Overview of Energy Harvesting EE174 – SJSU Tan Nguyen

Introduction to Energy Harvesting (EH) How does EH work? Sources of Energy Energy conversions EH Components EH system and EH Circuit Energy storage is a Must Application Future Research Issues OUTLINE

Introduction Energy Harvesting (EH) Energy harvesting (also known as power harvesting or energy scavenging) is the process in which energy is captured from a system's environment and converted into usable electric power. EH allows electronics to operate where there's no conventional power source, eliminating the need for wires or replacement of batteries. EH systems generally includes circuitry to charge an energy storage cell, and manage the power, providing regulation and protection. EH-powered systems need reliable energy generation, storage and delivery: Must have energy storage as EH transducer energy source is not always available (solar at night, motor vibration at rest, air-flow, etc.) EH can provide “endless energy” for the electronics lifespan. Ideal for substituting for batteries that are impractical, costly, or dangerous to replace.

Batteries – Wide spread availability, high reliability – Low-cost, mature technologies – Replacement/recharging is an issue Too numerous in the future Location is unreachable – Sensor size limited by battery size - Relative Improvement in Laptop Technology Portable Electric Energy Sources Available Battery energy is the slowest trend

How Energy Harvesting works? An energy harvester comprises one or more transducers, power conditioning, and energy storage. These technologies work together to collect energy and deliver power to the device. On the other hand, the device which uses the energy needs to be designed to work with energy harvesting as the power source. (Sources of Energy) (Devices)

How Energy Harvesting works? The transducer: converts energy from one energy type to a another energy type, usually electricity. Power conditioning: is necessary because the natural output of the transducer can be intermittent, and at the wrong frequency, voltage and current to directly drive the device. A specialised DC-DC converter microchip takes in power from the transducer and convert to voltages which can then be stored or used. Energy storage: is needed to balance the energy supply and energy demand. For applications where energy is used as soon it is collected (e.g. RFID and wireless light switches), no storage is needed. Usually however a rechargeable battery, capacitor, or supercapacitor is used. Batteries degrade over time, and so the lifetime of the storage device can often be the limiting factor in the overall lifetime of the harvester.

Energy harvesting uses unconventional sources to power circuitry. Light (captured by photovoltaic cells) Vibration or pressure (captured by a piezoelectric element) Temperature differentials (captured by a thermo- electric generator) Radio Frequency (captured by an antenna) Biochemically produced energy (such as cells that extract energy from blood sugar). Sources of Energy

Human Body: Mechanical and thermal (heat variations) energy can be generated from a human or animal body by actions such as walking and running; Natural Energy: Wind, water flow, ocean waves, and solar energy can provide limitless energy availability from the environment; Mechanical Energy: Vibrations from machines, mechanical stress, strain from high-pressure motors, manufacturing machines, and waste rotations can be captured and used as ambient mechanical energy sources; Thermal Energy: Waste heat energy variations from furnaces, heaters, and friction sources. Light Energy: This source can be divided into two categories of energy: indoor room light and outdoor sunlight energy. Light energy can be captured via photo sensors, photo diodes, and solar photovoltaic (PV) panels; and Electromagnetic Energy: Inductors, coils, and transformers can be considered as ambient energy sources, depending on how much energy is needed for the application. Additionally, chemical and biological sources and radiation can be considered ambient energy sources General Overview of Ambient Energy Sources

The first row shows the energy-harvesting sources. The second row shows actual implementation and tools are employed to harvest the energy from the source are illustrated. The third row shows the energy-harvesting techniques from each source. Block Diagram of General Ambient EH systems.

Solar Cells Commercial-off-the-shelf (COTS) energy harvesting 1cm x 1cm; 0.14 mW (much less inside) Recent research trend to improve the efficiency, robustness, costdown, etc. Often limited by the availability of direct sunlight and size. Portable Electric Energy Sources Available

Energy Harvesting Block Diagram

Energy Harvesting (EH) EH uses of ambient energy to provide electrical power for small electronic and electrical devices. An Energy Harvesting System consists of an Energy Harvester Module and a processor/transmitter block. Energy Harvesting Module captures milli-watts of energy from light, vibration, thermal or biological sources. A possible source of energy also comes from RF such as emitted from cell phone towers. The power is then conditioned and stored within a battery, an efficient quick charging capacitor or one of the newly developed thin film batteries. The system is then triggered at the required intervals to take a sensor reading, through a low power system. This data is then processed and transmitted to the base station. This kind of EH System eliminates the dependency of the system on battery power and reduces the need to service the system..

Biochemical Energy Production Catabolism: metabolic reactions in which large molecules are broken down into smaller molecules – Usually produce energy (but not always) Anabolism: metabolic reactions in which smaller molecules are joined to form larger molecules – Usually consume energy Metabolism

Almost all energy-harvesting scenarios require some sort of energy storage element or buffer. Even if the voltage and current requirements of an embedded application were so low as to be run directly on power captured or scavenged from the environment, such power would not flow in a constant way. Storage elements or buffers are implemented in the form of a capacitor, standard rechargeable lithium battery, or a new technology like thin-film batteries. What kind of energy storage is needed depends greatly on the application. Some applications require power for only a very short period of time, as short as the RC time constant discharge rate of a capacitor. Other applications require relatively large amounts of power for an extended duration, which dictates the use of a traditional AA or a rechargeable lithium battery Energy Storage is a Must

Li-Ion BatteryThin Film Battery Super Cap Recharge cyclesHundredsThousandsMillions Self-dischargeModerateNegligibleHigh Charge TimeHoursMinutesSec-minutes Physical SizeLargeSmallMedium Capacity mAHr μAHr μAHr Environmental Impact HighMinimal

Remote patient monitoring Efficient office energy control Surveillance and security Agricultural management Home automation Long range asset tracking Implantable sensors Structural monitoring Machinery/equipment monitoring Industry Applications

Design Consideration TI's TMS37157 could also be used to harness the RF energy into electrical energy. TI's MSP430 and Low Power RF parts combined with efficient DC/DC Converters and Battery Management parts are an ideal complement to these low power energy harvesting sources.MSP430Low Power RFDC/DCBattery Management With as low as 160 uA/MHz (microamp per megahertz) active power consumption and 1.5 uA standby power consumption, MSP430F5xx MCUs enable longer battery life or no batteries at all for energy harvesting systems that run off of solar power, vibration energy or temperature differences like found on human body.

References: arvesting_systemsLA-UR_8296.pdf must-work-together/ file:///C:/Users/test1/Downloads/Energy%20harvesting%20(1).pdf