Realising the full potential of energy harvesting and the IIoT

Picture credit: Tadiran

The market for industrial wireless devices is exploding, with wireless technology becoming central to a wide range of applications that will be essential to the Industrial Internet of Things (IIoT). These applications include AMR/AMI for utility metering, wireless mesh networks, structural sensors, machine to machine (M2M) and system control and data acquisition (SCADA), data loggers, measurement while drilling, oceanographic measurements, and emergency/safety equipment, to name a few.

Common to all these applications will be a growing need for technology convergence and interoperability throughout the IIoT: a growth curve that has been aided by the development of low-power communications protocols such as ZigBee, WirelessHART, LoRa, Bluetooth, DASH7, INSTEON, Z-WAVE and others. These protocols combine with low-power circuitry and intelligent software design to extend battery life with uncompromised product performance.

Identifying the ideal power supply

A remote wireless device is only as reliable as its power supply, which needs be optimised based on application-specific requirements. The vast majority of remote wireless devices continue to be powered by primary (non-rechargeable) lithium batteries. However, a rapidly growing number of applications are well suited for energy harvesting in combination with rechargeable Li-ion batteries or supercapacitors to store the harvested energy. Many types of renewable energy sources are available, including: solar, wind, thermal, vibration, kinetic, and RF/EM signals.

The decision of when to deploy an energy harvesting device should be based on numerous factors, including: the reliability of the device and its energy source; the required operating life of the device; average daily current draw; size and weight considerations; environmental requirements; and cost.

The typical energy harvesting device has five key components: a sensor, a transducer, an energy processor, a microcontroller, and an optional radio link. The sensor detects and measures environmental parameters such as motion, proximity, temperature, humidity, pressure, light, strain vibration, and pH. The transducer and energy processor work together to convert, collect, and store the electrical energy in either a rechargeable lithium battery or a supercapacitor. The microcontroller collects and processes the data, while the radio link communicates with a host receiver or data collection point.

While supercapacitors are often utilised in consumer grade devices, they have major drawbacks that limit their use in industrial grade applications. Supercapacitors suffer from high self-discharge rates that can cause premature battery failure, and their limited temperature range prohibits their use in extreme environments. Solutions involving multiple supercapacitors also require the use of balancing circuits that draw additional current and add to cost.

Industrial grade Li-ion batteries are now available

Rechargeable lithium battery technology continues to improve, with Lithium-ion (Li-ion) batteries remaining the most popular choice for both consumer and industrial applications. As a safety precaution, all Li-ion batteries require protection circuits to prevent over- or under-charging.

Consumer grade Li-ion cells are reasonably inexpensive and widely available, but have a limited life expectancy of roughly five years and 500 recharge cycles. These consumer cells are also designed to operate within a moderate temperature range (-10 to 60°C). In addition, they cannot deliver the high pulses required for advanced two-way communications and/or remote shut-off capabilities.

Industrial grade Li-ion batteries are highly recommended for long-term deployment in remote, inaccessible locations, offering extended operating life of up to 20 years and 5,000 full recharge cycles, an extended temperature range (-40°C to 85°C), and the ability to deliver high pulses (5 A for an AA-size cell). These ruggedly constructed batteries also feature a glass-to-metal hermetic seals, whereas consumer rechargeable batteries (table one, below) use crimped seals that may leak.

Due to high labour costs, replacing a battery can be far more expensive than the cost of the original battery. Therefore, for long-term deployments, you need to calculate the differential in total lifetime cost of using consumer grade Li-ion batteries that require replacement every 5 years and 500 recharge cycles versus choosing an industrial grade Li-ion battery that can operate maintenance-free for up to 20 years and 5,000 full recharge cycles.

Typical example of an urban energy harvesting application

The IIoT will eventually encompass virtually all conceivable external environments, creating distinctly unique power management challenges and opportunities for both urban and rural environments.

Within urban centres, extending the AC power grid to accommodate IIoT-enabled devices will be prohibitively expensive. For example, a solar-powered parking meter (main picture) was developed by the IPS Group that eliminates the need to bring power to every parking meter. Instead, energy harvesting devices and industrial grade rechargeable Li-ion batteries combine to provide a highly reliable, long-term, low-cost power management solution. These state-of-the-art wireless parking meters feature advanced functionality such as multiple payment system options, access to real-time data, integration to vehicle detection sensors, user guidance, and enforcement modules, and connectivity to a comprehensive web-based management system.

Miniaturised photovoltaic panels have been integrated into the parking meters, serving to gather solar energy that is then stored in industrial grade rechargeable Li-ion battery, providing sufficient available capacity to deliver 24/7/360 reliability along with high pulses to power advanced two-way wireless communications. Use of a 20-year battery also cuts long-term maintenance costs, and reduces the risk of lost revenue and reporting capabilities caused by recurring battery failures.

Long-life rechargeable Li-ion batteries are also essential for remote areas

The expanding IIoT is also create dynamic growth opportunities for wireless devices to serve highly remote locations, including extreme environments and locations far beyond the reach of the AC power grid.

A prime example where remote connectivity is required using energy harvesting as the power source is CattleWatch (below), an innovative solution that deploys solar-powered ‘smart collars’ to turn a herd of cattle into a remote wireless mesh network.

CattleWatch utilises solar-powered ‘smart collars’ that allow a herd of cattle to form a wireless mesh network. Ranchers can remotely manage their herd through connectivity via Iridium satellites to the IIoT. Industrial grade rechargeable Li-ion batteries enable the ‘smart collars’ to be light, compact, and more comfortable for cows to wear. 

All cows are equipped with RFID collars while a small number of cattle are outfitted with more sophisticated ‘hub collars’ that communicate to the internet cloud via Iridium satellites. Once formed, the wireless mesh network broadcasts continuously via satellite to provide the rancher with real-time data that monitors daily animal behavior, including herd location, walking time, grazing time, resting time, water consumption, in-heat condition and other health events. The rancher also receives instant notification if a potential threat is detected from predatory animals or poachers.

The hub collars are equipped with miniature PV panels that gather solar energy, while the industrial grade Li-ion batteries store sufficient energy to deliver the high pulses needed to initiate satellite communications. Industrial grade Li-ion batteries were chosen over bulkier supercapacitors because they enabled the ‘smart collars’ to be smaller, lighter, and more comfortable for the animals to wear.

These two examples illustrate the ‘tip of the iceberg’ in terms of the potential opportunities for IIoT-related applications to be powered by energy harvesting devices in combination with industrial grade Li-ion rechargeable batteries to provide maintenance-free operation for up to 20 years. Such a reliable long-term power supply solution could help reduce the total cost of ownership for a wide range of IIoT-related applications. 

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