page_title: Energy storage
section_title: Capacitor
hierarchical_section_title: Energy storage / Methods / Electrical methods / Capacitor
caption_attribution_description: English: A mylar-film, oil-filled capacitor. The capacitor was designed with extremely low inductance and low resistance. It is used to deliver very fast discharges that are required for a dye laser. The capacitor is rated for 6.5 microfarad at 5000 volts, and is capable of discharging 85 joules of energy in 1.2 microseconds, producing a pulsed-power level over 70 megawatts. The capacitor's size is 8 inches tall, 6 inches wide and 2 1/2 inches thick.
context_page_description: Energy storage is the capture of energy produced at one time for use at a later time.
  A device that stores energy is generally called an accumulator or battery.
  Energy comes in multiple forms including radiation, chemical, gravitational potential, electrical potential, electricity, elevated temperature, latent heat and kinetic.
  Energy storage involves converting energy from forms that are difficult to store to more conveniently or economically storable forms.
  Some technologies provide short-term energy storage, while others can endure for much longer.
  Bulk energy storage is currently dominated by hydroelectric dams, both conventional as well as pumped.
  Common examples of energy storage are the rechargeable battery, which stores chemical energy readily convertible to electricity to operate a mobile phone, the hydroelectric dam, which stores energy in a reservoir as gravitational potential energy, and ice storage tanks, which store ice frozen by cheaper energy at night to meet peak daytime demand for cooling.
context_section_description: A capacitor (originally known as a 'condenser') is a passive two-terminal electrical component used to store energy electrostatically. Practical capacitors vary widely, but all contain at least two electrical conductors (plates) separated by a dielectric (i.e., insulator). A capacitor can store electric energy when disconnected from its charging circuit, so it can be used like a temporary battery, or like other types of rechargeable energy storage system. Capacitors are commonly used in electronic devices to maintain power supply while batteries change. (This prevents loss of information in volatile memory.) Conventional capacitors provide less than 360 joules per kilogram, while a conventional alkaline battery has a density of 590 kJ/kg.
  Capacitors store energy in an electrostatic field between their plates. Given a potential difference across the conductors (e.g., when a capacitor is attached across a battery), an electric field develops across the dielectric, causing positive charge (+Q) to collect on one plate and negative charge (-Q) to collect on the other plate. If a battery is attached to a capacitor for a sufficient amount of time, no current can flow through the capacitor. However, if an accelerating or alternating voltage is applied across the leads of the capacitor, a displacement current can flow. Besides capacitor plates, charge can also be stored in a dielectric layer.
  Capacitance is greater given a narrower separation between conductors and when the conductors have a larger surface area. In practice, the dielectric between the plates emits a small amount of leakage current and has an electric field strength limit, known as the breakdown voltage. However, the effect of recovery of a dielectric after a high-voltage breakdown holds promise for a new generation of self-healing capacitors. The conductors and leads introduce undesired inductance and resistance.
  Research is assessing the quantum effects of nanoscale capacitors for digital quantum batteries.
caption: This mylar-film, oil-filled capacitor has very low inductance and low resistance, to provide the high-power (70 megawatts) and the very high speed (1.2 microsecond) discharges needed to operate a dye laser.
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