Thursday, November 24, 2022
Alternate energy solutions are essential to meet the rising power needs of electrical and electronic gadgets. Energy harvesting circuits are used to capture and convert the energy available in the environment into electrical energy. These advanced electronics are designed to manage diverse renewable resources like solar, wind, tidal, and geothermal, to name a few. Engineers are developing high-power PCBs to drive innovative power supply circuits for future generations.
Technological developments are now supporting many types of energy harvesting like biomass, piezotronics, pyroelectric, and RF energy, among others. But for high-power applications, energy harvesting circuits commonly use solar, thermoelectric, and wind energies. They are beneficial in powering electronic devices where accessing conventional power sources are difficult. They can eliminate long wirings running up to the end application devices and can minimize battery replacements in remote locations. They are environment-friendly and don’t require frequent maintenance.
Common energy harvesting circuits
Several renewable energies like solar and wind power are widely used in harvesting circuits. The energy sources like radio frequency, ambient vibrations, and static electricity can provide intermittent low power suitable for portable electronic devices and low-power wireless sensors. In high-power applications, the harvesting circuits have strict requirements to perform reliably in different operating environments.
A basic energy harvesting circuit includes a harvester that collects and converts the energy from a source. It is also called a transducer which can be a photovoltaic cell in the case of solar energy harvesting or turbines for wind energy harvesting. An energy storage unit like a battery or supercapacitor holds the converted energy. Next, a power management circuit is used to regulate and condition the converted electrical energy, making it suitable for the output load.
Components used in the energy harvesting system should have higher efficiency in collecting and storing intermittent energy packets with minimum leakage. The circuit should be tolerant to a broad range of electrical inputs and outputs. Some harvesting circuits can generate electrical energy from multiple sources.
In industrial and commercial applications, using energy harvesting circuits can extend the battery life of remote sensors that are not easily accessible. In low-power applications like smart homes, healthcare, and retails, energy harvesting circuits can boost efficiency and sustainability by removing the need for charging with a power cord.
High-power applications like microgrids, gensets, and electric vehicles require more consistent and large output circuits. Commonly used energy sources for such applications are discussed below.
Wind energy harvesting circuits
Wind energy is irregular yet infinite and is the highest used renewable source for electricity generation. Turbine generators convert the wind’s kinetic energy into electrical energy. Rotor blades and turbines are the transducers used in this energy harvesting circuit. Wind turbine design can be either on a vertical axis or a horizontal axis. They are installed on land or offshore. Land-based wind turbines are grouped to provide bulk energy to the power grids in the range of megawatts. Offshore turbines capture ocean wind power to generate a huge amount of energy, up to 7MW.
Solar energy harvesting circuits
Solar energy is amply available for energy harvesting and is utilized in industrial and consumer applications. Small photovoltaic cells are used to convert solar energy into electrical energy. The power generated from the solar cells is stored in a battery. Power supply circuits like inverters and DC-DC converters are required to stabilize the output power. Feedback circuits are used to improve the energy conversion efficiency and optimize the harvested power. Solar panels used for domestic purposes can produce energy in the range of 1-4kW.
Thermoelectric energy harvesting circuits
In electronic systems, energy gets dissipated as heat when high current flows through the conductor. This loss of energy can be used for harvesting electrical energy based on the Seebeck effect. It is a phenomenon in which a difference in the temperature of two semiconductors (electrical conductors) generates a voltage difference between those two materials. An array of thermocouples collectively known as a Thermoelectric Generator (TEG) is connected to a common heat source like a high-power transistor to generate electricity. A single TEG can generate power from 1W to 125W. This type of energy harvesting circuit is commonly used in high-temperature applications like military and aerospace.
Designing PCBs for energy harvesting circuits
There are several challenges in building PCBs to endure high power loads of energy harvesting systems. They have to follow rules similar to high-voltage PCB design and meet the performance requirements of energy harvesting circuits.
Many PCB manufacturers provide high-quality PCB fabrication and turnkey PCB assembly services specific to energy industry requirements. Collaboration with one such PCB producer is recommended while designing energy harvesting circuits.
Below are the guidelines to optimize your PCB design for high-power energy harvesting circuits:
• Choose a PCB material that can support the intended high-power operating environment.
• Select components that are fabricated for high-power applications with suitable electrical parameters.
• Component placement should consider the suggested spacing and clearance guidance to mitigate high-temperature effects on the PCB performance.
• Focus on the power distribution circuitry to implement heat dissipation strategies for thermal relief.
• During the layout design, heavy copper traces should be used for high-current signals.
• Energy harvesting PCBs should be immune to any kind of noise. Hence the designer should follow signal integrity rules effectively to minimize the EMI effect on the circuit board. Shields to be included if required.
• Applying a conformal coating like ENIG or HASL is recommended to protect the PCB from heat and external chemicals.
• The associated cable and harnesses should be customized to handle the extra load of high-power circuits.
• High-power PCBs are prone to overheating and can cause damage to the operator. Including safety features like board temperature monitors and automatic cut-off circuits are advised for user safety.
• Follow the generic IPC-2221 and IPC-9592B standards for high-voltage PCB design.
Converting the energy available in the immediate surroundings to electrical energy is a great alternative to the power supply circuit. But there are some challenges like intermittent availability of the source energy and the need for power filtering and conditioning circuits to provide a steady output. With improved design and implementation strategies, energy harvesting circuits have tremendous potential to power up electronic circuits for long durations with the least maintenance.
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