Supercapacitors Provide Power Holdup for Renewable Hybrid Energy Storage Systems

A hybrid energy storage capacitor contains much higher capacitance values than electrolytic or other capacitors while requiring lower voltage on its terminals. The hybrid’s construction provides higher charge density allowing use as a rechargeable battery for many applications. Higher charge density is supplied in two ways combining the effects of double-layer capacitance (DLC) with electrochemical pseudocapacitance. The combination of technologies results in the availability of large charge densities in a very compact size.

Hybrid energy storage capacitors are generally used along with other energy storage technologies, such as batteries, to provide a hybrid energy storage system (HESS). A HESS is able to meet the needs of renewable energy applications by delivering momentary backup power faster than batteries. The hybrid energy storage capacitor within a HESS has to ability to harvest and release power making them useful when batteries are drained or system power is unavailable.

Background for Hybrid Energy Storage Capacitors

Supercapacitors developed over several decades as experiments investigated porous carbon electrodes for the design of fuel cells and rechargeable batteries. The earliest patent was licensed to NEC who marketed supercapacitors to provide backup for computer memory. Further work by Brian Evans Conway distinguished characteristics between a supercapacitor and a battery. A supercapacitor employs both an electrolyte interior for developing charge layers together with a faradaic reaction with the electrode enabling charge transfer.

Additionally, an electrolytic-hybrid electrochemical capacitor was developed around the same time in an attempt to increase the capacitor’s electrolyte breakdown voltage. Increasing breakdown voltage was desired to increase energy content within the capacitor. Rather than using Helmholtz layers, these hybrids combined two slightly different technologies. The first utilized the same technology within an electrolytic capacitor at the anode; e-caps develop high dielectric strength at the anode with solid material. The second utilized faradaic reaction at the cathode.

Breakdown Voltage: Within a capacitor’s dielectric, this is the electric field strength limit. It is the product of dielectric strength and the separation between the conductors.

Charge Status (Q): The amount of electrical charge (Q) in the capacitor is proportional to the applied voltage (U).

Faradaic Current: The current generated by the reduction or oxidation of some chemical substance at an electrode.

Non-Faradaic Current: The current generated at the electrode by changing potential. Electrode. An electrical conductor used to make contact with a nonmetallic part of a circuit.

Electrolyte: A substance that produces an electrically conducting solution.

Helmholtz Double-Layer (DL): aka electrostatic double layer (EDL). An electrostatic double layer is a structure of ions that form two parallel layers of charge surrounding the object (see figure below).

Supercapacitor (SC): High charge density capacitor with large capacitance values within lower voltage limits. An SC bridges the gap between electrolytic capacitors and rechargeable batteries.

Helmholtz double layer

For purposes of this article hybrid energy storage capacitors and supercapacitors have the same combinational technologies. This is due to the parts we highlight below from Vishay’s line of hybrid energy storage capacitors which employ the same combinational technology as a supercapacitor.

Defining Characteristics of Hybrid Energy Storage Capacitors

Hybrid energy storage capacitors are part of a family that combines charge density collection technologies to achieve supercapacitance at low voltage. Other names for this type of technology are supercap, ultracapacitor, or hybrids. These supercapacitors use two types of material technology to achieve properties that make them desirable for renewable energy.

The combined material technologies are electrostatic double-layer capacitance (DLC) and electrochemical pseudocapacitance. DLC uses a liquid electrolyte to develop Helmholtz layers in a nano-area adjacent to the capacitor’s electrodes. The electrodes in these supercapacitors are made of carbon, or other ion-rich material, that collect charges from the electrolyte. The charges collected from the electrolyte to the electrode lattice continue on into the exterior circuit, returning to the anode electrode of the capacitor.

Electrochemical Cell: A cell that produces an electric current from energy released by a spontaneous redox reaction; this can be caused by electricity. Includes voltaic cells.

Electrolytic Capacitor (e-cap): A capacitor with a very thin dielectric oxide layer and enlarged anode surface providing high capacitance-voltage product per unit volume as compared to ceramic capacitors or film capacitors. Provide large capacitance as compared to ceramic or film capacitors.

Electrostatic Double Layer Capacitor (EDLC): EDLCs use carbon electrodes or derivatives with much higher electrostatic double-layer capacitance than electrochemical pseudocapacitance, achieving separation of charge in a Helmholtz double layer at the interface between the surface of a conductive electrode and an electrolyte. The separation of charge is much smaller than a conventional capacitor.

Hybrid Energy Storage System (HESS): A system characterized by a beneficial combination of two or more energy storage technologies (such as supercapacitors and batteries) with complementary characteristics to provide an optimal solution not achievable by any one technology.

Redox: Reduction-oxidation refers to an electrochemical process involving electron transfer.

Voltage (U): With respect to a capacitor, this is the applied voltage to the part.

This combination of a displacement-type current together with transfer charges build the supercapacitor.

Parameters to Consider When Selecting Vishay’s Hybrid Energy Storage Capacitors

Vishay produces several families of hybrid energy storage capacitors which are available on our website. We will be looking at four capacitors offered in their 196 HVC ENYCAP^™ family.

Vishay’s family of 196 HVC ENYCAP^™ capacitors

The 196 HVC ENYCAP^™ family of Vishay capacitors offer capacitance values of 4F, 15F, 45F, and 90F. They are offered in configurations incorporating either single or multiple cells with applied operating voltages at 1.4V for single cell, and multiple cells from two to six spanning 2.8V to 8.4V. Multiple configurations are available in different orientations, as well, including stacked through-hole (STH), stacked through-hole oval (PCBD), surface-mount flat (SMF), and lay flat configurations (LFC) with wire and connectors. Both stacked configurations come in either vertical or horizontal orientations.

The applications for these hybrid energy storage capacitors are numerous and include power backup for memory controllers, flash backup, RAID systems, SRAM, and DRAM. They work to eliminate power failure and provide write cache protection for enterprise SSD and HDD. Other functionality includes use as a real-time clock power-source, use to provide burse power support for flashlights and wireless transmitters, backup power for industrial PCs and industrial controls, storage devices for energy harvesting, and power source for emergency light and micro UPS. The hybrid energy storage capacitors are used in many industries such as automotive, avionics, computers, consumer electronics, industrial, medical, and telecommunications.

The following highlight four capacitors from Vishay’s 196 HVC ENYCAP^™ family of offerings. Each is lead-free and RoHS compliant, indicated by the suffix E3.

Vishay MAL219691203E3

This is a stacked through-hole configuration, vertical mount, comprised of 3 cells offering 15F across applied voltage of 4.2V.

Stacked through-hole, vertical orientation comprised of four cells

Vishay MAL219691152E3

This is a surface-mount flat configuration, comprised of two cells, offering 4F across an applied voltage of 2.8V.

Surface-mount flat comprised of two cells

Vishay MAL219690101E3

This is a stacked through-hole oval, comprised of 3 cells, offering 90F across an applied voltage of 4.2V.

Stacked through-hole oval, vertical orientation comprised of four cells

Vishay MAL219691216E3

This is a stacked through-hole configuration, horizontal mount comprised of 6 cells, offering 15F across an applied voltage of 8.4V.

Stacked through-hole, horizontal orientation with four cells

Hybrid energy storage capacitors are low-profile parts that may be used for holdup power in devices across many industries. They have high power density and can be used in place of a battery. Combined with batteries, they serve as a high energy storage system to meet the needs of many renewable energy applications.

If you have comments or suggestions on hybrid energy storage capacitors part selection, drop us a note in the comments below.

Stay up-to-date with our latest articles by signing up for our newsletter.