Remote monitoring devices have become an essential functional element within a huge array of industries and applications, from healthcare to agriculture, from industrial automation to environmental monitoring. They lie at the core of Industry 4.0 edge computing systems.
These devices gather and transmit data in real-time from locations that are often difficult to access, remote/distributed or hazardous, making them invaluable for operations where real-time feedback is necessary for complex control of distributed and interacting systems. They 'observe' real-world phenomena/conditions and convert these to virtual data that reflects reality in a machine-usable form.
One of the ever-present challenges in deploying such devices is ensuring they have a reliable power source, especially in remote locations. It is useful to explore the options in power sources for such remote monitoring devices, their relative advantages, and their often severe limitations.
Batteries remain central to remote-monitoring and IoT power systems across most applications — enhanced with local charging, or single use devices with operator visits is a strategic decision at the design stage. Source: partyvector/Adobe Stock
Why power sources matter for remote monitoring
Remote monitoring devices can be required to operate independently for long periods, often in isolated or human-excluding environments. Whether they are monitoring environmental conditions in a remote site, or collecting health data from wearable devices, or interpreting operational conditions in a production facility, such devices need a consistent power source to function effectively.
The selection of power source is crucial because it can define the device's performance, maintenance needs, operational hardware and overall lifespan. For remote monitoring systems, the power source must be reliable, long enduring and capable of operating without frequent (or any) maintenance or replacement.
Factors to consider when selecting a power source include the energy demand of the optimal-function device hardware, the operational environmental conditions, the service accessibility of the placement, and the required functional life and cost-tolerance of the application to the power source
Power source options
The spectrum of potential power sources is very wide, although many options are extreme-cost outliers that are entirely unsuited to typical applications.
Battery power
One of the most common power sources for remote monitoring devices is battery power. Batteries are portable, relatively inexpensive, and available in a wide range of sizes and capacities, making them suitable for various applications. There are several types of batteries used for powering remote devices, including:
Primary (non-rechargeable) batteries
These are disposable chemical batteries that have a variety of power capacities and shelf-lives:
Lithium manganese dioxide: These are widely used in remote monitoring devices due to their high energy density (~300Wh/kg), long shelf life and tolerance of wide operating temperatures. Lithium batteries can deliver current for as long as a decade without replacement, assuming they're not drained or corroded. This renders them ideal for devices in hard-to-reach locations, if sufficient current capacity can be integrated for the required endurance
Lithium thionyl chloride: Similar properties to lithium manganese cells, but with much improved power capacity (700Wh/kg) and even wider temperature tolerance which sets them apart for specific applications where environmental durability is a key requirement. These are likely the costliest and widely available type.
Alkaline manganese: Although less energy-dense (~100-150Wh/kg), alkaline batteries are cost-effective and commonly used for low-power remote devices. However, they may not perform as well in extreme temperatures or high-drain applications and their shelf life is around half that of lithium batteries.
Other chemistries: Silver oxide/zinc (button cells) can have long shelf life but offer very low current capacity. Zinc/air are very low cost, offer moderate current delivery but have short shelf life.
Advantages of the primary cell types commonly used in remote and high reliability applications are typically long shelf life and no need for recharging infrastructure.
The disadvantages of the class include limited net energy supply and relatively low peak capacity and requiring replacement, which is both costly and challenging for truly remote or hazard-area devices.
Secondary (rechargeable) batteries
Lithium-based rechargeables: These include lithium-ion (L-ion), lithium-polymer (Li-po), and lithium-Iron-phosphate (LiFe-po) which are among the most popular rechargeable battery options for remote monitoring devices. Collectively they offer a high energy density and are relatively lightweight. They are widely used in applications where the device can be recharged relatively easily from an external source (AC or DC)
Nickel-metal hydride (NiMH): These are another common rechargeable battery type. Although they have a lower energy density than Li-ion batteries, they are safer to use in certain environments and are considered to have a longer cycle life.
Lead acid and gel-cells: Despite being the lowest energy density (20-50Wh/kg) and typically offer a short service life. However, they can be deep cycle tolerant, offer very high current capacity and they're low cost.
Advantages of rechargeable batteries; recharging reduces the need for replacement, having long operational life when paired with a renewable energy source and generally not deep cycled and they contain options suitable for moderate to high-energy applications and a range of current scenarios.
Disadvantages vary considerably with type. Li-po and Li-ion can develop Li dendrites that cause internal short circuit and fire. NiMH batteries respond poorly to deep cycling. Lead acid cells lose charge relatively quickly.
In all cases they require a recharge source, such as solar panels, mains supply, a generator or one of a number of other options.
Solar power
Photovoltaic devices are perhaps the most practical and widespread renewable power sources for remote monitoring devices. Solar panels can be used to recharge batteries or more unusually to directly power devices, though energy consumption and storage demands are rarely solely diurnal.
Solar power is only for devices that can have easy access to good sunlight exposure, such as agricultural applications, weather stations or environmental monitoring systems in open spaces.
The advantages of solar power are well understood; it is renewable and abundant in many parts of the world, although of highly variable intensity/reliability with latitude and weather. The equipment is relatively low cost for small, low power installations and the infrastructure required is minimal.
The disadvantages are equally well understood; power is dependent on sunlight, which is commonly unreliable, implying a need to over-specify both panels and batteries to handle extended dark periods; it can require a significant upfront effort/investment for solar panel installation and batteries, for higher power demand or higher criticality installations
Energy harvesting
Energy harvesting is the process of capturing small amounts of typically transient energy from the surrounding environment and converting it into electrical power. This method is increasingly being used for low-power remote monitoring devices that need to operate for long periods without manual intervention.
Common energy sources for harvesting include vibration, using piezoelectric methods for higher frequency and magneto-mechanical methods for larger motion.
Thermal gradients such as piping and waste heat or sunshine-shade can be used to generate power through thermoelectric generators such as Peltier effect devices. These generate small current flows directly from heat transfer across the gradient.
Radio frequency (RF) waves can be harvested from nearby Wi-Fi or cellular signals to power very low-energy devices.
The advantages of energy harvesting are considerable where it is practical due to low power needs or when devices are in the presence of high-power sources. This obviates the need for battery replacement or recharging infrastructure, due to the potential for reliable, non-time-dependent supply.
The disadvantages of energy harvesting methods are clear: they typically offer limited power output, are suitable only for low-power devices in most cases, can involve inconsistent energy supply in fluctuating environmental conditions and require careful specification and optimization for the operational environment.
Fuel cells
Fuel cells generate electricity through chemical reactions, typically involving hydrogen or methane and oxygen. Fuel cells offer an efficient and long-lasting power source in high value applications.
Fuel cells offer some significant advantages in remote power for sensing applications, such as long-endurance and high power density, operation for months or years, suitability to environments where other power sources are impractical and minimal waste/exhaust production.
The disadvantages of fuel cells are overwhelming in many applications. Very high upfront cost and complexity in design and implementation is a barrier to all but high value applications and the requirement for fuel replenishment is a burden in some remote locations. There are an increasing range of smaller, lower power devices coming on the market that will tend to mitigate the cost issue, however
Wind power
Wind energy is a relatively simple renewable option, particularly useful for remote monitoring systems located in regions with consistent wind patterns, such as coastal areas, plains or offshore platforms. Turbines can be used for power either directly for the device or to charge a battery system that stores energy.
A hybrid wind/solar system improves the up-time for power supply, though a solution must still take into account still/overcast periods with sufficient battery capacity to endure the worst case.
Clearly, however, wind is an inconsistent energy source and can require higher maintenance than solar panels due to moving parts - particularly as small turbines tend to be low cost, low endurance devices
Considerations for choosing the right power source
Selecting the optimally appropriate power source for a remote monitoring device requires a careful balance of factors:
Energy requirements must be top priority. Higher energy demands from devices that transmit big data, perform complex processing locally or carry out local control operations require more robust power sources.
Location and accessibility are major considerations. Where devices are sited in remote locations and must rely on power sources that can function long term without intervention, fuel cells or hybrid energy-harvesting solutions are more suitable.
Environmental conditions can considerably influence selection. Harsh conditions, such as wide temperature swings, can influence performance. Lithium batteries are more robust to extreme cold than alkalines, while solar panels will be ineffective in cloudy or shaded areas.
Maintenance requirements must be minimized for remote sites. Rechargeable systems that rely on solar power or energy harvesting can reduce the frequency of maintenance visits but will require initial investment in more complex infrastructure.
Future trends in powering remote monitoring devices
The future of remote monitoring device power sources lies primarily in the continued development of renewable energy and energy-harvesting technologies and advances in low-power electronics. It is becoming increasingly feasible to power devices with minimal energy inputs for indefinite or at least prolonged use.
More efficient battery chemistries are being commercialized at a steady pace, improving remote power scenarios in some regards. The integration of artificial intelligence-based energy management systems to optimize energy consumption and maximize the lifespan of power sources is also incipient and becoming feasible. This is particularly relevant to adaptive and locally authorized management systems that report on events in a less passive mode and may be involved in local control and decision making. This increasingly relies upon hybrid solutions, offering the AI options in power management.
Conclusion
Powering remote monitoring devices is one of the most significant challenges in designing effective, long-lasting remote systems. The selection of power source depends heavily on the specifics of the application such as the operational environment, net-power demand and long-term maintenance/access feasibility.
By selecting and optimizing power sources carefully, system integrators and data users can be assured that their remote monitoring executions remain functional, reliable and cost-effective sufficient over time.
