Air quality measurement in Smart Cities: Self-sufficient 24/7 power supply for environmental sensors from Vaisala

Project description

Municipal air quality measurement and monitoring for smart cities

The measurement and monitoring of air quality is part of the "Smart City" concept for the digitalisation of infrastructure – here using the example of the city of Darmstadt / Germany. In order to achieve the most comprehensive monitoring of air quality, around 40 measuring locations were defined. To save the cost of laying new power supply lines, the sensor system consisting of the VAISALA AQT530 air quality transmitter and a gateway for data communication should be installed on site at the existing streetlights and supplied with 24 VDC via their 230 VAC power connection. Since the lighting only carries electricity in the dark, a continuous power supply was not guaranteed. That’s why, in close collaboration with Bicker Elektronik, a buffered 24/7 power supply with night charging was created for safe operation around the clock.

The challenge

Buffered outdoor power supply for environmental sensors and gateway

The challenge was to develop a UPS solution for harsh outdoor use that ensures an uninterrupted 24V power supply for sensors and gateway, as there is no permanent power supply available on site. These locations only have street lights that are powered by 230VAC during lighting times. The buffer storage must be optimally charged at night in order to have sufficient energy available throughout the day to supply the sensors and gateway.

Further challenges arose from the climatic and seasonal changes.

In summer, the UPS and battery technology must withstand high temperatures and enable a longer supply time for sensors and gateway as the lanterns are switched on later and switched off earlier. It was crucial that the energy storage could be sufficiently recharged even with the shorter lighting time and that the capacity was dimensioned accordingly.

In winter the opposite situation occurs. The UPS has to cope with extremely low temperatures. While the lanterns shine for longer and thereby shorten the bridging time required to supply the sensors and the gateway. Battery storage systems generally cannot be charged as efficiently or quickly at low temperatures.

The aim was to find a solution that would reliably supply the sensors and the gateway with 24VDC at all times under all conceivable conditions. The battery technology in particular had to meet the high requirements in terms of thermal properties as well as safety and longevity.

The solution

AC/DC UPS with LiFePO4 high-capacity battery and night charging

With the tailor-made UPS solution UPSI-2406IP-38AC, the engineers at Bicker Elektronik were able to optimally meet the requirements profile. The robust and weatherproof IP65 aluminum housing protects the highly efficient AC/DC converter with wide range input, the UPS control and charging technology and the newly developed LiFePO4 high-performance battery. This battery technology and the integrated battery management system (BMS) with cell balancing ensure maximum safety, a particularly long service life and excellent performance at temperatures from -20 to +50°C. This means that a particularly reliable and uninterrupted power supply is guaranteed at all times, even under demanding operating conditions.

The UPSI-2406IP-38AC converts the input AC supply voltage (90-264VAC) into 24VDC during the night and forwards this directly to the connected environmental sensors via the UPS output, charges the connected energy storage in parallel and monitors all relevant parameters and currents and voltages. In the event of a voltage dip or power failure – in this case due to the street lighting being switched off in the morning – a MOSFET disconnects the input within a few microseconds and the sensor with gateway is supplied uninterrupted from the LiFePO4 energy storage throughout the entire day. The UPSI-2406IP-38AC provides a constantly regulated 24VDC output voltage.

The integrated LiFePO4 energy storage of the UPSI-2406IP-38AC impresses with particularly stable battery chemistry, a long service life of at least 10 years and up to 6000 full charge and discharge cycles. Bicker Elektronik deliberately uses particularly safe lithium iron phosphate chemistry for all high-performance battery packs, which makes thermal runaway almost impossible.

In contrast to supposedly cheap lead-gel batteries, high-quality lithium iron phosphate cells have a service life and cycle stability that are approximately 15-20 times longer. When calculating the TCO (Total Cost of Ownership) over the entire period of use of at least 10 years, there is a significant cost advantage compared to lead-acid batteries, especially since the effort for maintenance and battery replacement with LiFePO4 is eliminated during this period.

The sealed housing elements and connections of the high-quality aluminum housing are resistant to water, ice, oil and dust in accordance with protection class IP65. An integrated pressure compensation element with a membrane prevents condensation inside the device. The mounting holes on the housing enable flexible wall or pole mounting. The optionally available pole mounting set PSZ-1100 is used for lamppost installation.

“We are working on innovations to better understand and predict weather and environmental phenomena. Thanks to the cooperation with Bicker Elektronik, completely new possibilities have opened up for using our measuring systems autonomously in 24/7 continuous operation.”

Jens Dickau, Sales Manager Road Weather Systems Vaisala GmbH

Advantages & customer benefits

Smart and cost-saving 24/7 power solution

By using the UPSI-2406IP-38AC, the complex and costly laying of new power lines for the permanent power supply of the environmental sensors could be avoided. Thanks to the intelligent and powerful outdoor UPS solution with LiFePO4 buffering, the time between the lighting intervals of the street lights can be safely bridged – even in the summer months with short charging times at night. The UPS system also offers reliable protection as an emergency power supply in the event of a power failure, flicker or voltage dips.