With remote monitoring also comes the need for an autonomous, efficient power supply to ensure the continuous operation of sensors, data loggers, and telemetry equipment. Systems installed at or near existing infrastructure can receive power from the electrical grid.
However, fixed power supplies are not available in many applications, so alternative means are required. In such cases, battery-based systems are commonly implemented. These can be standalone systems operating from reserve battery capacity alone, or regenerative systems where inputs from solar arrays, wind turbines, or other sources charge batteries.
The choice of power source depends on the specific application, location, and power requirements of the monitoring system. Prior to selecting equipment, each monitoring site should be surveyed and evaluated to determine the best approach. For systems that will implement battery systems with charging, a power budget analysis is a useful practice to ensure that the power system is appropriately sized for the payload and various field conditions it will experience.
Main (AC Power)
AC power is the most straightforward and reliable source of electricity for environmental monitoring systems when available. The constant power it supplies allows for frequent measurement and data transmission without concern for exhausting battery supplies. It can also support high-power instruments, such as a weather station with integrated heater for deicing in the winter.
Since environmental measurement systems often operate at a nominal DC (direct current) voltage like 12 VDC or 24 VDC, the voltage typically must be converted from AC (operating at 110 or 230 VAC) to the required DC voltage using an AC to DC power converter. A secure, waterproof connection is important for any sites where moisture or humidity is a concern.
In critical applications where downtime must be minimized, systems often include a reserve battery pack for operation in the event of a power outage.
Batteries
Since AC power is not available in many locations where remote monitoring stations are deployed, systems are commonly powered by batteries. In some cases, alkaline battery packs are used to power systems, though rechargeable batteries are more common. Two of the most common battery technologies used in rechargeable systems are sealed lead-acid (SLA) and lithium-ion (Li-ion) batteries.
SLA batteries are a robust and cost-effective option that provides reliable power and good capacity, particularly in applications with low rates of charge and discharge. This is often the case in environmental monitoring systems, which are designed for power efficiency and frequently spend time in a sleep state between measurement cycles. They can also accept charge at sub-freezing temperatures, so they are a good option for deployments in cold climates.
Lithium ion batteries offer the advantages of high energy density, lightweight cells, and long lifespan. They can be cycled more times than SLA batteries and work well at higher temperatures. They also do not require venting or upright orientation like SLA batteries, though they are more difficult to ship due to fire hazard and typically require special handling.
Solar Photovoltaic Cells
Solar photovoltaic (PV) cells convert sunlight into energy that can be used to charge batteries in environmental monitoring systems. Known as solar panels when linked in an array, they are rated in watts (W) based on their output potential. They are a common and reliable source of renewable energy in any location that receives direct sunlight. Once installed, solar PV cells require little maintenance other than periodic cleaning.
Solar PV cells typically produce a variable voltage depending on sunlight intensity. Charge controllers are used to regulate the voltage and ensure that the battery is charged at the correct voltage and current to maximize efficiency and battery life.
Solar power packs reliably charge batteries that power remote monitoring systems in any location that receives consistent sunlight.
Wind Generators
Wind generators, also known as wind turbines, convert kinetic energy from moving air into electrical power that can be used to charge batteries in environmental monitoring systems. They are well-suited for any location with consistent wind patterns and can complement solar charging systems to improve power supply reliability. Wind generators offer the ability to charge at night or during cloudy conditions when solar panels are less effective.
Similar to the variable voltage produced by solar panels depending on available sunlight, wind generator voltage varies with wind conditions and should be regulated for proper battery charging. Since wind turbines include moving parts, they should be inspected and cleaned regularly.
Wind turbines can supplement or be used as an alternative to solar power packs for battery charging in any location that receives consistent winds.
Alternative Energy Harvesting
Although solar and wind account for the vast majority of renewable energy sources for environmental monitoring systems due to their relative simplicity, alternative methods have been applied in certain cases. Examples include hydroelectric, geothermal, and ocean energy.
Hydroelectric power involves using the energy from flowing or falling water to generate electricity by means of mechanical turbines placed in the water. This can be applied in rivers or streams where there is constant water flow. It can provide a constant, reliable power source that is less dependent on daily cycles or weather patterns than solar and wind.
Geothermal energy generates electricity by harnessing the heat from the Earth’s interior. Like hydroelectric, it can provide a consistent energy source. However, it is more complex and expensive to establish, and it is most applicable to areas with high geothermal activity. These factors limit its usefulness for environmental monitoring applications.
Ocean energy refers to the harvesting of kinetic energy from waves or tides in the sea. Oceans offer a vast amount of energy that, in the case of tides, is also consistent and predictable. Additionally, since oceans are a common realm for environmental studies and measurements, it has potential for direct integration into marine monitoring systems.
However, ocean energy harvesting systems are relatively complex, potentially expensive, and may require frequent maintenance. They may also impact marine life and coastal ecosystems depending on how they are constructed.
Conclusion
Effective design and implementation of power management systems are essential for the continuous operation of environmental monitoring systems. The location of many remote systems does not allow for electronics to be directly connected to the power grid, so battery-based deployments are frequently required. Appropriately sized solar panels or wind generators are most often used for maintaining battery charge, though other means are sometimes implemented. By understanding and selecting the appropriate power sources, operators can ensure reliable and sustainable data collection.
Resources
- Power-Sonic. (n.d.). Lithium vs. Lead Acid Batteries. Power-Sonic. Retrieved from https://www.power-sonic.com/blog/lithium-vs-lead-acid-batteries/