime fuel savings of $200,000. A hybrid electric bus called tribrid vehicle, tribrid was unveiled in 2008 by the University of Glamorgan, Wales, for use as student transport. It is powered by hydrogen fuel or solar cells, batteries and ultracapacitors.

Motor racing

The FIA, a governing body for motor racing events, proposed in the ''Power-Train Regulation Framework for Formula 1'' version 1.3 of 23 May 2007 that a new set of power train regulations be issued that includes a hybrid drive of up to 200 kW input and output power using "superbatteries" made with batteries and supercapacitors connected in parallel (KERS). About 20% tank-to-wheel efficiency could be reached using the KERS system. The Toyota TS030 Hybrid LMP1 car, a racing car developed under Le Mans Prototype rules, uses a hybrid drivetrain with supercapacitors. In the 2012 24 Hours of Le Mans race a TS030 qualified with a fastest lap only 1.055 seconds slower (3:24.842 versus 3:23.787) than the fastest car, an Audi R18 e-tron quattro with flywheel energy storage. The supercapacitor and flywheel components, whose rapid charge-discharge capabilities help in both braking and acceleration, made the Audi and Toyota hybrids the fastest cars in the race. In the 2012 Le Mans race the two competing TS030s, one of which was in the lead for part of the race, both retired for reasons unrelated to the supercapacitors. The TS030 won three of the 8 races in the 2012 FIA World Endurance Championship season. In 2014 the Toyota TS040 Hybrid used a supercapacitor to add 480 horsepower from two electric motors.

Hybrid electric vehicles

Supercapacitor/battery combinations in electric vehicles (EV) and hybrid electric vehicles (HEV) are well investigated. A 20 to 60% fuel reduction has been claimed by recovering brake energy in EVs or HEVs. The ability of supercapacitors to charge much faster than batteries, their stable electrical properties, broader temperature range and longer lifetime are suitable, but weight, volume and especially cost mitigate those advantages. Supercapacitors' lower specific energy makes them unsuitable for use as a stand-alone energy source for long distance driving. The fuel economy improvement between a capacitor and a battery solution is about 20% and is available only for shorter trips. For long distance driving the advantage decreases to 6%. Vehicles combining capacitors and batteries run only in experimental vehicles. all automotive manufacturers of EV or HEVs have developed prototypes that uses supercapacitors instead of batteries to store braking energy in order to improve driveline efficiency. The Mazda 6 is the only production car that uses supercapacitors to recover braking energy. Branded as i-eloop, the regenerative braking is claimed to reduce fuel consumption by about 10%. Russian Yo-cars Ё-mobile series was a concept and crossover hybrid vehicle working with a gasoline driven Swing-piston engine, rotary vane type and an electric generator for driving the traction motors. A supercapacitor with relatively low capacitance recovers brake energy to power the electric motor when accelerating from a stop. Toyota's Yaris (Toyota), Yaris Hybrid-R concept car uses a supercapacitor to provide quick bursts of power. PSA Peugeot Citroen, Peugeot Citroën fit supercapacitors to some of its cars as part of its stop-start fuel-saving system, as this permits faster start-ups when the traffic lights turn green.

Gondolas

In Zell am See, Austria, an aerial lift connects the city with Schmittenhöhe mountain. The gondolas sometimes run 24 hours per day, using electricity for lights, door opening and communication. The only available time for recharging batteries at the stations is during the brief intervals of guest loading and unloading, which is too short to recharge batteries. Supercapacitors offer a fast charge, higher number of cycles and longer life time than batteries. Emirates Air Line (cable car), also known as the Thames cable car, is a 1-kilometre (0.62 mi) gondola line in London, UK, that crosses the Thames from the Greenwich Peninsula to the Royal Docks. The cabins are equipped with a modern infotainment system, which is powered by supercapacitors.

Developments

commercially available lithium-ion supercapacitors offered the highest gravimetric specific energy to date, reaching 15 Wh/kg (). Research focuses on improving specific energy, reducing internal resistance, expanding temperature range, increasing lifetimes and reducing costs. Projects include tailored-pore-size electrodes, pseudocapacitive coating or doping materials and improved electrolytes. Research into electrode materials requires measurement of individual components, such as an electrode or half-cell. By using a counterelectrode that does not affect the measurements, the characteristics of only the electrode of interest can be revealed. Specific energy and power for real supercapacitors only have more or less roughly 1/3 of the electrode density.

Market

worldwide sales of supercapacitors is about US$400 million. The market for batteries (estimated by Frost & Sullivan) grew from US$47.5 billion, (76.4% or US$36.3 billion of which was rechargeable batteries) to US$95 billion. The market for supercapacitors is still a small niche market that is not keeping pace with its larger rival. In 2016, IDTechEx forecast sales to grow from $240 million to $2 billion by 2026, an annual increase of about 24%. Supercapacitor costs in 2006 were US$0.01 per farad or US$2.85 per kilojoule, moving in 2008 below US$0.01 per farad, and were expected to drop further in the medium term.T2+2™ Market Overview
, Ch. Ahern, Supercapacitors, 10 December 2009, Project Number NET0007IO

Trade or series names

Exceptional for electronic components like capacitors are the manifold different trade or series names used for supercapacitors, like ''APowerCap, BestCap, BoostCap, CAP-XX, C-SECH, DLCAP, EneCapTen, EVerCAP, DynaCap, Faradcap, GreenCap, Goldcap, HY-CAP, Kapton capacitor, Super capacitor, SuperCap, PAS Capacitor, PowerStor, PseudoCap, Ultracapacitor'' making it difficult for users to classify these capacitors. (Compare with #Comparison of technical parameters)

Literature

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References

External links

Supercapacitors: A Brief Overview
pub 2003 {{DEFAULTSORT:Electric Double-Layer Capacitor Capacitors Emerging technologies Energy conversion ja:電気二重層コンデンサ zh:双电层电容器