Q&A
This page tries to answer any questions you may have. If you’re still in doubt, please feel free to send us a message!
WHAT ARE THE DIFFERENT ELEMENTS REQUIRED TO BUILD AN ENERGY HARVESTING SYSTEM?
To set up an energy harvesting system, you need a harvester, a storage element, and an AEM. The AEM is the central component of the system. It extracts the maximum power provided by the harvester and stores it in the storage element, so that this energy can be used later — and in some cases, it can even be used to directly power the application.
WHAT ARE THE POWER RANGES IN AN INDOOR AND OUTDOOR ENVIRONMENT?
The power generated depends on the type of harvester, its size, and the environment.
For example, in the case of Photovoltaic energy harvesting, the output power will depend on the size of the photovoltaic cell, the light intensity, and the PV cell technology used.
- Indoor Photovoltaic energy harvesting generates power in the range of hundreds of microwatts. (These values may vary depending on the size of the cell.)
- Outdoor Photovoltaic energy harvesting generates power that can reach tens of milliwatts. (These values may vary depending on the size of the cell.)
Other types of harvesters include thermal, RF, and vibration harvesters.
- Thermal energy harvesting (TEG) relies on temperature differences and typically generate power in the range of a few microwatts to several milliwatts, depending on the thermal gradient and the efficiency of the thermoelectric materials.
- RF (Radio Frequency) harvesting capture energy from ambient radio waves, such as those emitted by Wi-Fi, GSM, or TV signals. The power levels are usually very low, often in the microwatt range, and highly dependent on the distance from the emitter and the frequency band.
- Vibration or piezoelectric harvesters convert mechanical vibrations into electricity. The harvested power can vary from a few microwatts up to several milliwatts, depending on the frequency and amplitude of the vibrations as well as the mechanical structure of the harvester.
Each harvester type has its strengths and limitations, and the choice depends on the available energy in the environment and the application’s power requirements.
CAN I HARVEST ENERGY FROM MY WIFI?
Wi-Fi transmissions are limited by regulations to a maximum of +20 dBm at the transmitter. In most cases, this power level is insufficient for effective energy harvesting.
Significant losses occur as RF energy propagates through the air and along the RF path on the PCB. These losses are frequency-dependent and tend to be lower at lower frequencies.
To have full control over the emitted power, antenna characteristics, and transmission duty cycle, we recommend using a dedicated RF transmitter.
CAN THE APPLICATION BE POWERED DIRECTLY BY AN AEM?
AEMs can accept any type of storage elements with a voltage lower than 5 V. They are therefore compatible with supercapacitors, Li-ion batteries, LiPo, NiMH, hybrid supercapacitors, and more. However, there is an additional limitation on certain AEMs, which may have a lower voltage limit, such as the AEMxx920 for example.
HOW CAN WE CONFIGURE AN AEM?
AEMs can be configured using the GPIO pins by connecting them to a high state or to GND. However, some AEMs include I²C communication for the configuration and monitoring. This allows overriding the configurations set by the configuration pins and allows accessing to all the AEMs configurations, enabling wider range of settings and allowing live system monitoring
WHAT IS THE MAXIMUM POWER POINT VOLTAGE OF A HARVESTER?
The Maximum Power Point voltage is the voltage at which a power source (like a Photovoltaic cell or TEG) delivers its maximum power output. To optimise the extraction of the energy from the harvester, the AEM Source will regulate at this voltage.
HOW CAN WE FIND THE RIGHT SOURCE CONFIGURATION BASED ON THE SELECTED HARVESTER?
To find the right configuration for the source, it is crucial to understand the voltage/power behaviour of the harvester under various environmental conditions. The most straightforward approach is to perform a voltage sweep across the harvester terminals in a controlled environment and measure the current provided by the harvester at different voltages. By multiplying the voltage by the current, the power generated at different source voltages can be calculated. This process should be repeated for different environmental conditions.
Once the harvester is characterized under various conditions, it’s possible to determine whether constant voltage regulation or regulation based on the open-circuit ratio is required.
HOW CAN WE MEASURE THE EFFICIENCY OF THE AEM?
To measure the efficiency of the AEM simply connect an SMU to the input of the converter and another to the output. By dividing the output power by the input power, the efficiency of the converter can be determined.
For example, for measuring the system efficiency between STO and LOAD of the AEM10920, the input of the converter will be the STO pin, and the output will be the LOAD pin.
This efficiency measurement will include the quiescent current of the AEM and the power converter efficiency.
HOW CAN WE KNOW IF THE AEM IS AWAKE?
To determine if the AEM is awake, the AEM internal supply voltage can be measured of the AEM (Vbuck for the AEMx094x, VINT for the others). If the voltage is around 2.2V, the AEM is awake.
WHAT IS THE DIFFERENCE BETWEEN A STORAGE CHARGER ONLY AEM AND ANOTHER AEM?
Storage chargers only AEMs do not have a regulated output voltage to power directly the application circuit. The primary objective of a storage charger only AEM is to efficiently charge the storage element.
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