Energy consumption of your IoT sensors

Everything about energy consumption and lifespan of your IoT sensors and how you can optimize them

IoT sensors have 3 basic functions: to measure, communicate and standby. They can be placed anywhere and can be used for many purposes. Some examples are:

• Collecting energy consumption data in a commercial building.
• Monitoring key parameters of various equipment in an industrial building to predict possible failures and plan maintenance activities in advance.
• Providing good indoor air quality to protect the health of residents in a multi-family building.
• Monitoring the presence of employees or the occupancy of offices in an open space.

Since most IoT sensors are battery powered, it is important that energy consumption is as low as possible. Why is that important?

1. Positive ROI
To be cost-effective, most IoT sensors need to be able to operate for up to 10 years. For each sensor deployed, replacing batteries not only has material costs, but also labor costs. And in the case of mass deployment of sensors or sensors installed in hard-to-reach or roaming locations, these labor costs are much higher than the cost of the product itself. The cost of a site visit is generally estimated between €300 and €500.

2. More data available
The energy consumption of a sensor can be optimized by adjusting some parameters. This allows more frequent measurements without additional energy consumption. This increases the amount of data available.

3. Better radio transmission quality
Some protocols adjust the transmit power based on the radio quality. By minimizing the power consumption, the product can adapt to power fluctuations while maintaining the expected lifespan. It is therefore important to keep your IoT sensor 'alive' for as long as possible.

Calculation

The lifespan of an IoT sensor is determined by a simple calculation: battery capacity / average consumption. There are therefore 2 ways to optimize the lifespan of the battery:

• Reduce the amount of energy used by the IoT sensor
• Increase battery capacity

To achieve this, several compromises are required that must be implemented by both the IoT sensor manufacturer and the user of these sensors.

What are the possibilities to reduce the energy consumption of a battery powered IoT sensor as a manufacturer?

Adding a battery that can store more energy is the obvious way to improve the lifespan of an IoT sensor. Depending on the type of sensor and its use, this simple solution is not necessarily the best, as it has a strong influence on the size and cost of the sensor. For example, a dual 3.6V Lithium battery pack with a capacity of 8.2 Ah costs only a few euros to purchase! Environmental impact and ecological footprint are other factors to consider when choosing a battery type.
Regardless of the battery type chosen, it is crucial for a manufacturer to bring a sensor to market that consumes as little energy as possible. There are many factors that influence energy consumption. Here are some decisions that manufacturers must make to address energy optimization:

1. Energy saving components
The first possibility for optimization is to select energy-saving components. This selection should be based on an analysis of the technical specifications of each component. However, the energy consumption depends mainly on the way the components are used. It is therefore crucial to measure the actual power profile on prototypes in order to determine the power consumption of an IoT sensor as accurately as possible.

• Depending on the quantity measured by an on-board sensor (temperature, CO2, pulse, etc.), the energy required to perform the measurement can have a significant impact on the total consumption. What on-board sensors are available on the market and which references offer the best compromise between performance/consumption/price/availability? How should they be used? Continuously with low-energy modes or pulsed?
• Which microcontroller(s) to select?
• Should LEDs be integrated?

2. Software important for energy optimization
Regardless of the intrinsic power consumption of the embedded components such as external devices, microcontrollers or radio modules, if the software controlling them uses them in a non-optimized way, then all energy efforts at hardware level are in vain.

• Which algorithms should be developed to ensure the most energy-efficient operating mode?
• How can the electronic components in the IoT device be put into deep sleep as often as possible?

3. Focus on LPWAN communication technologies
The communication technology used by the sensor is another factor that affects the energy consumption of an IoT sensor. Low Power Wide Area Networks (LPWANs) have emerged as the preferred choice for manufacturers to enable battery-powered IoT sensors to communicate due to their long range, low power consumption, and low deployment costs.

LPWAN deployments fall into two broad categories: non-cellular LPWAN and cellular LPWAN.

While there are currently around 20 different LPWAN technologies in the IoT domain, 4 are particularly suited to today’s challenges and are widely deployed: LoRa, Sigfox, LTE-M and NB-IoT. According to IoT Analytics, these 4 technologies represent more than 92% of the LPWAN market!

The table below provides an overview of the performance of these 4 technologies in terms of range, power consumption, throughput and implementation costs:

Impact of LPWAN on the daily autonomy of an Adeunis COMFORT CO2 sensor in its default configuration.

Battery energy consumption in 1 year (in %)

Daily consumption:

The GSMA has clarified the different elements to be taken into account at modem level to facilitate the comparison of competing cellular IoT sensors. To evaluate the consumption of a cycle, it is necessary to add up the consumptions of the different phases of the modem's operation, as shown in the figure below.

Of course, the purchaser of IoT sensors is dependent on the design choices that manufacturers make. However, these technical choices can be comparison criteria to use in your purchasing process.

What are the possibilities to improve the battery life of IoT sensor as a user?

1. Simple but crucial: the choice of connectivity and location of the IoT sensor
Please note that radio conditions at the deployment site may cause IoT sensors to consume too much power, shortening their lifespan.

To reduce risks, experts can help you conduct a connectivity study on your sites and make recommendations on the choice of networks to use for installing your IoT sensors.

The positioning of the IoT sensor and more specifically its antenna also has an impact on consumption. The ideal location for the type of IoT sensor is usually indicated in the manufacturer's user manual.

2. Once selected, optimize the connectivity of the sensors
The wireless communication function is usually the most power-consuming in an IoT sensor. However, the battery life of a sensor can be easily improved by adjusting the following parameters:

• Reduction of the periodicity of data transfer.

Example: Adeunis LoRaWAN COMFORT CO2–sensor autonomy, in SF12:

• Enabling ADR (Adaptive Data Rate) in LORA which allows dynamically changing the transmission time of a frame by monitoring the connection parameters and adjusting the FS accordingly.
• Logging of measurements prior to transmission, so that communications circuits are only woken up when they have sufficient data for efficient transmission.
• Limiting the amount of data sent in each frame (uplink).

Example: Adeunis LoRaWAN COMFORT CO2 sensor lifespan at 24 frames/day:

• Limit the acknowledgement after sending a frame (uplink).
• Reduce the number of retries (Sigfox).
• Optimizing the use of FOTA and downlinks.

Example: Lifetime of the Adeunis Sigfox COMFORT CO2 sensor transmitting 24 frames/day

Lifespan 3 frames (2 retries)

Lifespan 3 frames (2 retries):

• For mobile technologies, use PSM (Power Saving Mode) and eDRX (Extended Discontinuous Reception) functions

Regardless of the LPWAN technology used, it is possible to turn off the radio module of an IoT device to reduce power consumption. However, the device usually needs to perform a tethering procedure to the network when the radio module is turned on again. Although each tethering procedure consumes a small amount of power, the cumulative power consumption caused by multiple tethering procedures over the lifetime of the sensor can have a significant impact on battery life.

To address this issue, NB-IoT and LTE-M mobile network operators have developed the PSM functionality that allows the sensor to go to sleep at fixed intervals and wake up only to take and send a measurement without initiating a network connection procedure. The sensor and the network together optimize this interval based on the application constraints.

Discontinuous reception works independently of the PSM mode and significantly extends the time interval during which an IoT device is not listening to the network.

For cellular IoT sensors, the choice of application communication protocol will also have an impact on total consumption (MQTT, LWM2M, HTTPS, etc.). To reduce the power consumption of its new range of NB-IoT and LTE-M sensors, Adeunis has chosen to integrate LWM2M.

3. Pay attention to the application settings
Optimization of the sensor sampling rate.

Example: Adeunis LoRaWAN COMFORT CO2 sensor

Optimizing the use of LEDs

Example: Adeunis LoRaWAN COMFORT CO2 sensor

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