Bench Talk

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Coal, petroleum, natural gas, and oil are all considered fossil fuels and were created from organisms such as plants and animals that died millions of years ago. As time passed, these organisms became fossilized. Fossilization is the process of an animal or plant becoming preserved in a hard-petrified form and eventually turning into carbon-rich sources such as coal and oil. According to octopus energy, we are expected to run out of our known oil deposits by 2052; while coal and natural gas are expected to last until 2060. Because these fossil fuels take millions of years to create, we can’t recreate them before they are depleted. It’s possible we could discover unknown reserves, but there is no guarantee. Renewable energy is the only viable solution to this problem. Energy sources such as solar, hydro, and wind energy are the most suitable and environmentally sound solutions.

Energy harvesting uses energy found in the ambient environment and converts it into usable electrical energy. Electrical energy is conditioned for either direct use or can be accumulated and stored as a source of power for applications at a later time. Here, we examine how energy harvesting can provide the energy required to power devices and circuits and offer solutions for battery-operated devices.

Many factors drive the global energy harvesting market. Demand for safe, power-efficient, and durable systems that require little or no maintenance is increasing on a daily basis. Since technology is evolving faster than ever, the extensive application of “Internet of Things” devices in building and home automation is increasing. Another major driving factor is the cost of renewable energy. The less expensive fuel for automobiles is electric energy versus fossil fuels. Electric cars are becoming more dominant over time. By 2030, studies have shown that the number of internal combustion engine (ICE) vehicles will be reduced by about 50 percent (Figure 1).

Figure 1: Concerns over fossil fuel depletion and the use of ICE vehicles put a greater emphasis on EV adoption. (Source: Herr Loeffler/Shutterstock.com )

To generate power, energy harvesting requires an energy source from which to harvest. Some main sources of energy are photovoltaics, kinetic, pyroelectric, piezoelectric, and radio frequency (RF) energy (Figure 2).

Figure 2: Photovoltaics, kinetic, pyroelectric, piezoelectric, and RF energy comprise the major sources of energy for Energy Harvesting Systems. (Source: KEMET Electronics)

Let’s discuss each of these energy sources.

Photovoltaic Energy

Photovoltaic (PV) devices generate electricity directly from sunlight. The solar cell is an example of a photovoltaic device (Figure 3). Solar cells are made of a material called semiconductors. Because of the structure of the semiconductor material, when sunlight strikes, electrons are released and forced in one direction, creating a flow of electrical current.

Kinetic Energy

The kinetic energy of an object is the energy the object can produce because of its motion. Wind turbines, ocean buoys, and hydroelectric energy are all examples of kinetic energy sources due to the motion of wind or water. Wind turbines create electricity by turning the propeller of the turbine around a rotor, which spins a generator, creating electricity. Just like the wind turbines, hydroelectricity is produced by spinning a generator using the flow of water.

Figure 3: Photovoltaic solar cells and wind turbines produce renewable energy and require little to no maintenance. (Source: Alberto Masnovo/Shutterstock.com )

Pyroelectric and Piezoelectric Energy

Pyroelectricity and piezoelectricity both have high thermodynamic efficiency and can only be used on a micro level. Pyroelectricity is the ability of certain materials to create electric current based on temperature change. Piezoelectricity is the ability of certain materials to convert mechanical energy such as sound or pressure into electrical energy.

Radio Frequency Energy

A radio frequency (RF) energy harvesting system can convert electromagnetic energy into usable direct current voltage. The system usually contains an antenna and a rectifier circuit which captures the RF power, which is alternating current, and converts it into DC power.

Capacitors Used in Energy Harvesting Storage

Almost all energy-harvesting scenarios require some sort of energy storage. A specialized DC-DC converter takes in power from the transducer and outputs electricity used to power devices. The system converter requires careful electronic design to minimize power losses. The energy storage balances the energy supply and demand. For applications where energy is used as soon as it is collected, storage is not necessary and, usually, an electrolytic capacitor is being employed. Determining the energy storage needed in an energy harvesting system depends greatly on the application.

Choosing Electrolytic Capacitors for Energy Harvesting Applications

KEMET’s technology roadmap features aluminum electrolytic solutions and on-line tools designed to meet the evolving needs of the Energy Harvesting sector. One of the most important factors to consider in energy harvesting design is the life expectancy and capacity of the selected electrolytic capacitor. KEMET offers a wide range of electrolytic capacitors, including the ALS Screw Terminal series that can operate from 6,000 to 20,000 hours depending on diameter at rated temperature (85ºC or 105ºC), rated voltage, and rated ripple current. In addition, KEMET provides an on-line Aluminum Electrolytic Capacitor Life Expectancy Calculator. The calculator helps designers determine which electrolytic capacitor is right for their application by calculating the device’s theoretical life using an application’s specific operating conditions (Figure 5).

Figure 5: KEMET’s Aluminum Electrolytic Capacitor Life Expectancy Calculator helps designers gauge the theoretical life expectancy of a KEMET electrolytic capacitor on a part number by part number basis using an application’s specific operating conditions. (Source: KEMET Electronics)

Table 1 shows an example of the possible results using the ALS70 and ALS80 Series Screw Terminal High CV Electrolytic Capacitors in a theoretical energy-harvesting application.

Table 1: Example of the calculated life expectancy of ALS70 and ALS80 Series Screw Terminal High CV Electrolytic Capacitors in a theorectical energy-harvesting application using the Aluminum Electrolytic Capacitor Life Expectancy Calculator. (Source: KEMET Electronics)

The world is expected to run out of oil deposits by 2052; while coal and natural gas are expected to last until 2060. As the demand for energy continues to increase, there is no choice but to turn to alternative and sustainable options. Energy Harvesting uses energy from the ambient environment such as photovoltaics, kinetic energy, pyroelectric, piezoelectric, and RF energy and converts it into usable electrical energy. Almost all energy-harvesting scenarios require some sort of energy storage to balance the energy supply and demand. For applications where energy is used as soon as it is collected, storage is not necessary and these applications frequently use aluminum electrolytic capacitors. As hours of life are one of the key parameters, designers must choose robust, long-life capacitors and work with the manufacturer to assure their application will continue to operate for years to come.