12.4 Energy harvesting for embedded systems
3 min read•august 7, 2024
Energy harvesting is a game-changer for embedded systems, allowing them to run without traditional power sources. This section covers various methods like solar, thermal, mechanical, and RF harvesting, along with the tech to manage and store that energy.
Understanding energy harvesting is crucial for designing self-sustaining embedded systems. We'll explore how to capture energy from the environment, maximize its efficiency, and use it smartly to keep our devices running longer without external power.
Solar and Thermal Energy Harvesting
Photovoltaic Cells
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- Convert light energy into electrical energy through the photovoltaic effect
- Consist of semiconductor materials (silicon) that generate a current when exposed to sunlight
- Efficiency depends on factors such as cell material, design, and environmental conditions (temperature, shading)
- Can be connected in series or parallel to increase voltage or current output
- Commonly used in outdoor embedded systems (, remote monitoring stations)
Thermoelectric Generators
- Convert temperature differences into electrical energy using the Seebeck effect
- Consist of two dissimilar conductors or semiconductors (bismuth telluride) connected at two junctions
- When a temperature gradient exists between the junctions, a voltage is generated
- Efficiency depends on the temperature difference and the properties of the thermoelectric materials
- Can harvest energy from waste heat sources (industrial processes, automotive exhaust)
Maximum Power Point Tracking (MPPT)
- Technique used to maximize the power output of and other energy harvesting sources
- Adjusts the electrical load to match the optimal operating point of the energy harvesting device
- Implemented using power electronic converters (DC-DC converters) and control algorithms
- Continuously tracks the maximum power point as environmental conditions change
- Improves the overall efficiency and of the energy harvesting system
Mechanical and RF Energy Harvesting
Piezoelectric Harvesters
- Convert mechanical energy from vibrations, stress, or strain into electrical energy
- Utilize piezoelectric materials (lead zirconate titanate, polyvinylidene fluoride) that generate a voltage when subjected to mechanical deformation
- Can be designed as cantilever beams, diaphragms, or stacks to match the frequency and amplitude of the vibration source
- Applications include harvesting energy from human motion (footsteps, heartbeats), machinery vibrations, and flow-induced vibrations
RF Energy Harvesting
- Captures and converts electromagnetic energy from ambient radio frequency (RF) sources into electrical energy
- Uses antennas and rectifier circuits (rectenna) to convert RF signals into DC power
- Can harvest energy from various RF sources (Wi-Fi, cellular networks, TV and radio broadcasts)
- Efficiency depends on factors such as the frequency, , and distance from the RF source
- Suitable for low-power embedded systems (wireless sensor nodes, ) in environments with abundant RF energy
Energy Management and Storage
Power Management ICs
- Integrated circuits designed to efficiently manage and regulate the power supply in embedded systems
- Perform functions such as voltage regulation, battery charging, and power sequencing
- Implement energy-saving techniques (dynamic voltage and frequency scaling, power gating) to minimize power consumption
- Provide protection features (overvoltage, overcurrent, thermal shutdown) to ensure safe and reliable operation
- Examples include low-dropout regulators (LDOs), switching regulators (buck, boost), and battery management ICs
Energy Storage Devices
- Store the harvested energy for later use when the energy source is not available or insufficient
- Common storage devices include rechargeable batteries (lithium-ion, nickel-metal hydride) and supercapacitors
- Batteries offer high energy density but limited cycle life and charge/discharge rates
- Supercapacitors have high power density, fast charge/discharge rates, and long cycle life but lower energy density
- Hybrid storage solutions combining batteries and supercapacitors can provide both high energy and power density
Energy-Neutral Operation
- Design principle for energy harvesting embedded systems that aims to balance energy consumption with energy harvesting
- Ensures that the average energy consumed by the system over time does not exceed the average energy harvested
- Requires careful management of energy resources, including adaptive duty cycling, power-aware scheduling, and energy prediction
- Involves modeling and estimating the energy harvesting profile and adapting the system's operation accordingly
- Enables long-term, self-sustaining operation of embedded systems without the need for battery replacements or external power sources
Key Terms to Review (25)
Ambient energy: Ambient energy refers to the naturally occurring energy present in the environment, which can be harnessed for various applications, especially in embedded systems. This energy can come from multiple sources such as solar, thermal, kinetic, and electromagnetic fields. Harnessing this energy is crucial for powering devices without reliance on traditional batteries or wired power sources, enhancing the sustainability and autonomy of embedded systems.
Conversion efficiency: Conversion efficiency is the measure of how effectively energy is transformed from one form to another within a system, particularly focusing on the percentage of input energy that is converted into useful output energy. This concept is crucial in evaluating the performance of energy harvesting technologies for embedded systems, as it directly influences the overall sustainability and effectiveness of these systems in utilizing available energy sources.
Energy budget: An energy budget refers to the comprehensive accounting of energy inputs and outputs within a system, ensuring that energy consumption does not exceed the available energy resources. It is crucial for the efficient operation of embedded systems, particularly those utilizing energy harvesting techniques, as it balances energy generation from sources like solar or kinetic energy with the energy consumed by the system's components and processes.
Energy storage devices: Energy storage devices are components or systems that store energy for later use, allowing for better energy management and supply in various applications. These devices play a crucial role in energy harvesting systems, enabling them to capture, store, and utilize energy efficiently, especially in embedded systems where power availability can be intermittent or limited.
Energy yield: Energy yield refers to the amount of usable energy that can be extracted from a particular energy source during the process of energy harvesting. It is a crucial factor in determining the efficiency and viability of various energy harvesting technologies, especially in embedded systems where power availability is often limited. Understanding energy yield helps in assessing how effectively an embedded system can convert ambient energy sources into usable electrical energy.
Energy-neutral operation: Energy-neutral operation refers to the ability of an embedded system to maintain its energy balance, meaning that it can harvest enough energy from its environment to operate without depleting its energy storage over time. This concept is crucial for devices that rely on energy harvesting techniques, as it ensures they can function indefinitely without needing frequent battery replacements or external power sources. The idea is to create self-sustaining systems that can continuously gather energy, making them ideal for remote or hard-to-reach applications.
Kinetic energy: Kinetic energy is the energy that an object possesses due to its motion. It depends on the mass of the object and the square of its velocity, represented by the formula $$KE = \frac{1}{2}mv^2$$, where m is mass and v is velocity. This concept is crucial in energy harvesting as it allows embedded systems to capture and convert mechanical movement into usable electrical energy.
Load matching: Load matching refers to the process of ensuring that the electrical load on a power source is compatible with the energy harvesting system's output capabilities. This alignment is crucial for optimizing the efficiency of energy transfer and maximizing the harvested energy, particularly in embedded systems utilizing energy harvesting technologies like solar, thermal, or vibration-based sources.
M. K. Gupta: M. K. Gupta is a prominent researcher and academic known for his contributions to the field of energy harvesting in embedded systems. His work emphasizes innovative techniques to harness energy from ambient sources, enabling devices to operate autonomously and sustainably. This focus on energy efficiency is crucial for the development of embedded systems, especially in applications requiring prolonged operation without external power sources.
Maximum power point tracking: Maximum power point tracking (MPPT) is a technique used in renewable energy systems to optimize the power output of solar panels or other energy sources by continuously adjusting the operating point to ensure that the maximum possible power is extracted. This technology is crucial in energy harvesting for embedded systems as it enhances efficiency and ensures that devices can operate effectively under varying environmental conditions.
Modular Design: Modular design is an approach that divides a system into smaller, manageable, interchangeable modules or components. This method not only simplifies the development process but also enhances maintainability and scalability, allowing for easier upgrades and modifications. By utilizing modular design, developers can create more efficient code structures and systems, which is particularly beneficial in embedded systems where resource constraints are common.
Mppt: Maximum Power Point Tracking (MPPT) is a technology used in renewable energy systems to optimize the power output from sources like solar panels. By continuously adjusting the electrical operating point of the modules, MPPT ensures that the maximum available power is extracted regardless of varying environmental conditions such as light intensity and temperature. This technology plays a crucial role in energy harvesting for embedded systems, enhancing efficiency and sustainability.
Photovoltaic cells: Photovoltaic cells are devices that convert light energy directly into electrical energy through the photovoltaic effect. These cells play a crucial role in renewable energy systems, providing a sustainable power source for various applications, including embedded systems, by harnessing sunlight and converting it into usable electricity.
Piezoelectric energy harvesting: Piezoelectric energy harvesting is the process of converting mechanical energy from movements or vibrations into electrical energy using piezoelectric materials. This method captures energy from everyday activities, such as walking or machinery vibrations, and is particularly relevant for powering small embedded systems without the need for batteries. Its efficiency in utilizing ambient mechanical energy makes it an attractive option for sustainable energy solutions in various applications.
Power Density: Power density refers to the amount of power (energy per unit time) generated or consumed per unit volume or area of a device. It is a critical measure in embedded systems as it helps evaluate how efficiently energy is utilized and how compactly power can be delivered. High power density indicates more power can be supplied in a smaller footprint, which is essential for portable and energy-constrained applications.
Power management ICs: Power management ICs (PMICs) are specialized integrated circuits designed to manage power requirements of a system by regulating voltage and current, and optimizing energy efficiency. They play a critical role in various applications by ensuring devices operate efficiently, extending battery life, and integrating multiple power functions like voltage regulation, battery management, and energy harvesting. In embedded systems, PMICs are essential for achieving low power consumption while maximizing performance.
Rf energy harvesting: RF energy harvesting is the process of capturing and converting radio frequency (RF) energy from the environment into usable electrical energy. This technique is essential for powering low-energy devices, especially in embedded systems, where minimizing reliance on batteries or external power sources is crucial for longevity and efficiency.
Self-sustainability: Self-sustainability refers to the ability of a system to maintain itself without external inputs or support. In the context of energy harvesting, this concept highlights the capacity of embedded systems to generate, store, and utilize energy autonomously, ensuring they operate efficiently without relying on traditional power sources. This independence is crucial for enhancing the longevity and reliability of devices deployed in remote or inaccessible environments.
Sharma et al.: Sharma et al. refers to a group of researchers, led by Sharma, who conducted significant studies in the field of energy harvesting for embedded systems. Their work primarily focuses on innovative techniques to capture energy from the environment, such as solar, thermal, and kinetic energy, to power embedded devices efficiently. This approach is crucial for developing sustainable and self-sufficient systems that can operate without conventional power sources.
Solar energy harvesting: Solar energy harvesting refers to the process of capturing and converting sunlight into usable electrical energy, primarily through photovoltaic cells. This method allows embedded systems to utilize renewable energy sources, reducing dependency on conventional power supplies and enhancing system sustainability. By integrating solar energy harvesting techniques, devices can operate autonomously, increasing their functionality and lifespan while contributing to energy efficiency.
System-on-chip integration: System-on-chip integration refers to the process of embedding all the necessary components of a complete electronic system onto a single chip. This includes integrating processors, memory, input/output interfaces, and other peripherals into one compact package, which leads to improved performance and efficiency. By minimizing the size and power consumption while enhancing functionality, system-on-chip integration plays a crucial role in modern embedded systems.
Thermal energy harvesting: Thermal energy harvesting is the process of capturing and converting waste heat generated by various sources into usable electrical energy. This technology is particularly important in embedded systems, where energy efficiency and sustainability are crucial. By leveraging temperature differences or waste heat, thermal energy harvesting can power devices without relying on traditional energy sources or batteries.
Thermoelectric generators: Thermoelectric generators (TEGs) are devices that convert heat energy directly into electrical energy through the Seebeck effect. This process is highly beneficial for energy harvesting in embedded systems, particularly in situations where traditional power sources are unavailable or impractical. TEGs can harness waste heat from various sources, making them valuable for improving energy efficiency and supporting sustainable energy solutions.
Wearable devices: Wearable devices are electronic gadgets that can be worn on the body, often incorporating sensors and software to collect data and provide various functionalities. These devices, like smartwatches, fitness trackers, and health monitors, are designed to seamlessly integrate into daily life, offering real-time insights into health metrics, activity levels, and connectivity with other devices. Their growing popularity is driving advancements in energy harvesting methods and paving the way for innovative technologies that enhance user experiences and applications.
Wireless Sensor Networks: Wireless sensor networks (WSNs) are composed of distributed autonomous sensors that monitor physical or environmental conditions and communicate the data wirelessly to a central location. They enable real-time data collection and analysis for various applications, such as environmental monitoring, healthcare, and smart cities. The deployment of these networks relies on energy-efficient communication and processing strategies, which makes energy harvesting a critical aspect of their functionality.